G-6-PD Worcester. A new variant, associated with X-linked optic atrophy

Comparison for functional aberration of G-6-PD deficiency variants with exon 10 mutations

Glucose-6-phosphate dehydrogenase (G-6-PD) deficiency is a common inherited enzyme deficiency in many parts of the world and there are many different variants described. Every G-6-PD deficiency variant has a unique underlying genetic defect, therefore it manifests specific properties. The single amino acid substitution in the globin chain is the commonest form of G-6-PD deficiency variant. Usually, the G-6-PD deficiency variant with the pathogenesis of a single amino acid substitution presents with only one aberration in secondary structure. Although many G-6-PD deficiency variants present similar structural abnormal points their functions sometimes are discordant. Here, the author performed a functional analysis on some alpha haemoglobinopathies using a novel bioinformatic tool, Polyphen. The mutations of five G-6-PD deficiency variants with exon 10 mutations, Guadalajara (386 Arg-->Cys), Beverly Hills (387 Arg-->His), Serres (361 Ala-->Val), Iowa (385 Lys-->Glu), and Clinic (405 Met-->Ile) were selected for further study in this investigation. According to the in silico mutation study, the functional change in the G-6-PD deficiency variants with exon 10 mutations studied is variable. Here, it indicates that the functional aberration in the G-6-PD deficiency variant is based on complex pathogenesis. The identification of the structural aberration only in a G-6-PD deficiency variant is not sufficient and should be supplemented with a further functional analysis for a better insight in this topic.

Glucose-6-phosphate dehydrogenase Guadalajara--a case of chronic non-spherocytic haemolytic anaemia responding to splenectomy and the role of splenectomy in this disorder

Glucose-6-phosphate dehydrogenase (G6PD) is an enzyme of the pentose phosphate shunt pathway a major function of which is to prevent cellular oxidative damage. Deficiency in red blood cells is associated with a number of varied clinical manifestations. Chronic non-spherocytic haemolytic anaemia is uncommon but is usually characterized by chronic haemolysis, often with severe anaemia. In the past splenectomy in this condition has been thought to be of questionable benefit. We report a case of G6PD Guadalajara where splenectomy produced transfusion independence and have reviewed the literature. Those cases with exon 10 mutations often have a severe clinical phenotype, which responds to splenectomy. This procedure should be considered in this condition.

Chronic non-spherocytic haemolytic disorders associated with glucose-6-phosphate dehydrogenase variants

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is the most common human enzyme defect, being present in over 400 million people world wide. In a small number of cases, G6PD deficiency can lead to mild-to-severe chronic haemolysis, which is further exacerbated by oxidative stress. Such G6PD variants have been described all over the world and are responsible for chronic non-spherocytic haemolytic anaemia (CNSHA). To date 61 G6PD molecular variants associated with CNSHA have been identified, only some of which can cause the severe reduction in stability of the red blood cell enzyme. The distribution of the different mutations shows a predominance of small mutational events, and many have been found repeatedly in different parts of the world. By revisiting the 61 class I variants described so far, we can observe that a low inhibition constant (Ki) for NADPH, a higher Km for substrates and a reduced thermostability are common.

Clinical and haematological consequences of recurrent G6PD mutations and a single new mutation causing chronic nonspherocytic haemolytic anaemia

We have determined the causative mutation in 12 cases of glucose-6-phosphate dehydrogenase deficiency associated with chronic non-spherocytic haemolytic anaemia. In 11 of them the mutation we found had been previously reported in unrelated individuals. These mutations comprise seven different missense mutations and a 24 base pair deletion. G6PD Nara, previously found in a Japanese boy. Repeated findings of the same mutations suggests that a limited number of amino acid changes can produce the CNSHA phenotype and be compatible with normal development. The one new mutation we have found, G6PD Serres, is 1082 C-->T causing a 361 Ala-->Val substitution in the dimer interface where most other severe G6PD mutations are found. Now that several patients with the same mutation have been reported we can compare the resulting clinical phenotypes. For each mutation we find a reasonably consistent clinical picture, ranging from mild (G6PD Clinic) through moderate (G6PD Nashville) to severe (G6PD Beverly Hills and G6PD Nara).

Molecular Analysis of Eight Biochemically Unique Glucose-6-Phosphate Dehydrogenase Variants Found in Japan

We analyzed the molecular mutations of eight known Japanese glucose-6-phosphate dehydrogenase (G6PD) variants with unique biochemical properties. Three of them were caused by novel missense mutations: G6PD Musashino by 185 C→T, G6PD Asahikawa by 695 G→A, and G6PD Kamiube by 1387 C→T. Predicted amino acid substitutions causing asymptomatic variants G6PD Musashino (62 Pro→Phe) and G6PD Kamiube (463 Arg→Cys) were located in regions near the amino or carboxyl end of the polypeptide chain, whereas an amino acid change 232 Cys→Tyr causing a class 1 variant G6PD Asahikawa was located in the region where amino acid alterations in some class 1 variants were clustered. The other five variants had known missense mutations, namely, G6PD Fukushima, 1246 G→A, G6PD Morioka, 1339 G→A, and G6PD Iwate, G6PD Niigata and G6PD Yamaguchi, 1160 G→A, which cause variants, G6PD Tokyo, G6PD Santiago de Cuba, and G6PD Beverly Hills, respectively.

X-recessive angiopathic opticopathy

A familial optic atrophy with X-recessive heredity, distinct from Leber's optic atrophy (LOA), is described. The symptoms are: slight to moderate pallor of the papillomacular bundle at the disc possibly preceded by some hyperaemia of the disc, telangiectasia on the disc with normal retinal vessels, occurrence in the second decade of life, slow progression with often subclinical visual loss, a small relative central scotoma with an intact peripheral visual field, slight acquired tritanopia and deuteranopia, and vasomotor headaches. The disease may exhibit severe exacerbations with loss of vision to 1/60, provoked by vasoconstrictors and reacting favourably to vasodilators. This acute loss of vision is associated with ischaemia of the disc, a deep central scotoma with marked disturbance of colour vision in the form of an acquired deuteranopia, and sensoparalytic pupils. This is followed by increasing pallor of the disc, slow resolution of the central scotoma with a permanent reduction in the central light sensitivity, markedly disturbed Visual Evoked Potentials (VEP), acquired deuteranopia and normal ERG and EOG. In contrast to all hereditary opticopathies so far described, fluorescein angiography showed a disturbance of perfusion in the peripapillary choroid and the prelaminar part of the optic nerve. A similar disturbance of perfusion is described in anterior ischaemic optic neuropathy (AION) and low-tension glaucoma. To these acquired, non-hereditary recessive vascular opticopathies, which usually occur late in life, will have to be added the X-recessive vascular optic atrophy which we describe here, for which we propose the name: X-recessive angiopathic opticopathy. The differential diagnosis from some other hereditary, especially X-recessive, optic atrophies is discussed.

Increased erythrocyte lipid peroxidation in hereditary xerocytosis

Xerocytosis is a chronic hemolytic anemia with abnormal membrane function manifested by an increase in passive potassium permeability. Xerocytes demonstrate a greater susceptibility to hydrogen peroxide manifested by the production of malondialdehyde (MDA). Xerocyte membrane phospholipid and fatty acid analysis is normal except for a slight increase in phosphatidyl choline, a commensurate decrease in sphingomyelin, as well as a decrease in linoleic acid. Metabolism and glutathione stability are normal as well as plasma vitamin E levels in patients with xerocytosis. The increased susceptibility to oxidant stress is exaggerated in the "older aged" xerocyte population and correlated well with decreased intracellular potassium concentration.

GD (--) Aachen, a new variant of deficient glucose-6-phosphate dehydrogenase. Clinical, genetic, biochemical aspects

A deficient G-6PD variant was discovered in 4 males of one family from northwestern Germany. Five generations of this family could be studied. The deficient G-6PD was a new variant, called "Gd (--) Aachen". Its main characteristics are the following: severe enzyme deficiency in erythrocytes (3% of normal), contrasting with an almost normal activity in leukocytes; normal molecular specific activity (i.e., normal ratio enzyme activity/cross-reacting material); slow mobility in starch gel electrophoresis (92-94% of normal); increased Michaelis constant for glucoes-6-phosphate (60-70 muM) and NADP+ (20-25 muM); decreased inhibition constant by NADPH with respect to NADP+ (7 muM); increased inhibition by ATP; normal utilization of the substrate analogues; slightly biphasic pH curve; thermal instability, and normal activation energy of the enzymatic reaction. The relationships between the hematologic disorders (severe and frequent hemolytic crises) and the unfavorable kinetic modifications are discussed.

Hemolytic anemia and G6PD deficiency

The severity of enzyme deficiency often does not correlate well with the clinical severity of genetic diseases. Thus, some G6PD variants associated with severe enzyme deficiency, such as Union and Markham, cause no hemolytic problem, while some variants associated with less severe deficiency, such as Manchester, Alhambra, and Tripler, cause chronic hemolytic anemia. The kinetic characteristics of these variant enzymes have not explained the discrepancy. However, examination of the normal and variant enzymes under simulated physiologic conditions, with the effects of various intermediate metabolites and co-enzymes in red cells being taken into consideration, reveal that the G6PD's from hemolytic variant subjects are strongly inhibited by a physiologic concentration of NADPH because of their high Michaelis constant for NADP or low inhibition constant for NADPH, and they are more sensitive to inhibition by ATP. These variant enzymes cannot generate enough NADPH in red cells to maintain an adequate concentration of reduced glutathione. The nonhemolytic variant enzymes are far less sensitive to the inhibition by NADPH because of their low Michaelis constant for NADP and high inhibition constant for NADPH. The physiologic activity of these nonhemolytic variant enzymes is estimated to be more than 30 percent of the activity of the normal G6PD, and this activity is adequate to maintain the red cells unhemolyzed.