Abetalipoproteinemia (ABL) is a rare monogenic familial hypobetalipoproteinemia disorder characterized by a secretion defect in apolipoprotein B (apoB)-containing lipoproteins.1 It is an autosomal recessive disorder resulting from bi-allelic loss-of-function variants in the microsomal triglyceride transfer protein (MTTP) gene (OMIM: 200100).2 MTTP is required for the assembly of apoB-containing lipoproteins in both the intestine and the liver.3 Individuals affected by ABL typically exhibit near complete absence of plasma lipids and severe fat-soluble vitamin deficiency. Total cholesterol is usually below 1.00 mmol/L and low-density lipoprotein cholesterol (LDL-C) is often below 0.04 mmol/L.4 ApoB is frequently below the limit of detection.4

ABL typically manifests in infancy with symptoms such as failure to thrive, fat malabsorption, steatorrhea, and vomiting.1 Additionally, it is also associated with hematologic manifestations such as acanthocytosis, anemia, reticulocytosis, and hemolysis with resultant hyperbilirubinemia.1,4 Other clinical features are attributed to fat-soluble vitamin deficiency, including bleeding diathesis, atypical pigmentation of the retina with loss of night and color vision, and various neuromuscular findings such as progressive loss of deep tendon reflexes, vibratory sense, proprioception, muscle weakness, dysarthria, and ataxia.1 Early diagnosis is crucial as most complications can be prevented by implementing a low-fat diet with adequate caloric intake to address growth deficiency, along with supplementation of high doses of vitamins A, D, E, and K.1,5

The prevalence of ABL is estimated to be 1 in 1,000,000.6 However, the prevalence is significantly higher in specific founder population, such as in Ashkenazi Jews from Israel (carrier estimate of 1:131).7 In this report, we present four cases of ABL, including one previously described by Berthier et al.,8 all originating from the same small French-Canadian population.