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46,XY gonadal dysgenesis (GD) is a disorder of sex development due to incomplete gonadal differentiation into testes, resulting in female to ambiguous external genitalia. Duplications at the Xp21.2 locus involving the NR0B1 (DAX1) gene have previously been associated with 46,XY GD. More recently, a complex structural variant not directly involving NR0B1 has been reported in 46,XY GD illustrating that the mechanism of how copy number variants (CNVs) at Xp21.2 may cause 46,XY gonadal dysgenesis is not yet fully understood. Here, we report on three families in which a duplication involving the NR0B1 gene was detected in the context of prenatal screening. This is the first report of duplications involving NR0B1 in three phenotypically normal males in two families. Fertility problems were present in one adult male carrier. The data reported here from an unbiased screening population broaden the phenotype associated with CNVs involving NR0B1, and this may aid clinicians in counseling and decision making in the prenatal context., (© 2024. The Author(s), under exclusive licence to European Society of Human Genetics.)

Maternally inherited 15q11-q13 duplications are generally found to cause more severe neurodevelopmental anomalies compared to paternally inherited duplications. However, this assessment is mainly inferred from the study of patient populations, causing an ascertainment bias towards patients at the more severe end of the phenotypic spectrum. Here, we analyze the low coverage genome-wide cell-free DNA sequencing data obtained from pregnant women during non-invasive prenatal screening (NIPS). We detect 23 15q11-q13 duplications in 333,187 pregnant women (0.0069%), with an approximately equal distribution between maternal and paternal duplications. Maternally inherited duplications are always associated with a clinical phenotype (ranging from learning difficulties to intellectual impairment, epilepsy and psychiatric disorders), while paternal duplications are normal or associated with milder phenotypes (mild learning difficulties and dyslexia). This data corroborates the difference in impact between paternally and maternally inherited 15q11-q13 duplications, contributing to the improvement of genetic counselling. We recommend reporting 15q11-q13 duplications identified during genome-wide NIPS with appropriate genetic counselling for these pregnant women in the interest of both mothers and future children., (© 2023. The Author(s), under exclusive licence to European Society of Human Genetics.)

Non-invasive prenatal testing has been introduced for the detection of Trisomy 13, 18, and 21. Using genome-wide screening also other "rare" autosomal trisomies (RATs) can be detected with a frequency about half the frequency of the common trisomies in the large population-based studies. Large prospective studies and clear clinical guidelines are lacking to provide adequate counseling and management to those who are confronted with a RAT as a healthcare professional or patient. In this review we reviewed the current knowledge of the most common RATs. We compiled clinical relevant parameters such as incidence, meiotic or mitotic origin, the risk of fetal (mosaic) aneuploidy, clinical manifestations of fetal mosaicism for a RAT, the effect of confined placental mosaicism on placental function and the risk of uniparental disomy (UPD). Finally, we identified gaps in the knowledge on RATs and highlight areas of future research. This overview may serve as a first guide for prenatal management for each of these RATs., (© 2022. The Author(s), under exclusive licence to European Society of Human Genetics.)

TBR1, a T-box transcription factor expressed in the cerebral cortex, regulates the expression of several candidate genes for autism spectrum disorders (ASD). Although TBR1 has been reported as a high-confidence risk gene for ASD and intellectual disability (ID) in functional and clinical reports since 2011, TBR1 has only recently been recorded as a human disease gene in the OMIM database. Currently, the neurodevelopmental disorders and structural brain anomalies associated with TBR1 variants are not well characterized. Through international data sharing, we collected data from 25 unreported individuals and compared them with data from the literature. We evaluated structural brain anomalies in seven individuals by analysis of MRI images, and compared these with anomalies observed in TBR1 mutant mice. The phenotype included ID in all individuals, associated to autistic traits in 76% of them. No recognizable facial phenotype could be identified. MRI analysis revealed a reduction of the anterior commissure and suggested new features including dysplastic hippocampus and subtle neocortical dysgenesis. This report supports the role of TBR1 in ID associated with autistic traits and suggests new structural brain malformations in humans. We hope this work will help geneticists to interpret TBR1 variants and diagnose ASD probands.

We aimed to identify novel deletions and variants of TP63 associated with orofacial clefting (OFC). Copy number variants were assessed in three OFC families using microarray analysis. Subsequently, we analyzed TP63 in a cohort of 1072 individuals affected with OFC and 706 population-based controls using molecular inversion probes (MIPs). We identified partial deletions of TP63 in individuals from three families affected with OFC. In the OFC cohort, we identified several TP63 variants predicting to cause loss-of-function alleles, including a frameshift variant c.569_576del (p.(Ala190Aspfs*5)) and a nonsense variant c.997C>T (p.(Gln333*)) that introduces a premature stop codon in the DNA-binding domain. In addition, we identified the first missense variants in the oligomerization domain c.1213G>A (p.(Val405Met)), which occurred in individuals with OFC. This variant was shown to abrogate oligomerization of mutant p63 protein into oligomeric complexes, and therefore likely represents a loss-of-function allele rather than a dominant-negative. All of these variants were inherited from an unaffected parent, suggesting reduced penetrance of such loss-of-function alleles. Our data indicate that loss-of-function alleles in TP63 can also give rise to OFC as the main phenotype. We have uncovered the dosage-dependent functions of p63, which were previously rejected.

Deletions on chromosome 15q14 are a known chromosomal cause of cleft palate, typically co-occurring with intellectual disability, facial dysmorphism, and congenital heart defects. The identification of patients with loss-of-function variants in MEIS2, a gene within this deletion, suggests that these features are attributed to haploinsufficiency of MEIS2. To further delineate the phenotypic spectrum of the MEIS2-related syndrome, we collected 23 previously unreported patients with either a de novo sequence variant in MEIS2 (9 patients), or a 15q14 microdeletion affecting MEIS2 (14 patients). All but one de novo MEIS2 variant were identified by whole-exome sequencing. One variant was found by targeted sequencing of MEIS2 in a girl with a clinical suspicion of this syndrome. In addition to the triad of palatal defects, heart defects, and developmental delay, heterozygous loss of MEIS2 results in recurrent facial features, including thin and arched eyebrows, short alae nasi, and thin vermillion. Genotype-phenotype comparison between patients with 15q14 deletions and patients with sequence variants or intragenic deletions within MEIS2, showed a higher prevalence of moderate-to-severe intellectual disability in the former group, advocating for an independent locus for psychomotor development neighboring MEIS2.

Au-Kline syndrome (AKS, OMIM 616580) is a multiple malformation syndrome, first reported in 2015, associated with intellectual disability. AKS has been associated with de novo loss-of-function variants in HNRNPK (heterogeneous ribonucleoprotein K), and to date, only four of these patients have been described in the literature. Recently, an additional patient with a missense variant in HNRNPK was also reported. These patients have striking facial dysmorphic features, including long palpebral fissures, ptosis, deeply grooved tongue, broad nose, and down-turned mouth. Patients frequently also have skeletal and connective tissue anomalies, craniosynostosis, congenital heart malformations, and renal anomalies. In this report, we describe six new patients and review the clinical information on all reported AKS patients, further delineating the phenotype of AKS. There are now a total of 9 patients with de novo loss-of-function variants in HNRNPK, one individual with a de novo missense variant in addition to 3 patients with de novo deletions of 9q21.32 that encompass HNRNPK. While there is considerable overlap between AKS and Kabuki syndrome (KS), these additional patients demonstrate that AKS does have a distinct facial gestalt and phenotype that can be differentiated from KS. This growing AKS patient cohort also informs an emerging approach to management and health surveillance for these patients.

Nance-Horan syndrome is a rare X-linked developmental disorder characterized by bilateral congenital cataract, dental anomalies, facial dysmorphism, and intellectual disability. Here, we identify a patient with Nance-Horan syndrome caused by a new nonsense NHS variant. In addition, the patient presented congenital diaphragmatic hernia. NHS gene expression in murine fetal diaphragm was demonstrated, suggesting a possible involvement of NHS in diaphragm development. Congenital diaphragmatic hernia could result from NHS loss of function in pleuroperitoneal fold or in somites-derived muscle progenitor cells leading to an impairment of their cells migration.

In inherited primary arrhythmia syndromes (PAS) and cardiomyopathies (CMP), the yield of genetic testing varies between 20 and 75% in different diseases according to studies performed in the pre next-generation sequencing (NGS) era. It is unknown whether retesting historical negative samples with NGS techniques is worthwhile. Therefore, we assessed the value of NGS-based panel testing in previously genotype negative-phenotype positive probands. We selected 107 patients (47 PAS and 60 CMP) with a clear phenotype who remained genotype negative after genetic analysis of the main genes implicated in their specific phenotype. Targeted sequencing of the coding regions of 71 PAS- and CMP-related genes was performed. Variant interpretation and classification was done according to a cardiology-specific scoring algorithm ('Amsterdam criteria') and the ACMG-AMP criteria. Co-segregation analysis was performed when DNA and clinical data of family members were available. Finally, a genetic diagnosis could be established in 21 patients (20%), 5 PAS (11%) and 16 CMP (27%) patients, respectively. The increased detection rate was due to sequencing of novel genes in 52% of the cases and due to technical failures with the historical analysis in 48%. A total of 118 individuals were informed about their carrier state and either reassured or scheduled for proper follow-up. To conclude, genetic retesting in clinically overt PAS and CMP cases, who were genotype negative with older techniques, resulted in an additional genetic diagnosis in up to 20% of the cases. This clearly supports a policy for genetic retesting with NGS-based panels.

16q24 deletion involving the ANKRD11 gene, ranging from 137 kb to 2 Mb, have been associated with a microdeletion syndrome characterized by variable cognitive impairment, autism spectrum disorder, facial dysmorphisms with dental anomalies, brain abnormalities essentially affecting the corpus callosum and short stature. On the other hand, patients carrying either deletions encompassing solely ANKRD11 or its loss-of-function variants were reported in association with the KBG syndrome, characterized by a very similar phenotype, including mild-to-moderate intellectual disability, short stature and macrodontia of upper incisors, with inter and intrafamilial variability. To assess whether the haploinsufficiency of ANKRD11-flanking genes, such as ZFPM1, CDH15 and ZNF778, contributed to either the severity of the neurological impairment or was associated with other clinical features, we collected 12 new cases with a 16q24.2q24.3 deletion (de novo in 11 cases), ranging from 343 kb to 2.3 Mb. In 11 of them, the deletion involved the ANKRD11 gene, whereas in 1 case only flanking genes upstream to it were deleted. By comparing the clinical and genetic features of our patients with those previously reported, we show that the severity of the neurological phenotype and the frequency of congenital heart defects characterize the deletions that, besides ANKRD11, contain ZFPM1, CDH15 and ZNF778 as well. Moreover, the presence of thrombocytopenia and astigmatism should be taken into account to distinguish between 16q24 microdeletion syndrome and KBG syndrome. The single patient not deleted for ANKRD11, whose phenotype is characterized by milder psychomotor delay, cardiac congenital malformation, thrombocytopenia and astigmatism, confirms all this data.

A challenge in clinical genomics is to predict whether copy number variation (CNV) affecting a gene or multiple genes will manifest as disease. Increasing recognition of gene dosage effects in neurodevelopmental disorders prompted us to develop a computational approach based on critical-exon (highly expressed in brain, highly conserved) examination for potential etiologic effects. Using a large CNV dataset, our updated analyses revealed significant (P < 1.64 × 10(-15)) enrichment of critical-exons within rare CNVs in cases compared to controls. Separately, we used a weighted gene co-expression network analysis (WGCNA) to construct an unbiased protein module from prenatal and adult tissues and found it significantly enriched for critical exons in prenatal (P < 1.15 × 10(-50), OR = 2.11) and adult (P < 6.03 × 10(-18), OR = 1.55) tissues. WGCNA yielded 1,206 proteins for which we prioritized the corresponding genes as likely to have a role in neurodevelopmental disorders. We compared the gene lists obtained from critical-exon and WGCNA analysis and found 438 candidate genes associated with CNVs annotated as pathogenic, or as variants of uncertain significance (VOUS), from among 10,619 developmental delay cases. We identified genes containing CNVs previously considered to be VOUS to be new candidate genes for neurodevelopmental disorders (GIT1, MVB12B and PPP1R9A) demonstrating the utility of this strategy to index the clinical effects of CNVs.

The 22q11.2 deletion syndrome is the most common microdeletion disorder, with wide phenotypic variability. To investigate variation within the non-deleted allele we performed targeted resequencing of the 22q11.2 region for 127 patients, identifying multiple deletion sizes, including two deletions with atypical breakpoints. We cataloged ~12,000 hemizygous variant positions, of which 84% were previously annotated. Within the coding regions 95 non-synonymous variants, three stop gains, and two frameshift insertions were identified, some of which we speculate could contribute to atypical phenotypes. We also catalog tolerability of 22q11 gene mutations based on related autosomal recessive disorders in man, embryonic lethality in mice, cross-species conservation and observations that some genes harbor more or less variants than expected. This extensive catalog of hemizygous variants will serve as a blueprint for future experiments to correlate 22q11DS variation with phenotype.

We report on seven novel patients with a submicroscopic 22q12 deletion. The common phenotype constitutes a contiguous gene deletion syndrome on chromosome 22q12.1q12.2, featuring NF2-related schwannoma of the vestibular nerve, corpus callosum agenesis and palatal defects. Combining our results with the literature, eight patients are recorded with palatal defects in association with haploinsufficiency of 22q12.1, including the MN1 gene. These observations, together with the mouse expression data and the finding of craniofacial malformations including cleft palate in a Mn1-knockout mouse model, suggest that this gene is a candidate gene for cleft palate in humans.

Noninvasive prenatal testing by massive parallel sequencing of maternal plasma DNA has rapidly been adopted as a mainstream method for detection of fetal trisomy 21, 18 and 13. Despite the relative high accuracy of current NIPT testing, a substantial number of false-positive and false-negative test results remain. Here, we present an analysis pipeline, which addresses some of the technical as well as the biologically derived causes of error. Most importantly, it differentiates high z-scores due to fetal trisomies from those due to local maternal CNVs causing false positives. This pipeline was retrospectively validated for trisomy 18 and 21 detection on 296 samples demonstrating a sensitivity and specificity of 100%, and applied prospectively to 1350 pregnant women in the clinical diagnostic setting with a result reported in 99.9% of cases. In addition, values indicative for trisomy were observed two times for chromosome 7 and once each for chromosomes 15 and 16, and once for a segmental trisomy 18. Two of the trisomies were confirmed to be mosaic, one of which contained a uniparental disomy cell line. As placental trisomies pose a risk for low-grade fetal mosaicism as well as uniparental disomy, genome-wide noninvasive aneuploidy detection is improving prenatal management.

KAT6B sequence variants have been identified previously in both patients with the Say-Barber-Biesecker type of blepharophimosis mental retardation syndromes (SBBS) and in the more severe genitopatellar syndrome (GPS). We report on the findings in a previously unreported group of 57 individuals with suggestive features of SBBS or GPS. Likely causative variants have been identified in 34/57 patients and were commonly located in the terminal exons of KAT6B. Of those where parental samples could be tested, all occurred de novo. Thirty out of thirty-four had truncating variants, one had a missense variant and the remaining three had the same synonymous change predicted to affect splicing. Variants in GPS tended to occur more proximally to those in SBBS patients, and genotype/phenotype analysis demonstrated significant clinical overlap between SBBS and GPS. The de novo synonymous change seen in three patients with features of SBBS occurred more proximally in exon 16. Statistical analysis of clinical features demonstrated that KAT6B variant-positive patients were more likely to display hypotonia, feeding difficulties, long thumbs/great toes and dental, thyroid and patella abnormalities than KAT6B variant-negative patients. The few reported patients with KAT6B haploinsufficiency had a much milder phenotype, though with some features overlapping those of SBBS. We report the findings in a previously unreported patient with a deletion of the KAT6B gene to further delineate the haploinsufficiency phenotype. The molecular mechanisms giving rise to the SBBS and GPS phenotypes are discussed.

Variants in PORCN are a cause of Goltz-Gorlin syndrome or Focal Dermal Hypoplasia, an X-linked dominant disorder affecting heterozygous females and until now considered to be embryonic lethal in males. Exome sequencing was performed in a family in which two male siblings were characterized by microphthalmia and additional congenital anomalies including diaphragmatic hernia, spina bifida and cardiac defects. Surprisingly, we identified a maternally inherited variant in PORCN present in both males as well as in two female siblings. This represents the first finding of a PORCN variant in non-mosaic males affected with Goltz-Gorlin syndrome. The apparently asymptomatic mother showed extreme skewing of X-inactivation (90%), an asymptomatic female sibling showed skewing of 88%, and the second female sibling affected with cutis aplasia of the scalp showed X-inactivation considered within the normal range.

Baraitser-Winter, Fryns-Aftimos and cerebrofrontofacial syndrome types 1 and 3 have recently been associated with heterozygous gain-of-function mutations in one of the two ubiquitous cytoplasmic actin-encoding genes ACTB and ACTG1 that encode β- and γ-actins. We present detailed phenotypic descriptions and neuroimaging on 36 patients analyzed by our group and six cases from the literature with a molecularly proven actinopathy (9 ACTG1 and 33 ACTB). The major clinical anomalies are striking dysmorphic facial features with hypertelorism, broad nose with large tip and prominent root, congenital non-myopathic ptosis, ridged metopic suture and arched eyebrows. Iris or retinal coloboma is present in many cases, as is sensorineural deafness. Cleft lip and palate, hallux duplex, congenital heart defects and renal tract anomalies are seen in some cases. Microcephaly may develop with time. Nearly all patients with ACTG1 mutations, and around 60% of those with ACTB mutations have some degree of pachygyria with anteroposterior severity gradient, rarely lissencephaly or neuronal heterotopia. Reduction of shoulder girdle muscle bulk and progressive joint stiffness is common. Early muscular involvement, occasionally with congenital arthrogryposis, may be present. Progressive, severe dystonia was seen in one family. Intellectual disability and epilepsy are variable in severity and largely correlate with CNS anomalies. One patient developed acute lymphocytic leukemia, and another a cutaneous lymphoma, indicating that actinopathies may be cancer-predisposing disorders. Considering the multifaceted role of actins in cell physiology, we hypothesize that some clinical manifestations may be partially mutation specific. Baraitser-Winter cerebrofrontofacial syndrome is our suggested designation for this clinical entity.

The Forkhead box G1 (FOXG1) gene encodes a transcriptional repressor essential for early development of the telencephalon. Intragenic mutations and gene deletions leading to haploinsufficiency cause the congenital variant of Rett syndrome. We here describe Rett syndrome-like patients, three of them carrying a balanced translocation with breakpoint in the chromosome 14q12 region, and one patient having a 14q12 microdeletion excluding the FOXG1 gene. The hypothesis of long-range FOXG1-regulatory elements in this region was supported by our finding of reduced FOXG1 mRNA and protein levels in platelets and skin fibroblasts from these cases. Given that FOXG1 is not only expressed in brain but also in platelets, we have studied platelet morphology in these patients and two additional patients with FOXG1 mutations. Electron microscopy of their platelets showed some enlarged, rounder platelets with often abnormal alpha, and fewer dense granules. Platelet function studies were possible in one 14q12 translocation patient with a prolonged Ivy bleeding time and a patient with a heterozygous FOXG1 c.1248C>G mutation (p.Tyr416X). Both have a prolonged PFA-100 occlusion time with collagen and epinephrine and reduced aggregation responses to low dose of ADP and epinephrine. Dense granule ATP secretion was normal for strong agonists but absent for epinephrine. In conclusion, our study shows that by using platelets functional evidence of cis-regulatory elements in the 14q12 region result in reduced FOXG1 levels in patients' platelets having translocations or deletions in that region. These platelet functional abnormalities deserve further investigation regarding a non-transcriptional regulatory role for FOXG1 in these anucleated cells.

New genetic technologies are capable of returning far more information than the single answer to the single question posed when conducting a given genetic test. Genetics contexts consequently stand on the brink of an explosion of what have traditionally been called 'incidental findings'. However, the continued use of this term is controversial. Various replacements for 'incidental findings' have been attempted, but none with widespread success. Agreement on terminology and definitions is vital so that the legal and ethical debate around incidental findings can proceed. We highlight the difficulties raised by the various terms currently used as alternatives, and end by defending our choice for the term 'secondary variants'.

Any test that produces visual images or digital or genetic sequences will tend to produce incidental findings because more will be visible than what was originally sought. We conducted a systematic review of the ethical reasons presented in the literature for and against the disclosure of incidental findings arising in clinical and research genetics contexts. A search of electronic databases resulted in 13 articles included for systematic review. Articles presented reasons for and against disclosure, and reasons for proceeding with caution when making decisions about disclosure. One major recommendation of the reviewed articles is in favor of qualified disclosure: incidental findings with confirmed clinical utility where there is the possibility of treatment or prevention should be disclosed, with exceptions. A second type of recommendation is that disclosure should proceed with caution, especially in the context of new genetic technologies and genetic testing involving minors. It is also recommended that the number of possible incidental findings be limited even before genetic testing is carried out. Such a policy, which we advocate, would show preference for non-disclosure.

Wolf-Hirschhorn syndrome is caused by anomalies of the short arm of chromosome 4. About 55% of cases are due to de novo terminal deletions, 40% from unbalanced translocations and 5% from other abnormalities. The facial phenotype is characterized by hypertelorism, protruding eyes, prominent glabella, broad nasal bridge and short philtrum. We used dense surface modelling and pattern recognition techniques to delineate the milder facial phenotype of individuals with a small terminal deletion (breakpoint within 4p16.3) compared to those with a large deletion (breakpoint more proximal than 4p16.3). Further, fine-grained facial analysis of several individuals with an atypical genotype and/or phenotype suggests that multiple genes contiguously contribute to the characteristic Wolf-Hirschhorn syndrome facial phenotype.

The tyrosine kinase receptor ErbB4 (erythroblastic leukemia viral oncogene homolog 4) plays a crucial role in numerous neurobiological processes in the developing and adult brain. Moreover, recent molecular genetics studies implicate ErbB4 in the pathophysiology of schizophrenia. However, the phenotypic consequences of haploinsufficiency of ErbB4 are not known, as no coding mutations have been identified until now. Here, we present a patient with early myoclonic encephalopathy and profound psychomotor delay with a de novo reciprocal translocation t(2;6)(q34;p25.3), disrupting the ErbB4 gene. This patient represents the first case of haploinsufficiency for one of the ErbB family members of tyrosine kinase receptors.

We describe an individual with autism and a coloboma of the eye carrying a mosaicism for a ring chromosome consisting of an inverted duplication of proximal chromosome 14. Of interest, the ring formation was associated with silencing of the amisyn gene present in two copies on the ring chromosome and located at 300 kb from the breakpoint. This observation lends further support for a locus for autism on proximal chromosome 14. Moreover, this case suggests that position effects need to be taken into account, when analyzing genotype-phenotype correlations based on chromosomal imbalances.

We report a Belgian patient with early-onset cerebellar ataxia, progressive spasticity, learning difficulties and moderate perceptive hearing loss. Array-Comparative Genomic Hybridisation (aCGH) detected a 1.54 Mb deletion on chromosome 13q12.12. This microdeletion occurred de novo and encompasses the SACS gene. Mutations in SACS are known to cause a recessive condition, similar to the patient's phenotype, called autosomal recessive spastic ataxia of Charlevoix-Saguenay (ARSACS). Sequencing of the remaining SACS allele revealed a hemizygous mutation c.10517T>C in exon 9, resulting in an amino-acid substitution (p.F3506S). This is the first patient with ARSACS that carries a de novo chromosomal deletion comprising SACS. We demonstrate the presence of homologous segmental duplications at the breakpoint-containing regions. This suggests non-allelic homologous recombination as the mechanism generating this deletion and explains the previous description of copy number variations of this region. This finding confirms the contribution of aCGH to gene identification in autosomal recessive disorders.

Array-based whole genome investigation or molecular karyotyping enables the genome-wide detection of submicroscopic imbalances. Proof-of-principle experiments have demonstrated that molecular karyotyping outperforms conventional karyotyping with regard to detection of chromosomal imbalances. This article identifies areas for which the technology seems matured and areas that require more investigations. Molecular karyotyping should be part of the genetic diagnostic work-up of patients with developmental disorders. For the implementation of the technique for other constitutional indications and in prenatal diagnosis, more research is appropriate. Also, the article aims to provide best practice guidelines for the application of array comparative genomic hybridisation to ensure both technical and clinical quality criteria that will optimise and standardise results and reports in diagnostic laboratories. In short, both the specificity and the sensitivity of the arrays should be evaluated in every laboratory offering the diagnostic test. Internal and external quality control programmes are urgently needed to evaluate and standardise the test results between laboratories.

ATR-X syndrome is a rare syndromic X-linked mental retardation disorder. We report that some of the patients suspected of ATR-X carry large intragenic duplications in the ATRX gene, leading to an absence of ATRX mRNA and of the protein. These findings underscore the need for including quantitative analyses to mutation analysis of the ATRX gene.

Autism is a genetic neurodevelopmental disorder of unknown cause and pathogenesis. The identification of genes involved in autism is expected to increase our understanding of its pathogenesis. Infrequently, neurodevelopmental disorders like autism are associated with chromosomal anomalies. To identify candidate genes for autism, we initiated a positional cloning strategy starting from individuals with idiopathic autism carrying a de novo chromosomal anomaly. We report on the clinical, cytogenetic and molecular findings in a male person with autism, no physical abnormalities and normal IQ, carrying a de novo balanced paracentric inversion 46,XY,inv(10)(q11.1;q21.3). The distal breakpoint disrupts the TRIP8 gene, which codes for a protein predicted to be a transcriptional regulator associated with nuclear thyroid hormone receptors. However, no link between thyroid gland and autism has been reported so far. In addition, the same breakpoint abolishes expression of a nearby gene, REEP3, through a position effect. Receptor Expression-Enhancing Proteins (REEP) 3 is one of the six human homologs of yeast Yop1p, a probable regulator of cellular vesicle trafficking between the endoplasmatic reticulum and the Golgi network. These observations suggest that TRIP8 and REEP3 are both positional candidate genes for autism. In addition, our data indicate that in the selection of positional candidate genes when studying chromosomal aberrations, position effects should be taken into account.

The prevalence of congenital heart defects is approximately 1% of all live births. Identifying the genes responsible for cardiac malformation is the first step to understand pathogenesis. Heterozygous mutations in the CSX/NKX2-5 (NKX2E) gene have been identified to cause atrial septal defect (ASD) and/or atrioventricular (AV) conduction disturbance in some families. However, there is great variability in expressivity of the phenotype between the patients with a CSX/NKX2-5 mutation. We screened four sporadic patients and three index cases of families with ASD and/or conduction defects. In one of them, a CSX/NKX2-5 mutation was identified. This novel mutation (p.Tyr256X) was inherited in a three-generation family causing five individuals to have cardiac anomalies ranging from ASD to arrhythmias. Interestingly, all the observed AV conduction disturbances were at the nodal level, manifesting first as an AV block of the first degree and evolving toward a second-degree block. Atrial fibrillation, previously reported in three individuals with CSX/NKX2-5 mutations, was observed in three patients.

The identification of all people with a diagnosis of Prader-Willi syndrome (PWS) confirmed by DNA methylation analysis living in Flanders was attempted through contact with the four genetic centres and the PWS Association. The birth incidence for the period 1993-2001 was 1:26 676, the minimum prevalence at 31 December 2001 was 1:76 574. A decreasing number of cases with age was found, which can be explained by a number of missing cases in the older population, a higher neonatal mortality in the past and an increasing mortality with age. Childhood death is usually sudden and associated with respiratory infection and high temperature, while the cause of death in adults is considered to be circulatory or respiratory in origin.

Hereditary predisposition to lipomas is observed in familial multiple lipomatosis (OMIM 151900) and benign cervical lipomatosis (OMIM 151800) and can also be associated with mutations in the MEN1 and PTEN genes (OMIM 131100 and 153480, respectively). In addition, a recent report indicates that a few patients with hereditary retinoblastoma also have lipomas. Here we report on an extended family segregating a splice site mutation in the RB1 gene. Almost all adult carriers of this mutation had multiple lipomas while penetrance for retinoblastoma was incomplete. In an unrelated pedigree, which was reported previously, the identical mutation was only associated with low-penetrance retinoblastoma but not lipomas. Our data indicate that lipoma predisposition in hereditary retinoblastoma is not associated with specific RB1 gene mutations but is influenced by modifying factors linked to this gene.

Terminal deletions of chromosome 10p result in a DiGeorge-like phenotype that includes hypoparathyroidism, heart defects, immune deficiency, deafness and renal malformations. Studies in patients with 10p deletions have defined two non-overlapping regions that contribute to this complex phenotype. These are the DiGeorge critical region II (refs 1, 2), which is located on 10p13-14, and the region for the hypoparathyroidism, sensorineural deafness, renal anomaly (HDR) syndrome (Mendelian Inheritance in Man number 146255), which is located more telomeric (10p14-10pter). We have performed deletion-mapping studies in two HDR patients, and here we define a critical 200-kilobase region which contains the GATA3 gene. This gene belongs to a family of zinc-finger transcription factors that are involved in vertebrate embryonic development. Investigation for GATA3 mutations in three other HDR probands identified one nonsense mutation and two intragenic deletions that predicted a loss of function, as confirmed by absence of DNA binding by the mutant GATA3 protein. These results show that GATA3 is essential in the embryonic development of the parathyroids, auditory system and kidneys, and indicate that other GATA family members may be involved in the aetiology of human malformations.

Patients with a microdeletion on chromosome 22q11 demonstrate the clinical picture of the velocardiofacial syndrome. We report on three members of the same family with this microdeletion and velocardiofacial syndrome, all having an increase in platelet size and a mild decrease in platelet number. Their platelet function, however, tested by aggregation and by adherence to collagen in a whole blood perfusion system, was normal. We retrospectively studied the files of 35 other patients with 22q11 deletion and also found that their platelets had an increased size compared with cardiac controls. Moreover, their platelet size correlated negatively with platelet number. Knowing that patients with 22q11 deletion are obligate carriers for a heterozygous glycoprotein Ib beta deletion, these patients can be considered to be heterozygous Bernard-Soulier patients. In addition, a significant increase in platelet size may be a positive predictor for the clinical diagnosis of the velocardiofacial syndrome.