Familial hypercholesterolemia (FH) is the most common autosomal dominant inherited disease with a prevalence of 1/300. The disease causes greatly elevated levels of LDL cholesterol and is strongly associated with premature cardiovascular disease and premature death. Genetically, FH is associated with mutations in the LDLR, APOB or PCSK-9 genes, but despite a well-characterized phenotype, such a mutation is only identified in about 50-60% of cases. Since establishing a genetic diagnosis in the probands facilitates further diagnosis of relatives, especially in children, it is of great value to explore both hitherto unknown molecular mechanisms and to evaluate new sequencing techniques to improve genetic diagnostics in FH. The discovery of a new molecular mechanism resulting in a phenotypic FH could also give rise to a drug candidate. In a well-characterized FH family, with verified hypercholesterolemia in three generations where mutation in known FH gene has been excluded, evaluate Nanopore whole genome sequencing in comparison with classical NGS and to try to identify a new candidate gene/candidate area where a mutation can cause hypercholesterolemia. The nanopore technology enables analysis of significantly longer sequences than classical NGS and thus reduces the risk of missing copy number variations (CNV). In this project, we have analyzed three individuals from a family with verified hypercholesterolemia for three generations, two with phenotypic FH where mutation in the classic FH genes was excluded, and one individual with normal cholesterol levels. An unusual (<1% in population) or previously undescribed variation identified in the two individuals with phenotypic FH but not in the one with normal cholesterol may be a suitable candidate for further functional analysis. Identification of a novel disease mechanism that causes a phenotypic FH leads to improved genetic diagnosis in this patient group. The discovery could also eventually generate new lipid-lowering drugs that would benefit more patient groups than the one with FH.