Whole-exome sequencing improves the diagnosis yield in sporadic infantile spasm syndrome.

Infantile spasms syndrome (ISs) is characterized by clinical spasms with ictal electrodecrement, usually occurring before the age of 1 year and frequently associated with cognitive impairment. Etiology is widely heterogeneous, the cause remaining elusive in 40% of patients. We searched for de novo mutations in 10 probands with ISs and their parents using whole-exome sequencing (WES). Patients had neither consanguinity nor family history of epilepsy. Common causes of ISs were excluded by brain magnetic resonance imaging (MRI), metabolic screening, array-comparative genomic hybridization (CGH) and testing for mutations in CDKL5, STXBP1, and for ARX duplications. We found a probably pathogenic mutation in four patients. Missense mutations in SCN2A (p.Leu1342Pro) and KCNQ2 (p.Ala306Thr) were found in two patients with no history of epilepsy before the onset of ISs. The p.Asn107Ser missense mutation of ALG13 had been previously reported in four females with ISs. The fourth mutation was an in-frame deletion (p.Phe110del) in NR2F1, a gene whose mutations cause intellectual disability, epilepsy, and optic atrophy. In addition, we found a possibly pathogenic variant in KIF3C that encodes a kinesin expressed during neural development. Our results confirm that WES improves significantly the diagnosis yield in patients with sporadic ISs.

Screening of mutations in genes that predispose to hereditary paragangliomas and pheochromocytomas.

Thirty per cent of the paragangliomas and pheochromocytomas reported are hereditary. Mutations in SDHB, SDHC, SDHD, and more recently SDHAF2 and TMEM127 genes have been described in these hereditary tumors. We looked for mutations in these 5 genes in a series of 269 patients with paragangliomas and/or pheochromocytomas. The SDHB, SDHC, and SDHD genes were analyzed in a series of 269 unrelated index patients with paragangliomas and/or pheochromocytomas using dHPLC screening of point mutations followed by direct sequencing and Multiplex PCR Liquid Chromatography to detect large rearrangements confirmed by quantitative PCR. In a second phase, we adapted Multiplex PCR Liquid Chromatography to the SDHAF2 and TMEM127 genes. This method and direct sequencing were applied to 230 patients without the SDHB, C, D mutations. Of the 269 patients, 44 carried a mutation (16.3%). Thirty-seven different mutations were identified: 18 in SDHB (including 2 large deletions), 8 in SDHD, 6 in SDHC, 5 in TMEM127, and no mutations in SDHAF2. Thirteen mutations have not been published so far. An exhaustive study of the different genes is needed to make possible a familial genetic diagnosis in paraganglioma and pheochromocytoma hereditary syndromes. Although mutations in SDHC and TMEM127 are less frequent than mutations in SDHB and SDHD, they also have less evident clinical feature indicators. Analyzing SDHAF2 must be restricted to familial extra-adrenal paragangliomas. Multiplex PCR Liquid Chromatography is a sensitive, fast, and inexpensive method for screening large rearrangements, which are infrequent in these syndromes.