• A 4-year-old boy had typical features of homozygous type II hyperlipoproteinemia with planar xanthomas, a plasma cholesterol level greater than 600 mg/dl, and an estimated β-lipoprotein cholesterol concentration greater than 500 mg/dl. Both he and his sister, who had the biochemical features of the heterozygous state, responded unusually well to a diet low in saturated fat and cholesterol content. These features, combined with the finding of normocholesterolemic parents, are highly suggestive of a newly described syndrome, pseudohomozygous type II hyperlipoproteinemia.
Maurice A. Mishkel. Pseudohomozygous and Pseudoheterozygous Type II Hyperlipoproteinemia. Am J Dis Child. 1976;130(9):991–993. doi:10.1001/archpedi.1976.02120100081013