Degradation of ¹²⁵I-labeled LDL by cultured skin fibroblasts and EBV- lymphocytes from individuals in family 1. Cells were preincubated for 16 hours in medium containing LPDS and then for 4 hours with ¹²⁵I-labeled LDL. Saturable degradation of LDL was determined as the difference in the amount of trichloroacetic acid–soluble (TCA-soluble), non-iodide radioactivity in the medium of cells incubated in the presence and absence of an excess of unlabeled LDL (1 mg/ml); values are the mean of duplicate dishes. Nonsaturable degradation of LDL by normal cells was always less than 5% of the total. Data shown are representative of at least two separate experiments. (a) Cultured skin fibroblasts from the proband in family 1 (ARH^–/–), and from a normolipemic control (ARH^+/+). (b) EBV-lymphocytes from the proband in family 1 (ARH^–/–), her heterozygous sibling (ARH^+/–), and a sibling who does not carry the mutant allele (ARH^+/+).