Two siblings with Niemann-Pick disease (NPD) type B: clinical findings and novel mutations of the acid sphingomyelinase gene.

Acid sphingomyelinase deficiency leads to the accumulation of sphingomyelin in cells, causing Niemann-Pick disease (NPD) types A/B. RF (13.66 y) and HF (3 y) are brother and sister. RF growth was markedly delayed at the age of 12.66 y (123 cm; -3.25 SD), while at the age 3 y his sister is 86 cm (-2.75 SD). The brother had a huge liver (13 cm) and spleen (12 cm). His sister also had an enlarged liver, but presented no other symptoms. The fibroblast cultivation had a reduced sphingomyelinase activity in the fibroblasts (0.68 mkat/kg protein), β-galaktosidase (937 mkat/kg) and glucosilceramidase (125.4 mkat/kg) were elevated. Mutational analysis demonstrated the siblings are compound heterozygotes (V112M and H554Y). The mother is carrier of V112M and the father carries H554Y. This is the first report of NPD type B in Macedonia. The novel mutation results in a moderately severe phenotype of NPD type B.