At least two mutant alleles of ornithine delta-aminotransferase cause gyrate atrophy of the choroid and retina in Finns.

Abstract

Gyrate atrophy of the choroid and retina (GA) is an inherited chorioretinal degeneration caused by deficiency of ornithine 8-aminotransferase (OAT; L-ornithine: 2-oxo-acid aminotransferase; EC 2.6.1.13). GA is one of the "Finnish genetic diseases," a group of several rare monogenic disorders that occur with increased frequency in the Finnish population. Using a combination of RNase A protection, genomic cloning, and polymerase chain reaction amplification of genomic DNA, we found one of two missense mutant OAT alleles to be present in each of 16 Finnish GA pedigrees. The first mutation R180T, in which arginine-180 is replaced by threonine, was present in homozygous form in patients from two pedigrees. The second mutation L402P, in which leucine-402 is replaced by proline, was present in homozygous form in patients from 14 pedigrees. Neither mutation was present in 19 Finnish controls. L402P was not present in 18 non-Finnish GA patients but R180T was found in an American GA patient. We constructed full-length mutant cDNAs by amplifying patient cDNA with the polymerase chain reaction and cloning a restriction fragment containing the mutation into an otherwise normal human OAT cDNA. These mutant cDNAs were then expressed in CHO-K1 cells, which lack endogenous OAT. Both R180T and L402P inactivate OAT. These results show molecular heterogeneity in GA alleles even in the Finnish population.Ornithine 8-aminotransferase (OAT; L-ornithine:2-oxo-acid aminotransferase; EC 2.6.1.13) is a mitochondrial matrix enzyme that catalyzes the reversible transamination of ornithine to Al-pyrroline 5-carboxylate (1). Deficiency of OAT in man causes the autosomal recessive chorioretinal degeneration, gyrate atrophy of the choroid and retina (GA). To study the cell biology of OAT and the mutations causing GA, we have cloned and sequenced a near full-length human liver OAT cDNA and have determined the structure of the human OAT structural gene, which has 11 exons and spans 22 kilobases (kb) (2). We (2, 3) and others (4, 5) have shown that the OAT structural gene is located on chromosome 10 and that there is a group of nonfunctional OAT-related sequences on the X chromosome.Three missense mutations of OAT causing GA have been reported. The first mutation, in which the initiation methionine was replaced with an isoleucine, was found in affected members of two unrelated pedigrees of Lebanese Maronite descent (6). GA probands from 17 pedigrees of a variety of other ethnic backgrounds, including Finnish, were shown to lack this mutation (6). The second mutation was the Val-332 -* Met change found in a pyridoxine-responsive patient, and the third was the Asn-54 --Lys change (7). The ethnic background of the latter two patients was not provided.The Finnish population, which expanded from -250,000 in 1700 A.D. to -5 million at present, has been isolated genetically by geographical, linguistic, and cultural barriers (8). For these reasons, the variety and frequency of monogenic disorders in Finns is quite different from other European pop...

Aspartylglycosaminuria in the Finnish population: identification of two point mutations in the heavy chain of glycoasparaginase.

“…Gyrate atrophy of the choroid and retina caused by deficiency of ornithine 3-aminotransferase (EC 2.6.13) is one such Finnish genetic disease. Surprisingly, at least two different mutant alleles of ornithine 8-aminotransferase have been found in the Finnish population (21). In this study, we have shown that in eight Finnish aspartylglycosaminuria patients from different pedigrees two separate point mutations are found close to the carboxylterminal end of the heavy chain of glycoasparaginase.…”

Molecular Enzymology of Mammalian Δ1-Pyrroline-5-carboxylate Synthase

“…R13516) from the National Genome Center, Lawrence Livermore National Laboratory (Livermore, CA) and sequenced the cDNA insert. Using this putative P5CS EST clone as a probe, we screened Ͼ5 ϫ 10 5 plaques from both the human kidney and small intestine cDNA library as described (30,31). We purified two positive plaques, one (HsP5CS.K5) from kidney cDNA library and the other (HsP5CS.G1) from the small intestine cDNA library, through two additional cycles of screening, subcloned the inserts (HsP5CS.K5, 2.7 kb; HsP5CS.G1, 2.8 kb) into pBluescript II KS(ϩ), and sequenced them.…”

Minisequencing: A Specific Tool for DNA Analysis and Diagnostics on Oligonucleotide Arrays

“…The mutations were selected as targets because they occur with a high frequency in the Finnish population and populationbased screening for them would be clinically relevant. Five of the mutations cause severe recessive disorders [infantile neuronal ceroid lipofuscinosis (INCL; Vesa et al 1995), aspartylglucosaminuria (AGU; Ikonen et al 1991), gyrate atrophy (GA; Mitchell et al 1989) and nonketotic hyperglycinemia (NKH; Kure et al 1992)] belonging to the ''Finnish disease heritage,'' (for review, see Peltonen et al 1995) and occur with a combined population frequency of carriers of ∼0.05. Three mutations in the low-density lipoprotein receptor (LDLR) gene (Aalto-Setälä et al 1989;Koivisto et al 1991Koivisto et al , 1995 that cause familial hypercholesterolemia (FH) with the estimated prevalence of 1 in 500, both in Finland and worldwide, were also included in the panel.…”