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.

Expanding the spectrum of FOXC1 and PITX2 mutations and copy number changes in patients with anterior segment malformations.

PURPOSE: Anterior segment dysgenesis (ASD) comprises a heterogeneous group of developmental abnormalities that affect several structures of the anterior segment of the eye. The main purpose of this study was to assess the proportion of FOXC1 and PITX2 mutations and copy number changes in 80 probands with ASD. METHODS: The patients were examined for FOXC1 and PITX2 copy number changes and mutations using MLPA (multiplex ligation-dependent probe amplification) and direct sequencing. Subsequently, the identified copy number changes were fine-mapped using high-resolution microarrays. In the remaining mutation-negative patients, sequencing of the FOXC1 andPITX2 3' untranslated regions (UTRs) and three other candidate genes (P32, PDP2, and FOXC2) was performed. RESULTS: Thirteen FOXC1 and eight PITX2 mutations were identified, accounting for 26% (21/80) of the cases. In addition, six FOXC1 and five PITX2 deletions were found, explaining 14% (11/80) of the cases. The smallest FOXC1 and PITX2 deletions were 5.4 and 1.6 kb in size, respectively. Six patients carrying FOXC1 deletions presented with variable extraocular phenotypic features such as hearing defects (in 4/6) and mental retardation (in 2/6). No further genetic defects were found in the remaining mutation-negative patients. CONCLUSIONS: FOXC1 and PITX2 genetic defects explain 40% of our large ASD cohort. The current spectrum of intragenic FOXC1 and PITX2 mutations was extended considerably, the identified copy number changes were fine mapped, the smallest FOXC1 and PITX2 deletions reported so far were identified, and the need for dedicated copy number screening of the FOXC1 and PITX2 genomic landscape was emphasized. This study is unique in that sequence and copy number changes were screened simultaneously in both genes.

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.