Investigations
1st investigations to order
fasting lipid panel
Test
Key to a clinical diagnosis for abetalipoproteinaemia.[1]
Result
total cholesterol: <0.78 mmol/L (<30 mg/dL); triglycerides: <0.34 mmol/L (<30 mg/dL); low or absent VLDL; absent LDL and apolipoprotein B (apo B) levels
vitamin A, D, E, K blood levels
Test
Vitamin D is activated on the skin by ultraviolet rays from endogenously produced metabolites but levels may still be subnormal.
Result
low or absent
blood smear
apo B and MTTP genetic testing
Test
Genetic testing for mutations in microsomal triglyceride transfer protein (MTTP) gene associated with abetalipoproteinaemia confirms the diagnosis in a patient suspected to be affected. Over 30 variants in MTTP associated with abetalipoproteinaemia have been described.[7]
The apolipoprotein B (apo B) gene should also be screened as homozygous familial hypobetalipoproteinaemia can give a similar biochemical and clinical phenotype to abetalipoproteinaemia.[7]
Result
abnormal MTTP or apo B gene
Investigations to consider
stool smear
Test
Lack of MTTP facilitated lipidation of chylomicrons in the small intestine causes lipid accumulation in enterocytes with associated malabsorption, steatorrhoea, and diarrhoea.[1]
Result
increased fat
(aPTT) PTT
Test
A consequence of abetalipoproteinaemia is deficiency of fat-soluble vitamins. Vitamin K deficiency can lead to a significant bleeding diathesis.[1]
Result
may be prolonged
serum iron levels
Test
Iron deficiency secondary to malabsorption.[1]
Result
may be decreased
liver transaminases
Test
Hepatic involvement includes steatosis and elevated serum transaminase levels.[2]
Result
may be elevated
intestinal biopsy
Test
Not necessary for diagnosis, but is often performed to identify causes of fat malabsorption.
Result
villus tips with lacy appearance; lipid droplets within enterocytes; yellowish discoloration of mucosa (increased lipid content); lack of apolipoprotein B on immunofluorescence
direct or indirect ophthalmoscope
Test
Not necessary for diagnosis, but may be found upon ophthalmologist referral in progressive disease.[23]
Result
retinal degeneration
electromyelogram
Test
Not necessary for diagnosis, but may be found upon neurologist referral in progressive disease.
Determines whether the neuropathy is primarily axonal or demyelinating.
Result
evidence of peripheral nerve demyelination
evoked potential electrodiagnostic test
Test
Not necessary for diagnosis, but may be found upon neurologist referral in progressive disease.
Result
abnormal somatosensory conduction velocity
nerve conduction study
Test
Not necessary for diagnosis, but may be found upon neurologist referral in progressive disease.
Result
conduction velocity may be slowed with decreased amplitude of sensory potentials
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