A novel homozygous mutation in SZT2 gene in Saudi family with developmental delay, macrocephaly and epilepsy.

Epileptic encephalopathies are genetically heterogeneous disorders which leads to epilepsy and cause neurological disorders. Seizure threshold 2 (SZT2) gene located on chromosome 1p34.2 encodes protein mainly expressed predominantly in the parietal and frontal cortex and dorsal root ganglia in the brain. Previous studies in mice showed that mutation in this gene can confers low seizure threshold, enhance epileptogenesis and in human may leads to facial dysmorphism, intellectual disability, seizure and macrocephaly. Objective of this study was to find out novel gene or novel mutation related to the gene phenotype. We have identified a large consanguineous Saudi family segregating developmental delay, intellectual disability, epilepsy, high forehead and macrocephaly. Exome sequencing was performed in affected siblings of the family to study the novel mutation. Whole exome sequencing data analysis, confirmed by subsequent Sanger sequencing validation study. Our results showed a novel homozygous mutation (c.9368G>A) in a substitution of a conserved glycine residue into a glutamic acid in the exon 67 of SZT2 gene. The mutation was ruled out in 100 unrelated healthy controls. The missense variant has not yet been reported as pathogenic in literature or variant databases. In conclusion, the here detected homozygous SZT2 variant might be the causative mutation that further explain epilepsy and developmental delay in this Saudi family.

Novel ATRX gene damaging missense mutation c.6740A>C segregates with profound to severe intellectual deficiency without alpha thalassaemia.

BACKGROUND & OBJECTIVES: ATRX is a recessive X-linked intellectual deficiency (X-LID) gene causing predominately alpha-thalassaemia with a wide and clinically heterogeneous spectrum of intellectual deficiency syndromes. Although alpha-thalassaemia is commonly present, some patients do not express this sign despite the ATRX gene being altered. Most pathological mutations have been localized in two different major domains, the helicase and the plant homeo-domain (PHD)-like domain. In this study we examined a family of three males having an X-linked mental deficiency and developmental delay, and tried to establish a genetic diagnosis while discussing and comparing the phenotype of our patients to those reported in the literature. METHODS: Three related males with intellectual deficiency underwent clinical investigations. We performed a karyotype analysis, CGH-array, linkage study, and X-exome sequencing in the index case to identify the genetic origin of this disorder. The X-inactivation study was carried out in the mother and Sanger sequencing was achieved in all family members to confirm the mutation. RESULTS: a0 novel ATRX gene missense mutation (p.His2247Pro) was identified in a family of two uncles and their nephew manifesting intellectual deficiency and specific facial features without alpha-thalassaemia. The mutation was confirmed by Sanger sequencing. It segregated with the pathological phenotype. The mother and her two daughters were found to be heterozygous. INTERPRETATION & CONCLUSIONS: The novel mutation c.6740A>C was identified within the ATRX gene helicase domain and confirmed by Sanger sequencing in the three affected males as well as in the mother and her two daughters. This mutation was predicted to be damaging and deleterious. The novel mutation segregated with the phenotype without alpha-thalassaemia and with non-skewed X chromosome.

Nonsyndromic X-linked intellectual deficiency in three brothers with a novel MED12 missense mutation [c.5922G>T (p.Glu1974His)].

X-linked intellectual deficiency (XLID) is a large group of genetic disorders. MED12 gene causes syndromic and nonsyndromic forms of XLID. Only seven pathological mutations have been identified in this gene. Here, we report a novel mutation segregating with XLID phenotype. This mutation could be in favor of genotype-phenotype correlations.