Hiroshi Chikaoka

Characterization of mutant holocarboxylase synthetase (HCS) : A Km for biotin was not elevated in a patient with HCS deficiency

Holocarboxylase synthetase (HCS) is an essential enzyme for the biotinylation of several mammalian carboxylases. A deficiency of HCS is accountable for early onset biotin-responsive multiple carboxylase deficiency. To address the mechanism of biotin responsiveness, we analyzed the kinetic properties of the previously identified mutant. L237P, and another mutant, V550M, described in this report. The V550M mutant contains a G to A transition at position 1935, which is within the putative biotin binding site, whereas the mutation in L237P occurs outside the biotin binding site.Km and Vmax values for the mutant proteins were determined by overexpressing cDNAs encoding the mutants in transformed fibroblasts from an HCS-deficient patient. Enzyme activity assays were performed using apocarboxyl carrier protein as a substrate. AKm for biotin that was larger than the value found for the wild-type cDNA was observed in fibroblasts transfected with the V550M cDNA, but not the L237P cDNA. The Vmax for the expressed L237P cDNA was 4.3% of that observed for the wild-type cDNA. Biotin-responsiveness in the patient with the L237P mutation was neither due to an increased affinity for biotin nor a restoration of stability of the mutant by biotin treatment. A new mechanism of biotin responsiveness in HCS deficiency is presented.

Case of insertion, inversion and deletion of chromosome 6

The infant boy involved in the present study was the only child born to Japanese healthy unrelated parents. The pregnancy was complicated by breech presentation, oligohydramnios and intrauterine growth retardation (IUGR). He had a left-sided hydronephrosis in his mother’s uterine. His mother took traditional Chinese medicine (Toki-inshi and Daio-kanzo-to) and oxatomide because of atopic dermatitis. At the 39th week of pregnancy, he was delivered by cesarean section because of fetal distress. His birthweight was 2592 g and his body length was 48.5 cm. Apgar scores were nine and 10 at 1 and 5 min, respectively. The infant required oxygen therapy for 13 days because of dyspnea. During the clinical course, the following manifestations were observed: developmental delay; hypotonia; auricular fistula; failure to thrive; hypertelorism; patent foramen ovale (PFO); patent ductus arteriosus (PDA); cleft lip; cleft palate; left hydronephrosis; sensorineural deafness; hyperuricemia; overlapping in the lower legs; bell-shaped thorax and dyspnea. He had recurrent episodes of respiratory tract infections with dyspnea. Patent foramen ovale and PDA were shown by echocardiogram. Left-sided hydronephrosis was shown by magnetic resonance imaging at the age of 5 months. According to the auditory brainstem response he had a sensorineural deafness. At the age of 5 months, he was admitted to our hospital for a cleft lip operation. However, the operation was postponed because he had an upper respiratory infection, which was treated with antibiotics and discharged once recovered. At the age of 7 months, he underwent a cleft lip operation. His bodyweight was 6590 g (–2.1 SD) and his body length was 66.0 cm (–1.5 SD). At the age of 8 months, he was admitted to our hospital for pneumonia and bronchial asthma. He was treated with theophylline for bronchial asthma. After 14 days of treatment, his uric acid became higher than 10 mg/dL. He was given allopurinol initially, with a dose of 20 mg daily and thereafter in doses of 40 mg daily. We also used sodium bicarbonate for his hyperuricemia. After 61 days of this treatment, his hyperuricemia improved. At the age of 11 months, his bodyweight was 6040 g (–3.3 SD) and body length was 66.4 cm (–3.1 SD). Anterior fontanel was 3.5 × 3.0 cm. Patellar tendon reflex was brisker than average. Scarf sign, head lag and loose shoulder were all positive. He could not achieve head control and he could not sit. He was discharged after recovery from pneumonia and bronchial asthma.