Acid Sphingomyelinase Deficiency
What is Acid Sphingomyelinase Deficiency?
Acid Sphingomyelinase Deficiency (ASMD), also known as Niemann-Pick Disease Types A (NPD A) and Type B (NPD B), is a very rare, but serious and potentially life-threatening genetic disorder that causes accumulation of the unmetabolized lipid sphingomyelin in cells, resulting in damage to major organ systems. ASMD classified as a lysosomal storage disease.
If a patient has infantile neurovisceral ASMD, the live expectancy is about 3 years of age. Chronic ASMD patients with complications can die in childhood, but may patients reach adulthood.
What are the symptoms of Acid Sphingomyelinase Deficiency?
Common symptoms of ASMD include the following:
- Swollen liver and spleen
- Progressive neurological symptoms
- Cholesterol abnormalities
- Reduced platelet counts
- Pulmonary damage
- Cherry red maculae
- Feeding problems
- Failure to thrive
What causes Acid Sphingomyelinase Deficiency?
ASMD is caused by mutations in the SMPD1 gene that encodes for the enzyme acid sphingomyelinase (ASM), which metabolizes sphingomyelin (a lipoid). ASMD is an autosomal recessive genetic disorder
in which the patient inherited two mutated genes, one from each parent. Typically the parents are both carriers of ASMD, but their health is rarely affected. Sphingomyelin is involved in a variety of functions in the cell which includes both cell proliferation and cell cycle progression. When not metabolized, it accumulates and can cause substantial damage to the lungs, spleen and liver. Neuronopathic damage has been noted in severe cases.
How is Acid Sphingomyelinase Deficiency diagnosed?
ASMD is very rare and the differential diagnosis can be quite difficult to resolve, which can result in delayed diagnosis and management of patients. An initial diagnosis is often based on biochemical testing showing low residual ASM enzyme activity using dried blood spots as blood-based assays. Additional confirmatory testing options of ASM activity include leukocytes, peripheral blood lymphocytes, and skin fibroblast cultures.
What are the treatments for Acid Sphingomyelinase Deficiency?
ASMD does not have an approved treatment option.
Where can I find out more about Acid Sphingomyelinase Deficiency?