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We recently described a new neurodevelopmental syndrome (TAF1/MRXS33 intellectual disability syndrome) (MIM# 300966) caused by pathogenic variants involving the X-linked gene TAF1, which participates in RNA polymerase II transcription. The initial study reported eleven families, and the syndrome was defined as presenting early in life with hypotonia, facial dysmorphia, and developmental delay that evolved into intellectual disability (ID) and/or autism spectrum disorder (ASD). We have now identified an additional 27 families through a genotype-first approach. Familial segregation analysis, clinical phenotyping, and bioinformatics were capitalized on to assess potential variant pathogenicity, and molecular modelling was performed for those variants falling within structurally characterized domains of TAF1. A novel phenotypic clustering approach was also applied, in which the phenotypes of affected individuals were classified using 51 standardized Human Phenotype Ontology (HPO) terms. Phenotypes associated with TAF1 variants show considerable pleiotropy and clinical variability, but prominent among previously unreported effects were brain morphological abnormalities, seizures, hearing loss, and heart malformations. Our allelic series broadens the phenotypic spectrum of TAF1/MRXS33 intellectual disability syndrome and the range of TAF1 molecular defects in humans. It also illustrates the challenges for determining the pathogenicity of inherited missense variants, particularly for genes mapping to chromosome X. This article is protected by copyright. All rights reserved., (This article is protected by copyright. All rights reserved.)

Mutations in CASK cause a wide spectrum of phenotypes in humans ranging from mild X-linked intellectual disability to a severe microcephaly (MC) and pontocerebellar hypoplasia syndrome. Nevertheless, predicting pathogenicity and phenotypic consequences of novel CASK mutations through the exclusive consideration of genetic information and population-based data remains a challenge. Using whole exome sequencing, we identified four novel CASK mutations in individuals with syndromic MC. To understand the functional consequences of the different point mutations on the development of MC and cerebellar defects, we established a transient loss-of-function zebrafish model, and demonstrate recapitulation of relevant neuroanatomical phenotypes. Furthermore, we utilized in vivo complementation studies to demonstrate that the three point mutations confer a loss-of-function effect. This work endorses zebrafish as a tractable model to rapidly assess the effect of novel CASK variants on brain development., (© 2018 Wiley Periodicals, Inc.)

Autosomal recessive microcephaly or microcephaly primary hereditary (MCPH) is a genetically heterogeneous neurodevelopmental disorder characterized by a reduction in brain volume, indirectly measured by an occipitofrontal circumference (OFC) 2 standard deviations or more below the age- and sex-matched mean (-2SD) at birth and -3SD after 6 months, and leading to intellectual disability of variable severity. The abnormal spindle-like microcephaly gene (ASPM), the human ortholog of the Drosophila melanogaster "abnormal spindle" gene (asp), encodes ASPM, a protein localized at the centrosome of apical neuroprogenitor cells and involved in spindle pole positioning during neurogenesis. Loss-of-function mutations in ASPM cause MCPH5, which affects the majority of all MCPH patients worldwide. Here, we report 47 unpublished patients from 39 families carrying 28 new ASPM mutations, and conduct an exhaustive review of the molecular, clinical, neuroradiological, and neuropsychological features of the 282 families previously reported (with 161 distinct ASPM mutations). Furthermore, we show that ASPM-related microcephaly is not systematically associated with intellectual deficiency and discuss the association between the structural brain defects (strong reduction in cortical volume and surface area) that modify the cortical map of these patients and their cognitive abilities., (© 2017 Wiley Periodicals, Inc.)

The FMR1 gene contains an unstable CGG repeat in its 5' untranslated region. Premutation alleles range between 55 and 200 repeat units and confer a risk for developing fragile X-associated tremor/ataxia syndrome or fragile X-associated primary ovarian insufficiency. Furthermore, the premutation allele often expands to a full mutation during female germline transmission giving rise to the fragile X syndrome. The risk for a premutation to expand depends mainly on the number of CGG units and the presence of AGG interruptions in the CGG repeat. Unfortunately, the detection of AGG interruptions is hampered by technical difficulties. Here, we demonstrate that single-molecule sequencing enables the determination of not only the repeat size, but also the complete repeat sequence including AGG interruptions in male and female alleles with repeats ranging from 45 to 100 CGG units. We envision this method will facilitate research and diagnostic analysis of the FMR1 repeat expansion., (© 2016 WILEY PERIODICALS, INC.)

Intellectual disability (ID) is a heterogeneous disorder with an unknown molecular etiology in many cases. Previously, X-linked ID (XLID) studies focused on males because of the hemizygous state of their X chromosome. Carrier females are generally unaffected because of the presence of a second normal allele, or inactivation of the mutant X chromosome in most of their cells (skewing). However, in female ID patients, we hypothesized that the presence of skewing of X-inactivation would be an indicator for an X chromosomal ID cause. We analyzed the X-inactivation patterns of 288 females with ID, and found that 22 (7.6%) had extreme skewing (>90%), which is significantly higher than observed in the general population (3.6%; P = 0.029). Whole-exome sequencing of 19 females with extreme skewing revealed causal variants in six females in the XLID genes DDX3X, NHS, WDR45, MECP2, and SMC1A. Interestingly, variants in genes escaping X-inactivation presumably cause both XLID and skewing of X-inactivation in three of these patients. Moreover, variants likely accounting for skewing only were detected in MED12, HDAC8, and TAF9B. All tested candidate causative variants were de novo events. Hence, extreme skewing is a good indicator for the presence of X-linked variants in female patients., (© 2016 WILEY PERIODICALS, INC.)

Dominant missense mutations in FLNB, encoding the actin-cross linking protein filamin B (FLNB), cause a broad range of skeletal dysplasias with varying severity by an unknown mechanism. Here these FLNB mutations are shown to cluster in exons encoding the actin-binding domain (ABD) and filamin repeats surrounding the flexible hinge 1 region of the FLNB rod domain. Despite being positioned in domains that bind actin, it is unknown if these mutations perturb cytoskeletal structure. Expression of several full-length FLNB constructs containing ABD mutations resulted in the appearance of actin-containing cytoplasmic focal accumulations of the substituted protein to a degree that was correlated with the severity of the associated phenotypes. In contrast, study of mutations leading to substitutions in the FLNB rod domain that result in the same phenotypes as ABD mutations demonstrated that with only one exception disease-associated substitutions, surrounding hinge 1 demonstrated no tendency to form actin-filamin foci. The exception, a substitution in filamin repeat 6, lies within a region previously implicated in filamin-actin binding. These data are consistent with mutations in the ABD conferring enhanced actin-binding activity but suggest that substitutions affecting repeats near the flexible hinge region of FLNB precipitate the same phenotypes through a different mechanism., (© 2011 Wiley Periodicals, Inc.)

Haploinsufficiency of TBX1, encoding a T-box transcription factor, is largely responsible for the physical malformations in velo-cardio-facial /DiGeorge/22q11.2 deletion syndrome (22q11DS) patients. Cardiovascular malformations in these patients are highly variable, raising the question as to whether DNA variations in the TBX1 locus on the remaining allele of 22q11.2 could be responsible. To test this, a large sample size is needed. The TBX1 gene was sequenced in 360 consecutive 22q11DS patients. Rare and common variations were identified. We did not detect enrichment in rare SNP (single nucleotide polymorphism) number in those with or without a congenital heart defect. One exception was that there was increased number of very rare SNPs between those with normal heart anatomy compared to those with right-sided aortic arch or persistent truncus arteriosus, suggesting potentially protective roles in the SNPs for these phenotype-enrichment groups. Nine common SNPs (minor allele frequency, MAF > 0.05) were chosen and used to genotype the entire cohort of 1,022 22q11DS subjects. We did not find a correlation between common SNPs or haplotypes and cardiovascular phenotype. This work demonstrates that common DNA variations in TBX1 do not explain variable cardiovascular expression in 22q11DS patients, implicating existence of modifiers in other genes on 22q11.2 or elsewhere in the genome., (© 2011 Wiley Periodicals, Inc.)

Kabuki Syndrome (KS) is a rare syndrome characterized by intellectual disability and multiple congenital abnormalities, in particular a distinct dysmorphic facial appearance. KS is caused by mutations in the MLL2 gene, encoding an H3K4 histone methyl transferase which acts as an epigenetic transcriptional activator during growth and development. Direct sequencing of all 54 exons of the MLL2 gene in 45 clinically well-defined KS patients identified 34 (75.6%) different mutations. One mutation has been described previously, all others are novel. Clinically, all KS patients were sporadic, and mutations were de novo for all 27 families for which both parents were available. We detected nonsense (n=11), frameshift (n=17), splice site (n=4) and missense (n=2) mutations, predicting a high frequency of absent or non-functional MLL2 protein. Interestingly, both missense mutations located in the C-terminal conserved functional domains of the protein. Phenotypically our study indicated a statistically significant difference in the presence of a distinct facial appearance (p=0.0143) and growth retardation (p=0.0040) when comparing KS patients with an MLL2 mutation compared to patients without a mutation. Our data double the number of MLL2 mutations in KS reported so far and widen the spectrum of MLL2 mutations and disease mechanisms in KS., (© 2010 Wiley-Liss, Inc.)

Noonan syndrome (NS) is an autosomal dominant disorder caused by mutations in PTPN11, KRAS, SOS1, and RAF1. We performed SOS1, RAF1, BRAF, MEK1, and MEK2 mutation analysis in a cohort of 102 PTPN11- and KRAS-negative NS patients and found pathogenic SOS1 mutations in 10, RAF1 mutations in 4, and BRAF mutations in 2 patients. Three novel SOS1 mutations were found. One was classified as a rare benign variant and the other remains unclassified. We confirm a high prevalence of pulmonic stenosis and ectodermal abnormalities in SOS1-positive patients. Three patients with SOS1 mutations presented with tumors (embryonal rhabdomyosarcoma, Sertoli cell testis tumor, and granular cell tumors of the skin). One patient with a RAF1 mutation had a lesion suggestive for a giant cell tumor. This is the first report describing different tumor types in NS patients with germ line SOS1 mutations.

Costello syndrome is a mental retardation syndrome characterized by high birth weight, postnatal growth retardation, coarse face, loose skin, cardiovascular problems, and tumor predisposition. De novo heterozygous missense mutations in HRAS codon 12 and 13 disturbing the intrinsic GTP hydrolysis cause Costello syndrome. We report a patient with typical Costello syndrome and a novel heterozygous missense mutation in codon 117 (c.350A>G, p.Lys117Arg) of the HRAS gene, resulting in constitutive activation of the RAS/MAPK pathway similar to the typical p.Gly12Ser and p.Gly12Ala mutations. Recombinant HRAS p.Lys117Arg demonstrates normal intrinsic GTP hydrolysis and responsiveness to GTPase-activating proteins, but the nucleotide dissociation rate is increased 80-fold. Consistent with the biochemical data, the crystal structure of the p.Lys117Arg mutant indicates an altered interaction pattern of the side chain that is associated with unfavorable nucleotide binding properties. Together, these data show that a RAS mutation that only perturbs guanine nucleotide binding has similar functional consequences as mutations that impair GTP hydrolysis and causes human disease., ((c) 2007 Wiley-Liss, Inc.)

Arterial tortuosity syndrome (ATS) is a rare autosomal recessive connective tissue disease, characterized by widespread arterial involvement with elongation, tortuosity, and aneurysms of the large and middle-sized arteries. Recently, SLC2A10 mutations were identified in this condition. This gene encodes the glucose transporter GLUT10 and was previously suggested as a candidate gene for diabetes mellitus type 2. A total of 12 newly identified ATS families with 16 affected individuals were clinically and molecularly characterized. In addition, extensive cardiovascular imaging and glucose tolerance tests were performed in both patients and heterozygous carriers. All 16 patients harbor biallelic SLC2A10 mutations of which nine are novel (six missense, three truncating mutations, including a large deletion). Haplotype analysis suggests founder effects for all five recurrent mutations. Remarkably, patients were significantly older than those previously reported in the literature (P=0.04). Only one affected relative died, most likely of an unrelated cause. Although the natural history of ATS in this series was less severe than previously reported, it does indicate a risk for ischemic events. Two patients initially presented with stroke, respectively at age 8 months and 23 years. Tortuosity of the aorta or large arteries was invariably present. Two adult probands (aged 23 and 35 years) had aortic root dilation, seven patients had localized arterial stenoses, and five had long stenotic stretches of the aorta. Heterozygous carriers did not show any vascular anomalies. Glucose metabolism was normal in six patients and eight heterozygous individuals of five families. As such, overt diabetes is not related to SLC2A10 mutations associated with ATS., ((c) 2007 Wiley-Liss, Inc.)

A tiling X-chromosome-specific genomic array with a theoretical resolution of 80 kb was developed to screen patients with idiopathic mental retardation (MR) for submicroscopic copy number differences. Four patients with aberrations previously detected at lower resolution were first analyzed. This facilitated delineation of the location and extent of the aberration at high resolution and subsequently, more precise genotype-phenotype analyses. A cohort of 108 patients was screened, 57 of which were suspected of X-linked mental retardation (XLMR), 26 were probands of brother pairs, and 25 were sporadic cases. A total of 15 copy number changes in 14 patients (13%) were detected, which included two deletions and 13 duplications ranging from 0.1 to 2.7 Mb. The aberrations are associated with the phenotype in five patients (4.6%), based on the following criteria: de novo aberration; involvement of a known or candidate X-linked nonsyndromic(syndromic) MR (MRX(S)) gene; segregation with the disease in the family; absence in control individuals; and skewed X-inactivation in carrier females. These include deletions that contain the MRX(S) genes CDKL5, OPHN1, and CASK, and duplications harboring CDKL5, NXF5, MECP2, and GDI1. In addition, seven imbalances were apparent novel polymorphic regions because they do not fulfill the proposed criteria. Taken together, our data strongly suggest that not only deletions but also duplications on the X chromosome contribute to the phenotype more often than expected, supporting the increased gene dosage mechanism for deregulation of normal cognitive development., (Copyright 2007 Wiley-Liss, Inc.)

Subtelomeric imbalances are identified in approximately 5% of patients with idiopathic mental retardation (MR) and multiple congenital anomalies (MCA). Because of this high incidence, screening for subtelomeric anomalies became part of the routine genetic evaluation of MCA/MR patients. In contrast to the general view that subtelomeric imbalances cause MCA/MR, we report here 15 subtelomeric copy-number changes in 12 families in which the imbalance is inherited from a phenotypically normal parent. We detected inherited deletions at subtelomeres 2q, 3p, 4p, 4q, 6q, 10q, 17p, 17q, Xp, and Yq and duplications at 1q, 4q, 10q, and 11q. Interestingly, in addition to small deletions (<1 Mb) also unexpected large deletions and duplications up to 7.8 Mb were detected. Taken together with previous reports, a total of 16 subtelomeric duplications and 18 deletions inherited from a phenotypically normal parent have now been reported. Clearly, more extensive genotype-phenotype correlations are needed to better understand the phenotypic consequences of these subtelomeric copy number variations and to resolve the current uncertainty for genetic counseling in postnatal and prenatal diagnosis., (Copyright 2007 Wiley-Liss, Inc.)

In a new cohort of 141 unrelated patients affected by Kallmann syndrome we identified FGFR1 sequence variants in 17 patients, all in the heterozygous state. The fifteen novel variants consist of 10 missense (p.N77K, p.C101F, p.R250W, p.G270D, p.P283R, p.S332C, p.H621R, p.S685F, p.I693F, p.R822C), two nonsense (p.E324X, p.R661X), a frameshift (p.S439fs), and two splice site (c.1081G>C and c.1977+1G>A) changes. However, the p.N77K and p.R822C changes were also found in two and one out of 150 healthy control individuals, respectively, and therefore, their pathogenic effect is questionable. Notably, three alterations (p.E324X, p.S332C, c.1081G>C) are located in the alternative exon 8B that codes for the FGFR1c isoform, thus indicating that this isoform plays a crucial role in the development of the olfactory system in man. Moreover, the presence of cleft palate in a patient carrying the p.E324X change shows that FGFR1c is important for palate morphogenesis too., ((c) 2006 Wiley-Liss, Inc.)

Townes-Brocks syndrome (TBS) is an autosomal dominantly inherited disorder characterized by ear, anal, limb, and renal malformations, and results from mutations in the gene SALL1. All SALL1 mutations previously found in TBS patients create preterminal termination codons. In accordance with the findings of pericentric inversions or balanced translocations, TBS was initially assumed to be caused by SALL1 haploinsufficiency. This assumption was strongly contradicted by a Sall1 mouse knock-out, because neither hetero- nor homozygous knock-out mutants displayed a TBS-like phenotype. A different mouse mutant mimicking the human SALL1 mutations, however, showed a TBS-like phenotype in the heterozygous situation, suggesting a dominant-negative action of the mutations causing TBS. We applied quantitative real time PCR to detect and map SALL1 deletions in 240 patients with the clinical diagnosis of TBS, who were negative for SALL1 mutations. Deletions were found in three families. In the first family, a 75 kb deletion including all SALL1 exons had been inherited by two siblings from their father. A second, sporadic patient carried a de novo 1.9-2.6 Mb deletion including the whole SALL1 gene, and yet another sporadic case was found to carry an intragenic deletion of 3384 bp. In all affected persons, the TBS phenotype is rather mild as compared to the phenotype resulting from point mutations. These results confirm that SALL1 haploinsufficiency is sufficient to cause a mild TBS phenotype but suggest that it is not sufficient to cause the severe, classical form. It therefore seems that there is a different contribution of SALL1 gene function to mouse and human embryonic development., (2006 Wiley-Liss, Inc.)

Human piebaldism is a rare autosomal dominant disorder that comprises congenital patchy depigmentation of the scalp, forehead, trunk and limbs. It is caused by mutations in the cell-surface receptor tyrosine kinase gene (KIT, also c-kit). We screened three families and three isolated cases of piebaldism from different countries for mutations in the KIT gene using automated sequencing methods. We report six novel KIT point mutations: three missense (C788R, W835R, P869S) at highly conserved amino acid sites; one nonsense (Q347X) that results in termination of translation of the KIT gene in exon 6; and two splice site nucleotide substitutions (IVS13+2T>G, IVS17-1G>A) that are predicted to impair normal splicing. These mutations were not detected in over 100 normal individuals and are likely to be the cause of piebaldism in our subjects., (Copyright 2002 Wiley-Liss, Inc.)

Non-syndromic cardiac septation defects are common, yet the causative factors remain largely uncharacterised. Septation defects are an integral part of many syndromes, some of which are associated with chromosomal alterations. For the majority, the physiopathogenesis is believed to be multi-factorial, hindering the identification of causative factors. Ten mutations in the gene encoding the transcription factor CSX/NKX2-5 have been described in individuals with ASD and/or atrioventricular conduction defects. In addition, several other cardiac abnormalities were observed, yet the mildest forms are reminiscent of non-syndromic septation defects. The CSX/NKX2-5 gene is thus a good candidate for various cardiopathies. We have collected two families with inherited predisposition to cardiac abnormalities. Some members of the families presented ASD and AV block. In both families a novel CSX/NKX2-5 mutation was identified in the homeodomain. Variable expressivity in the phenotype was observed in both families. Importantly, mutation carriers did not present any symptoms at young age. In addition, anomalous venous return, a phenotype not previously associated to CSX/NKX2-5 mutations, was observed in one of the families. We also screened the CSX/NKX2-5 gene in sporadic and familial cases of other cardiopathies. As additional mutations were not found, substitutions in CSX/NKX2-5 gene seem to be a rare cause of cardiopathies without conduction defect., (Copyright 2002 Wiley-Liss, Inc.)

In this report, we describe two siblings, a brother and a sister, with mental retardation and limb abnormalities (brachymetacarpy and brachymetatarsy in the brother and clinodactyly in his sister). Fluorescent in situ hybridization analysis (FISH) using subtelomeric probes proved that the patients carried an unbalanced subtelomeric rearrangement with 2qter deletion involving the Glypican 1 gene. Given the expression pattern in the developing limb bud, Glypican 1 gene represents a good candidate for brachydactyly E., (Copyright 2002 Wiley-Liss, Inc.)

We report a 13-week-old female fetus with early onset fetal akinesia deformation sequence (FADS) and hydranencephaly. In a previous pregnancy, the same ultrasonographic findings were noted at 13 weeks. Fetopathological examination of both female fetuses confirmed FADS with severe arthogryposis, multiple pterygia, and muscular hypoplasia. Neuropathological examination showed massive cystic dilatation of the cerebral ventricles (hydranencephaly) with calcification of the basal ganglion and brain stem and a proliferative vasculopathy throughout the central nervous system. The findings in the two female siblings document the earliest echographic diagnosis of hydranencephaly, Fowler type, and this observation further supports autosomal recessive inheritance of this distinct type of hydranencephaly., (Copyright 2002 Wiley-Liss, Inc.)

We report the second trimester prenatal diagnosis of severe symmetrical limb deficiencies with posterior fossa cyst and cardiac anomaly in a female fetus. Fetopathological examination revealed additional anomalies: renal-hepatic-pancreatic dysplasia, cleft palate, and Müllerian duct anomaly. The spectrum of congenital malformations in the present observation is difficult to classify into a single syndrome entity and presents an overlap with several syndromes: Roberts syndrome, Goldston syndrome, and renal-hepatic-pancreatic dysplasia., (Copyright 2001 Wiley-Liss, Inc.)

We present further evidence for autosomal recessive inheritance of the bilateral tibial agenesis/ectrodactyly dysostosis. A consanguineous Turkish couple gave birth to three children with malformations. The first, a boy, died neonatally of pulmonary hypertension with congenital alveolar capillary dysplasia and also had tibial agenesis and ectrodactyly. A second child, a girl, died after birth with the same abnormality of the lungs without skeletal malformations. After the birth of three unaffected children, echographic examination at 15 weeks of gestation in the sixth pregnancy documented agenesis of tibiae and symmetrical ectrodactyly of hands and feet. Autopsy did not show additional malformations, and lung development was normal for gestational age. This observation also confirms the autosomal recessive inheritance pattern of congenital alveolar capillary dysplasia., (Copyright 2001 Wiley-Liss, Inc.)

We present a patient with heterotaxy and a de novo, apparently balanced reciprocal translocation with breakpoints at 6q21 and 20p13. Another patient with heterotaxy was previously reported with a de novo balanced translocation involving chromosome band 6q21. The breakpoints in both patients on 6q21 were found to be located in the same chromosomal region spanning maximally 2 Mb. We speculate that the two breakpoints lead to the disruption of the function of a single gene, either directly or through long distance effects. Alternatively, the present observation suggests additional heterogeneity in heterotaxy in humans., (Copyright 2001 Wiley-Liss, Inc.)

This study presents a family with a syndromic form of X-linked mental retardation in which four males in two generations present severe mental retardation, slowly progressive spastic paraplegia, facial hypotonia, and maxillary hypoplasia. Multipoint linkage analysis with 24 highly polymorphic markers indicated two possible candidate regions: Xp21.1-Xq21.3 (flanking markers DXS1214 and DXS990) and Xq23-Xq27.1 (flanking markers DXS8020 and DXS984). The two known loci for X-linked mental retardation and spastic paraplegia are excluded: proteolipid protein in Xp21 and L1 cell adhesion molecule in Xq28. Therefore, the syndrome in this family appears to represent a previously undescribed X-linked spastic paraplegia-mental retardation syndrome., (Copyright 2000 Wiley-Liss, Inc.)

In this contribution we review current knowledge of the chromosome 22q11 deletion syndrome, with special emphasis on the clinical characteristics, including physical features, cognitive-behavioral spectrum, and psychiatric complications.

We report on a 31-year-old mentally retarded woman with minor facial anomalies and a heteromorphic chromosome 9 with tandem duplication of the 9p11-q13 pericentromeric region. To the best of our knowledge, this is the first report of tandem duplication of this region. An identical chromosome 9 morphology was found in the healthy and phenotypically normal sister of the proposita. The usefulness of double-color FISH techniques and the presumed mechanism accounting for the origin of the chromosomal anomaly and for the phenotypic discordance observed between the two sisters are discussed., (Copyright 2000 Wiley-Liss, Inc.)

Ninety-six adults with Down syndrome (DS) from an institutional setting of 591 mentally retarded were investigated systematically with respect to cytogenetic diagnosis, mental functioning and dementia, ophthalmological and audiological abnormalities, and thyroid function. Seventy of the 96 DS patients (73%) were older than 40 years. Only 4.2% were females. Trisomy 21 was found in 86% and mosaic trisomy 21 in 13%. Eighty-two percent of the patients were moderately or severely mentally retarded, 15% were profoundly retarded, and only 3% mildly retarded. Nineteen percent of the patients had dementia. This number increased to 42% of the patients above the age of 50 years. Epileptic seizures were present in 16.7% of all patients, and in 50% of the patients with dementia. Only 17% of the patients in the present study had normal visual acuity, one-third had at least moderately reduced vision. This number increased significantly with age: in the age group 50-59 years almost half of the patients had moderate to severe vision loss. Seventy percent of the patients had moderate, severe, or very severe hearing loss, which was undiagnosed before systematic hearing testing was performed. Increased (48%) or decreased (1%) TSH level was found in 49% of the patients examined for thyroid functions. We suggest a regular screening of all adults with DS to diagnose early dementia, epilepsy, hypothyroidism, and early loss of visual acuity and hearing, with special attention to the group of patients who are severely to profoundly mentally retarded and those with advanced age. Cytogenetic studies are necessary to confirm the clinical diagnosis and are essential for genetic counseling purposes., (Copyright 1999 Wiley-Liss, Inc.)

Two families with nonspecific X-linked mental retardation (MRX) are presented. In the first family, MRX51, three male patients showed mild to borderline mental retardation. Multipoint linkage analysis yielded a maximal LOD score of 2.10 between markers DXS8012 and DXS1003, localizing the MRX51 gene at Xp11.3-p11.23. In the second family, XLMR7, three men showed moderate mental retardation (MR), and one possible female carrier had mild MR. Multipoint linkage analysis yielded an LOD score of 1.80 between markers DXS8063 and DXS1047, situating the disease gene at Xq23-q26.1. When the analysis was performed considering the affected female to be an expressing heterozygote carrier of the disease mutation, a maximal LOD score of 2.10 was found in the same region., (Copyright 1999 Wiley-Liss, Inc.)

Two families with nonspecific X-linked mental retardation (XLMR) are presented. In the first family, MRX49, 5 male patients in 2 generations showed mild to moderate mental retardation. Two-point linkage analysis with 28 polymorphic markers, dispersed over the X-chromosome, yielded a maximal LOD score of 2.107 with markers DXS7107 and DXS8051 at theta = 0.0, localizing the MRX49 gene at Xp22.3-p22.2, between Xpter and marker DXS8022. Multipoint linkage analysis showed negative LOD values over all other regions of the chromosome. In the second family, MRX50, 4 males in 2 generations showed moderate mental retardation. Pairwise linkage analysis with 28 polymorphic markers yielded a LOD score of 2.056 with markers DXS8054, DXS1055, and DXS1204, all at theta = 0.0. Flanking markers were DXS8012 and DXS991, situating the MRX50 gene at Xp11.3-Xp11.21, in the pericentromeric part of the short arm of the X chromosome.

We report the clinical findings in 5 patients with a terminal deletion of the short arm of chromosome 8. Mild developmental delay was constantly present, in association with microcephaly in 4 of 5 patients. Facial anomalies were mild or absent. A congenital heart defect was present in 3 patients: an atrioventricular septal defect (AVSD) in 2 and an atrial septal defect type II (ASDII) with pulmonary stenosis in one. A highly similar pattern of behavioural difficulties was present in the 3 older children (8-11 years), with outbursts of aggressiveness and destructive behaviour. Follow-up in one patient showed that at the age of 16 years, these behavioural problems had largely disappeared. This observation suggests that in addition to mental retardation, microcephaly, congenital heart defect (typically AVSD), a terminal deletion of chromosome 8p may be associated with a characteristic behavioural phenotype during childhood.

We report 2 families with X-linked infantile spasms syndrome (X-linked West syndrome). Data from clinical examination, biochemical analysis, neuroimaging, and neuropathology are discussed. In these families, genetic linkage analysis was able to locate the disease gene to the distal part of the short arm of the X chromosome, between Xpter and Xp11.4. This is the first report of linkage with genetic markers in this disorder. Although most cases are sporadic, further unraveling of the genetic background of the familial cases might greatly improve our understanding of infantile spasms.

A neonate presented with the fetal hypokinesia sequence and signs of spinal muscular atrophy (SMA). Severe pathological changes including ballooned neurons and neuronophagia were found not only in the motor nerve nuclei but also in the thalamic, cerebellar, and brainstem nuclei as well as in the dorsal root ganglia. Direct DNA analysis showed the presence of a chimeric SMN gene, with a rearrangement occurring between exon 7 of the centromeric SMN gene and exon 8 of the telomeric SMN gene. Circumstantial evidence suggests that only a single copy of this gene is present, with transcriptional characteristics of a centromeric SMN gene. In addition, a homozygous deletion in the NAIP genes was demonstrated. This observation demonstrates that at least some cases with fetal hypokinesia and SMA may represent the severe end of a spectrum of disorders caused by deletions in the SMA locus on chromosome 5q13. In addition, these findings are compatible with a modifying role for the centromeric SMN genes and the NAIP genes in the severity of the SMA phenotype.

We report on 2 sibs with consanguineous parents, and an identical progressive extrapyramidal movement disorder with onset in adolescence and associated with progressive alopecia and primary hypogonadism. To our knowledge, this syndrome has not been reported, and probably represents a newly recognized autosomal recessive condition.

In this report, we describe a 2.5-year-old severely mentally retarded boy with peculiar appearance and generalized ichthyosis, born to consanguineous Turkish parents. The histological finding in the skin biopsy of unusually large oval keratohyalin granules in the granular cells is unique, and hitherto has not been reported in other ichthyosis-mental retardation syndromes.

We report on a newborn infant with male pseudohermaphroditism and glomerular lesions (Denys-Drash syndrome) but without Wilms tumor. A constitutional heterozygous mutation in the WT1 gene (366Arg to His) was identified. In addition the child had a large diaphragmatic hernia, so far not described in Denys-Drash syndrome. The expression of the WT1 gene in pleural and abdominal mesothelium and the occurrence of diaphragmatic hernia in transgenic mice with a homozygous WT1 deletion strongly suggests that the diaphragmatic hernia in this patient is part of the malformation pattern caused by WT1 mutations.