Answers-2 The genetic dislipidaemias occur in one third of patients who have suffered from their first myocardial infarction below the age of 50 years in men. The commonest is familial combined hyperlipidaemia (two thirds), with a fifth due to familial hypercholesterolaemia. The former can be diagnosed only on family studies, and there is elevation of fasting plasma tricglycerides not associated with hypercylomicronaemia. It is autosomal dominant, and some family members may have hypercylomicronaemia. Only 20% of children have elevated triglycerides before the age of 25. Obesity, insulin resistance, hyperinsulinaemia, glucose intolerance, and hyperuricaemia are associated. Heterozygous familial hypercholesterolaemia is dominantly inherited, and results from defects in the LDL receptor. The most important clinical manifestation is premature coronary artery disease, particularly with onset between the third or fourth decade. Tendon xanthomata and arcus cornea are rarely present in children, but are very important signs to identify.