De novo variants in FBXO11 cause a syndromic form of intellectual disability with behavioral problems and dysmorphisms

Determining pathogenicity of genomic variation identified by next-generation sequencing techniques can be supported by recurrent disruptive variants in the same gene in phenotypically similar individuals. However, interpretation of novel variants in a specific gene in individuals with mild-moderate intellectual disability (ID) without recognizable syndromic features can be challenging and reverse phenotyping is often required. We describe 24 individuals with a de novo disease-causing variant in, or partial deletion of, the F-box only protein 11 gene (FBXO11, also known as VIT1 and PRMT9). FBXO11 is part of the SCF (SKP1-cullin-F-box) complex, a multi-protein E3 ubiquitin-ligase complex catalyzing the ubiquitination of proteins destined for proteasomal degradation. Twenty-two variants were identified by next-generation sequencing, comprising 2 in-frame deletions, 11 missense variants, 1 canonical splice site variant, and 8 nonsense or frameshift variants leading to a truncated protein or degraded transcript. The remaining two variants were identified by array-comparative genomic hybridization and consisted of a partial deletion of FBXO11. All individuals had borderline to severe ID and behavioral problems (autism spectrum disorder, attention-deficit/hyperactivity disorder, anxiety, aggression) were observed in most of them. The most relevant common facial features included a thin upper lip and a broad prominent space between the paramedian peaks of the upper lip. Other features were hypotonia and hyperlaxity of the joints. We show that de novo variants in FBXO11 cause a syndromic form of ID. The current series show the power of reverse phenotyping in the interpretation of novel genetic variances in individuals who initially did not appear to have a clear recognizable phenotype.

Lamin A/C-Related Cardiac Disease: Late Onset With a Variable and Mild Phenotype in a Large Cohort of Patients With the Lamin A/C p.(Arg331Gln) Founder Mutation

BACKGROUND

Interpretation of missense variants can be especially difficult when the variant is also found in control populations. This is what we encountered for the LMNA c.992G>A (p.(Arg331Gln)) variant. Therefore, to evaluate the effect of this variant, we combined an evaluation of clinical data with functional experiments and morphological studies.

METHODS AND RESULTS

Clinical data of 23 probands and 35 family members carrying this variant were retrospectively collected. A time-to-event analysis was performed to compare the course of the disease with carriers of other LMNA mutations. Myocardial biopsies were studied with electron microscopy and by measuring force development of the sarcomeres. Morphology of the nuclear envelope was assessed with immunofluorescence on cultured fibroblasts. The phenotype in probands and family members was characterized by atrioventricular conduction disturbances (61% and 44%, respectively), supraventricular arrhythmias (69% and 52%, respectively), and dilated cardiomyopathy (74% and 14%, respectively). LMNA p.(Arg331Gln) carriers had a significantly better outcome regarding the composite end point (malignant ventricular arrhythmias, end-stage heart failure, or death) compared with carriers of other pathogenic LMNA mutations. A shared haplotype of 1 Mb around LMNA suggested a common founder. The combined logarithm of the odds score was 3.46. Force development in membrane-permeabilized cardiomyocytes was reduced because of decreased myofibril density. Structural nuclear LMNA-associated envelope abnormalities, that is, blebs, were confirmed by electron microscopy and immunofluorescence microscopy.

CONCLUSIONS

Clinical, morphological, functional, haplotype, and segregation data all indicate that LMNA p.(Arg331Gln) is a pathogenic founder mutation with a phenotype reminiscent of other LMNA mutations but with a more benign course.

Delayed onset of ambulation in boys with Duchenne muscular dystrophy: Potential use as an endpoint in clinical trials

Individuals with Duchenne muscular dystrophy (DMD) often exhibit delayed motor and cognitive development, including delayed onset of ambulation. Data on age when loss of independent ambulation occurs are well established for DMD; however, age at onset of walking has not been well described. We hypothesize that an effective medication given in early infancy would advance the age when walking is achieved so that it is closer to age-matched norms, and that this discrete event could serve as the primary outcome measure in a clinical trial. This study examined three data sets, Muscular Dystrophy Surveillance, Tracking, and Research Network (MD STARnet); Dutch Natural History Survey (DNHS); and Parent Project Muscular Dystrophy (PPMD). The distribution of onset of ambulation in DMD (mean ± SD) and median age, in months, at the onset of ambulation was 17.3 (±5.5) and 16.0 in MD STARnet, 21.8 (±7.1) and 20.0 in DNHS, and 16.1 (±4.4) and 15 in PPMD. Age of ambulation in these data sets were all significantly later (P <0.001) than the corresponding age for typically developing boys, 12.1 (±1.8). A hypothetical clinical trial study design and power analyses are presented based on these data.

Truncating de novo mutations in the Krüppel-type zinc-finger gene ZNF148 in patients with corpus callosum defects, developmental delay, short stature, and dysmorphisms

BACKGROUND

Krüppel-type zinc finger genes (ZNF) constitute a large yet relatively poorly characterized gene family. ZNF genes encode proteins that recognize specific DNA motifs in gene promotors. They act as transcriptional co-activators or -repressors via interaction with chromatin remodeling proteins and other transcription factors. Only few ZNF genes are currently linked to human disorders and identification of ZNF gene-associated human diseases may help understand their function. Here we provide genetic, statistical, and clinical evidence to support association of ZNF148 with a new intellectual disability (ID) syndrome disorder.

METHODS

Routine diagnostic exome sequencing data were obtained from 2172 patients with ID and/or multiple congenital anomalies.

RESULTS

In a cohort of 2172 patient-parent trios referred for routine diagnostic whole exome sequencing for ID and/or multiple congenital anomalies (MCA) in the period 2012-2016, four patients were identified who carried de novo heterozygous nonsense or frameshift mutations in the ZNF148 gene. This was the only ZNF gene with recurrent truncating de novo mutations in this cohort. All mutations resulted in premature termination codons in the last exon of ZNF148. The number of the de novo truncating mutations in the ZNF148 gene was significantly enriched (p = 5.42 × 10^-3). The newly described ZNF148-associated syndrome is characterized by underdevelopment of the corpus callosum, mild to moderate developmental delay and ID, variable microcephaly or mild macrocephaly, short stature, feeding problems, facial dysmorphisms, and cardiac and renal malformations.

CONCLUSIONS

We propose ZNF148 as a gene involved in a newly described ID syndrome with a recurrent phenotype and postulate that the ZNF148 is a hitherto unrecognized but crucial transcription factor in the development of the corpus callosum. Our study illustrates the advantage of whole exome sequencing in a large cohort using a parent-offspring trio approach for identifying novel genes involved in rare human diseases.

Whole-exome sequencing is a powerful approach for establishing the etiological diagnosis in patients with intellectual disability and microcephaly

Background

Clinical and genetic heterogeneity in monogenetic disorders represents a major diagnostic challenge. Although the presence of particular clinical features may aid in identifying a specific cause in some cases, the majority of patients remain undiagnosed.

Here, we investigated the utility of whole-exome sequencing as a diagnostic approach for establishing a molecular diagnosis in a highly heterogeneous group of patients with varied intellectual disability and microcephaly.

Methods

Whole-exome sequencing was performed in 38 patients, including three sib-pairs, in addition to or in parallel with genetic analyses that were performed during the diagnostic work-up of the study participants.

Results

In ten out of these 35 families (29 %), we found mutations in genes already known to be related to a disorder in which microcephaly is a main feature. Two unrelated patients had mutations in the ASPM gene. In seven other patients we found mutations in RAB3GAP1, RNASEH2B, KIF11, ERCC8, CASK, DYRK1A and BRCA2. In one of the sib-pairs, mutations were found in the RTTN gene. Mutations were present in seven out of our ten families with an established etiological diagnosis with recessive inheritance.

Conclusions

We demonstrate that whole-exome sequencing is a powerful tool for the diagnostic evaluation of patients with highly heterogeneous neurodevelopmental disorders such as intellectual disability with microcephaly. Our results confirm that autosomal recessive disorders are highly prevalent among patients with microcephaly.

Electronic supplementary material

The online version of this article (doi:10.1186/s12920-016-0167-8) contains supplementary material, which is available to authorized users.

Compound heterozygosity of low-frequency promoter deletions and rare loss-of-function mutations in TXNL4A causes Burn-McKeown syndrome

Mutations in components of the major spliceosome have been described in disorders with craniofacial anomalies, e.g., Nager syndrome and mandibulofacial dysostosis type Guion-Almeida. The U5 spliceosomal complex of eight highly conserved proteins is critical for pre-mRNA splicing. We identified biallelic mutations in TXNL4A, a member of this complex, in individuals with Burn-McKeown syndrome (BMKS). This rare condition is characterized by bilateral choanal atresia, hearing loss, cleft lip and/or palate, and other craniofacial dysmorphisms. Mutations were found in 9 of 11 affected families. In 8 families, affected individuals carried a rare loss-of-function mutation (nonsense, frameshift, or microdeletion) on one allele and a low-frequency 34 bp deletion (allele frequency 0.76%) in the core promoter region on the other allele. In a single highly consanguineous family, formerly diagnosed as oculo-oto-facial dysplasia, the four affected individuals were homozygous for a 34 bp promoter deletion, which differed from the promoter deletion in the other families. Reporter gene and in vivo assays showed that the promoter deletions led to reduced expression of TXNL4A. Depletion of TXNL4A (Dib1) in yeast demonstrated reduced assembly of the tri-snRNP complex. Our results indicate that BMKS is an autosomal-recessive condition, which is frequently caused by compound heterozygosity of low-frequency promoter deletions in combination with very rare loss-of-function mutations.

Central 22q11.2 deletions

22q11.2 deletion syndrome is one of the most common microdeletion syndromes. Most patients have a deletion resulting from a recombination of low copy repeat blocks LCR22-A and LCR22-D. Loss of the TBX1 gene is considered the most important cause of the phenotype. A limited number of patients with smaller, overlapping deletions distal to the TBX1 locus have been described in the literature. In these patients, the CRKL gene is deleted. Haploinsufficiency of this gene has also been implicated in the pathogenesis of 22q11.2 deletion syndrome. To distinguish these deletions (comprising the LCR22-B to LCR22-D region) from the more distal 22q11.2 deletions (located beyond LCR22-D), we propose the term "central 22q11.2 deletions". In the present study we report on 27 new patients with such a deletion. Together with information on previously published cases, we review the clinical findings of 52 patients. The prevalence of congenital heart anomalies and the frequency of de novo deletions in patients with a central deletion are substantially lower than in patients with a common or distal 22q11.2 deletion. Renal and urinary tract malformations, developmental delays, cognitive impairments and behavioral problems seem to be equally frequent as in patients with a common deletion. None of the patients had a cleft palate. Patients with a deletion that also encompassed the MAPK1 gene, located just distal to LCR22-D, have a different and more severe phenotype, characterized by a higher prevalence of congenital heart anomalies, growth restriction and microcephaly. Our results further elucidate genotype-phenotype correlations in 22q11.2 deletion syndrome spectrum.

Periconceptional folic acid associated with an increased risk of oral clefts relative to non-folate related malformations in the Northern Netherlands: a population based case-control study

Periconceptional folic acid has been associated with a reduced risk of neural tube defects, but findings on its effect in oral clefts are largely inconclusive. This case-control study assesses the effects of periconceptional folic acid on cleft risk, using complementary data from the Dutch Oral Cleft Registry and a population-based birth defects registry (Eurocat) of children and foetuses born in the Northern Netherlands between 1997 and 2009. Cases were live-born infants with non-syndromic clefts (n = 367) and controls were infants or foetuses with chromosomal/syndromal (n = 924) or non-folate related anomalies (n = 2,021). We analyzed type/timing/duration of supplement use related to traditional cleft categories as well as to their timing (early/late embryonic periods) and underlying embryological processes (fusion/differentiation defects). Consistent supplement use during the aetiologically relevant period (weeks 0-12 postconception) was associated with an increased risk of clefts (adjusted odds ratio 1.72, 95% confidence interval 1.19-2.49), especially of cleft lip/alveolus (3.16, 1.69-5.91). Further analysis systematically showed twofold to threefold increased risks for late differentiation defects-mainly clefts of the lip/alveolus-with no significant associations for early/late fusion defects. Effects were attributable to folic acid and not to other multivitamin components, and inclusion of partial use (not covering the complete aetiologically relevant period) generally weakened associations. In conclusion, this study presents several lines of evidence indicating that periconceptional folic acid in the Northern Netherlands is associated with an increased risk of clefts, in particular of cleft lip/alveolus. This association is strengthened by the specificity, consistency, systematic pattern, and duration of exposure-response relationship of our findings, underlining the need to evaluate public health strategies regarding folic acid and to further investigate potential adverse effects.

Germline mutations in DIS3L2 cause the Perlman syndrome of overgrowth and Wilms tumor susceptibility

Perlman syndrome is a congenital overgrowth syndrome inherited in an autosomal recessive manner that is associated with Wilms tumor susceptibility. We mapped a previously unknown susceptibility locus to 2q37.1 and identified germline mutations in DIS3L2, a homolog of the Schizosaccharomyces pombe dis3 gene, in individuals with Perlman syndrome. Yeast dis3 mutant strains have mitotic abnormalities. Yeast Dis3 and its human homologs, DIS3 and DIS3L1, have exoribonuclease activity and bind to the core RNA exosome complex. DIS3L2 has a different intracellular localization and lacks the PIN domain found in DIS3 and DIS3L1; nevertheless, we show that DIS3L2 has exonuclease activity. DIS3L2 inactivation was associated with mitotic abnormalities and altered expression of mitotic checkpoint proteins. DIS3L2 overexpression suppressed the growth of human cancer cell lines, and knockdown enhanced the growth of these cells. We also detected evidence of DIS3L2 mutations in sporadic Wilms tumor. These observations suggest that DIS3L2 has a critical role in RNA metabolism and is essential for the regulation of cell growth and division.

MYT1L is a candidate gene for intellectual disability in patients with 2p25.3 (2pter) deletions

A partial deletion of chromosome band 2p25.3 (2pter) is a rarely described cytogenetic aberration in patients with intellectual disability (ID). Using microarrays we identified deletions of 2p25.3, sized 0.37-3.13 Mb, in three adult siblings and three unrelated patients. All patients had ID, obesity or overweight and/or a square-shaped stature without overt facial dysmorphic features. Combining our data with phenotypic and genotypic data of three patients from the literature we defined the minimal region of overlap which contained one gene, i.e., MYT1L. MYT1L is highly transcribed in the mouse embryonic brain where its expression is restricted to postmitotic differentiating neurons. In mouse-induced pluripotent stem cell (iPS) models, MYT1L is essential for inducing functional mature neurons. These resemble excitatory cortical neurons of the forebrain, suggesting a role for MYT1L in development of cognitive functions. Furthermore, MYT1L can directly convert human fibroblasts into functional neurons in conjunction with other transcription factors. MYT1L duplication was previously reported in schizophrenia, indicating that the gene is dosage-sensitive and that shared neurodevelopmental pathways may be affected in ID and schizophrenia. Finally, deletion of MYT1, another member of the Myelin Transcription Factor family involved in neurogenesis and highly similar to MYT1L, was recently described in ID as well. The identification of MYT1L as candidate gene for ID justifies further molecular studies aimed at detecting mutations and for mechanistic studies on its role in neuron development and on neuropathogenic effects of haploinsufficiency.

The international dystrophic epidermolysis bullosa patient registry: an online database of dystrophic epidermolysis bullosa patients and their COL7A1 mutations

Dystrophic epidermolysis bullosa (DEB) is a heritable blistering disorder that can be inherited autosomal dominantly (DDEB) or recessively (RDEB) and covers a group of several distinctive phenotypes. A large number of unique COL7A1 mutations have been shown to underlie DEB. Although general genotype-phenotype correlation rules have emerged, many exceptions to these rules exist, compromising disease diagnosing and genetic counseling. We therefore constructed the International DEB Patient Registry (http://www.deb-central.org), aimed at worldwide collection and sharing of phenotypic and genotypic information on DEB. As of May 2011, this MOLGENIS-based registry contains detailed information on 508 published and 71 unpublished patients and their 388 unique COL7A1 mutations, and includes all combinations of mutations. The current registry RDEB versus DDEB ratio of 4:1, if compared to prevalence figures, suggests underreporting of DDEB in the literature. Thirty-eight percent of mutations stored introduce a premature termination codon (PTC) and 43% an amino acid change. Submission wizards allow users to quickly and easily share novel information. This registry will be of great help in disease diagnosing and genetic counseling and will lead to novel insights, especially in the rare phenotypes of which there is often lack of understanding. Altogether, this registry will greatly benefit the DEB patients.

The inversa type of recessive dystrophic epidermolysis bullosa is caused by specific arginine and glycine substitutions in type VII collagen

BACKGROUND

The inversa type of recessive dystrophic epidermolysis bullosa (RDEB-I) is a rare variant of dystrophic epidermolysis bullosa, characterised by blistering in the body flexures, trunk, and mucosa. The cause of this specific distribution is unknown. So far, 20 COL7A1 genotypes have been described in RDEB-I and genotype-phenotype correlations have not been studied extensively. The aim of the study was to gain more insight into the pathophysiology of this intriguing RDEB-I phenotype.

METHODS

Twenty Dutch and British RDEB-I patients, and full genotypes in 18 of them, were identified. The literature on RDEB-I genotypes was reviewed and an extensive genotype-phenotype correlation study for RDEB-I was conducted.

RESULTS

All 20 patients had generalised blistering at birth and during early infancy. In most patients, the age of transition from generalised to inversa distribution was before the age of 4 years. A spectrum of disease severity, ranging from the mildest 'mucosal only' phenotype to the severest phenotype with limited acral involvement, was noted. The 29 genotypes of these RDEB-I patients and those reported in the literature revealed that RDEB-I is associated with specific recessive arginine and glycine substitutions in the triple helix domain of type VII collagen.

DISCUSSION AND CONCLUSION

Why these specific arginine and glycine substitutions cause the inversa distribution remains unknown. It was not possible to identify clear differences in location and nature of substituting amino acids between these mutations and missense mutations causing other RDEB phenotypes. It is hypothesised that the higher skin temperature in the affected areas plays an important role in the pathophysiology of RDEB-I.

The unfolding clinical spectrum of holoprosencephaly due to mutations in SHH, ZIC2, SIX3 and TGIF genes

Holoprosencephaly is a severe malformation of the brain characterized by abnormal formation and separation of the developing central nervous system. The prevalence is 1:250 during early embryogenesis, the live-born prevalence is 1:16 000. The etiology of HPE is extremely heterogeneous and can be teratogenic or genetic. We screened four known HPE genes in a Dutch cohort of 86 non-syndromic HPE index cases, including 53 family members. We detected 21 mutations (24.4%), 3 in SHH, 9 in ZIC2 and 9 in SIX3. Eight mutations involved amino-acid substitutions, 7 ins/del mutations, 1 frame-shift, 3 identical poly-alanine tract expansions and 2 gene deletions. Pathogenicity of mutations was presumed based on de novo character, predicted non-functionality of mutated proteins, segregation of mutations with affected family-members or combinations of these features. Two mutations were reported previously. SNP array confirmed detected deletions; one spanning the ZIC2/ZIC5 genes (approx. 100 kb) the other a 1.45 Mb deletion including SIX2/SIX3 genes. The mutation percentage (24%) is comparable with previous reports, but we detected significantly less mutations in SHH: 3.5 vs 10.7% (P=0.043) and significantly more in SIX3: 10.5 vs 4.3% (P=0.018). For TGIF1 and ZIC2 mutation the rate was in conformity with earlier reports. About half of the mutations were de novo, one was a germ line mosaic. The familial mutations displayed extensive heterogeneity in clinical manifestation. Of seven familial index patients only two parental carriers showed minor HPE signs, five were completely asymptomatic. Therefore, each novel mutation should be considered as a risk factor for clinically manifest HPE, with the caveat of reduced clinical penetrance.

Holoprosencephaly and agnathia spectrum: Presentation of two new patients and review of the literature

Holoprosencephaly (HPE), the most common developmental disorder of the human forebrain, is occasionally associated with the spectrum of agnathia, or virtual absence of the mandible. This condition results in a constellation of structural cerebral and craniofacial abnormalities. Here we present two new patients and review 30 patients from the literature with HPE and variants of agnathia. The majority of these patients are female and have the most severe forms of HPE, with cyclopia present more frequently than is usually observed in cohorts of patients with HPE. Also, many patients have additional clinical findings not typical in patients with classic HPE, particularly situs abnormalities. Recent animal studies suggest that the association of HPE and agnathia may relate to alterations in signaling from forebrain and foregut endoderm organizing centers and subsequent first pharyngeal arch development, although present models are inadequate to explain all of the clinical findings of this enigmatic human syndrome. Further research is required to better elucidate the causal and pathogenic basis of this association.

Holoprosencephaly and ectrodactyly: Report of three new patients and review of the literature

Holoprosencephaly (HPE) and ectrodactyly represent congenital malformations of the developing forebrain and developing digits, respectively. The combination of these conditions is rare, with only 15 cases known to date (12 previously reported, and 3 new cases described here). While the findings in these patients overlap with previously described genetic conditions, the similarity in phenotypes among these patients has led to the establishment of a at least one distinct syndrome: HPE, ectrodactyly, and bilateral cleft lip-palate syndrome (OMIM 300571). There has been great interest in identifying a genetic cause for the findings in patients with HPE and ectrodactyly; however the cause(s) of this rare association still remain unknown.

Long-term follow-up of patients with recessive dystrophic epidermolysis bullosa in the Netherlands: expansion of the mutation database and unusual phenotype-genotype correlations

BACKGROUND

The current classification of recessive dystrophic epidermolysis bullosa (RDEB) comprises two major subtypes: 'severe generalized RDEB' (RDEB-sev gen) with early-onset, extensive, generalized blistering and scarring, complete absence of type VII collagen, and bi-allelic COL7A1 null mutations; milder 'generalized other RDEB' (RDEB-O) with reduced-to-normal type VII collagen expression, and non-null genotypes.

OBJECTIVE

To search for previously unrecognized phenotype-genotype correlations in 33 Dutch RDEB families.

METHODS

We analyzed extensive clinical follow-up data, available for all patients up to 19 years, detailed type VII collagen immunostaining and genotypes, and correlated clinical phenotype to molecular phenotype and genotype.

RESULTS

We identified 20 novel COL7A1 mutations. In 14 of 15 RDEB-sev gen patients type VII collagen was completely absent, one had strongly reduced type VII collagen, and all carried bi-allelic null mutations. Five of 11 RDEB-O patients developed pseudosyndactyly of the fingers preceded by skin atrophy and flexion contractures later in childhood and adolescence. All five had esophageal involvement and growth retardation. Type VII collagen immunostaining ranged from strongly reduced to slightly reduced in RDEB-O patients with pseudosyndactyly, whereas RDEB-O patients without pseudosyndactyly had slightly reduced to normal type VII collagen staining. There was no difference in genotypes between both groups, although we unexpectedly found bi-allelic null mutations in two of five RDEB-O patients with pseudosyndactyly.

CONCLUSION

Pseudosyndactyly occurs in approximately half of RDEB-O patients when type VII collagen is strongly reduced. The prognosis in RDEB cannot always be simply predicted from the COL7A1 genotype.

Ectrodactyly with fibular aplasia: a separate entity?

E/FA is the combination of ectrodactyly (split hand/foot malformation, SHFM) and fibular aplasia. It is a rare disorder considered to be inherited in an autosomal dominant fashion with reduced penetrance and variable expression. In order to determine recurrence risks for the two patients we describe, the literature on inheritance of E/FA was carefully reviewed. In our opinion, only two of the eight families previously reported as examples of familial E/FA may fit this judgment. Until mutation analysis of all SHFM genes is possible, the question remains whether these familial cases represent autosomal dominant E/FA, or an allelic variant of an SHFM subtype. Many sporadic patients with presumed E/FA may represent the fibular developmental field defect, which is a non-genetic entity with a low recurrence risk. We therefore suggest that the high recurrence risk associated with autosomal dominant inheritance should not be counselled in patients with E/FA unless their family shows the following characteristics: (1) at least one patient shows typical SHFM combined with fibular aplasia, (2) multiple limbs are affected, and (3) multiple family members are affected in at least two generations.

Mutation screening of the Ectodysplasin-A receptor gene EDAR in hypohidrotic ectodermal dysplasia

Hypohidrotic ectodermal dysplasia (HED) can be caused by mutations in the X-linked ectodysplasin A (ED1) gene or the autosomal ectodysplasin A-receptor (EDAR) and EDAR-associated death domain (EDARADD) genes. X-linked and autosomal forms are sometimes clinically indistinguishable. For genetic counseling in families, it is therefore important to know the gene involved. In 24 of 42 unrelated patients with features of HED, we found a mutation in ED1. ED1-negative patients were screened for mutations in EDAR and EDARADD. We found mutations in EDAR in 5 of these 18 patients. One mutation, p.Glu354X, is novel. In EDARADD, a novel variant p.Ser93Phe, probably a neutral polymorphism, was also found. Clinically, there was a difference between autosomal dominant and autosomal recessive HED patients. The phenotype in patients with mutations in both EDAR alleles was comparable to males with X-linked HED. Patients with autosomal dominant HED had features comparable to those of female carriers of X-linked HED. The teeth of these patients were quite severely affected. Hypohidrosis and sparse hair were also evident, but less severe. This study confirms Chassaing et al's earlier finding that mutations in EDAR account for approximately 25% of non-ED1-related HED. Mutations leading to a premature stop codon have a recessive effect except when the stop codon is in the last exon. Heterozygous missense mutations in the functional domains of the gene may have a dominant-negative effect with much variation in expression. Patients with homozygous or compound heterozygous mutations in the EDAR gene have a more severe phenotype than those with a heterozygous missense, nonsense or frame-shift mutation.

Two related Dutch families with a clinically variable presentation of cardioskeletal myopathy caused by a novel S13F mutation in the desmin gene

Desmin-related myopathy is characterised by skeletal muscle weakness often combined with cardiac involvement. Mutations in the desmin gene have been described as a cause of desmin-related myopathy (OMIM 601419). We report here on two distantly related Dutch families with autosomal dominant inheritance of desmin-related myopathy affecting 15 family members. A highly heterogeneous clinical picture is apparent, varying from isolated dilated cardiomyopathy to a more generalised skeletal myopathy and mild respiratory problems. Morphological analysis of muscle biopsies revealed intracytoplasmic desmin aggregates (desmin and p62 staining). In both families we identified an identical novel pathogenic heterozygous missense mutation, S13F, in the 'head' domain of the desmin gene which cosegregates with the disease phenotype. This is the 5th reported missense mutation located at the 'head' domain of the desmin gene and the first reported Dutch family with desmin-related myopathy. This article illustrates the importance of analysing the desmin gene in patients with (familial) cardiac conduction disease, dilated cardiomyopathy and/or a progressive skeletal myopathy resembling limb-girdle muscular dystrophy.

Shah-Waardenburg syndrome and PCWH associated with SOX10 mutations: a case report and review of the literature

Shah-Waardenburg syndrome is a rare congenital disorder with variable clinical expression, characterised by aganglionosis of the rectosigmoïd (Hirschsprung disease), and abnormal melanocyte migration, resulting in pigmentary abnormalities and sensorineural deafness (Waardenburg syndrome). Mutations in the EDN, EDNRB and SOX10 genes can be found in patients with this syndrome. SOX10 mutations are specifically associated with a more severe phenotype called PCWH: peripheral demyelinating neuropathy, central dysmyelinating leukodystrophy, Waardenburg syndrome, and Hirschsprung disease. Neuronal expression of SOX10 occurs in neural crest cells during early embryonic development and in glial cells of the peripheral and central nervous systems during late embryonic development and in adults. We present a 4-year-old girl with the PCWH phenotype associated with a de novo nonsense mutation (S384X) in SOX10. Main clinical features were mental retardation, peripheral neuropathy, deafness, Hirschsprung disease, distal arthrogryposis, white hairlock, and growth retardation. She presented with hypotonia, developmental delay, reduced peripheral nerve conduction velocities, and radiologically assessed central hypomyelination. Subsequently, the formation of abnormal myelin within the central and peripheral nervous system was functionally and radiologically assessed. Children presenting with features of Waardenburg syndrome and neurological dysfunction should be tested for mutations in the SOX10 gene to enable diagnosis and counselling.

Renal defects and limb deficiencies in 197 infants: is it possible to define the "acrorenal syndrome"?

Dieker and Opitz in 1969 described the simultaneous occurrence of limb deficiencies (LDs) and renal anomalies (RAs) in three patients. Curran and Curran introduced in 1972 the term "acrorenal syndrome." Since then, the term "acrorenal syndrome" is used occasionally, but a well-circumscribed definition has never been established. On the other hand, the concept of an acrorenal polytopic developmental field defect was postulated by Opitz and others to explain the association between RAs and LDs. We undertook this study to investigate whether this acrorenal "syndrome" could be identified in a large group of cases with congenital RAs and a limb deficiency. Eleven birth defect registries that are part of the International Clearinghouse for Birth Defects Monitoring (i.e., registries of ICBDMS in Finland, France [Paris and Strasbourg], Israel, Italy [IPIMC and Emilia Romagna], Mexico, Northern Netherlands, South America, Spain, and the United States [Atlanta]) provided data on 815 infants who had a LD and at least one other major congenital anomaly. These 815 cases were ascertained among 5,163,958 births. We selected the 197 cases who had both a limb deficiency and a renal or urinary tract anomaly. In about 50% of these cases a diagnosis or a recognized phenotype was reported, with chromosomal aberrations and VACTERL being most frequent. In the group with no diagnosis or recognized phenotype (95 cases), we looked for (a) clustering of specific types of LDs and RAs, and (b) for clustering of associated anomalies, in order to find evidence for and be able to define better the term "acrorenal syndrome." Our data suggest that an association exists between LDs and RAs, possibly explained by the concept of the acrorenal polytopic developmental field defect. However, our dataset does not yield evidence for the existence of one distinct "syndrome," defined as a pattern of causally related multiple anomalies. Therefore, use of the term "acrorenal syndrome" should be avoided.

Pigmentary mosaicism following the lines of Blaschko in a girl with a double aneuploidy mosaicism: (47,XX,+7/45,X)

We report on a 6-year-old girl with linear streaks of apparent hypopigmentation and hyperpigmentation following the Blaschko lines, growth retardation, bupthalmos of the left eye, and mild mental retardation. She had a 45,X karyotype in lymphocytes. In cultured fibroblasts a double aneuploidy mosaicism was detected, consisting of a cell line with trisomy for chromosome 7 and a cell line with monosomy for the X-chromosome and no cell line with a normal karyotype. Cutis tricolor or three levels of pigmentation in different skin areas suggested presence of a third, probably normal cell line. Double aneuploidy mosaicism of a cell line with monosomy X and a cell line with trisomy of an autosome is a rare finding. The combination of monosomy X with trisomy of chromosomes 8, 10, 13, 18, and 21 has been reported, but not the combination with trisomy 7. In the 45,X cell line, microsatellite analysis showed loss of the maternal X-chromosome, and presence of a maternal and paternal chromosome 7. The 47,XX,+7 cell line showed a paternal and a maternal X-chromosome, and a paternal and two identical maternal chromosomes 7. Mechanisms that might explain this double aneuploidy mosaicism are discussed.

The natural history, including orofacial features of three patients with Ehlers-Danlos syndrome, dermatosparaxis type (EDS type VIIC)

Ehlers-Danlos syndrome (EDS) dermatosparaxis type (type VIIC) and the related disease of cattle dermatosparaxis, are recessively inherited connective tissue disorders, caused by a deficient activity of procollagen I N-proteinase, the enzyme that excises the N-terminal propeptide in procollagen type I, type II, and type III. Although well documented in cattle, to date only seven human cases have been recorded, most of them aged under 2 years. We document the natural history of three patients with EDS dermatosparaxis type, two of whom have been reported before the age of 2 years, and one new patient. The phenotype of the patients, and especially the facial resemblance, is striking, making this a clinically recognizable condition. The most consistent anomalies during the first years of life are premature rupture of the membranes, extreme skin fragility and easy bruising, large fontanels, blue sclerae, puffy eyelids, micrognathia, umbilical hernia, and short fingers. Joint hypermobility becomes more important with age. The children are at risk for rupture of internal organs due to soft tissue fragility, as is illustrated by different internal events in two of the three patients described here. Orofacial features include micrognathia, a frontal open bite, and gingival hyperplasia with varying degrees of hyperkeratosis. The deciduous dentition shows abnormal morphology of the molars, obliteration of the tooth pulp, and severe enamel attrition. The permanent dentition shows agenesis and microdontia of several teeth. Tooth discoloration, dysplastic roots, and tooth pulp obliteration are present in a restricted number of permanent teeth.

Novel Types of Mutation Responsible for the Dermatosparactic Type of Ehlers–Danlos Syndrome (Type VIIC) and Common Polymorphisms in the ADAMTS2 Gene

Ehlers-Danlos syndrome (EDS) type VIIC, or dermatosparactic type, is a recessively inherited connective tissue disorder characterized, among other symptoms, by an extreme skin fragility resulting from mutations inactivating ADAMTS-2, an enzyme excising the aminopropeptide of procollagens type I, II, and III. All previously described mutations create premature stop codons leading to a marked reduction in the level of mRNA. In this study, we analyzed the ADAMTS2 cDNA sequences from five patients displaying clinical and/or biochemical features consistent with a diagnosis of either typical or potentially mild form of EDS type VIIC. Three different alterations were detected in the two patients with typical EDS type VIIC. The first patient was homozygous for a genomic deletion causing an in-frame skipping of exons 3-5 in the transcript. In the second patient, the allele inherited from the mother lacks exon 3, generating a premature stop codon, whereas the paternal allele has a genomic deletion resulting in an in-frame skipping of exons 14-16 at the mRNA level. Although the exons 3-5 or 14-16 encode protein domains that have not been previously recognized as crucial for ADAMTS-2 activity, the aminoprocollagen processing was strongly impaired in vitro and in vivo, providing evidence for the requirement of these domains for proper enzyme function. The three other patients with a phenotype with some resemblance to EDS type VIIC only had silent and functionally neutral variations also frequently found in a normal population.

Unreported manifestations in two Dutch families with Bartsocas-Papas syndrome

Bartsocas-Papas syndrome (BPS) is a severe autosomal recessive syndrome characterized by neonatal or intrauterine death in most cases, severe popliteal webbing, oligosyndactyly, genital abnormalities, and typical face with short palpebral fissures, ankyloblepharon, hypoplastic nose, orofacial clefts, and small mouth. Until now at least 23 cases with this syndrome in 11 families were described, mostly from Mediterranean origin. We report on two Dutch families with six affected children having BPS. One of the patients was prenatally diagnosed by ultrasound examination. Additional unreported findings were omphalocele and aplasia of the urethra. The intrafamilial resemblance in severity is of importance for the genetic counseling of families and prenatal detection by ultrasound. We discuss possible pathogenic mechanisms and review similar cases from the literature.

DGGE-based whole-gene mutation scanning of the dystrophin gene in Duchenne and Becker muscular dystrophy patients

Duchenne and Becker muscular dystrophy (DMD and BMD) are caused by mutations in the dystrophin gene. Large rearrangements in the gene are found in about two-thirds of DMD patients, with approximately 60% carrying deletions and 5-10% carrying duplications. Most of the remaining 30-35% of patients are expected to have small nucleotide substitutions, insertions, or deletions. To detect these subtle changes within the coding and splice site determining sequences of the dystrophin gene, we established a semiautomated denaturing gradient gel electrophoresis (DGGE) mutation scanning system. The DGGE scan covers the dystrophin gene with 95 amplicons, PCRed either individually or in a multiplex setup. PCR and pooling were performed semiautomatically, using a pipetting robot and 384-well plates, enabling concurrent amplification of DNA of four patients in one run. Amplification of individual fragments was performed using one PCR program. The products were pooled just before gel loading; DGGE requires only a single gel condition. Validation was performed using DNA samples harboring 39 known DMD variants, all of which could be readily detected. DGGE mutation scanning was applied to analyze 135 DMD/BMD patients and potential DMD carriers without large deletions or duplications. In DNA from 25 out of 44 DMD patients (57%) and from 5 out of 39 BMD patients (13%), we identified clear pathogenic changes. All mutations were different, with the exception of one DMD mutation, which occurred twice. In DNA from 10 out of 44 potential DMD carriers, including four obligate carriers, we detected causative changes, including one pathogenic change in every obligate carrier. In addition to these pathogenic changes, we detected 15 unique unclassified variants, i.e., changes for which a pathogenic nature is uncertain.

Referral for genetic counseling after the birth of a child with a congenital anomaly in the Northern Netherlands

Children/fetuses born with a congenital anomaly are recorded in a local registry of congenital anomalies in the Northern Netherlands. Parents of these children/fetuses often have questions about cause, prognosis, and recurrence risk. Referral to a genetic clinic is one way to obtain information concerning these questions. We were interested in determining to what extent parents were referred for genetic counseling, and investigated the non-referred cases for the estimated need for referral. Furthermore, we measured whether referral rates had improved following the study carried out by Cornel et al. [1992] for the same region. We evaluated data on couples referred or not referred for 2,964 registered children/fetuses during the birth years 1992-1997. The parents of 528 cases (18%) had been referred for genetic counseling. Investigation of the 2,436 non-referred cases showed a high number (1287/53%) of cases with a supposedly "low need for referral." If we consider the remaining 1,149 cases with a moderate or high need for referral to the genetic clinic, the ideal uptake rate is 57% (1149 +/- 528 = 1677 cases) instead of the previously mentioned 18% (528 cases). We concluded that nearly four out of 10 parents of children/fetuses with a congenital anomaly who were considered suitable for referral to the genetic clinic did not make use of this option. Despite increased familiarity with genetics over the years among the community in general and health-care professionals in particular, the EUROCAT registry does not show an improvement in the uptake rate of cases registered with the genetic clinic.

ABCD syndrome is caused by a homozygous mutation in the EDNRB gene

ABCD syndrome is an autosomal recessive syndrome characterized by albinism, black lock, cell migration disorder of the neurocytes of the gut (Hirschsprung disease [HSCR]), and deafness. This phenotype clearly overlaps with the features of the Shah-Waardenburg syndrome, comprising sensorineural deafness; hypopigmentation of skin, hair, and irides; and HSCR. Therefore, we screened DNA of the index patient of the ABCD syndrome family for mutations in the endothelin B receptor (EDNRB) gene, a gene known to be involved in Shah-Waardenburg syndrome. A homozygous nonsense mutation in exon 3 (R201X) of the EDNRB gene was found. We therefore suggest that ABCD syndrome is not a separate entity, but an expression of Shah-Waardenburg syndrome.