Incomplete Timothy syndrome secondary to a mosaic mutation of the CACNA1C gene diagnosed using next-generation sequencing.

Autosomal dominant genetic diseases can occur de novo and in the form of somatic mosaicism, which can give rise to a less severe phenotype, and make diagnosis more difficult given the sensitivity limits of the methods used. We report the case of female child with a history of surgery for syndactyly of the hands and feet, who was admitted at 6 years of age to a pediatric intensive care unit following cardiac arrest. The electrocardiogram (ECG) showed a long QT interval that on occasions reached 500 ms. Despite the absence of facial dysmorphism and the presence of normal psychomotor development, a diagnosis of Timothy syndrome was made given the association of syndactyly and the ECG features. Sanger sequencing of the CACNA1C gene, followed by sequencing of the genes KCNQ1, KCNH2, KCNE1, KCNE2, were negative. The subsequent analysis of a panel of genes responsible for hereditary cardiac rhythm disorders using Haloplex technology revealed a recurrent mosaic p.Gly406Arg missense mutation of the CACNA1C gene in 18% of the cells. This mosaicism can explain the negative Sanger analysis and the less complete phenotype in this patient. Given the other cases in the literature, mosaic mutations in Timothy syndrome appear more common than previously thought. This case demonstrates the importance of using next-generation sequencing to identify mosaic mutations when the clinical picture supports a specific mutation that is not identified using conventional testing. © 2016 Wiley Periodicals, Inc.

A Laboratory Phenotype/Genotype Correlation of 1167 French Patients From 670 Families With von Willebrand Disease: A New Epidemiologic Picture.

von Willebrand disease (VWD) is a genetic bleeding disease due to a defect of von Willebrand factor (VWF), a glycoprotein crucial for platelet adhesion to the subendothelium after vascular injury. VWD include quantitative defects of VWF, either partial (type 1 with VWF levels <50 IU/dL) or virtually total (type 3 with undetectable VWF levels) and also qualitative defects of VWF (type 2 variants with discrepant antigenic and functional VWF levels). The most bleeding forms of VWD usually do not concern type 1 patients with the mildest VWF defects (VWF levels between 30 and 50 IU/dL). The French reference center for VWD performed a laboratory phenotypic and genotypic analysis in 1167 VWD patients (670 families) selected by their basic biologic phenotype: type 3, type 2, and type 1 with VWF levels <30 IU/dL. In these patients indeed, to achieve an accurate diagnosis of VWD type and subtype is crucial for the management (treatment and genetic counseling). A phenotype/genotype correlation was present in 99.3% of cases; 323 distinct VWF sequence variations (58% of novel) were identified (missense 67% versus truncating 33%). The distribution of VWD types was: 25% of type 1, 8% of type 3, 66% of type 2 (2A: 18%, 2B: 17%, 2M: 19%, 2N: 12%), and 1% of undetermined type. Type 1 VWD was related either to a defective synthesis/secretion or to an accelerated clearance of VWF. In type 3 VWD, bi-allelic mutations of VWF were found in almost all patients. In type 2A, the most frequent mechanism was a hyper-proteolysis of VWF. Type 2B showed 85% of patients with deleterious mutations (distinct from type 2B New York). Type 2M was linked to a defective binding of VWF to platelet glycoprotein Ib or to collagen. Type 2N VWD included almost half type 2N/3. This biologic study emphasizes the complex mechanisms for both quantitative and qualitative VWF defects in VWD. In addition, this study provides a new epidemiologic picture of the most bleeding forms of VWD in which qualitative defects are predominant.

Familial frameshift SRY mutation inherited from a mosaic father with testicular dysgenesis syndrome.

CONTEXT: The SRY gene encodes a transcription factor responsible for initiating testis differentiation. Mutations in SRY almost always result in XY sex reversal with pure gonadal dysgenesis and an increased risk of gonadal tumor. Most of these mutations are de novo, affecting only one individual in a family. Only a small subset of mutations is shared between a phenotypically normal father and one or more of his affected children. Incomplete penetrance and somatic mosaicism are two hypotheses that may explain a normal phenotype in a father carrying a SRY mutation. PATIENTS AND RESULTS: We describe a family with two sisters with XY sex reversal and pure gonadal dysgenesis and a phenotypically normal brother. A novel constitutional frameshift SRY mutation was identified in both sisters and was absent in the brother. The single base pair deletion (c.71delA) led to a premature stop codon in position 60 of the protein, removing entirely the high-mobility group domain and the DNA-binding domain of SRY. The father of the three children presented with hypospadias; cryptorchidism; testicular seminoma and oligoasthenozoospermia, an association termed testicular dysgenesis syndrome (TDS); and the SRY mutation in a mosaic state in the peripheral blood and the tumor. CONCLUSIONS: This observation of somatic and germinal mosaicism for a SRY mutation may explain the variable penetrance in some familial gonadal dysgenesis. Importantly, the present report is the first one describing the association of SRY mutation in a male with TDS. This suggests that mutations in a sex-determining gene may contribute to the pathogenesis of TDS.

An update on mutations of the SLC39A4 gene in acrodermatitis enteropathica.

Acrodermatitis enteropathica (AE) is a very rare inherited recessive disease caused by severe zinc deficiency. It typically occurs in early infancy and is characterized by periorificial and acral dermatitis, alopecia, and diarrhea. In 2002, both we and others identified the AE SLC39A4 gene located at 8q24.3, and described the first causative mutations for the disease. The SLC39A4 gene encodes a zinc-specific transporter belonging to the Zinc/Iron-regulated transporter-like family, which is highly expressed in the duodenum and jejunum. The SLC39A4 mutations are spread over the entire gene and include many different types of mutations. We report here the identification of five novel variants, including three likely pathogenic mutations. Since the first description, 31 mutations or unclassified variants of SLC39A4 have been reported in this gene. Although most of the patients with AE carry homozygous or compound heterozygous mutations, some of them have either no SLC39A4 mutation or only a monoallelic mutation. Thus, a genotype-phenotype correlation is not easily defined for all AE patients, and the molecular basis of the disease could be more complex than previously described. In cases unexplained by current genetic analyses, the most plausible molecular causes could be a dysregulation of the SLC39A4 gene transcription -- involving either metal response elements (MREs) or a modifier gene -- or the existence of another putative AE gene. In this review, we summarize the current knowledge of SLC39A4 mutations, as well as the future prospects to fully unravel the pathogenesis of AE.