Background and Aims

Hypobetalipoproteinemias (HBL) represent a heterogeneous group of disorders characterized by plasma levels of total cholesterol (TC), low density lipoprotein-cholesterol (LDL-C) and apolipoprotein B (apoB) below the 5th percentile of the distribution in the population. Two major monogenic forms of HBL are well characterized: 1) FHBL1 (familial hypobetalipoproteinemia 1, OMIM#615558), a co-dominant disorder due to mutations in APOB gene or, less frequently, in PCSK9 gene; 2) FHBL2 (familial hypobetalipoproteinemia 2, OMIM#605019) due to mutations in ANGPTL3 gene. The approach to molecular diagnosis of HBL has changed in the last years with Next-generation sequencing approach (NGS) replacing the traditional sequencing methods.

In this study, we described a novel diagnostic workflow for the molecular characterization of HBL by NGS approach.

Methods

We designed a custom panel in order to analyze known genes involved in HBL by Ion Torrent PGM. The analysis was conducted on 25 patients, 3 families and 22 unrelated subjects

Results

The HBL-custom panel allowed to identify 4 novel pathogenic APOB gene mutations. In 19 patients, targeted next generation DNA sequencing revealed several rare variants (MAF≤0.005) predicted by informatics tools to be possible/probably damaging allowed to filter different significant variants in APOB, PCSK9 and ANGPTL3 genes and in other genes known to regulate LDL-C levels through different pathways (ie, ANGPTL8, LDLR, MYLIP, PEMT, SORT1).

Conclusions

In several patients the HBL phenotype could be due to the oligogenic interaction involving multiple rare variants in different genes, each of which may contribute to determine the clinical and biochemical phenotype.