Molecular genetic analysis of a female patient with pyruvate dehydrogenase deficiency: detection of a new mutation and differential expression of mutant gene product in cultured cells.
A new 18 bp insertion mutation in the gene for the alpha subunit of pyruvate dehydrogenase (E1 alpha) was found in a female patient with congenital lactic acidaemia. Cultured skin fibroblasts and Epstein-Barr virus-transformed lymphoblastoid cells from this patient showed decreased and normal pyruvate dehydrogenase complex (PDHC) activity, respectively. This 18 bp insertion was a de novo mutation, because it was not present in her parents. Although this female patient was heterozygous for the normal and the mutant alleles, 97% of cultured skin fibroblasts expressed the mutant allele, while 100% of cultured lymphoblastoid cells, 94% of peripheral blood lymphocytes and 98% of IL-2-activated T-cells expressed the normal allele. These results suggest that in this patient the X chromosome containing the normal allele was predominantly inactivated in fibroblasts and the X chromosome containing the mutant allele was predominantly inactivated in lymphocytes. The diagnosis of E1 alpha deficiency is usually established by measurement of PDHC activity and the level of immunoreactive proteins. However, these methods are not sufficient to diagnose the disorder in female patients with E1 alpha deficiency due to differential inactivation of the X chromosome. Therefore, it is necessary to develop a new method to firmly establish the diagnosis of E1 alpha deficiency.