Types A and B Niemann-pick disease

Types A and B Niemann-Pick disease (NPD) are two distinct forms of a lysosomal storage disease (LSD) caused by the inherited deficiency of acid sphingomyelinase (ASM) activity. The three forms of NPD are referred to as infantile neurovisceral (type A), chronic neurovisceral (type A/B), and chronic visceral (type B) ASM deficiency (ASMD). ASMD is a rare genetic disease, and limited information is available regarding its demographics and incidence. Several polymorphisms also have been found within the gene, including a varying number of repeated nucleotides within the ASM signal peptide region. Identification of mutations in ASM-deficient NPD patients has permitted the first genotype/phenotype correlations for this disease and the first genetic screening efforts. The primary organ systems affected in all ASM deficient patients are the spleen, liver, and lung. Infants with type A NPD typically develop failure to thrive by 15 months of age as their neurologic disease begins its rapid progression.