Identification and characterization of three novel missense mutations in mevalonate kinase cDNA causing mevalonic aciduria, a disorder of isoprene biosynthesis

Mevalonic aciduria is a rare autosomal recessive metabolic disorder, charac terized by psychomotor retardation, failure to thrive, hepatosplenomegaly, anemia and recurrent febrile crises. The disorder is caused by a deficient activity of mevalonate kinase due to mutations in the encoding gene. Thus f ar, only two disease-causing mutations have been identified. We now report four different missense mutations including three novel ones, which were id entified by sequence analysis of mevalonate kinase cDNA from three mevaloni c aciduria patients. All mutations affect conserved amino acids. Heterologo us expression of the corresponding mutant mevalonate kinases as fusion prot eins with glutathione S-transferase in Escherichia coli showed a profound e ffect of each of the mutations on enzyme activity. In addition, immunoblot analysis of fibroblast lysates from patients using specific antibodies agai nst mevalonate kinase identified virtually no protein. These results demons trate that the mutations affect not only the activity but also the stabilit y of the mutant proteins.