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We discovered the missense mutation, A226V, in the ornithine-delta-aminotransferase (OAT) genes of two unrelated patients with gyrate atrophy of the choroid and retina (GA). One patient, who was a compound for A226V and for the premature termination allele R398ter, showed a significant (P < .01) decrease in mean plasma ornithine levels, following pyridoxine supplementation with a constant protein intake: 826 +/- 128 microM (n = 5; no pyridoxine supplementation) versus 504 +/- 112 microM (n = 6; 500 mg pyridoxine/d) and 546 +/- 19 microM (n = 6; 1,000 mg pyridoxine/d). In extracts of fibroblasts from a second GA patient homozygous for A226V and from Chinese hamster ovary cells expressing an OAT-cDNA-containing A226V, we found that OAT activity increased from undetectable levels to approximately 10% of normal when the concentration of pyridoxal phosphate was increased from 50 to 600 microM. A226V is the fourth disease-causing pyridoxine-responsive human mutation to be reported.

Six new mutations have been identified in the CFTR gene. These mutations, representing three different categories--missense (R31L, W1098R), nonsense (E1104X), and frameshift (441delA, 681delC, 1461ins4)--are located in exons 2, 4, 5, 9, and 17b of the gene and presumed to cause cystic fibrosis (CF) in patients. All these mutations are probably rare in the population, as no additional examples were found for any of them in a cohort of 545 CF patients. Our study also revealed a benign sequence variation (3499 + 45T-->C) in intron 17b.

3-Hydroxy-3-methylglutaryl coenzyme A lyase (HL) catalyzes the final step of ketogenesis, an important pathway of mammalian energy metabolism. HL deficiency is an autosomal recessive inborn error in man leading to episodes of hypoglycemia and coma. Using the N-terminal peptide sequence of purified chicken liver HL, we designed degenerate sequence primers and amplified an 89-base pair (bp) chicken liver HL cDNA fragment. Longer cDNA clones for chicken (1384 bp) and human (1575 bp) HL were obtained by library screening. The peptide sequence predicted from the chicken clone contains two peptides from purified chicken HL. Mature human and chicken HL are 298-residue peptides. The sequence of the human clone predicts a 27-residue mitochondrial leader and a 31.6-kDa mature HL peptide. Human fibroblast and liver RNA contain a single 1.7-kilobase HL message. Two Acadian French-Canadian siblings with HL deficiency were homozygous for a 2-base pair deletion within the Ser-69 codon (S69fs(-2)), predicted to result in a truncated nonfunctional HL peptide lacking a complete active site. S69fs(-2) was not present in 12 other HL-deficient patients of 10 other ethnic origins, showing that HL deficiency is genetically heterogeneous.

T-2 toxin, a trichothecene mycotoxin, inhibits the growth of Saccharomyces cerevisiae. We have isolated nine spontaneous S. cerevisiae mutants resistant to this toxin. The mutants were distinguished from the wild type according to their degree of resistance to T-2 toxin on media with dextrose or glycerol as the carbon source. Generation time, mutation stability and level of cross-resistance to roridin A, another trichothecene, were determined for each mutant. The T-2 toxin resistant mutants were further characterized by subsequent tests involving cross-resistance and collateral sensitivity to chlorampenicol, neomycin, paromomycin, ethidium bromide and thiolutin. Mutants have been placed into three subgroups and the mechanism of T-2 toxin resistance in each group has been postulated. Mutant HK1 is the first S. cerevisiae isolate resistant to roridin A. One particular isolate, mutant HK11, carries a single recessive nuclear mutation. This mutation was termed ttt (for T-2 toxin resistant).