FH phenotype: monogenic, polygenic and other causes

Familial Hypercholesterolaemia (FH) is a monogenic disorder characterised by high LDL-C concentrations and increased cardiovascular risk. However, in clinically defined FH cohorts worldwide, an FH-causing variant is only found in 40-50% of the cases. The aim of this work was to characterise the genetic cause of the FH phenotype in Portuguese clinical FH patients. Methods and Results Between 1999 and 2017, 731 index patients (311 children and 420 adults) who met the Simon Broome diagnostic criteria had been referred to our laboratory. LDLR, APOB, PCSK9, APOE, LIPA, LDLRAP1, ABCG5/8 genes were analysed by PCR amplification and Sanger sequencing. The 6-SNP LDL-C genetic risk score (GRS) for polygenic hypercholesterolaemia was validated in the Portuguese population and cases with a GRS over the 25th percentile were considered to have a high likelihood of polygenic hypercholesterolaemia. An FH-causing mutation was found in 39% of patients (94% in LDLR, 5% APOB and 1% PCSK9), while at least 29% have polygenic hypercholesterolaemia and 1% have other lipid disorders. A genetic cause for the FH phenotype was found in 503 patients (69%). All known causes of the FH phenotype should be investigated in FH cohorts to ensure accurate diagnosis and appropriate management.Cibelle Mariano was supported by a PhD student grant [SFRH/BD/52494/2014]. Marta Futema is supported by the Fondation Leducq Transatlantic Networks of Excellence Program grant (no 14 CVD03). The work of Marilia Antunes is partially funded by UID/MAT/000016/2019. SEH acknowledges funding from the British Heart Foundation grant (BHF PG08/008) and from the NIHR UCLH BRC. MB acknowledges funding from Science and Technology Foundation (PIC/IC/83020/2007) (PIC/IC/83333/2007) for the e_COR and Portuguese FH Study and from Portuguese Cardiology Society for the Portuguese FH Study.