In our center we have been trying to determine the prevalence of severe heterozygous FH in the United States, meaning patients with coronary heart disease (CHD) and an LDL-C level >200 mg/dL despite maximum medical therapy, or patients without CHD and an LDL-C level >300 mg/dL despite maximum medical therapy – in other words, patients who would be considered eligible for LDL apheresis.

Across numerous studies the average LDL-C level for heterozygous FH patients is about 251 mg/dL.  Of those individuals, about 17% will already have CHD, and after treatment, the LDL-C level is about 135 mg/dL. 

What about the patients who are refractory to standard LDL-C lowering therapy?  Based on the results from multiple clinical trials, it is estimated that on maximum lipid lowering therapy, about 0.02% of all FH patients will have an LDL-C level >300 mg/dL and no CHD and a further 1–2% will have an LDL-C level ≥200 mg/dL and documented CHD.

In fact, 7.8% of patients with FH and CHD following maximum lipid lowering therapy will have an LDL-C level ≥200 mg/dL, but since some of this group is already represented in the 17% who have CHD, then to be conservative, the estimate becomes 1–2% of all FH patients have an LDL-C level ≥200 mg/dL.

The prevalence then of severe heterozygous FH in the United States is about 1 in 36,000 (range 1 in 10,000 to 1 in 50,000), a level that is not common but that is certainly more common than the 1 in 1,000,000 with homozygous FH.