Most mutations interfere with the translation of full-length apoB mRNA and cause the production of truncated apoBs of various size; only few nonsynonymous, nontruncating mutations have been reported so far as cause of FHBL.5–7 Homozygous FHBL is extremely rare and it is associated with fatty liver, steatorrhea, intestinal fat malabsorption, and neurological abnormalities; FHBL heterozygotes may be asymptomatic or present with fatty liver disease and mild elevation of serum liver enzymes.5 This evidence concerns the gene APOB and familial hypobetalipoproteinemia 1.