Spectrum of novel mutations found in Waardenburg syndrome types 1 and 2: implications for molecular genetic diagnostics.

OBJECTIVES: Till date, mutations in the genes PAX3 and MITF have been described in Waardenburg syndrome (WS), which is clinically characterised by congenital hearing loss and pigmentation anomalies. Our study intended to determine the frequency of mutations and deletions in these genes, to assess the clinical phenotype in detail and to identify rational priorities for molecular genetic diagnostics procedures. DESIGN: Prospective analysis. PATIENTS: 19 Caucasian patients with typical features of WS underwent stepwise investigation of PAX3 and MITF. When point mutations and small insertions/deletions were excluded by direct sequencing, copy number analysis by multiplex ligation-dependent probe amplification was performed to detect larger deletions and duplications. Clinical data and photographs were collected to facilitate genotype-phenotype analyses. SETTING: All analyses were performed in a large German laboratory specialised in genetic diagnostics. RESULTS: 15 novel and 4 previously published heterozygous mutations in PAX3 and MITF were identified. Of these, six were large deletions or duplications that were only detectable by copy number analysis. All patients with PAX3 mutations had typical phenotype of WS with dystopia canthorum (WS1), whereas patients with MITF gene mutations presented without dystopia canthorum (WS2). In addition, one patient with bilateral hearing loss and blue eyes with iris stroma dysplasia had a de novo missense mutation (p.Arg217Ile) in MITF. MITF 3-bp deletions at amino acid position 217 have previously been described in patients with Tietz syndrome (TS), a clinical entity with hearing loss and generalised hypopigmentation. CONCLUSIONS: On the basis of these findings, we conclude that sequencing and copy number analysis of both PAX3 and MITF have to be recommended in the routine molecular diagnostic setting for patients, WS1 and WS2. Furthermore, our genotype-phenotype analyses indicate that WS2 and TS correspond to a clinical spectrum that is influenced by MITF mutation type and position.

Waardenburg syndrome type I with heterochromia iridis and circumscribed hypopigmentation of the skin.

We report a 3-year-old girl with autosomal dominant inherited Waardenburg syndrome type I showing circumscribed hypopigmentation of the skin, heterochromia iridis, sensorineural deafness, and dental aberrations. Clinical diagnosis was confirmed by the identification of an underlying missense mutation (C811T) in the PAX3 gene. Early diagnosis of Waardenburg syndrome among children with pigment anomalies enables a successful interdisciplinary medical care.

Utility of MLPA in deletion analysis of GCH1 in dopa-responsive dystonia.

We applied multiple ligation-dependent probe amplification (MLPA) to patients from three families with characteristic dopa-responsive dystonia (DRD) but no base change in the gene GCH1. We found a complete deletion of GCH1 in affected members of family 1, and partial deletions in affected individuals of family 2 (exons 4-6) and of family 3 (exons 2-6). The findings were confirmed by quantitative real-time PCR. Our investigations demonstrate the utility of MLPA for routine deletion analysis of GCH1 in DRD patients with no sequence changes in this gene.

Recurrent granular dystrophy of the cornea: an unusual case.

PURPOSE: To describe a case of severe corneal granular dystrophy with clinicopathologic and molecular genetic findings. METHODS: The DNAs of a 53-year-old male patient suffering from corneal granular dystrophy and nonaffected family members were analyzed by molecular genetic methods. Clinical features, and histopathologic and immunohistochemical findings from the penetrating keratoplasty specimen, are described. RESULTS: Histopathologic and molecular genetic findings confirmed the diagnosis. A new genetic polymorphism is described. Histopathologic evidence supports the assumption of the epithelial origin of the described dystrophy. CONCLUSIONS: A severe course of corneal granular dystrophy can be present in the absence of evidence of a homozygous mutational status, or a novel mutation. Molecular genetic analysis revealed a new polymorphism in this patient. The histopathologic findings support the assumption of an epithelial origin of the granular corneal deposits. Phototherapeutic keratectomy and penetrating keratoplasty may improve vision, but cannot prevent recurrence of the disease.

Four new cases of congenital secondary hypothyroidism due to a splice site mutation in the thyrotropin-beta gene: phenotypic variability and founder effect.

Isolated TSH deficiency is a rare cause of congenital hypothyroidism. We here report four children from two consanguineous Turkish families with isolated TSH deficiency. Affected children who were screened at newborn age had an unremarkable TSH result and a low serum TSH level at diagnosis. Age at diagnosis and clinical phenotype were variable. All affected children carried an identical homozygous splice site mutation (IVS2 + 5 G--> A) in the TSHbeta gene. This mutation leads to skipping of exon 2 and a loss of the translational start codon without ability to produce a TSH-like protein. However, using specific monoclonal antibodies, we detected a very low concentration of authentic, heterodimeric TSH in serum, indicating the production of a small amount of correctly spliced TSH mRNA. By genotyping all family members with polymorphic markers at the TSHbeta locus, we show that the mutation arose on a common ancestral haplotype in three unrelated Turkish families indicating a founder mutation in the Turkish population. These results suggest that this TSHbeta mutation is among the more common TSHbeta gene mutations and stress the need for a biochemical and molecular genetic workup in children with symptoms suggestive of congenital hypothyroidism, even when the neonatal TSH screening is normal.

Mutations in the PDS gene in German families with Pendred's syndrome: V138F is a founder mutation.

Pendred's syndrome, an autosomal-recessive condition characterized by congenital sensorineural hearing loss and goiter, is caused by mutations in the PDS gene. Located on chromosome 7q22-q31, it encodes a chloride-iodide transporter expressed in the thyroid, inner ear, and kidney. We investigated the PDS gene of six affected individuals from four unrelated families with Pendred's syndrome by direct sequencing. PDS mutations were identified in homozygous or compound heterozygous state in all six cases. A homozygous missense mutation leading to the amino acid substitution S133T was detected in a family of Turkish origin. The mutations found in the other affected individuals, who originate from Germany, were V138F/Y530H, V138F/E384G, and V138F/V138F. Because V138F was found in the German patients with Pendred's syndrome on at least one allele, we genotyped five microsatellite markers located in the PDS region. All affected German individuals shared a common haplotype at three microsatellite markers located close to or within the PDS gene. We therefore concluded that V138F is a founder mutation in our cohort of German families with Pendred's syndrome.