Intestinal lipid malabsorption, resulting from an impaired formation or secretion of chylomicrons and associated with severe hypobetalipoproteinemia (HBL), may be due to biallelic mutations in APOB (homozygous FHBL type-1), MTTP (abetalipoproteinemia), or SAR1B (chylomicron retention disease).
Thus, enterocytes in HBL edit the mutant mRNAs similarly to the apoB mRNA of normal enterocytes and the small intestine of heterozygotes with truncations longer than apoB-48 produce only apoB-48, as the apoB-48 stop codon terminates translation proximal to the mutant stop codon.
These data are most consistent with a mutation in the coding portion of the apoB gene in HBL patients, leading to an abnormal apoB protein and apoB mRNA instability.