Hypercholesterolaemia familial

Familial hypercholesterolaemia is characterized by a significant elevation in plasma LDL concentration. The basic metabolic defect appears to be abnormal LDL receptor function, arising from mutations in the LDL receptor gene. Several receptor mutations have been identified and hypercholesterolaemia severity as well as the age of onset of ischaemic heart disease has recently been demonstrated to vary according to the type of LDL receptor gene defect (Moorjani et al., 1993). 

Approximately half of the male heterozygote population for familial hypercholesterolaemia develop ischaemic heart disease by the age of 50 and the homozygpte... 

Moorjani, S., Betard, C., Brun, D., Roy, M., Gagne, C., Davignon, J., Torres, A., Lambert, M. and Lupien, P. (1993). Mutations of the LDL receptor gene, variations in plasma cholesterol and expression of coronary heart disease in homozygous familial hypercholesterolaemia. Lancet 341, 1303-1306. 

Heath KE, Gahan M, Whittall RA, Humphries SE. Low-density lipoprotein receptor gene (LDLR) world-wide website in familial hypercholesterolaemia update, new features and mutation analysis. Atherosclerosis 2001 154 243-246. 

Vuorio AF, Ojala JP, Sarna S, Turtola H, Tikkanen MJ, Kontula K. Heterozygous familial hypercholesterolaemia the influence of the mutation type of the low-density-lipoprotein receptor gene and PvuII polymorphism of the normal allele on serum lipid levels and response to lo-vastatin treatment. J Intern Med 1995 237 43-48. 

Heath KE, Gudnason V, Humphries SE, Seed M. The type of mutation in the low density lipoprotein receptor gene influences the cholesterol-lowering response of the HMG-CoA reductase inhibitor simvastatin in patients with heterozygous familial hypercholesterolaemia. Atherosclerosis 1999 143 41-54. 

Feher MD, Webb JC, Patel DD, Lant AF, Mayne PD, Knight BL, et al. Cholesterol-lowering drug therapy in a patient with receptor-negative homozygous familial hypercholesterolaemia. Atherosclerosis 1993 103 171-180. 

Myant NB. Familial defective apolipoprotein B-100 a review, including some comparisons with familial hypercholesterolaemia [published erratum appears in Atherosclerosis 1994 Feb 105[2] 253[. Atherosclerosis 1993 104 1-18. 

Klausen IC, Gerdes LU, Meinertz H, Hansen FA, Faergeman O. Apolipopro-tein(a) polymorphism predicts the increase of Lp(a) by pravastatin in patients with familial hypercholesterolaemia treated with bile acid sequestration. Eur J Clin Invest 1993 23 240-245. 

The choice of target cells is another point worthy of discussion. In some instances, this choice is predetermined, e.g. treatment of the genetic condition, familial hypercholesterolaemia, would require insertion of the gene coding for the low-density lipoprotein receptor specifically in hepatocytes. 

Kozarsky, K.F., Jooss, K., Donahee, M., Strauss, J.F., III, Wilson, J.M. (1996). Effective treatment of familial hypercholesterolaemia in the mouse model using adenovirus-mediated transfer of the VLDL receptor gene. Nature Genet., 13, 54—62. 

Scientific Steering Committee on behalf of the Simon Broome Register Group (1991) Risk of fatal coronary heart disease in familial hypercholesterolaemia. Scientific Steering Committee on behalf of the Simon Broome Register Group. BMJ 303 893-896... 

Soutar, A. K., Myant, N. B., and Thompson, G. R., The metabolism of very low density and intermediate density lipoproteins in patients with familial hypercholesterolaemia. Atherosclerosis 43, 217-231 (1982). 

Grossman M, Rader DJ, Muller DWM, et al A pilot study of ex vivo gene therapy for homozygous familial hypercholesterolaemia. Nat Med 1 1148-1154,1995. 

Of the many disorders of lipoprotein metabolism (Tables 5.2 and 5.3), familial hypercholesterolaemia type II may be the most prevalent in the general population. It is an autosomal dominant disorder that results from mutations affecting the structure and function of the ceU-surface receptor that binds plasma LDLs and removes them from the circulation. The defects in LDL-receptor interaction result in lifelong elevation of LDL cholesterol in the blood. The resultant hypercholesterolaemia leads to premature coronary artery disease and atherosclerotic plaque formation. Familial hypercholesterolaemia was the first inherited disorder recognised as being a cause of myocardial infarction (heart attack). 

Receptor defects, such as several forms of familial hypercholesterolaemia, are the result of genetic defects in the gene encoding the receptor for LDL. These defects result in the synthesis of abnormal LDL receptors that are incapable of binding to LDLs, or that bind LDLs such that the receptor/LDL complexes are not properly internalised and degraded. The outcome is an elevation in serum cholesterol levels and increased propensity toward the development of atherosclerosis. 

D. Fass, S. Blacklow, P S. Kim, and J.M. Berger. 1997. Molecular basis of familial hypercholesterolaemia from structure ofLDL receptor module Aatwre 388 691-693. (PubMed)... 

Familial hypercholesterolaemia Sickle cell anaemia Phenylketonuria... 

Patients with familial hypercholesterolaemia exhibit lower levels of plasma cholesterol after an operation for portacaval anastomosis, and it has now been shown in rats that such an operation causes an increase in HMG-CoA reductase and cholesterol 7a -hydroxylase activities. Many transplantable human and rodent hepatomas do not control the rate of sterol biosynthesis and HMG-CoA reductase levels in response to dietary cholesterol as normal liver cells do. However, certain hepatoma cells have now been found that, although lacking feedback regulation of choles-terologenesis in vivo, retain their regulatory ability in vitro It thus appears that malignant transformation is not necessarily linked to the loss of regulation by the cell of HMG-CoA reductase activity or sterol synthesis. 

Pass, D., Blacklow, S., Kim, P. S., and Berger, J. M. 1997. VIolecular basis of familial hypercholesterolaemia from structure of LDL receptor module. Nature 388 601-693. 

Patients with familial hypercholesterolaemia have a mutation in the gene specifying the LDL receptor. In these patients, LDL degradation through the physiologic... 

The l.DL receptor (Fig. 3), a glycoprotein present on the surface of all cells, spans the cell membrane and is concentrated in special membrane recesses, called coated pits. It binds to lipoproteins containing apolipoprotein B and E. and itilemalizcs them for breakdown within the cell. Receptors are then recycled to the cell surface. The number and function of receptors dictate the level of circulating LDL. When the cell has sufficient cholesterol, the synthesis of receptors is down-regulated when the cell is cholesterol depleted, the receptors increa.se in number. Inherited malfunction or absence of the.se receptors leads to familial hypercholesterolaemia (FH). 

The physical signs of the hyperlipidaemias are not specific for any particular disease and may sometimes be present in normolipidaemic patients, e.g. arcus senilis (Fig. 4). Their presence is. however, highly suggestive of raised lipids. Tendon xanthomas (Fig. 3) are particularly associated with familial hypercholesterolaemia. 

Fig. 5 Tendon xanthomas. These are pathognomic for familial hypercholesterolaemia and are often first seen on the achilles tendon as in this patient.

Though the plasma cholesterol level is not significantly altered in non-fasting blood samples, this woman s hypercholesterolaemia should be confirmed on a fasting plasma sample in which her triglyceride and HDL cholesterol should also be measured. Secondary causes of hyperlipidaemia such as hypothyroidism and diabetes mellitus should be excluded. If her plasma triglyceride is normal and she has primary hypercholesterolaemia, a likely diagnosis is familial hypercholesterolaemia (FH). 

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