Thirty-Eight-Year Follow-Up of Two Sibling Lipoid Congenital Adrenal Hyperplasia Patients Due to Homozygous Steroidogenic Acute Regulatory (STARD1) Protein Mutation. Molecular Structure and Modeling of the STARD1 L275P Mutation

The acute response of steroidogenic cells to trophic hormone stimulation is the mobilization of cholesterol from cellular stores to the mitochondrial outer membrane and the transfer of this cholesterol to the mitochondrial inner membrane where the first enzymatic step in steroidogenesis occurs. The transfer of cholesterol across the mitochondrial membranes is dependent upon de novo protein synthesis, and this is the regulated step in the process. Although the newly synthesized regulatory protein(s) have yet to be identified, we previously have proposed a candidate protein which we identified in MA-10 cells that is synthesized in response to luteinizing hormone stimulation and that is localized to the mitochondria. In the present study, we report the isolation of a cDNA that encodes this luteinizing hormone-induced protein. Analysis of the cDNA and protein sequences reveals this is a novel protein. Importantly, we demonstrate for the first time that expression of the protein in MA-10 cells in the absence of hormone stimulation is sufficient to induce steroid production. We conclude that this protein is required in the acute regulation of steroidogenesis and propose to call this protein the Steroidogenic Acute Regulatory protein (StAR).

Congenital lipoid adrenal hyperplasia is an autosomal recessive disorder that is characterized by impaired synthesis of all adrenal and gonadal steroid hormones. In three unrelated individuals with this disorder, steroidogenic acute regulatory protein, which enhances the mitochondrial conversion of cholesterol into pregnenolone, was mutated and nonfunctional, providing genetic evidence that this protein is indispensable normal adrenal and gonadal steroidogenesis.

Congenital lipoid adrenal hyperplasia results in severe impairment of steroid biosynthesis in the adrenal glands and gonads that is manifested both in utero and postnatally. We recently found mutations in the gene for the steroidogenic acute regulatory protein in four patients with this syndrome, but it was not clear whether all patients have such mutations or why there is substantial clinical variation in these patients. We directly sequenced the gene for steroidogenic acute regulatory protein in 15 patients with congenital lipoid adrenal hyperplasia from 10 countries. Identified mutations were confirmed and recreated in expression vectors, transfected into cultured cells, and assayed for the presence and activity of steroidogenic acute regulatory protein. Fifteen different mutations in the gene for steroidogenic acute regulatory protein were found in 14 patients; the mutation Gln258Stop was found in 80 percent of affected alleles from Japanese and Korean patients, and the mutation Arg182Leu was found in 78 percent of affected alleles from Palestinian patients. We developed diagnostic tests for these and eight other mutations. Thirteen of the 15 mutations were in exons 5, 6, or 7, and all rendered the steroidogenic acute regulatory protein inactive in functional assays. Some mutants with amino acid replacements were capable of normal mitochondrial processing, indicating that the activity of steroidogenic acute regulatory protein is not associated with its translocation into mitochondria. Steroidogenic cells lacking the protein retained low levels of steroidogenesis. This explains the secretion of some steroid hormones by the ovaries after puberty before affected cells accumulate large amounts of cholesterol esters. The congenital lipoid adrenal hyperplasia phenotype is the result of two separate events, an initial genetic loss of steroidogenesis that is dependent on steroidogenic acute regulatory protein and a subsequent loss of steroidogenesis that is independent of the protein due to cellular damage from accumulated cholesterol esters.