PCSK9 and familial hypobetalipoproteinemia 1: In some kindred, FHBL was linked to a locus on chromosome 3 (3p21) but the candidate gene was unknown.22 Subsequently, a FHBL- like phenotype was observed in carriers of LOF mutation of the proprotein convertase subtilisin Kexin-9 (PCSK9) gene that was not associated with fatty liver - as shown in FHBL due to APOB gene mutations.24,25 However, no mutations in either APOB or PCSK9 were detected in a large proportion of FHBL subjects.