Effectiveness of alternative strategies to define index case phenotypes to aid genetic diagnosis of familial hypercholesterolaemia
- Rosemary E J Clarke1,
- Soundrie T Padayachee2,
- Rebecca Preston2,
- Zofia McMahon1,
- Mitchell Gordon3,
- Colin Graham4,
- Martin A Crook1,
- Anthony S Wierzbicki5
- 1Department of Metabolic Medicine, Guy's and St Thomas Hospitals, St Thomas Hospital, London, UK
- 2Department of Radiology, Guy's and St Thomas Hospitals, St Thomas Hospital, London, UK
- 3Department of Blood Sciences, GSTS Pathology, Guy's and St Thomas Hospitals, St Thomas Hospital, London, UK
- 4Department of Genetics, Northern Ireland Regional Genetics Centre, City Hospital, Belfast, UK
- 5Department of Chemical Pathology, Guy's and St Thomas’ Hospital, London, UK
- Correspondence to Dr Anthony S Wierzbicki, Department of Chemical Pathology, St Thomas’ Hospital, Lambeth Palace Road, London SE1 7EH, UK;
- Received 3 September 2012
- Revised 31 October 2012
- Accepted 6 November 2012
- Published Online First 4 December 2012
Objective To determine the utility of secondary stratification measures to improve the ascertainment of index cases of familial hypercholesterolaemia (FH).
Design A retrospective study of genotyped index patients with Simon Broome (SB) FH.
Setting University teaching hospital.
Patients 204 patients aged 55±14 years; 36% had tendon xanthoma (TX), 21% had coronary heart disease (CHD), low-density lipoprotein cholesterol (LDL-C) was 6.20±2.24 mmol/l and 55% had genetic FH.
Interventions The effects of different staging systems (SB vs Dutch criteria), presence of TX, use of LDL-C level, personal history of CHD and imaging evidence of atheroma by carotid intima-media thickness or coronary artery calcium score to identify genetic FH was explored.
Outcome measures Changes in C-statistic and net reclassification index (NRI).
Results SB criteria gave a C-statistic of 0.64 comprising C=0.65 in TX(+) and C=0.5 in TX(−) patients. Genetic FH was present in 75% of TX(+) compared with 44% in TX(−) patients. The Dutch criteria gave C=0.72. Addition of imaging criteria to prior CHD raised C=0.64 to C=0.65 in all patients with a NRI of 19% (p=0.06). In TX(−) patients imaging raised C=0.50 to C=0.65 with a NRI of 0.38 (p=0.001) and a weighted comparison index of 0.28, implying the detection of 14 more FH cases per thousand.
Conclusions Patients with tendon xanthoma (definite FH) should be genotyped. In patients with possible FH, the presence of a personal history of CHD or imaging evidence of increased atheroma offers the best method of identifying index patients likely to have monogenic FH.