Adult-onset Niemann-Pick type C disease. Clinical, biochemical, and genetic study.

BACKGROUND: Niemann-Pick type C disease is an autosomal recessive neurometabolic disorder of unknown origin mapped to chromosome 18q11-12 in most of the studied families. In contrast to the sphingomyelin lipidoses, in Niemann-Pick type C disease, fibroblasts are impaired in intracellular homeostatic responses to exogenous low-density lipoprotein (LDL) cholesterol. Biochemical heterogeneity of the disorder in relation to abnormal LDL processing is associated with various clinical presentations, but adult-onset Niemann-Pick type C disease is rare and has not been comprehensively characterized. OBJECTIVE: To describe clinical, biochemical, and genetic features of adult-onset Niemann-Pick type C disease in 3 siblings. DESIGN AND SETTING: Case series in a tertiary care center. PATIENTS: The 3 siblings manifested a variable combination of vertical supranuclear ophthalmoplegia, ataxia, and splenomegaly. Brain magnetic resonance imaging showed cerebellar atrophy; brainstem auditory evoked responses were unobtainable, and bone marrow examination disclosed typical foam cells. The patients were 20, 26, and 28 years old and belonged to a sibship of 13 born of consanguineous healthy parents. METHODS: Esterification of exogenous LDL cholesterol in cultured skin fibroblasts and filipin staining for free intracellular cholesterol. Polymerase chain reaction-based DNA linkage study using AC microsatellite markers D18S40, D18S44, D18S480, and D18S66. RESULTS: Fibroblasts of the 3 patients showed a 23% to 58% block in the induced cholesterol esterification after 4 1/2 hours and a mild to moderate accumulation of free cholesterol. DNA study demonstrated linkage to the major 18q11-12 Niemann-Pick type C locus and identified unaffected carriers. CONCLUSIONS: These results confirm the diagnosis of the least biochemically affected Niemann-Pick type C phenotype in this family with adult-onset disease and support a correlation between the mild laboratory and clinical findings in this age group.