2.2.1 Subjects screened for new LPL mutations.
2.2.1.1 Subjects with type I or type V hyperlipoproteinaemia (HLP).
Twenty unrelated probands diagnosed with type I HLP, based on triglyceride levels (generally > 20mmol/L at time of diagnosis) and the presence of chylomicrons in fasting plasma, or type V HLP with LPL deficiency, were recruited for this study. Most patients (17/20) were identified in infancy or childhood, either through routine blood sampling or due to recurrent episodes of abdominal pain and vomiting. In older subjects, secondary causes for hyperlipidaemia were ruled out. DNA from these individuals was used for the studies described in chapter 3. Details of clinical presentation, with biometrical and biochemical data, is presented in Table 3.1.
Five of the subjects were patients at the Institute of Child Health, London, 4 at the Royal Infirmary, Manchester, 4 at the Lipid Clinic, St. Thomas’ Hospital, London, 3 at the Middlesex Hospital Lipid Clinic, London. The remaining four probands were recruited via paediatricians and GPs in the UK (1), Sweden (2) (Lithell et al., 1978) and Italy (1). Nine of the patients were of English descent, 7 were from the Indian subcontinent, 2 were Swedish and 2 were of Mediterranean descent.
2.2.1.2 Individuals with low LPL activity
Fifteen patients with combined hyperlipidaemia recruited at Charing Cross Hospital, London as part of a larger study (see section 2.2.2.S) and ten Swedish individuals taking part in a case-control study of MI before the age of 45 (see section 2.2.2.1) were also screened for new mutations/common variants in the LPL gene. Low LPL activity (in the lower third of the distribution) was used as the selection criterion.
2.2.2 Population samples screened for LPL variants
DNA samples from 2992 subjects originating from the UK (England, Northern Ireland and Scotland), France, Sweden and the Netherlands were used in the course of the studies presented in chapter 4. The various groups are briefly described below and their general characteristics are summarised in Table 4.7.
2.2.2.1 Swedish patients and controls I
This first sample consisted of Swedish patients and controls participating in a case-control study of myocardial infarction at a young age (< 4 5 yrs). The two sub groups will further be referred to as Young MI (YMI) patients and controls. Data on lipid, lipoprotein, lipase activity and haemostatic variables have been presented elsewhere (Hamsten et al., 1986, 1987; Peacock et al., 1992).
The group of patients consisted of 143 individuals from Stockholm county who were recruited as described in Hamsten et al., (1986) and had suffered an MI before the age of 45. Patients with serum cholesterol levels above 9.5 mM or a diagnosis of familial hypercholesterolaemia, diabetes or porphyria were excluded from the lipid analysis. DNA studies were performed on a sample of 100 of these patients (76 men, 24 women). They were age-matched with 93 randomly selected, healthy male residents of Stockholm county that were free of clinical signs of CAD.
2.2.2.2 Swedish patients and controls II
A second group of randomly selected Swedish male individuals aged between 40 and 50 years old were included in our studies. They had participated in a community- based study on hypertriglyceridaemia in Stockholm county and were divided as follows:
65 hypertriglyceridaemic individuals (fasting serum Tg above 95th percentile, 3.1 mmol/1) and 60 age-matched normotriglyceridaemic individuals (Tg < 3.1 mmol/1). They will be referred to as Swedish HTG and Swedish NTG respectively. A detailed description of this sample can be found in Asplund-Carlson and Carlson, 1994.
2.2.2.S Dutch combined hyperlipidaemics
A sample of 240 patients (149 males and 91 females) with combined hyperlipidaemia (chol and Tg values above the 95th percentile) were recruited and followed at the Lipid Research Clinic of the University of Amsterdam and had a mean age of 47.2 yrs. This group will be called Dutch CHL. Familial hypercholesterolaemia was ruled out on clinical grounds and familial dysbetalipoproteinaemia was excluded by determination of the apo E genotype.
2.2.2.4 Dutch controls
A companion control group of 190 normolipidaemic, healthy Dutch males, age- matched with the Dutch CHL patient group, was recruited independently for a risk factor study. Individuals with plasma lipids above the 95th percentile for age and gender were excluded from our studies.
2.2.2.5 Charing Cross Hospital combined hyperlipidaemics
Forty-one consecutive patients (30 males and 11 females with age ranging from 27-69 yrs) with combined hyperlipidaemia (chol > 6.5 mM, fasting TG > 2.2 mM) were recruited from the Lipid Clinic of Charing Cross Hospital, London for a study of the relationship between lipoprotein lipase and hepatic lipase activities, and combined
hyperlipidaemia. They will be further referred to as CX CHL. All had a family history of hyperlipidaemia or CHD and/or personal history of CHD. Lipid and lipoprotein data concerning this sample has recently been published (Seed et al., 1994) and lipoprotein lipase activity data will be presented in section 4.1. In this highly selected sample, 38 individuals had a family history of hyperlipidaemia, 32 had a family history of CHD and 26 had clinical manifestations of CHD. Patients with familial HTG (fasting TG > SmM), diabetes mellitus or thyroid disease were excluded. Familial dysbetalipoproteinaemia was probable in one individual based on apo E genotype.
2.2.2.6 General population controls from the UK
This group consisted of 773 male subjects aged 40 to 64 attending two general practices: 360 men were from the Camberley area in Southern England and 413 men from the St. Andrews district in Scotland. All had been recruited as part of the Northwick Park Heart Study II of risk factors for heart disease and were free of clinical signs of disease at the time of entry into the study. Part of the lipid and haemostatic data pertaining to the Camberley group has been published (Humphries et al., 1994) while the St. Andrews material was generously made available to us by Dr. George Miller.
2.2.2.7 ECTIM case-control study
This sample included 1430 male subjects, aged 25 to 64 years, participating in the ECTIM multi-centre case-control study (Etude Cas-Témoins sur ITnfarctus du Myocarde)(Parra et al., 1992). The subjects originating from four MONICA-WHO centres (Belfast, Lille, Strasbourg and Toulouse) were subdivided as follows: 404
subjects from Belfast (202 controls and 202 cases), 371 from Toulouse (220 controls and 151 cases), 223 from Lille (155 controls and 68 cases) and 432 from Strasbourg (211 controls and 221 cases). All individuals included in the ECTIM study had four grandparents bom in Europe (French centres) or Ulster (Belfast subjects) and their families had been residing locally for at least two generations. All cases had survived a myocardial infarction three to nine months prior to enrolment in the study. The controls were drawn from the local electoral rolls and age-matched with their related patient group. The aim of this study was to investigate the large difference in CHD incidence between France and Northern Ireland. One method used to achieve this objective involved the comparison of DNA polymorphisms and their association with measured levels of risk factors for MI (lipoproteins and coagulation factors) in groups with differing risks of MI.
2.2.3 Family studies
2.2.3.1 Type I hyperlipoproteinaemia
In addition to the twenty type I probands, DNA samples from 25 relatives of these individuals (from 8 families) were obtained for study. These were relatives o f the five Institute of Child Health probands, of St.Thomas’ Hospital proband MA, of Swedish proband LA and of the italian proband CB. Partial lipid and LPL activity data was available for 18 of these individuals.