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.

[pyruvate dehydrogenase deficiency]

A new 18 bp insertion mutation in the gene for the alpha subunit of pyruvate dehydrogenase (E 1 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 E 1 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 E 1 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 E 1 alpha deficiency .