Identification of a mutation cluster in mevalonate kinase deficiency, including a new mutation in a patient of Mennonite ancestry

Mevalonate kinase (MKase) deficiency (MKD) is a rare autosomal recessive di sorder in the pathway of cholesterol and nonsterol isoprenoid biosynthesis. Thus far, two disease-causing missense alleles have been identified, N301T and A334T. We report four additional mutations associated with MKD: L264F, T243I, L265P and 1268T, the last found in a patient of Mennonite ancestry. Electrophoretic analysis of bacterially expressed wildtype and mutant MKas e indicated that I268T and T243I mutants produced normal or somewhat reduce d amounts of MKase protein; conversely, L264F and L265P mutations resulted in considerably decreased, or absent, MKase protein. Immunoblot analysis of MKase from all patients suggested that the MKase polypeptide was grossly i ntact and produced in amounts comparable to control levels. Three mutations resulted in significantly diminished MKase enzyme activity (<2%), whereas the I268T allele yielded similar to 20% residual enzyme activity. Our resul ts should allow more-accurate identification of carriers and indicate a mut ation "cluster" within amino acids 240-270 of the mature MKase polypeptide.