Acid sphingomyelinase deficiency (ASMD, Niemann-Pick disease types A/B)

What happens in this disease?

An enzyme called acid sphingomyelinase is missing in the cells. Because of this, a fat called sphingomyelin cannot be broken down and builds up in the cells. The liver, spleen, lungs and bone marrow are affected. In the severe type, the brain is also affected.

Which symptoms can occur?

The disease has a severe infantile type (type A) and a milder type (type B). Types in between are also seen. Symptoms vary greatly from person to person.

• Enlarged liver and spleen (common)
• Poor weight gain and slow growth
• Frequent lung infections and shortness of breath
• Low platelets in the blood, easy bruising and bleeding
• Abnormal blood fat levels (in type B)
• Thinning of the bones
• Loss of developmental skills (in type A)

How is it diagnosed?

The doctor examines the person and checks the size of the liver and spleen. The activity of the enzyme acid sphingomyelinase is measured in the blood. The diagnosis is confirmed with a genetic test that looks at the SMPD1 gene.

Treatment and care

There is an approved enzyme treatment specific to the disease. This treatment reduces the build-up in the liver, spleen and lungs. However, it does not act on the effects in the brain. Nutritional support, breathing support, physiotherapy and regular follow-up are also part of care. People with a large spleen should avoid contact sports. The doctor who follows the disease decides which treatment is suitable.

For the family: inheritance and genetic counselling

The disease is passed on through recessive inheritance. The mother and father are usually healthy carriers. For a couple who are both carriers, the chance of having an affected child is 1 in 4 in each pregnancy. Diseases of this kind may be more common in marriages between relatives. Carrier testing and testing during pregnancy are possible. Genetic counselling is recommended.