Summary
Abetalipoproteinemia/ homozygous familial hypobetalipoproteinemia (ABL/HoFHBL) is a severe form of familial hypobetalipoproteinemia (see this term) characterized by permanently low levels (below the 5th percentile) of apolipoprotein B and LDL cholesterol, and by growth delay, malabsorption, hepatomegaly, and neurological and neuromuscular manifestations. It is very rare, with an estimated prevalence of less than 1/1,000,000. ABL/HoFHBL manifests during the first year of life or in young childhood. It is often associated with growth delay, hepatomegaly with steatosis, diarrhea with steatorrhea, and fat malabsorption. Spastic ataxia, atypical retinitis pigmentosa, acanthocytosis, a low level of liposoluble vitamins, major cytolysis and even cirrhosis can occur. Abetalipoproteinemia is inherited in a recessive manner and is a result of mutations of two alleles of the MTTP gene (MTP ; 4q24). Other severe early familial hypobetalipoproteinemia are inherited in a codominant manner and are a result of mutations of two alleles of the APOB gene (2p24-p23). Diagnosis is based on lipid analysis, after 12 hours of fasting, carried out on the patient and their parents to measure serum levels of LDL (<0.10g/L), triglycerides (<0.20 g/L), and apolipoprotein B (<0.10g/L). Identification of steatorrhea and truncated apolipoprotein B after taking lipids orally, measurement of liposoluble vitamins (A, E, K), research of acanthocytosis (on blood smear), complete neurological examination, hepatic ultrasound and eye examination can also be carried out. The evidence of mutations of the MTTP or APOB genes confirms the diagnosis. Differential diagnoses include metabolic diseases with hepatic overload, with steatosis and/or hepatomegaly, atypical diseases of the central and peripheral nervous system, and secondary causes of hypocholesterolemia (iatrogenic or systemic). Prenatal diagnosis is possible when the causal mutations in both parents are known. Management occurs in specialist centers. The prognosis is severe, with a very reduced life expectancy. *Author: Dr P. Benlian (May 2009)*.
