Homozygosity mapping to chromosome 5p15 of a gene responsible for Hartnup disorder.

Hartnup disorder is an autosomal recessive phenotype involving a transporter for monoamino-monocarboxylic acids. Genetic analysis of the mouse model mapped its locus to human chromosome 11q13 (8). We report here the results of linkage analysis in two Japanese first cousin-marriage families. In the first family, the proband had Hartnup disorder and his deceased older brother was reported to have had typical Hartnup symptoms. The younger brother of the proband was shown to have decreased tryptophan absorption by oral loading test. In the second family, a 6-year-old girl, the proband, had specific hyperaminoaciduria. DNA was isolated from either blood samples or umbilical cord stumps. Genome-wide screening by homozygosity mapping was conducted. Taking into account that the older brother was affected and the younger brother was a carrier in the first family, homozygosity mapping (LOD score = 3.55) and GENEHUNTER (LOD score = 3.28) locates the locus of the Hartnup disorder on 5p15.

A cluster of lysinuric protein intolerance (LPI) patients in a northern part of Iwate, Japan due to a founder effect. The Mass Screening Group.

Lysinuric protein intolerance is an autosomal recessive disease characterized by defective transport of the dibasic aminoacids. Mutational analysis of LPI patients in the northern part of Japan revealed that six were homozygous for the R410X mutation and two others were compound heterozygotes of R410X and other unknown mutations. In the population epidemiology study in a local cluster in the northern part of Iwate, ten heterozygotes were found in 1190 newborn babies leading to an estimated LPI incidence of 1/57,000. Polymorphism analysis revealed two major alleles, A and B, in intron 8. While the population frequency of allele A was 0.9 and that of allele B was 0.1 in the northern part of Japan the R410X mutations were exclusively on allele B in 31 chromosomes suggesting a founder effect. Genetic analysis in patients revealed strong linkage disequilibrium with D14S283 and TCRA indicating that the R410X mutation occurred before at least 130 generations ago (about 2600 years). The R410X mutation was shown to be useful as a molecular marker for screening LPI patients in the northern part of Japan.

Probable involvement of a germ-line mutation of an unknown mismatch repair gene in a Japanese Muir-Torre syndrome phenotype.

A combination of haplotype analysis and direct sequencing were conducted on Japanese Muir-Torre syndrome kindred. In the kindred, two females revealed a hereditary non-polyposis colon cancer (HNPCC) phenotype and one male had a sebaceous tumor in addition to a HNPCC phenotype. Haplotype analysis and direct sequencing failed to show involvement of the known mismatch repair genes, with the exception of MSH5, in this kindred. Analysis of large fragments (from 3.9 to 6. 2 kb) covering the entire 25 kb MSH5 gene in the proband revealed the absence of gross changes in the promoter region and exons. The direct sequencing of the promoter region and all 25 exons failed to demonstrate any mutations in the coding regions except for a CA repeat polymorphism in intron 3 and a C/A polymorphism in intron 15. Taken together present results indicate that a novel and yet unknown mismatch repair gene is likely involved in the HNPCC in this kindred.

Sequence analysis of the human tyrosinase promoter from a patient with tyrosinase-negative oculocutaneous albinism.

We examined the tyrosinase gene from a patient with tyrosinase-negative oculocutaneous albinism (OCA). First we studied the protein coding region, exon/intron junctions, and the proximal promoter region (positions -300 to +1) of her tyrosinase gene by direct sequencing. Although the results showed that she was heterozygote for the R77Q mutation, we could find no other mutation. To find a second mutation and compare the sequence in the 5'-flanking region of her tyrosinase gene between two OCA alleles, we amplified a 2422-bp stretch (positions -2065 to +357, including R77Q mutation site) by PCR, and cloned it into a plasmid vector. As a result, we discovered a difference between two OCA alleles in the GA repeat region. Therefore, we expect that the polymorphism in the GA repeat region of the tyrosinase gene will be used as a flanking marker of the OCA allele.

R278TER and P431L mutations of the tyrosinase gene exist in Japanese patients with tyrosinase-negative oculocutaneous albinism.

We examined the tyrosinase gene of two Japanese patients with tyrosinase-negative oculocutaneous albinism by allele-specific amplification analysis on two known point mutations in Japanese, and the results indicated that they were compound heterozygouts, namely, one allele of the tyrosinase gene harbored one of two known mutations and another allele probably had a mutation unknown in Japanese patients. Therefore, we have cloned and sequenced the tyrosinase gene of the two patients and identified two different point mutations. One is a nonsense mutation, codon 278CGA (Arg) to TGA (TER), and the other is a substitution mutation, codon 431CCA (Pro) to CTA (Leu). However, these same mutations have already been observed in a Guyanan and a Moroccan Jewish patient, and in an Indo-Pakistani patient, respectively.