Challenges and opportunities for identifying people with Familial hypercholesterolaemia in the UK: Evidence from the National FH PASS database.

Background: Familial Hypercholesterolaemia (FH) is a monogenic disorder that causes high levels of low-density lipoprotein (LDL) cholesterol. Cascade testing, where relatives of known individuals with FH ('index') are genetically tested, is effective and cost-effective, but implementation in the UK varies.

Objective: This study aims to provide evidence on current UK FH cascade yields and to identify common obstacles cascade services face and individual- and service-level predictors of success.

Methods: Electronic health records from 875 index families and 5,958 linked relatives in the UK's Welsh and Wessex FH services (2019) were used to explore causes for non-testing and to estimate testing rates, detection yields, and how relative characteristics and contact methods relate to the probability of relatives being tested (using logistic regression).

Results: In Wales (Wessex), families included 7.35 (7.01) members on average, with 2.41 (1.66) relatives tested and 1.35 (0.96) diagnosed with FH per index. Cascade testing is limited by individualised circumstances (too young, not at-risk, etc.) and FH services' reach, with approximately one in four relatives out-of-area. In Wales, first-degree relatives (odds ratio (OR):1.55 [95 % confidence interval (CI):1.28,1.88]) and directly contacted relatives (OR:2.11 [CI:1.66,2.69]) were more likely to be tested. In Wales and Wessex, women were more likely to be tested than men (ORs:1.53 [CI:1.28,1.85] and 1.74 [CI:1.32,2.27]).

Conclusion: In Wales and Wessex less than a third of relatives of an index are tested for FH. Improvements are likely possible by integrating geographically dispersed families into cascade testing, services directly contacting relatives where possible, and finding new ways to encourage participation, particularly amongst men.