ASMD has a spectrum of clinical phenotypes that range from a severe infantile form (ASMD type A), with severe and rapid neurodegeneration and death in early infancy, to chronic progressive forms (ASMD type A/B and ASMD type B).
The most common presentations of ASMD are hepatosplenomegaly and interstitial lung disease. Other manifestations include recurrent respiratory infections, liver dysfunction, dyslipidemia characterized by low HDL cholesterol, thrombocytopenia, bleeding, delayed growth and puberty in children, fatigue, bone and joint pain, and osteopenia. Neurological involvement is present in more severe disease phenotypes.1
A definitive diagnosis of ASMD requires the determination of the level of ASM in circulating leukocytes, fibroblast skin cultures, or dried blood spots.12 A diagnosis of ASMD is confirmed when ASM activity is absent or significantly reduced.
Genetic testing through sequencing of the SMPD1 gene must be used as additional evidence to confirm a diagnosis of ASMD and help establish genotype–phenotype correlation.2
Enzyme replacement therapy (ERT) is an effective treatment option for non-CNS manifestations of ASMD in children and adults.
If ERT is not available or considered inappropriate disease management is aimed at symptom control including dietary modifications and/or statin therapy to lower cholesterol levels, oxygen to treat severe cases of interstitial lung disease, and blood transfusions to treat patients with acute episodes of bleeding due to splenomegaly and low platelet counts.1 Bone marrow transplantation has been associated with reductions in liver and spleen size, although complications secondary to the transplant procedure may be severe.1
Life expectancy is typically reduced in patients with ASMD. Respiratory dysfunction and liver failure are the leading causes of death in patients with ASMD type B and A/B.3
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Incidence
It is estimated that ASMD affects approximately 0.4 to 0.6 in every 100,000 newborns. Ashkenazi Jewish descents have higher incidences of NPA and NPB have higher frequencies in the Maghreb region of North Africa (Tunisia, Morocco and Argelia).
Prevalence
ASMD occurs in persons of both sexes equally and is present in persons of all races. Real birth prevalence is likely to be higher as many cases remain undiagnosed or inaccurately diagnosed due to low disease knowledge and awareness.
Age of onset
ASMD type A typically presents within the first few months of life. ASMD type A/B usually presents in infancy or childhood, whereas ASMD type B may present from infancy to adulthood, with a slower disease progression compared to ASMD type A.
References
1. Schuchman EH, Desnick RJ. Types A and B Niemann-Pick disease. Mol Genet Metab. 2017;120:27-33.
2. Villarrubia J et al. Type B Nieman-Pick Disease. Brit J Hematol. 2105;doi:10.1111/bjh.13846.
3. Guillemot N et al. Lung disease in Niemann-Pick disease. Pediatr Pulmonol. 2007;42:1207–1214.
4. Baldi BG et al. Lung cyst: an unusual manifestation of Niemann-Pick disease. Respirol. 2009;14:134–136.