Genetic complementation analysis of 3-Hydroxy-3-methylglutaryl-CoA lyase deficiency in cultured fibroblasts

Abstract

3-Hydroxy-3-methylglutaryl-CoA(HMG-CoA)lyase deficiency is an inborn error of leucine catabolism,characterized by metabolic acidosis and hypoketotic hypoglycemia,leading to vomiting, lethargy and coma.The clinical phenotype is variable,with severe illness neonatally in some patients,and a milder course in others. We studied cultured fibroblasts from 7 patients in an attempt to clarify the biochemical and genetic basis of this heterogeneity.The residual activity of HMG-CoA lyase was 1.1 ± 0.3%(mean±SD)of normal,with no significant differences between the patients.Genetic complementation was studied in heterokaryons obtained by fusion with polyethylene glycol. When cells with HMG-CoA lyase deficiency were combined with cells from patients with isovaleric acidemia or methylcrotonyl-CoA carboxylase deficiency,the incorporation of 1-14-C-isovaleric acid into protein increased from less than 5% to 30% of normal(positive controls).However,none of the fusions between the 7 HMG-CoA lyase deficient cell lines resulted in increased incorporation.Thus,no evidence was obtained for biochemical or genetic heterogeneity in this disease.