Biochemical and molecular analysis of the ALDH7 A1 gene in 31 patients with Pyridoxine-dependent epilepsy

Abstract

Most cases of pyridoxine dependent epilepsy (PDE) (MIM #266100) are caused by mutations of the antiquitin gene (ALDH7 A1), leading to α-aminoadipic acid semialdehyde dehydrogenase deficiency This enzyme is involved in the cerebral lysine degradation pathway. The accumulating compound piperideine 6-carboxylate (P6C) inactivates pyridoxalphosphate, causing severe cerebral pyridoxine deficiency. We report on biochemical and molecular findings in 31 Caucasian PDE patients with neonatal seizure onset, 13 of whom have not been reported previously. Pipecolic acid (PA) was measured by GCMS and α-aminoadipic acid semialdehyde (α-AASA) determined by LC-MS/MS. Mutation analysis was done by complete sequencing and confirming restriction fragment polymorphism analysis. In all patients with ALDH7 A1 mutations urinary α-AASA and plasma PA were elevated 1.6 to 62- fold and 1.5 to 38– fold, respectively. AASA and PA concentrations were higher in the 3 patients with pre-treatment sampling. Within 60 of the 62 alleles a total of 16 different mutations were identified. Several mutations had increased prevalence, as p.Glu399Gln (exon 14; 34%), c.1482–1G>T acceptor splice site mutation (intron 17, 12%), Arg82X (exon 4; 10%) and a „silent mutation“, p.V250V (exon 9; 9%). In 7 patients of 6 unrelated families 6 novel mutations were found: an insertion in exon 1, c.57insA (p.Arg20ThrfsX8), a donor splice site mutation, c.689+2T>C (intron 8), and 4 missense mutations (p.Arg82Gly (exon 4), p.Asn167Ser (exon 6), p.Asn420Lys (exon 15) and p.Gln425Pro (exon 15). All these mutations showed familiar cosegregation and were not present in 120 control alleles.