Satoru Komaki

The polymorphic 43Thr bcl-2 protein confers relative resistance to autoimmunity: an analytical evaluation

We have found a novel polymorphic (Ala43Thr; ACC→GCC) bcl-2 allele in a Japanese population. An in vitro expression study with a mouse IL-7-dependent pre-B cell line has revealed that inhibition of the programmed cell death function of 43Thr bcl-2 protein is suppressed compared with that of normal 43Ala bcl-2 protein. Since bcl-2 expression in B-lymphoid cells elicits autoimmune disease in mice, we have investigated the possibility of whether a bcl-2 polymorphism has a different susceptibility to autoimmune disease. To evaluate the clinical impact of this polymorphism, the frequency of bcl-2 polymorphism was investigated in 221 children with insulin-dependent diabetes mellitus (IDDM), 237 adults with autoimmune disease (105 with rheumatoid arthritis, 57 with systemic lupus erythematosus, 55 with Sjögren’s syndrome, and 20 others), and 290 healthy Japanese children and adults. The frequency of the 43Thr bcl-2 allele, either homozygous or heterozygous, was 14.5% in normal controls, 6.8% (P<0.01) in children with IDDM, and 8.0% (P<0.025) in adults with autoimmune disease. These results suggest that the 43Thr allele of bcl-2 confers resistance to autoimmune disease. The different anti-apoptotic function resulting from the different expression of bcl-2 protein in lymphocytes seems to be associated with the development of autoimmune disease, indicating that the bcl-2 gene affects human autoimmune disease.

Phenotypic variability in male patients carrying the mutant ornithine transcarbamylase (OTC) allele, Arg40His, ranging from a child with an unfavourable prognosis to an asymptomatic older adult.

In five different Japanese families, we identified six male hemizygotes (aged 6, 9, 15, 17, 56, and 65 years) and a putative candidate (aged 48 years), carrying a mutant allele of the ornithine transcarbamylase (OTC) gene, a G to A substitution at nucleotide 119 in exon 2 generating histidine in place of arginine. OTC activity in the necropsied liver tissue was reduced to approximately 12% of the control and that of COS 1 cells transfected with Arg40His OTC cDNA was 10.2 +/- 1.8% of the control transfected with wild type OTC cDNA. Clinical features ranged from death during a hyperammonaemic attack (a 9 year old) to a 65 year old asymptomatic man. We consider that the amount of protein ingested by these subjects may be one predisposing factor leading to the manifestation of this disease.

Familial lethal inheritance of a mutated paternal gene in females causing X-linked ornithine transcarbamylase (OTC) deficiency

A Leu148Phe substitution of the ornithine transcarbamylase (OTC) gene was identified in a 2-year-old girl with OTC deficiency (14% of control). Her two elder sisters died in childhood of hyperammonemia, and the patient also died of OTC deficiency. Enzyme activity in Cos1 cells transfected by the mutant cDNA was undetectable, thereby indicating a definite pathogenic mutation. Familial gene analysis showed that the mother had wild-type OTC alleles on both X-chromosomes and the father was a mosaic for the mutant allele in his lymphocytes and spermatozoa. This clinical case shows that a somatic and germline mosaicism for a single-gene disorder led to an unusual pattern of X-linked inheritance in the family, and all three daughters in the family died of OTC deficiency. The possibility that inherited factors will lead to skewed X-inactivation needs to be considered.

Specificity of PCR-SSCP for detection of the mutant ornithine transcarbamylase (OTC) gene in patients with OTC deficiency

Ornithine transcarbamylase (OTC) (EC 2.1.3.3), the second enzyme of the hepatic urea cycle, is required for detoxication of ammonia and for biosynthesis of urea. The enzyme is apparently expressed only in the liver and small intestine. OTC deficiency is an X-linked genetic disease and the most common of the urea cycle disorders • (Brusilow and Horwich 1989; Nagata et al 1991a). Approximately one-third of male patients fall in the neonatal-onset group, and most die in early infancy of hyperammonaemic coma (Matsuda et al 1991). Those who do survive are severely mentally retarded and have an abnormal EEG and a severely damaged brain (Msall et al 1984; Nagata et al 1991b). Most male patients belonging to the late-onset group are normal or have moderate signs and symptoms with adequate treatment (Finkelstein et al 1990a; Matsuda et al 1991). Female heterozygotes have manifestations ranging from asymptomatic to mild or severe because of the allelic heterogeneity (Rowe et al 1986; Matsuda et al 1984) and random inactivation of the Xchromosome in hepatocytes (Lyone 1961). The human OTC cDNA was cloned by Horwich et al (1984) and by Hata et al (1988). Structural organization of the human OTC gene was reported by Hata et al (1988). There is a wide spectrum of mutations of the OTC gene, including deletions (Old et al 1985; Rozen et al 1985, 1986; Maddalena et al 1988a; Grompe et al 1991), point mutations in exons (Grompe et al 1991; Maddalena et al 1988b; Finkelstein et al 1990b; Hata et al 1989, 1991; Hentzen et al 1991; Matsuura et al 1993a,b) and point mutations in introns that resulted in splicing abnormalities (Carstens et al 1991). We examined the reliability of polymerase chain reaction single-strand conformation polymorphisms (PCRSSCP) for detecting involved exons of the OTC gene, using seven known and four unknown mutant alleles.

Identification of two new aberrant splicings in the ornithine carbamoyltransferase (OCT) gene in two patients with early and late onset OCT deficiency

SummaryOrnithine carbamoyltransferase (OCT) is a liver-specific enzyme located in the mitochondrial matrix. OCT deficiency is an X-linked disease with a heterogeneous phenotype, even in affected males. We studied two male patients (K.M., K.G.) with early and late onset, respectively. OCT activity was zero in the autopsied liver of patient K.M. and was 6% of control in the biopsied liver of K.G. Sequencing of OCT cDNAs revealed exon 5 skipping in K.M., resulting from a T-to-C transition of the initial dinucleotide of the 5′ splicing donor site of intron 5, and a G-to-T transversion at position +45 in exon 9 (L304F) in K.G., providing three OCT mRNAs of different lengths: a normally spliced transcript, 23 bp insertion of intron 8 and the first 50bp missing within exon 9. Exon 5 skipping and two other aberrant splicings produced stop codons early downstream in mature OCT mRNAs. Expression study of a missense allele, L304F, transfected to cultured Cos 1 cells revealed a 34.4% value of the control. The difference of OCT activities between the patient liver and transfected cells (6% vs. 34%) can be explained by this splicing abnormality.

Expression of four mutant human ornithine transcarbamylase genes in cultured Cos 1 cells relates to clinical phenotypes

Ornithine transcarbamylase (OTC) deficiency is an X-linked disease with a heterogeneous phenotype, even in affected males. To detect mutations in the OTC gene using genomic DNA, we have developed a method in which all exons and adjacent introns are amplified and sequenced. Although this approach detected mutations in many cases, the relationship between a mutation and the OTC phenotype was not firmly established. Therefore, we investigated the issue by expression analysis of mutant OTC cDNA in cultured cells. Four mutant OTC cDNAs were constructed, based on the reported cases, using our newly developed method. The normal (wild-type) human OTC cDNA was reproducibly expressed at high levels in these Cos 1 cells. Predicted OTC activities of mutant OTC cDNAs ranged from 0% to 8.9% of the normal level together with variable amounts of the enzyme protein. The predicted enzyme activities account for the clinical phenotype of the disease. Our observations confirm that these mutations are responsible for OTC deficiency in these patients.