An initiator codon mutation in ornithine-delta-aminotransferase causing gyrate atrophy of the choroid and retina.

Abstract

Gyrate atrophy of the choroid and retina (GA) is an autosomal recessive chorioretinal degeneration caused by deficiency of the mitochondrial matrix enzyme, ornithine-5-aminotransferase (OAT). To study the molecular basis of the mutations causing GA, we cloned and sequenced the human OAT cDNA and determined the intron-exon arrangement of the structural gene. Using the cDNA template, we synthesized antisense RNA probes and performed RNase A protection experiments with RNA from four Lebanese GA patients. We found a probe-target mismatch at the 5' end of the first coding exon and amplified this region of the patients' genomic DNA using the polymerase chain reaction. Sequence analysis showed a G A transition, changing the initiator ATG (methionine) codon to ATA. This mutation segregates with the GA allele in both pedigrees. Initiation of translation at the closest in-frame methionine codon would truncate OAT by 138 amino acids, eliminating the entire mitochondrial leader sequence and 113 amino acids of the mature peptide.

Ankyrin‐linked hereditary spherocytosis in an African–American kindred

“…However, there has been growing recognition of the use of alternate initiation codons in mammalian cells, often producing proteins with very different functions [39][40][41], as well as recognition of new mechanisms of translational control of protein structure and function [42,43]. Initiator codon mutations are uncommon, but typically they are associated with null alleles as no functional protein is produced [44][45][46][47]. However, in a few cases, translation of the mutant allele initiates from a downstream methionine or other amino acid, producing a truncated protein that retains partial or full function [48][49][50].…”

A single nucleotide substitution that abolishes the initiator methionine codon of the GLDC gene is prevalent among patients with glycine encephalopathy in Jerusalem

“…Total RNA samples were prepared from two control subjects (cont 1 and 2) and two patients (pt 1 and 2) and subjected to reverse transcription and multiplex PCR (RT + lanes). As a negative control, the same amount of total RNA was used for multiplex PCR amplification without reverse transcription (RTlanes) of the choroid and retina (Mitchell et al 1988). As in our patients, the protein product of the mutated gene was expected to truncate 138 amino acids of the ornithine amino transferase enzyme, thus eliminating the entire mitochondrial leader sequence and abolishing enzyme activity (Mitchell et al 1988).…”

“…As a negative control, the same amount of total RNA was used for multiplex PCR amplification without reverse transcription (RTlanes) of the choroid and retina (Mitchell et al 1988). As in our patients, the protein product of the mutated gene was expected to truncate 138 amino acids of the ornithine amino transferase enzyme, thus eliminating the entire mitochondrial leader sequence and abolishing enzyme activity (Mitchell et al 1988). Likewise, Frank et al (1999) reported two mutations in the initiation codon of the protoporphyrinogen oxidase gene, leading to variegate porphyria due to a non-functional protein.…”

Vitamin B6-Responsive Ornithine Aminotransferase Deficiency with a Novel Mutation G237D

“…The OAT gene on chromosome 10q26 spans 21 kb of DNA (Mitchell et al 1988a), encoding a transcript of 2.2 kb in 11 exons (Mitchell et al 1988b). OAT deficiency patients have been reported worldwide with diverse ethnic and racial backgrounds.…”