Cholesteryl Ester Storage Disease: Relationship between Molecular Defects andin SituActivity of Lysosomal Acid Lipase

The molecular defects in theLIPAgene encoding the lysosomal acid lipase (LAL) were investigated in two unrelated patients affected with cholesteryl ester storage disease (CESD), an autosomal recessive disorder associated with LAL-deficient activity. In cell lysates from both patients there was a severely reduced LAL activity. In a female patient, nucleotide sequencing of amplified LAL genomic DNA or reverse-transcribed mRNA demonstrated that she was a compound heterozygote for two previously reported mutations, a G → A transition at position −1 of the exon 8 splice donor site, resulting in skipping of the complete exon 8, and a C923→ T substitution leading to the replacement of His274to Tyr. The second, male CESD patient was heterozygous for the splice junction mutation and a yet undescribed C → T substitution at position 233, which introduces a premature in-frame termination codon. The functional consequences of these genetic alterations were evaluated for the first time by studying the catabolic turnover of radiolabeled cholesteryl oleate in intact cells. A lowerin situresidual LAL activity was found in cells carrying the stop codon mutation than in cells having the His274→ Tyr substitution. Since the severely reduced LAL activity was seen in cells from an adult patient with a mild CESD, we conclude that there is no simple direct correlation between the LAL molecular lesions and the biochemical and clinical phenotypes.