Novel mutations ofAPOB cause ApoB truncations undetectable in plasma and familial hypobetalipoproteinemia

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Abstract
Familial hypobetalipoproteinemia (FHBL) is a genetic disorder characterized by low levels of apoB‐100 and LDL cholesterol. Truncation‐producing mutations of apoB (chromosome 2) are among several potential causes of FHBL in patients. Ten new families with FHBL linked to chromosome 2 were identified. In Family 8, a 4432delT in exon 26 produces a frame‐shift and a premature stop codon predicted to produce a truncated apoB‐30.9. Even though this truncation is just 10 amino acid shorter than the well‐documented apoB‐31, which is readily detectable in plasma, apoB‐30.9 is undetectable. Most truncations shorter than apoB‐30 are not detectable in plasma. In Family 34, an acceptor splicing mutation at position –1 of exon 14 changes the acceptor splice site AG to AA. Two families (Family 50 and 52) had mutations (apoB‐9 and apoB‐29) reported previously. In Family 98, a novel point mutation in exon 26 (11163T>G) causes a premature stop codon, and produces a truncated apoB‐80.5 readily detectable in plasma. Sequencing of the ApoB gene in families 1, 5, 18, 58, and 59 did not reveal mutations.