A novel point mutation in a 3' splice site of the NADH-cytochrome b sub(5) reductase gene results in immunologically undetectable enzyme and impaired NADH-dependent ascorbate regeneration in cultured fibroblasts of a patient with type II hereditary methemoglobinemia

• Published in: American journal of human genetics 1995-01, Vol.57 (2), p.302-310
• Main Authors: Shirabe, K, Landi, M T, Takeshita, M, Uziel, G, Fedrizzi, E, Borgese, N
• Format: Article
• Language: English
• ISSN: 0002-9297

Hereditary methemoglobinemia with generalized deficiency of NADH-cytochrome b sub(5) reductase (b sub(5)R) (type II) is a rare disease characterized by severe developmental abnormalities, which often lead to premature death. Although the molecular relationship between the symptoms of this condition and the enzyme deficit are not understood, it is thought that an important cause is the loss of the lipid metabolizing activities of the endoplasmic reticulum-located reductase. However, the functions of the form located on outer mitochondrial membranes have not been considered previously. In this study, we have analyzed the gene of an Italian patient and identified a novel G arrow right T transversion at the splice-acceptor site of the 9th exon, which results in the complete absence of immunologically detectable b sub(5)R in blood cells and skin fibroblasts. In cultured fibroblasts of the patient, NADH-dependent cytochrome c reductase, ferricyanide reductase, and semidehydroascorbate reductase activities were severely reduced. The latter activity is known to be due to b sub(5)R located on outer mitochondrial membranes. Thus, our results demonstrate that the reductase in its two membrane locations, endoplasmic reticulum and outer mitochondrial membranes, is the product of the same gene and suggest that a defect in ascorbate regeneration may contribute to the phenotype of hereditary methemoglobinemia of the generalized type.