Whilst conducting a scientific study, an elevated plasma plant sterol concentration of 3.07 mg/dL was established in one proband. Similar levels found in his mothers plasma (2.73 mg/dL) were suggestive of a heterozygous sitosterolemia. The resulting gene analysis for ATP binding cassette transporter G5/G8 (ABCG5/G8) revealed a heterozygous polymorphism in ABCG8 (Thr400Lys, rs4148217), which the proband had inherited from his father. However, a heterozygous amino acid exchange (Arg406Gln) in exon 9 of ABCG5 was revealed, which was inherited from his mother. Although not sufficient evidence exists to regard this sequence variation as a mutation, this previously unreleased sequence variation occurred in a "hot spot" area for sitosterolemia of the ABCG5 gene (exon 9) and the similar increased plasma plant sterol concentrations of the heterozygous mother contribute to the notion, that this very likely presents an inactivating mutation.
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