Genetic heterogeneity in acatalasemia

Detection of a novel familial catalase mutation (Hungarian type D) and the possible risk of inherited catalase deficiency for diabetes mellitus

The enzyme catalase is the main regulator of hydrogen peroxide metabolism. Recent findings suggest that a low concentration of hydrogen peroxide may act as a messenger in some signalling pathways whereas high concentrations are toxic for many cells and cell components. Acatalasemia is a genetically heterogeneous condition with a worldwide distribution. Yet only two Japanese and three Hungarian syndrome-causing mutations have been reported. A large-scale (23 130 subjects) catalase screening program in Hungary yielded 12 hypocatalasemic families. The V family with four hypocatalasemics (60.6 +/- 7.6 MU/L) and six normocatalasemic (103.6 +/- 23.5 MU/L) members was examined to define the mutation causing the syndrome. Mutation screening yielded four novel polymorphisms. Of these, three intron sequence variations, namely G-->A at the nucleotide 60 position in intron 1, T-->A at position 11 in intron 2, and G-->T at position 31 in intron 12, are unlikely to be responsible for the decreased blood catalase activity. However, the novel G-->A mutation in exon 9 changes the essential amino acid Arg 354 to Cys 354 and may indeed be responsible for the decreased catalase activity. This inherited catalase deficiency, by inducing an increased hydrogen peroxide steady-state concentration in vivo, may be involved in the early manifestation of type 2 diabetes mellitus for the 35-year old proband.

A new type of inherited catalase deficiencies: its characterization and comparison to the Japanese and Swiss type of acatalasemia

Thirteen Hungarian families that exhibited inherited catalase deficiencies have been detected. Differences between the deficiencies reported from Hungary and the previously reported Swiss acatalasemia were characterized using biochemical analysis of the catalase proteins. Molecular biological methods were used to compare the previously reported types of catalase deficiencies in Japan and the Hungarian deficiencies. Three mutations (a GA insertion in exon 2, a G insertion in exon 2, and a T to G substitution in intron 7) are responsible for decreased catalase activity in 7 of the 13 Hungarian kindreds; the other 6 families have not yet been characterized. These are not the mutations observed in Japan. Changes in lipid and carbohydrate metabolism and the high incidence (12.7%) of diabetes mellitus in the Hungarian kindreds suggest that individuals with inherited catalase deficiency are at risk of atherosclerosis and diabetes mellitus. The Hungarian subjects were detected during screening of a large population for catalase activity; no overt disease state was associated with the deficiencies. We hypothesize that the increased risk of disease may be due to prolonged exposure to elevated levels of blood hydrogen peroxide due to the lack of normal removal of hydrogen peroxide by blood catalase.

A novel catalase mutation detected by polymerase chain reaction-single strand conformation polymorphism, nucleotide sequencing, and western blot analyses is responsible for the type C of Hungarian acatalasemia

Polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) screening was used for searching mutations of the catalase gene in two Hungarian hypocatalasemic families. A syndrome-causing mutation was found in a PCR product containing exon 7 and its boundaries. Nucleotide sequence analyses detected a G to T substitution at position 5 of intron 7. The effect of this splice site mutation was confirmed by Western blot analyses demonstrating a decreased catalase protein level in these patients. These findings represent a novel type (C) of catalase mutations in the Hungarian acatalasemic/hypocatalasemic patients.

Anovel catalase mutation (a GA insertion) causes the Hungarian type of acatalasemia

Acatalasemia, a deficiency of enzyme catalase, is an autosomal recessive syndrome with an incidence of 5:106 in Hungary. We have examined the first Hungarian acatalasemic family for the disease-causing mutation. All exons of the catalase gene were screened by PCR-SSCP, PCR-heteroduplex, and nucleotide sequence analysis. The heteroduplex formation detected in exon 2 was verified by nucleotide sequence analysis. We found a GA insertion at nucleotide position 138, increasing the GA repeat number from 4 to 5. This GA insertion caused a frameshift in the amino acid sequence from position 68 to 133 and generated a TGA terminating codon at amino acid position 134. This truncated protein lacks the essential amino acid (histidine 74) in the active center. This finding can explain the decreased blood catalase activity in the Hungarian acatalasemic family.

Genetic heterogeneity of the 5' uncoding region of the catalase gene in Hungarian acatalasemic and hypocatalasemic subjects

The 5' uncoding region (165 bp), exon 1 (63 bp) and part of intron 1 (20 bp) of the catalase gene was amplified by PCR in acatalasemic (2), hypocatalasemic (19) patients and healthy individuals (10). The single strand conformational polymorphism of PCR products showed a highly polymorphic pattern. This polymorphism was supported by nucleotide sequence analyses yielding eight mutations. They are A to T, C to A and C to T at positions -21, -20, -18 of the 5' flanking region, T to C at positions 4, 44, 49 of the non-coding region and C to T and C to A at positions 12, 27 of exon 1. Of these nucleotide substitutions, the fourth, fifth, seventh and eighth are novel mutations. The mutations 1, 3, 6, 8 were present at least at heterozygous level in all acatalasemics and hypocatalasemics. None of these mutations may be the causal mutation(s) of acatalasemia as each of these nucleotide substitutions were detected in healthy subjects with normal blood catalase activity.

Further genetic heterogeneity in acatalasemia

A T-deletion at position 10 of exon 4 for catalase gene was reported as a novel mutation, causing a new genetic type of acatalasemia in Japan. This mutation, destroying a Hinf1 recognition site, was searched for in Hungarian acatalasemic (2) and hypocatalasemic (22) patients and in controls (27) by Hinf1 digestion and sequence analyses of a 203 bp polymerase chain reaction (PCR) product containing the entire exon 4. The Hinf1 polymorphism did not reveal any difference between controls and hypocatalasemic as well as acatalasemic patients. These results were confirmed by sequence analyses showing the T nucleotide for the two acatalasemic and for one unrelated hypocatalasemic patient, as well as for two controls. These findings represent further evidence that acatalasemia is heterogeneous at the DNA level.

Polymorphism of 5' of the catalase gene in Hungarian acatalasemia and hypocatalasemia

The amplified fragment length polymorphism of Hinf1 on the promoter region of the catalase gene in Hungarian acatalasemic and hypocatalasemic patients yielded three different patterns with five bands in total. The sequence analyses revealed A-to-T, C-to-A, and C-to-T mutations at positions -21, -20, and -18 upstream of the translational initiation site. The -21 A-to-T mutations were more frequent in acatalasemic and hypocatalasemic patients (36/2) than in controls (18/14). This mutation had been detected in Japanese acatalasemic patients while the other two are novel mutations. Two extra bands in the Hinf1 pattern are due to star-like activity that cleaved a G/ATTT sequence at position -4 to 0 upstream of the initiation site.