Niemann-Pick disease
Niemann-Pick disease is a group of inherited metabolic disorders characterized by the harmful accumulation of lipids in various body organs and tissues.
Overview
Niemann-Pick disease is divided into four main types—A, B, C1, and C2—classified by their genetic cause and clinical presentation. The disease affects many body systems and varies significantly in severity.
Types and Symptoms
- Type A: Infants typically develop hepatosplenomegaly (enlarged liver and spleen) by age 3 months and experience failure to thrive. By age 1, they undergo psychomotor regression and develop interstitial lung disease. A characteristic cherry-red spot in the eye is present; survival is generally limited to early childhood.
- Type B: Symptoms appear in mid-childhood and are less severe than Type A. Features include hepatosplenomegaly, recurrent lung infections, thrombocytopenia, short stature, and delayed bone age. Survival into adulthood is common.
- Types C1 and C2: These types share similar symptoms, including ataxia, vertical supranuclear gaze palsy, dystonia, severe liver disease, and interstitial lung disease. Patients experience progressive speech and swallowing difficulties, intellectual decline, and sometimes seizures. Survival into adulthood is possible.
Causes
The disease is caused by mutations that disrupt the body's ability to move or break down lipids:
- Types A and B: Caused by mutations in the SMPD1 gene, which leads to a shortage of the enzyme acid sphingomyelinase. This causes sphingomyelin to accumulate in lysosomes, leading to cell malfunction and death.
- Types C1 and C2: Caused by mutations in the NPC1 or NPC2 genes. These genes produce proteins responsible for moving cholesterol and other lipids within cells. A shortage of these proteins leads to lipid accumulation and subsequent tissue and organ damage.
Inheritance
Niemann-Pick disease is inherited in an autosomal recessive pattern, meaning both copies of the gene in each cell must have mutations for the condition to occur.