Lipid Storage Diseases - Niemann-Pick Disease

Comparison Table

Niemann-Pick Disease Types A, B, and C Comparison

Feature	Type A (NPD-A)	Type B (NPD-B)	Type C (NPC)
Enzyme/Protein Defect	Acid sphingomyelinase (ASM) deficiency	Acid sphingomyelinase (ASM) deficiency	NPC1 (~95%) or NPC2 (~5%) mutations
Gene Involved	SMPD1	SMPD1	NPC1 or NPC2
Inheritance	Autosomal recessive	Autosomal recessive	Autosomal recessive
Pathogenesis	Sphingomyelin accumulation in neurons and visceral organs	Sphingomyelin accumulation mainly in visceral organs	Defective cholesterol and lipid transport from lysosomes
Onset	Infantile (3–6 months)	Childhood to adulthood	Neonatal to adult; variable
Neurological Involvement	Severe, progressive neurodegeneration	Mild or absent in most cases	Progressive neurodegeneration (ataxia, gaze palsy, dementia)
Hepatosplenomegaly	Early and severe	Common and progressive	Neonatal onset or variable; less common in older children
Pulmonary Disease	Interstitial lung disease	Progressive lung disease	May occur; less prominent
Retinal Cherry Red Spot	Common by 12 months	Seen in ~1/3 of cases	Rare
Other Features	Hypotonia, psychomotor delay, failure to thrive	Short stature, delayed bone age, dyslipidemia	Cholestatic liver disease, ascites, dysphagia, sea-blue histiocytes
Prognosis	Death by age 3	Variable; survival into adulthood	Progressive neurological decline; variable survival
Diagnosis	ASM activity <10%; SMPD1 genetic testing	ASM activity <10%; SMPD1 genetic testing	Genetic testing (NPC1/NPC2); fibroblast studies; bone marrow/liver biopsy
Management	Supportive; feeding support, therapy, monitoring	Supportive; avoid contact sports, monitor organs	Supportive; neuro/pulmonary consults, feeding support, bowel regimen

I. General Epidemiology & Definitions of lipid storage diseases

• Inherited metabolic disorders causing harmful lipid accumulation in lysosomes of brain, liver, nerves, spleen, and bone marrow.
• Inheritance is autosomal recessive, except for Fabry disease (X-linked).
• Incidence varies by disorder and population.

II. Lipid Metabolism Overview

• Lipids are catabolized in lysosomes by acid hydrolases.
• Glycosphingolipids (GSLs) are carbohydrate-ceramide complexes involved in cell signaling.
• Loss of glucosylceramide biosynthesis is incompatible with life.
• Includes cholesterol ester storage disorders.
• Liver is variably affected in most lipid storage diseases.

III. Common Clinical Presentations

Infants

• Hepatosplenomegaly
• Failure to thrive
• Frequent emesis
• Developmental delay
• Occasionally acute liver failure

Older Children

• Massive hepatosplenomegaly
• Growth problems
• Lung disease
• Neurological issues
• Developmental delay

Laboratory

• Elevated aminotransferases in infancy or early childhood

IV. Niemann-Pick Disease Types A & B (Acid Sphingomyelinase Deficiency)

A. Pathogenesis & Subtypes

• Deficiency of acid sphingomyelinase (ASM) due to SMPD1 gene variants
• Leads to sphingomyelin accumulation in reticuloendothelial and ganglion cells
• Subtypes:
  • Type A: Infantile-onset, neuronopathic; death by age 3
  • Type B: Later-onset, visceral form
  • Intermediate cases: rare
• Prevalence ~1:250,000; higher in Ashkenazi Jews, North Africans, Chileans, Saudis, and Turks

B. Clinical Features

Type A

• Hepatosplenomegaly by 3–6 months
• Elevated aminotransferases
• Failure to thrive, vomiting, diarrhea
• Interstitial lung disease, recurrent infections
• Cherry red spot on retina by 12 months
• Progressive hypotonia, severe psychomotor delay

Type B

• Hepatosplenomegaly with hypersplenism → thrombocytopenia
• Progressive lung disease
• Cherry red spot in ~1/3 of cases
• Neurological signs in ~1/3: cerebellar signs, nystagmus, intellectual disability
• Short stature, delayed bone age, ↓ IGF-1
• Dyslipidemia, early coronary artery disease

C. Diagnosis

• Genetic testing for SMPD1 variants
• ASM activity in lymphocytes or fibroblasts (<10%)

D. Management

• Nutrition support; feeding tube if needed
• Therapies: occupational, physical, speech
• Ophthalmologic and neurodevelopmental assessments
• Monitor: LFTs, CBC, lipid profile
• Pulmonary function tests, chest imaging
• Bone age evaluation
• Genetic counseling
• Avoid contact sports (splenic rupture risk)

V. Niemann-Pick Disease Type C (NPC)

A. Pathogenesis

• Defect in cholesterol transport from lysosomes
• Accumulation of sphingolipids and LDL cholesterol due to impaired efflux
• >90% due to NPC1 gene mutations; ~5% due to NPC2
• Prevalence: ~1:150,000 in Western Europe

B. Clinical Features

• Highly variable phenotype
• Classic childhood onset: ataxia, seizures, gaze palsy, dementia
• Neonatal presentation: cholestatic liver disease, hepatosplenomegaly, ascites, hypotonia, cirrhosis
• Hepatosplenomegaly less common in older children/adults
• Progressive dysphagia and dysarthria

C. Diagnosis

• Genetic testing for NPC1/NPC2 mutations
• Subnormal sphingomyelinase activity in fibroblasts
• Bone marrow: foamy cells, sea-blue histiocytes
• Liver biopsy: giant cell transformation, variable findings
• EM: cholesterol ester crystals in autophagosomes

D. Management

• Nutrition support; feeding tube if needed
• Therapies: occupational, physical, speech
• Regular bowel regimen for older children
• Neurology and pulmonology referrals
• Genetic counseling