Ayumi Uematsu

Hyperinsulinism-hyperammonemia syndrome caused by mutant glutamate dehydrogenase accompanied by novel enzyme kinetics.

Abstract Hyperinsulinism-hyperammonemia syndrome (HHS) is a recently identified genetic disorder characterized by hyperinsulinemic hypoglycemia with concomitant hyperammonemia. In patients with HHS, activating mutations in the glutamate dehydrogenase (GDH) gene have been identified. GDH is a key enzyme linking glutamate metabolism with the Krebs cycle and catalyzes the conversion of glutamate to α-ketoglutarate. The activity of GDH is controlled by allosteric inhibition by GTP and, so far, all the mutations of HHS patients have been located within the GTP-binding site. Characteristically, GDH from these individuals have therefore normal basal activity in conjunction with a loss of GTP inhibition. In this study, however, we have identified a novel variant GDH in a patient with a more severe form of HHS. The mutation is located outside the GTP-binding site and the patient’s GDH shows consistently higher activity, even in the absence of allosteric effectors. These results further support the hypothesis that the activating mutation of GDH is the cause of HHS. The mechanism leading to the activation of GDH, however, is not always related to the loss of GTP inhibition as was originally suggested.

X-inactivation pattern in the liver of a manifesting female with ornithine transcarbamylase (OTC) deficiency

Ornithine transcarbamylase (OTC) deficiency is the most common urea cycle disorder. It is X‐linked and hemizygous new‐born males usually suffer fatal hyperammonemia. In contrast, carrier females manifest variable phenotypes, ranging from asymptomatic carriers to those with severe hyperammonemia. In order to understand the correlation between X‐inactivation status and the clinical phenotype of carrier females with this disorder, we analyzed the X‐inactivation pattern of peripheral blood leukocytes in a family consisting of a clinically normal mother and two daughters with severe manifestation. In addition, we obtained tissue samples from various parts of the liver of one of these daughters and analyzed X‐inactivation patterns and the residual OTC activities. The X‐inactivation of peripheral blood leukocytes was nearly random in these carrier females and showed no correlation with the disease phenotype. However, the X‐inactivation of the liver was much more skewed and correlated well with the OTC activity of all samples. Interestingly, the degree of X‐inactivation varied considerably, even within the same liver.

Uniparental and functional X disomy in Turner syndrome patients with unexplained mental retardation and X derived marker chromosomes.

We analysed parental origin and X inactivation status of X derived marker (mar(X)) or ring X (r(X)) chromosomes in six Turner syndrome patients. Two of these patients had mental retardation of unknown cause in addition to the usual Turner syndrome phenotype. By FISH analysis, the mar(X)/r(X) chromosomes of all patients retained the X centromere and the XIST locus at Xq13.2. By polymorphic marker analysis, both patients with mental retardation were shown to have uniparental X disomy while the others had both a maternal and paternal contribution of X chromosomes. By RT-PCR analysis and the androgen receptor assay, it was shown that in one of these mentally retarded patients, the XIST on the mar(X) was not transcribed and consequently the mar(X) was not inactivated, leading to functional disomy X. In the other patient, the XIST was transcribed but the r(X) appeared to be active by the androgen receptor assay. Our results suggest that uniparental disomy X may not be uncommon in mentally retarded patients with Turner syndrome. Functional disomy X seems to be the cause of mental retardation in these patients, although the underlying molecular basis could be diverse. In addition, even without unusual dysmorphic features, Turner syndrome patients with unexplained mental retardation need to be investigated for possible mosaicism including these mar(X)/r(X) chromosomes.

Cerebral infarction and pancreatitis: possible complications of patients with 3-hydroxy-3-methylglutaryl-CoA lyase deficiency.

Mitochondrial 3-hydroxy-3-methylglutaryl-CoA lyase (HL, EC 4.1.3.4.) is a key enzyme of lipid and amino acid metabolism. It catalyses the cleavage of HMG-CoA to form acetyl-CoA and acetoacetate, which is the ¢nal step of the ketogenic pathway and leucine catabolism. De¢cient individuals (McKusick 246450) usually present with acute episodes of vomiting, hypotonia and lethargy in the neonatal period or in infancy. Laboratory tests reveal metabolic acidosis with nonketotic hypoglycaemia, hyperammonaemia, and abnormal results of liver function tests. The disorder is fatal in about 20% of cases, although the symptoms tend to be milder after childhood. The incidence is quite low except in Saudi Arabia, where HL de¢ciency is the most common organic acidaemia. Otherwise, only 41 cases have been reported in the English literature. In this report, we describe a Japanese patient with HL de¢ciency whose clinical course was complicated by an episode of cerebral infarction in the neonatal period and by recurrent episodes of pancreatitis in childhood. Both are likely to represent insu¤ciently recognized complications of this disorder. The patient was born normally to healthy Japanese parents, and weighed 3180 g at birth. On the second day, he was referred to a regional hospital because of convulsions, hypoglycaemia (23 mg/dl, normal range 72^116), and liver dysfunction (AST 555 IU/L, normal range 13^29; ALT 794 IU/L, normal range 8^28). He had another episode of liver dysfunction (AST 4150 IU/L, ALT 2200 IU/L) at 5 months. At 6 months, brain magnetic resonance imaging revealed bilateral occipital porencephaly of which the distribution did not precisely coincide with that of blood supplies. White-matter changes as described by Ozand et al (1991) were not present. At 1 year 1 month, another episode of hypoglycaemia was noted and the patient was referred to our hospital. Urinary organic acid analysis showed markedly elevated levels of 3-hydroxy-3-methylglutaric, 3-methylglutaconic, 3-methylglutaric and 3-hydroxyisovaleric acids, suggesting the diagnosis of HL de¢ciency. The diagnosis was con¢rmed by the totally de¢cient activity of HL in cultured skin ¢broblasts. He continued to have repeated episodes of hypoglycaemia despite protein restriction and the administration of L-carnitine. After 3 years, he frequently showed elevation of pancreatic amylase/lipase during these episodes. One such episode led to frank pancreatitis accompanied by severe abdominal pain, which required complete starvation and administration of nafamostat mesilate. J. Inherit. Metab. Dis. 23 (2000) 636^637 # SSIEM and Kluwer Academic Publishers. Printed in the Netherlands.

Analysis of the SRY gene in Turner syndrome patients with Y chromosomal material

Editor—Turner syndrome is one of the most common chromosomal abnormality syndromes affecting 1 in 2500 liveborn females. The syndrome is characterised by short stature, gonadal dysgenesis, congenital heart disease, renal anomalies, and a variety of somatic features including neck webbing, cubitus valgus, short neck, and widely set nipples. Nearly half of the patients have a classical 45,X karyotype while others have structurally abnormal sex chromosomes (for example, 46,X,i(Xq)) or are mosaics with other cell lines with normal (46,XX) or abnormal sex chromosomes.1-4 Among these, patients with Y chromosomal material require specific attention since many of these 45,X/46,XY Turner syndrome patients develop gonadoblastoma or dysgerminoma later in life.5 6 Conventional chromosomal analysis indicates that 4-20% of patients with Turner syndrome have a Y chromosome or its derivatives.1-4 These figures could be even higher, since the more sensitive PCR based analysis has shown that 15-60% of cytogenetically 45,X females have Y chromosomal material.7-9 These findings mean that 10-50% of all Turner syndrome patients have Y chromosomal material and therefore are, to some extent, at risk of developing gonadoblastoma. A more precise understanding of the mechanism leading to generation of a 45,X/46,XY karyotype is therefore important for providing better care for these patients. Karyotypes such as 45,X/46,XY are presumably caused by mitotic loss of the Y chromosome from the originally 46,XY fetus. It is not known, …

Relatively longer hand in patients with Ullrich-Turner syndrome

We analyzed the total hand length (HL) and length of noncarpal bones (NCL) in 50 Japanese patients with Ullrich-Turner syndrome (UTS) and in 443 other patients with short stature used as controls. In each patient group we calculated relative HL (RHL= HL/height) and relative NCL (RNCL= NCL/height). UTS patients had significantly greater RHL than controls. The greater RHL in UTS patients is mainly due to their longer, short tubular bones. The RHL is not affected by ages and karyotypes of UTS patients or growth hormone treatments given to them. We conclude that relatively longer hands are a common manifestation of UTS and that this parameter is useful for the diagnosis of the syndrome among short females, who usually need chromosome analysis.

Identification of a novel single base-pair polymorphism in the glutamate dehydrogenase (GLUD1) gene

AbstractA novel single base-pair polymorphism, G/A at ntd 955, was identified within the coding region of the glutamate dehydrogenase gene (GLUD1). This polymorphism should prove useful for the study of human disorders with altered ammonia and/or blood glucose levels.