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Abstract Background Synpolydactyly (SPD) is mainly caused by mutations of polyalanine expansion (PAE) in the transcription factor gene HOXD13 and the involved cell types and signal pathway are still not clear possible pathways and single-cell expression characteristics of limb bud in HOXD13 PAE mice was analyzed in this study. Method We investigated a previous study of a mouse model with SPD and conducted weighted gene co-expression network analysis (WGCNA) using a single-cell RNA sequencing dataset from limb bud cells of SPD mouse model of HOXD13 + 7A heterozygote. Results Analysis of WGCNA revealed that synpolydactyly-associated Hoxd13 PAEs alter the immune response and osteoclast differentiation, and enhance DNA replication. Bmp4, Hand2, Hoxd12, Lnp, Prrx1, Gmnn, and Cdc6 were found to play potentially key roles in synpolydactyly. Conclusions These findings evaluated the main genes related to SPD with PAE mutations in HOXD13 and advance our understanding of human limb development.

Background: Synpolydactyly (SPD) is mainly caused by mutations of polyalanine expansion (PAE) in the transcription factor gene HOXD13 and the involved cell types and signal pathway are still not clear possible pathways and single-cell expression characteristics of limb bud in HOXD13 PAE mice was analyzed in this study. Method: We investigated a previous study of a mouse model with SPD and conducted weighted gene co-expression network analysis (WGCNA) using a single-cell RNA sequencing dataset from limb bud cells of SPD mouse model of HOXD13 + 7A heterozygote. Results: Analysis of WGCNA revealed that synpolydactyly-associated Hoxd13 PAEs alter the immune response and osteoclast differentiation, and enhance DNA replication. Bmp4, Hand2, Hoxd12, Lnp, Prrx1, Gmnn, and Cdc6 were found to play potentially key roles in synpolydactyly. Conclusions: These findings evaluated the main genes related to SPD with PAE mutations in HOXD13 and advance our understanding of human limb development. [ABSTRACT FROM AUTHOR]

Synpolydactyly (SPD) is caused by mutations in the transcription factor gene HOXD13. Such mutations include polyalanine expansion (PAE), but further study is required for the phenotypic spectrum characteristics of HOXD13 PAE. We investigated four unrelated Chinese families with significant limb malformations. Three PAEs were found in the HOXD13 polyalanine coding region: c.172_192dup (p.Ala58_Ala64dup) in Family 1, c.169_192dup (p.Ala57_Ala64dup) in Family 2, and c.183_210dup (p.Ala62_Ala70dup) in Family 3 and Family 4. Interestingly, we identified a new manifestation of preaxial polydactyly in both hands in a pediatric patient with an expansion of seven alanines, a phenotype not previously noted in SPD patients. Comparing with the wild-type cells and mutant cells with polyalanine contractions (PACs), the HOXD13 protein with a PAE of nine-alanine or more was difficult to enter the nucleus, and easy to form inclusion bodies in the cytoplasm, and with the increase of PAE, the more inclusion bodies were formed. This study not only expanded the phenotypic spectrum of SPD, but also enriched our understanding of its pathogenic mechanisms. [ABSTRACT FROM AUTHOR]

Synpolydactyly (SPD) is a digital malformation with the typical clinical phenotype of the webbing of 3/4 fingers and/or 4/5 toes, and combined with polydactyly. In this study, we investigated a Chinese family with SPD and genetic analysis found that all of the affected individuals in the family carry a heterozygous 11,451 bp microdeletion at chr2:176933872‐176945322 (GRCh37), which is located upstream of HOXD13 gene, the known disease gene for SPD1. All the affected individuals in the family carry the heterozygous deletion variant, and the variant co‐segregated with SPD in the family. Thus, we speculate that the 11,451 bp microdeletion is the disease‐causing variant in the family. To date, the microdeletion associating with SPD1 which we identified is the smallest deletion upstream of the HOXD13 gene and not altering the sequence of the HOXD13 gene. [ABSTRACT FROM AUTHOR]

Synpolydactyly (SPD) is a hereditary congenital limb malformation with distinct syndactyly designated as SPD1, SPD2, and SPD3. SPD1 is caused by mutations of HOXD13, which is a homeobox transcription factor crucial for limb development. More than 143 SPD patients have been reported to carry HOXD13 mutations, but there is a lack of genotype–phenotype correlation. We report a novel missense mutation of c. 925A > T (p.I309F) in an individual with atypical synpolydactyly inherited from her father with mild clinodactyly and three other different alanine insertion mutations in HOXD13 identified by whole exome sequencing (WES) in 12 Chinese SPD families. Unlike polyalanine extension, which tends to form α-helix and causes protein aggregation in the cytoplasm as shown by molecular simulation and immunofluorescence, the c. 925A > T mutation impairs downstream transcription of EPHA7. We compiled literature findings and analyzed genotype–phenotype features in 173 SPD individuals of 53 families, including 12 newly identified families. Among the HOXD13-related individuals, mutations were distributed in three regions: polyalanine, homeobox, and non-homeobox. Polyalanine extension was the most common variant (45%), followed by missense mutations (32%) mostly in the homeobox compared with the loss-of-function (LOF) variants more likely in non-homeobox. Furthermore, a more severe degree and classic SPD were associated with polyalanine mutations although missense variants were associated with brachydactyly and syndactyly in hands and feet and LOF variants with clinodactyly in hands. Our study broadens the HOXD13 mutation spectrum and reveals the profile of three different variants and their severity of SPD, the genotype–phenotype correlation related to the HOXD13 mutation site provides clinical insight, including for genetic counseling.

Synpolydactyly (SPD) is a hereditary congenital limb malformation with distinct syndactyly designated as SPD1, SPD2, and SPD3. SPD1 is caused by mutations of HOXD13 , which is a homeobox transcription factor crucial for limb development. More than 143 SPD patients have been reported to carry HOXD13 mutations, but there is a lack of genotype–phenotype correlation. We report a novel missense mutation of c. 925A > T (p.I309F) in an individual with atypical synpolydactyly inherited from her father with mild clinodactyly and three other different alanine insertion mutations in HOXD13 identified by whole exome sequencing (WES) in 12 Chinese SPD families. Unlike polyalanine extension, which tends to form α-helix and causes protein aggregation in the cytoplasm as shown by molecular simulation and immunofluorescence, the c. 925A > T mutation impairs downstream transcription of EPHA7. We compiled literature findings and analyzed genotype–phenotype features in 173 SPD individuals of 53 families, including 12 newly identified families. Among the HOXD13 -related individuals, mutations were distributed in three regions: polyalanine, homeobox, and non-homeobox. Polyalanine extension was the most common variant (45%), followed by missense mutations (32%) mostly in the homeobox compared with the loss-of-function (LOF) variants more likely in non-homeobox. Furthermore, a more severe degree and classic SPD were associated with polyalanine mutations although missense variants were associated with brachydactyly and syndactyly in hands and feet and LOF variants with clinodactyly in hands. Our study broadens the HOXD13 mutation spectrum and reveals the profile of three different variants and their severity of SPD, the genotype–phenotype correlation related to the HOXD13 mutation site provides clinical insight, including for genetic counseling. [ABSTRACT FROM AUTHOR]

Abstract Background Polydactyly is one of the most common congenital hand/foot malformations in humans. Mutations in GLI3 have been reported to cause syndromic and non-syndromic forms of preaxial and postaxial polydactylies. Case presentation The patient was a 2-year-old boy who underwent surgery in our hospital. The right hand and left foot of the patient were labelled as postaxial polydactyly type B, and there was cutaneous webbing between the 3rd and 4th fingers of the left hand. We identified a novel c. 1622C > T variant in GLI3 leading to an isolated postaxial synpolydactyly. Conclusions The patient carries a novel autosomal dominant heterozygous missense mutation. This mutation c.1622C > T;p.(Thr541Met) in the GLI3 gene may affect the normal function of the zinc finger domain (ZFD) in a different way. However, it seems that more research is needed to determine the exact effects of this mutation.

Background: Polydactyly is one of the most common congenital hand/foot malformations in humans. Mutations in GLI3 have been reported to cause syndromic and non-syndromic forms of preaxial and postaxial polydactylies. Case presentation: The patient was a 2-year-old boy who underwent surgery in our hospital. The right hand and left foot of the patient were labelled as postaxial polydactyly type B, and there was cutaneous webbing between the 3rd and 4th fingers of the left hand. We identified a novel c. 1622C > T variant in GLI3 leading to an isolated postaxial synpolydactyly. Conclusions: The patient carries a novel autosomal dominant heterozygous missense mutation. This mutation c.1622C > T;p.(Thr541Met) in the GLI3 gene may affect the normal function of the zinc finger domain (ZFD) in a different way. However, it seems that more research is needed to determine the exact effects of this mutation. [ABSTRACT FROM AUTHOR]

Syndactyly type II (synpolydactyly, SPD) is a rare autosomal dominant inherited disease with higher incomplete penetrance. Currently, several variants in HOXD13 and one deletion in FBLN1 have been associated with SPD. However, the causative variants in several SPD families and their etiological mechanism are still largely unknown. Whole exome and PCR-sanger sequencing followed by two-point linkage analysis were performed to identify the pathogenic variant in a six-generation Chinese pedigree. Homology modeling in combination with the RNAi and qRT-PCR experiments was used for revealing the pathogenic mechanism of the TTC30B variant. A six-generation SPD family was reported. The affected subjects in this family had no other clinical malformation beyond SPD. A rare missense variant c.1157C>T [p.Ala375Val] (chr2:178416368, hg19) in TTC30B was demonstrated to be responsible for this SPD family. The modeling structure indicated that the Ala375 was evolutionarily and structurally conserved. The variant p.Ala375Val was predicted to be deleterious for protein structure and/or stability. Two-point linkage analysis resulted in a maximum LOD score of 3.1444 (P = 0.000071). Furthermore, we found that TTC30B was regulated by the Shh signaling pathway and the abnormal expression of TTC30B will affect the activation of the Shh signaling pathway in human retinal pigment epithelial cells. This study demonstrates for the first time that an IFT (intraflagellar transport) - related gene TTC30B is implicated with SPD. Unlabelled Image • SPD, a rare autosomal dominant inherited disease, depicts higher incomplete penetrance with variable and asymmetrical expressivity. • A six-generation synpolydactyly pedigree including 94 individuals was reported. • A rare non-synonymous variant in TTC30B was associated with SPD in a Chinese pedigree. • TTC30B , encoding a core component of intraflagellar transport complex B, participate in the digit patterning through sonic hedgehog pathway. [ABSTRACT FROM AUTHOR]

Synpolydactyly is a congenital limb malformation characterized by incomplete separation and duplication in fingers and/or toes, which is mainly caused by mutations in the homeobox D13 (HOXD13) gene. Here, a four-generation family with variant phenotypes of synpolydactyly was analyzed, in which the proband had bilateral preaxial synpolydactyly in toes with normal fingers, the father had clinodactyly in the fifth fingers, while the mother and grandma was normal. Trio whole-exome sequencing (trio-WES) is a high throughput sequencing targeting whole genome for detecting exonic variants from the proband and the parents in a family. Through trio-WES followed by Sanger sequencing and enzyme digestion, a heterozygous nonsense mutation (c.859 C>T/p.Gln287Ter) was newly identified in the homeodomain of the HOXD13 gene from the proband and the affected father, but not from the unaffected mother, the unaffected grandma, or the normal control. Mutation Taster, Human Splicing Finder and EX-SKIP predicted that the heterozygous mutation (c.859 C>T) would result in haploinsufficiency of HOXD13 protein through nonsense-mediated mRNA decay (NMD) and splicing abnormality, which might disrupt the integrity and reduce the expression level of the HOXD13 protein (loss-of-function). In short, a heterozygous nonsense mutation in the HOXD13 gene was newly identified in two patients with mild phenotypes of synpolydactyly, which extends the mutation spectrum in HOXD13 gene. Moreover, the findings we presented here deepen our understanding of the clinical consequences of non-syndromic synpolydactyly and may provide a new clue for further studies of the pathogenic mechanism of the mutation that causes aberrant splicing of HOXD13 gene. [ABSTRACT FROM AUTHOR]

Syndactyly is a condition where in two or more digits are fused together. A newborn female baby showed not only webbing of the fingers but also toes. X-ray of both hands and feet showed no bony fusion. Syndactyly is a rare anomaly that has surgical and psychological implications. Normally mesenchyme between prospective digits in hand and foot plates is removed by cell death (apoptosis) when this process fails the result is fusion between two or more digits. It occurs as one in every 2000 to 2500 births and twice as common in males. Though it is very rare it can be corrected surgically and child can live a normal life. The knowledge of digit formation and causes for abnormalities in the digits and toes are important for radiologists, obstetricians and surgeons for accurate diagnostic interpretation.

Synpolydactyly (SPD) is an autosomal dominant limb malformation with a distinctive combination of syndactyly and polydactyly. SPD is clinically heterogeneous and could be genetically classified into three types. The clinical phenotype of SPD is complicated by its variable expressivity. In the present study, whole exome sequencing (WES) was used to identify the affected gene(s) in a Chinese family with atypical SPD phenotype. Our results showed that a novel heterogenous nonsense mutation (c.556C > T, p.R186X) in HOXD13 was associated with this SPD case. Due to variable expressivity, the diagnosis of a clinical heterogenous disease such as SPD is usually difficult. Our results also suggested that WES is an efficient tool to assist with these diagnoses. [ABSTRACT FROM AUTHOR]

Purpose: This case series describes a novel condition characterized by familial pseudotail associated with scoliosis, and synpolydactyly that has not been previously reported in literature.Methods: The authors present three siblings and one cousin from the same family living in the northern region of the Arabian Peninsula. All cases presented with pseudotail, scoliosis, and complex synpolydactyly. The authors demonstrated complete clinical and radiological descriptions in addition the detailed performed surgeries.Results: The histopathological result of the resected pseudotail specimens revealed bony lesion covered with thick fibrous tissue and evidence of mature adipocytes within trabecular spaces.Conclusions: The described cases represent a novel condition that has not been previously reported in the literature. Familial pseudotail scoliosis synpolydactyly syndrome is a newly recognized form of familial pseudotail. [ABSTRACT FROM AUTHOR]

Synpolydactyly (SPD) is a rare congenital limb disorder characterized by syndactyly between the third and fourth fingers and an additional digit in the syndactylous web. In most cases SPD is caused by heterozygous mutations in HOXD13 resulting in the expansion of a N-terminal polyalanine tract. If homozygous, the mutation results in severe shortening of all metacarpals and phalanges with a morphological transformation of metacarpals to carpals. Here, we describe a novel homozygous missense mutation in a family with unaffected consanguineous parents and severe brachydactyly and metacarpal-to-carpal transformation in the affected child. We performed whole exome sequencing on the index patient, followed by Sanger sequencing of parents and patient to investigate cosegregation. The DNA-binding ability of the mutant protein was tested with electrophoretic mobility shift assays. We demonstrate that the c.938C>G (p.313T>R) mutation in the DNA-binding domain of HOXD13 prevents binding to DNA in vitro. Our results show to our knowledge for the first time that a missense mutation in HOXD13 underlies severe brachydactyly with metacarpal-to-carpal transformation. The mutation is non-penetrant in heterozygous carriers. In conjunction with the literature we propose the possibility that the metacarpal-to-carpal transformation results from a homozygous loss of functional HOXD13 protein in humans in combination with an accumulation of non-functional HOXD13 that might be able to interact with other transcription factors in the developing limb. © 2015 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Synpolydactyly (SPD, OMIM 186000) is a rare congenital limb disorder characterized by syndactyly between the third and fourth fingers and between the fourth and fifth toes, with partial or complete digit duplication in the syndactylous web. The majority of these anomalies co-segregate with mutations in the HOXD13 gene, a homeobox transcription factor crucial for distal limb development. Different classes of HOXD13 mutations are involved in the pathogenesis of synpolydactyly, but an unequivocal genotype-phenotype correlation cannot always be achieved due to the clinical heterogeneity and reduced penetrance of SPD. All mutations identified so far mapped to the N-terminal polyalanine tract or to the C-terminal homeodomain of HOXD13, causing typical or atypical features of SPD, respectively. However, mutations outside of these domains cause a broad variety of clinical features that complicate the differential diagnosis. The existing animal models that are currently used to study HOXD13 (mal)function are therefore instrumental in unraveling potential genotype-phenotype correlations. Both mouse- and chick-based approaches allow the in vivo study of the pathogenic mechanism by which HOXD13 mutations cause SPD phenotypes as well as help in identifying the transcriptional targets. Developmental Dynamics 243:37-48, 2014. © 2013 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Abstract: Introduction: Human synpolydactyly (SPD), belonging to syndactyly (SD) II, is caused by mutations in homeobox d13 (HOXD13). Here, we describe the study of a two-generation Chinese family with a variant form of synpolydactyly. Materials and methods: The sequence of the HOXD13 gene was analyzed. Luciferase assays were conducted to determine whether the mutation affected the function of the HOXD13 protein. Results: We identified a novel c.659G>C (p.Gly220Ala) mutation outside the HOXD13 homeodomain responsible for the disease in this family. This mutation was not found in any of the unaffected family members and healthy control. Luciferase assays demonstrated that this mutation affected the transcriptional activation ability of HOXD13 (only approximately 84.7% of wild type, p<0.05). Conclusion: Phenotypes displayed by individuals carrying the novel mutation present additional features, such as the fifth finger clinodactyly, which is not always associated with canonical SPD. This finding enhances our understanding about the phenotypic spectrum associated with HOXD13 mutations and advances our understanding of human limb development. [Copyright &y& Elsevier]

Abstract: Purpose: The 5′ HoxD genes and their paralogs in the HoxD cluster are crucial for normal vertebrate limb development. Mutations in HOXD13 and HOXD13 have been found to cause human limb malformation. Here we describe a two-generation Chinese family with a variant form of mild synpolydactyly. Methods: Sequence analysis of HOXD13 gene in a two-generation Chinese family with six individuals. Results: Gene scan and linkage analysis suggested that HOXD13 might be responsible for the disease of this family. An LOD around 1.8 was observed at three markers (P =2E−3). We identified a novel c.893G>A (p.Arg298Gln) mutation in the HOXD13 homeodomain. And the mutation affected the transcriptional activation ability of HOXD13. Conclusion: This finding expands the phenotypic spectrum associated with HOXD13 mutations and advances our understanding of human limb development. [Copyright &y& Elsevier]

Abstract: Human synpolydactyly (SPD), belonging to syndactyly (SD) II, is an inherited autosomal-dominant limb malformation characterized by SD of finger 3 or 4 or toe 4 or 5, usually with digit duplication. Previous studies have demonstrated that homeobox protein D13 (HOXD13) is responsible for this Mendelian disorder. In this paper, we report on a family with SPD — 7 members show typical SPD malformations. We used PCR and Sanger sequencing of DNA from peripheral blood samples and found an 8-Ala expansion in exon 1 of HOXD13 by mutation detection; this variant was absent in unaffected members and in 50 unaffected non-related subjects. This study further confirmed the correlation between SPD and alanine expansion in HOXD13. [Copyright &y& Elsevier]

Abstract: Synpolydactyly (SPD) is a rare congenital limb disorder caused by mutations in the HOXD13 gene, a homeobox transcription factor crucial for autopod development. The hallmarks of SPD are the webbing between the third and the fourth finger and the fourth and the fifth toe, with a partial or complete digit duplication in the syndactylous web. Different classes of HOXD13 mutations are involved in the pathogenesis of synpolydactyly, but an unequivocal genotype–phenotype correlation cannot always be achieved due to the lack of structure–function data of HOXD13. Mutations in DNA binding or polyalanine tract domains of HOXD13 result in predictable clinical outcomes. However, mutations outside of these domains cause a broad variety of clinical features that complicate the differential diagnosis. In this review, we summarize the different classes of HOXD13 mutations causing synpolydactyly phenotypes with respect to their underlying pathogenic mechanism of action. In addition, we emphasize the importance of the chicken embryo as an animal model system for the study of (limb) development and potential genotype–phenotype correlations in SPD or other human malformation syndromes. [Copyright &y& Elsevier]

Abstract: Synpolydactyly (SPD) is an autosomal dominant limb malformation caused by mutations in the gene HOXD13. We investigated a Chinese family in which three individuals across three generations were affected with distinctive limb malformations. We extracted genomic DNA from the affected and three unaffected individuals from this family as well as 100 unrelated controls, for mutation detection by DNA sequencing. The family was characterized by camptodactyly and symphalangism of fingers two to five, transverse phalanx and osseous fusion of the third metacarpal with the proximal phalanx, as well as the coexistence of mild and more severe bilateral phenotypes. We identified a duplication mutation, c. 186–212dup, in exon 1 of the HOXD13 gene in the affected individuals from this family; it was not present in the unaffected individuals or the 100 unrelated individuals. And we also did not find polymorphism among the controls. This study has expanded the phenotypic spectrum of known HOXD13 polyalanine repeat mutations and provided more information about the polymorphic nature of the polyalanine repeat. In addition, new clinical manifestations have been added to the spectrum of possible synpolydactyly phenotypes. [Copyright &y& Elsevier]

Synpolydactyly (SPD) is a rare limb deformity showing a distinctive combination of syndactyly and polydactyly. Of the nine non-syndromic syndactylies, it is clinically and genetically one of the most heterogeneous malformation. SPD families may show clinical features consistent with the Temtamy and McKusick criteria as well as additional phenotypic variants, which vary from case to case. In certain instances, these variants predominate in a given family, while the typical SPD features remain less explicit. We have reviewed all the clinical variants occurring in well-documented SPD families. We conclude that typical SPD features can be delineated from minor clinical variants. Then, we propose to lump all the phenotypic variants, manifesting themselves in SPD families into three categories: (i) typical SPD features, (ii) minor variants, and (iii) unusual phenotypes. Next, we discuss the likely reasons for the occurrence of minor variants and the obvious lack of penetrance in SPD families. Finally, we show that for the SPD phenotype associated with HOXD13 mutations, a straightforward genotype–phenotype correlation is weak. Our lumping and splitting scheme for SPD phenotypic variants could be useful for the understanding of this interesting malformation. [ABSTRACT FROM AUTHOR]

Abstract: Synpolydactyly (SPD) is an autosomal dominant malformation of the distal limbs caused by mutations in the homeobox gene HOXD13 located on chromosome 2q31. We detail the clinical findings in a consanguineous Pakistani family segregating a HOXD13 7-residue polyalanine tract expansion. Three members of this pedigree were heterozygotes with features typical of SPD. Two further members demonstrate a more severe phenotype consistent with homozygosity for the familial mutation. We also report a child from a consanguineous Somali family homozygous for the same molecular lesion. Characteristic changes include a complex central polydactyly in the hands, abnormal modelling of the metacarpals and metatarsals, an increased number of carpal bones with abnormal shapes, hypoplasia or absence of the fifth digital rays in the feet, hypoplasia of the middle phalanges and abnormally long proximal phalanges in hands and feet. These cases illustrate the distinct phenotype associated with homozygosity for a HOXD13 mutation and also highlight the importance of considering homozygosity for a dominant mutation in consanguineous pedigrees. [Copyright &y& Elsevier]

Syndactyly type II or synpolydactyly (SPD) is the second most frequent syndactyly type and is inherited in an autosomal dominant fashion. The cardinal features of this malformation are the cutaneous or bony fusion of third and fourth fingers, and fourth and fifth toes associated with additional digital elements within the web. It shows incomplete penetrance and high inter- and intrafamilial phenotypic variability. Two loci are known for SPD (MIM 186000, MIM 608180) associated with mutations in HOXD13 and FBLN1, respectively. Here, we report further genetic heterogeneity for SDP. Employing a whole genomic screen, we demonstrate, in a large Pakistani kindred, that the classical phenotype of SPD maps on a new locus at chromosome 14q11.2-q12. The highest LOD score ( Zmax = 4.06) was obtained with microsatellite marker D14S264, and the multipoint LOD score reached a maximum of 5.01. Haplotype analysis revealed that the disease interval is flanked by microsatellite markers D14S283 and D14S1060, encompassing a physical distance of 10.72 Mb. We propose to allocate to this locus the symbol SPD3 (synpolydactyly 3), and to name the loci associated with HOXD13 or FBLN1 mutations SPD1 and SPD2, respectively. [ABSTRACT FROM AUTHOR]

In the United States, Japan, United Kingdom, and Sweden, birth defects affecting the growth and development of the genitourinary (GU) regions are becoming increasingly prevalent, with incidences ranging as high as 1 in 125 live births. To understand the basis for these malformations, scientists have begun to examine the function of developmental genes in GU tissues. At the forefront of these investigations are studies examining the role of the 5′ HOX proteins during the formation of the GU region. In this report we discuss what is known about HOXA13 and HOXD13 function during GU development, highlighting some of the cellular and molecular mechanisms controlled by these proteins during the GU formation. Finally, the translational benefits of identifying HOX target genes are discussed; first to explain the prevalence of some GU defects as well as a mechanism to facilitate their prevention in the birth population. [ABSTRACT FROM PUBLISHER]

A large kindred which was first described in 1995 was investigated again. We present the clinical, radiological, genetic and surgical findings of the hand deformities found in homozygote individuals which we called “hypoplastic synpolydactyly”.There were 125 affected (heterozygote or homozygote) people out of 245 subjects in the five last generations. We identified seven marriages of two affected people. Twelve offsprings, of these marriages had a homozygote genetic pattern and “hypoplastic synpolydactyly”. From both the clinical and surgical perspectives, their hand deformity was distinctive from that of their parents. We surgically treated both hands of three individuals with this deformity.The hand deformity of these homozygotes was so complicated and distinctive that it can be evaluated as a new subgroup of synpolydactyly. [ABSTRACT FROM PUBLISHER]

We have investigated the recessive mouse mutant synpolydactyly homolog (spdh) as a model for human synpolydactyly (SPD). As in human SPD, the spdh phenotype consists of central polydactyly, syndactyly and brachydactyly and is caused by the expansion of a polyalanine encoding repeat in the 5′ region of the Hoxd13 gene. We performed a detailed phenotypic and functional analysis of spdh/spdh embryos using skeletal preparations, histology, in situ hybridization, BrdU labeling of proliferating cells, and in vitro expression studies. The absence of normal phalangeal joints and the misexpression of genes involved in joint formation demonstrate a role for Hox-genes in joint patterning. The spdh mutation results in abnormal limb pattering, defective chondrocyte differentiation, and in a drastic reduction in proliferation. Abnormal chondrocyte differentiation and proliferation persisted after birth and correlated with the expression of the mutant Hoxd13 and other Hox-genes during late-embryonic and postnatal growth. [Copyright &y& Elsevier]

Expansions of amino acid repeats occur in >20 inherited human disorders, and many occur in intrinsically disordered regions (IDRs) of transcription factors (TFs). Such diseases are associated with protein aggregation, but the contribution of aggregates to pathology has been controversial. Here, we report that alanine repeat expansions in the HOXD13 TF, which cause hereditary synpolydactyly in humans, alter its phase separation capacity and its capacity to co-condense with transcriptional co-activators. HOXD13 repeat expansions perturb the composition of HOXD13-containing condensates in vitro and in vivo and alter the transcriptional program in a cell-specific manner in a mouse model of synpolydactyly. Disease-associated repeat expansions in other TFs (HOXA13, RUNX2, and TBP) were similarly found to alter their phase separation. These results suggest that unblending of transcriptional condensates may underlie human pathologies. We present a molecular classification of TF IDRs, which provides a framework to dissect TF function in diseases associated with transcriptional dysregulation. • Repeat expansions in transcription factors (TFs) alter their phase separation capacity • Repeat expansions in TFs perturb the composition of TF-containing condensates • Hoxd13 repeat expansions alter the transcriptional program in a synpolydactyly model • Features of intrinsically disordered regions in TFs are linked to condensation behavior Disease-associated repeat expansions within transcription factors alter their capacity to co-condense with transcriptional co-activators. [ABSTRACT FROM AUTHOR]

A family with middle–ring–little finger syndactyly is reported to demonstrate that the responsible autosomal gene may be expressed as either simple syndactyly or synpolydactyly. [Copyright &y& Elsevier]

During animal development, HOX transcription factors determine the fate of developing tissues to generate diverse organs and appendages. The power of these proteins is striking: mis-expressing a HOX protein causes homeotic transformation of one body part into another. During development, HOX proteins interpret their cellular context through protein interactions, alternative splicing, and post-translational modifications to regulate cell proliferation, cell death, cell migration, cell differentiation, and angiogenesis. Although mutation and/or mis-expression of HOX proteins during development can be lethal, changes in HOX proteins that do not pattern vital organs can result in survivable malformations. In adults, mutation and/or mis-expression of HOX proteins disrupts their gene regulatory networks, deregulating cell behaviors and leading to arthritis and cancer. On the molecular level, HOX proteins are composed of DNA binding homeodomain, and large regions of unstructured, or intrinsically disordered, protein sequence. The primary roles of HOX proteins in arthritis and cancer suggest that mutations associated with these diseases in both the structured and disordered regions of HOX proteins can have substantial functional effects. These insights lead to new questions critical for understanding and manipulating HOX function in physiological and pathological conditions., (© 2020 Elsevier Inc. All rights reserved.)

Synpolydactyly is a congenital limb malformation characterized by incomplete separation and duplication in fingers and/or toes, which is mainly caused by mutations in the homeobox D13 (HOXD13) gene. Here, a four-generation family with variant phenotypes of synpolydactyly was analyzed, in which the proband had bilateral preaxial synpolydactyly in toes with normal fingers, the father had clinodactyly in the fifth fingers, while the mother and grandma was normal. Trio whole-exome sequencing (trio-WES) is a high throughput sequencing targeting whole genome for detecting exonic variants from the proband and the parents in a family. Through trio-WES followed by Sanger sequencing and enzyme digestion, a heterozygous nonsense mutation (c.859 C>T/p.Gln287Ter) was newly identified in the homeodomain of the HOXD13 gene from the proband and the affected father, but not from the unaffected mother, the unaffected grandma, or the normal control. Mutation Taster, Human Splicing Finder and EX-SKIP predicted that the heterozygous mutation (c.859 C>T) would result in haploinsufficiency of HOXD13 protein through nonsense-mediated mRNA decay (NMD) and splicing abnormality, which might disrupt the integrity and reduce the expression level of the HOXD13 protein (loss-of-function). In short, a heterozygous nonsense mutation in the HOXD13 gene was newly identified in two patients with mild phenotypes of synpolydactyly, which extends the mutation spectrum in HOXD13 gene. Moreover, the findings we presented here deepen our understanding of the clinical consequences of non-syndromic synpolydactyly and may provide a new clue for further studies of the pathogenic mechanism of the mutation that causes aberrant splicing of HOXD13 gene.

Synpolydactyly (SPD) is an autosomal dominant congenital limb disorder due to mutations in HOXD13 . It is a phenotypically heterogeneous condition characterized by syndactyly of the third finger (F3), fourth finger (F4) and/or fourth toe (T4), and fifth toe (T5) with variably associated polydactyly. We report on a mother and fetus with SPD. The mother has a novel mutation (c.708&#95;708delC) in the HOXD13 gene that was also seen in the fetus. However, the fetus had congenital omphalocele in addition to SPD that is an association not reported to date. A chromosomal microarray in the fetus was normal. We report a novel mutation in HOXD13 and document co-occurrence of an omphalocele and SPD in a fetus.

Synpolydactyly 1(SPD1) is a dominantly inherited distal limb anomaly that is characterized by incomplete digit separation and increased number of digits. SPD1 is most commonly caused by polyalanine repeat expansions and mutations in the homeodomain of the HOXD13. We report a splice donor site mutation in HOXD13 associated in most cases with cortical bone thinning. In vitro study of transcripts and truncated protein analysis indicated that c.781+1G>A mutation results in truncated HOXD13 protein p.G190fsX4. Luciferase assay indicated that the truncated HOXD13 protein failed to bind to DNA. The mechanism for this phenotype was truncated protein loss of function., (© 2013.)

Synpolydactyly is a relatively rare malformation. Recently, we came across a male infant with a familial synpolydactyly of the hands and feet. As most familial synpolydactyly syndromes have not been linked to any specific mutations, we felt further investigation was warranted. Using microarray and fluorescent in situ hybridization analysis, we identified a novel mutation of the SLC25A21 gene on chromosome 14.

Ellis Van Creveld syndrome (EVC), also known as chondroectodermal dysplasia, presents at birth with short limbs accompanied by postaxial polydactyly, nail dysplasia, and dental anomalies. Other manifestations of EVC include atrial septum defects and other congenital heart diseases. We report a case of the EVC syndrome with postaxial polydactyly (Synpolydactyly with seven fingers on the right side and hexadactyly on the left side) and a partial atrioventricular canal defect diagnosed antenatally. This variation of EVS has not been reported in English literature till date.