A NOVEL APOB MUTATION IDENTIFIED BY EXOME SEQUENCING COSEGREGATES WITH STEATOSIS, LIVER CANCER AND HYPOCHOLESTEROLEMIA

Abstract

Objective. In familial hypobetalipoproteinemia (FHBL), fatty liver is a characteristic feature, and there are several reports of associated cirrhosis and hepatocarcinoma. We investigated a large kindred in which low-density lipoprotein (LDL) cholesterol, fatty liver and hepatocarcinoma displayed an autosomal dominant pattern of inheritance. Approach and Results. The proband was a 25 year-old female with low plasma cholesterol and hepatic steatosis. Low plasma levels of total cholesterol and fatty liver were observed in 10 more family members; 1 member was affected by liver cirrhosis and four more subjects died of either hepatocarcinoma or carcinoma on cirrhosis. To identify the causal mutation in this family, we performed exome sequencing in two participants with hypocholesterolemia and fatty liver. Approximately 22,400 single nucleotide variants were identi- ed in each sample. After variant ltering, 300 novel shared variants remained. A nonsense variant, p.K2240X due to an A>T mutation in exon 26 of APOB (c.6718A>T) was identi ed and this variant was con rmed by Sanger sequencing. The gentotypic analysis of 16 family members in total showed that this mutation segregated with the low cholesterol trait. In addition, genotyping of the PNPLA3 p.I148M did not show signi cant frequency differences between carriers and non-carriers of the c.6718A>T APOB gene mutation. Conclusions. We used exome sequencing to discover a novel nonsense mutation in exon 26 of APOB (p.K2240X) responsible for low cholesterol and fatty liver in a large kindred. This mutation may also be responsible for cirrhosis and liver cancer in this family.