Molecular basis of hereditary methaemoglobinaemia, types I and II: two novel mutations in the NADH-cytochrome b5 reductase gene

Hereditary methaemoglobinaemia, caused by deficiency of NADH-cytochrome b₅ reductase (b5R), has been classified into two types, an erythrocyte (type I) and a generalized (type II). We analysed the b5R gene of two Thai patients and found two novel mutations. The patient with type II was homozygous for a C-to-T substitution in codon 83 that changes Arg (CGA) to a stop codon (TGA), resulting in a truncated b5R without the catalytic portion. The patient with type I was homozygous for a C-to-T substitution in codon 178 causing replacement of Ala (GCG) with Val (GTG). To characterize effects of this missense mutation, we investigated enzymatic properties of mutant b5R (Ala 178 Val). Although the mutant enzyme showed normal catalytic activity, less stability and different spectra were observed. These results suggest that this substitution influenced enzyme stability due to the slight change of structure. In conclusion, the nonsense mutation led to type II because of malfunction of the truncated protein. On the other hand, the missense mutation caused type I, due to degradation of the unstable mutant enzyme with normal activities in patient's erythrocytes, because of the lack of compensation by new protein synthesis during the long life-span of erythrocytes.     

Status of endothelial dependent vasodilation in patients with hyperuricemia

Hyperuricemia has been associated with an increased risk for cardiovascular disease and increased mortality. However, the biologic mechanisms that link elevated serum uric acid to cardiovascular disease are uncertain. This study tested the hypothesis that elevated serum uric acid is associated with impaired endothelial function in hyperuricemic patients without any overt cardiovascular disease. Seventeen male patients with hyperuricemia (mean age 42+/-4 years) and 9 control subjects (mean age 45+/-5 years) were studied. All subjects were nonsmokers. All patients had never been treated for hyperuricemia, were on no medications, and were free of any other known diseases. Endothelial function was evaluated by flow-mediated dilation measured by ultrasound. Flow-mediated dilation was significantly impaired in patients with hyperuricemia (4.0+/-0.7%) compared with control subjects (6.4+/-0.8%) (p=0.044). Flow-mediated dilation correlated inversely with uric acid levels (r=-0.4, p=0.05). Nitrate-induced dilation was 12.3+/-1.0% in patients with hyperuricemia and 11.8+/-2.3% in control subjects (p=0.82). Impaired endothelial-dependent vasodilation is present in hyperuricemic patients even in the absence of any overt cardiovascular disease. The elevated serum uric acid, per se, may constitute a novel risk factor for endothelial dysfunction.     

Development of sarcoidosis during etanercept therapy

This report describes a 65-year-old woman who developed granulomatous lesions consistent with sarcoidosis during etanercept therapy for rheumatoid arthritis. Hilar and mediastinal lymphadenopathy and multiple nodules in both lung fields developed 21 months after administration of etanercept. Noncaseating epithelioid cell granulomas consistent with sarcoidosis were detected in a lung biopsy specimen and in the parietal pleura obtained via thoracotomy. Diseases showing similar histologic changes were excluded, and a diagnosis of sarcoidosis was made. Etanercept was discontinued, which resulted in symptomatic relief, improvement of oxygenation and radiologic findings. There is substantial evidence of tumor necrosis factor-alpha involvement in the induction and maintenance of granuloma formation; however, we should keep in mind that granulomatous disease, such as sarcoidosis, can develop during treatment with a tumor necrosis factor-alpha blocking agent, such as etanercept.     

Alteration in the retinoblastoma gene associated with immortalization of human fibroblasts treated with60Co gamma rays

Genetic analysis was carried out in human fibroblasts (KMST-6) immortalized by treatment with⁶⁰Co gamma rays in order to determine if any genetic change was involved in the immortal transformation of human cells. Analysis by restriction fragment length polymorphism revealed an alteration in chromosome 13q12–14, in which the retinoblastoma (RB) gene locus (13q14) is located. Then the RB gene itself was examined. Structural abnormalities in the RB gene were detected by Southern blot analysis. Furthermore, abnormal RB protein (pRB) was expressed in immortalized KMST-6 cells, as shown by in vitro phosphorylation, whereas normal KMS-6 cells expressed the intact pRB. These findings indicated that inactivation of the RB gene is one of the key events of the immortalization of human cells.Abbreviations RB retinoblastoma - pRB retinoblastoma gene product (protein) - T simian virus 40 large T antigen - E1A adenovirus E1A protein