Abetalipoproteinemia/ homozygous familial hypobetalipoproteinemia (ABL/HoFHBL) is a severe form of familial hypobetalipoproteinemia 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.