Genetic investigation of the ubiquitin-protein ligase E3A gene as putative target in Angelman syndrome

BACKGROUND Angelman syndrome(AS)is caused by maternal chromosomal deletions,imprinting defects,paternal uniparental disomy involving chromosome 15 and the ubiquitin-protein ligase UBE3A gene mutations.However the genetic basis remains unclear for several patients.AIM To investigate the involvement of UBE3A gene in AS and identifying new potential genes using exome sequencing.METHODS We established a cohort study in 50 patients referred to Farhat Hached University Hospital between 2006 and 2021,with a strong suspicion of AS and absence of chromosomal aberrations.The UBE3A gene was screened for mutation detection.Two unrelated patients issued from consanguineous families were subjected to exome analysis.RESULTS We describe seven UBE3A variants among them 3 none previously described including intronic variants c.2220+14T>C(intron14),c.2507+43T>A(Exon15)and insertion in Exon7:c.30-47_30-46.The exome sequencing revealed 22 potential genes that could be involved in AS-like syndromes that should be investigated further.CONCLUSION Screening for UBE3A mutations in AS patients has been proven to be useful to confirm the diagnosis.Our exome findings could rise to new potential alternative target genes for genetic counseling.

Hypomagnesemia with Secondary Hypocalcemia Linked to a Novel TRPM6 Gene Mutation

Hypomagnesemia with secondary hypocalcemia (HSH) is a rare inherited disorder, characterized by extremely low levels of serum magesium associated with symptomatic hypocalcemia. HSH manifests in the new born period with neurological symptoms, including generalized seizures, which are refractory to anticonvulsant treatment. In this disorder, the basic abnormality is the defective intestinal absorption of magnesium. Mutations in TRPM6, the gene encoding the transient receptor potential cation channel subfamily member 6 have been found to be responsible for this disease. We report on a four-month-old Tunisian girl who presented with convulsions. Laboratory evaluation yielded extremely low serum magnesium levels, low calcium levels, and abnormal PTH levels. The diagnosis of HSH was confirmed by mutation analysis which identified the novel mutation c.1307A >G in exon 11 of TRPM6 (Lys436Arg). Our patient was homozygous for this mutation. Prenatal diagnosis was done during second pregnancy. DNA from trophoblast biopsy showed the same mutation as the proband.