Aim
Familial Hypercholesterolemia (FH) is characterized by high LDL plasma concentrations from birth, leading to premature CHD. Worldwide only 40%-50% of clinical FH patients have a mutation causing disease in the 3 FH genes. Other causes of FH phenotype must be sought.
Methods
A total of 18 genes involved in monogenic dyslipidaemias were selected for functional characterization and targeted sequencing of 185 FH-mutation negative (FH/M-). From the 18 genes, 7 have been previously functionally characterized; LDLR and the remaining 11 genes (ABCG5/8, STAP1, LIPA, APOC2, GPIHBP1, APOA5, LMF1, GPD1, LMNA, LIPC) were functionally tested as follows: gene knockdown was performed in Hela-Kyoto cells by two independent siRNAs, where LDL-uptake was measured by high-throughput automated microscopy. Carriers’ phenotype was compared to those of LDLR/M+ subjects (Portuguese FH study) and unaffected controls (e-COR population study).
Results
LDLR knockdown resulted in the strongest reduction of LDL-uptake. Seven genes (ABCG8, APOC2, GPIHBP1, APOA5, LMF1, GPD1, LMNA) showed the same pattern as observed with LDLR. In age and sex-matched groups, average total cholesterol levels in ABCG5-8/M+ and GDP1/M+ groups are significantly higher than controls and significantly lower than LDLR/M+ subjects.
Conclusions
Functional screenings indicated that the knockdown of known dyslipidaemia genes significantly alter LDL-uptake and cholesterol cellular dynamics. In FH/M- carriers of ABCG5-8 and GDP1 rare putative pathogenic variants these are the cause of high plasma cholesterol.

05 - FUNCTIONAL GENOMICS IN A COHORT OF FH MUTATION NEGATIVE PATIENTS