Molecular defects underlying Wolman disease appear to be more heterogeneous than those resulting in cholesteryl ester storage disease

Human lysosomal acid lipase/cholesteryl ester hydrolase (hLAL) is essential for the intralysosomal metabolism of cholesteryl esters and triglycerides taken up by receptor-mediated endocytosis of lipoprotein particles. The key role of the enzyme in intracellular lipid homeostasis is illustrated by tw o lysosomal storage diseases inherited as autosomal recessive traits. Wolma n disease, associated with deficient hLAL activity, leads to massive intrac ellular substrate accumulation and is always fatal in early infancy. Choles teryl ester storage disease (CESD), in contrast, is characterized by very l ow levels of enzymic activity sufficient to allow survival of the affected patients into adulthood. In order to elucidate the underlying molecular def ects in Wolman disease, we have characterized the hLAL gene in two female W olman patients of German and Turkish origin by SSCP and DNA sequence analys is. Our results demonstrate that the German proband was compound heterozygo us for an 8-bp deletion in exon 3 and a 2-bp deletion in exon 4 of the hLAL gene, These frameshift mutations lead to protein truncation at amino acid positions 24 and 116 and to complete loss of hydrolytic activity, The Turki sh proband, in contrast, was homozygous for a G(1064)-->T substitution in e xon 10 of the hLAL gene which converts the completely conserved glycine (GG G) residue at position 321 of the mature enzyme to tryptophan (TGG), In vit ro expression of the hLAL(Gly(321)-->Trp) cDNA construct revealed that the amino acid replacement results in a more than 99% reduction of neutral lipi d hydrolysis. The mutations provide new insights into the molecular basis o f Wolman disease which is apparently more heterogeneous at the genetic leve l than cholesteryl ester storage disease.