The prevalence of heterozygous familial hypercholesterolemia is 1 in 200 to 1 in 500 worldwide. In America, prevalence differs among races. For instance, the frequency of heterozygous familial hypercholesterolemia is around 1 in 250 among White and Black individuals, whereas for Mexican American individuals and individuals of other races, it is around 1 in 414 and 1 in 343, respectively. Homozygous familial hypercholesterolemia is far rarer, occurring around 1 in 1 000 000. Among certain founder populations, this frequency can be much higher. For instance, in French Canadian individuals in Quebec, the estimated rate is around 1 in 275 000; in Afrikaner individuals in Gauteng, South Africa, this estimated rate is around 1 in 30 000; for Christian Lebanese people, this estimated rate is around 1 in 100 000; and, for Tunisian people, this estimated rate is around 1 in 125 000. In addition to ethnic differences affecting the prevalence rate of familial hypercholesterolemia, gender and racial differences contribute to health disparities among those with the genetic disease. For instance, being a female and/or of Asian or African descent is independently associated with a decreased likelihood of achieving LDL-cholesterol treatment goals as opposed to White patients.
Patients with heterozygous familial hypercholesterolemia tend to present with an LDL-C level that is 2-3 times higher than normal levels, whereas homozygous individuals can present with LDL concentrations up to 10 times higher. Subsequently, there can be premature coronary atherosclerosis and cardiac-related death. In fact, patients with homozygous familial hypercholesterolemia may suffer from a myocardial infarction (MI) in childhood, whereas those who are heterozygous may suffer from an MI in their thirties. Furthermore, there may be subclinical atherosclerosis and increased risk of peripheral arterial disease.
In addition, tendinous xanthomata, which are composed of foam cells from intracellular accumulation of lipids and connective tissue, are present in approximately 30%-50% of those with familial hypercholesterolemia. Locations include the Achilles tendon and tendons on and around the elbows, knees, and hands. There may be tuberoeruptive and tuberous xanthomas, planar xanthomas, including xanthelasma, and lipid deposition in the cornea (corneal arcus).
Two commonly used diagnostic tools for familial hypercholesterolemia that do not require genetic testing and are globally respected are the Simon Broome Register Group criteria (United Kingdom) and the Dutch Lipid Clinic Network criteria.
Related topic: familial defective apolipoprotein B-100
E78.01 – Familial hypercholesterolemia
398036000 – Familial hypercholesterolemia
Differential Diagnosis & Pitfalls
- Sitosterolemia is characterized by prominent skin (tuberous) and tendinous xanthomata. Due to a mutation in the ATP binding cassette transporter G5 and G8, there is hyperabsorption of cholesterol and plant sterols and impaired biliary secretion of the sterols. Patients will thus have elevated levels of LDL-C and plant sterols.
- Cerebrotendinous xanthomatosis is an autosomal recessive sterol storage disorder due to a mutation in sterol 27-hydroxylase, an enzyme involved in the bile acid synthesis pathway. There will be abnormal deposition of cholesterol and cholestanol in multiple tissues, including the central nervous system. Serum and tissue levels of cholestanol are elevated to 5-10 times normal levels, whereas serum cholesterol levels are normal or decreased. Symptoms may include dementia, spinal cord paresis, cerebellar ataxia, intractable diarrhea, premature cataracts, tendinous xanthomata, premature atherosclerosis, and cardiovascular disease.
- Secondary hyperlipidemia may be due to diabetes mellitus, hypothyroidism, nephrotic syndrome, cholestatic liver disease, or drug-induced causes.
- Familial combined hyperlipidemia can be due to any number of genetic causes affecting the lipid metabolic cycle. Unlike familial hypercholesterolemia, however, tendinous xanthomata, xanthelasma, and corneal arcus are rare.
- Familial dysbetalipoproteinemia (hyperlipoproteinemia type III) is due to a genetic defect of apolipoprotein E. Patients tend to have elevated triglyceride levels (> 300 mg/dL) as well as LDL-C levels (> 220 mg/dL). Signs include discolored palmar creases and tuberoeruptive xanthomas of elbows and knees.