A novel compound heterozygous mutation in the steroidogenic acute regulatory protein gene in a patient with congenital lipoid adrenal hyperplasia

Congenital lipoid adrenal hyperplasia (CLAH) is an autosomal recessive disorder characterized by impaired synthesis of all adrenal and gonadal steroid hormones. Recently, it was reported that mutations in the steroidogenic acute regulatory protein (StAR) gene cause CLAH. In the present study, we have analyzed the StAR gene of a Japanese patient with CLAH. PCR amplification and subsequent nucleotide sequencing of the StAR gene and those of her parents revealed that the patient has a compound heterozygous mutation of this gene. In one allele, an undescribed G to C transversion in codon 217, which occurred at the last base of exon 5 and thus altered the splice donor site sequence, apparently resulted in a substitution of Arg to Thr (AGG to ACG: R217T), and in the other allele, a C to T transition in codon 218 caused a substitution of Ala to Val (GCG to GTG: A218V), which has been previously shown to abolish StAR activity. In vitro expression analysis of an allelic minigene that consists of exons 4-6 of the R217T mutant StAR gene showed that the G to C transversion in the splice donor site of exon 5 caused by the R217T mutation disrupts normal splicing, resulting in the complete skipping of exon 5, which alters the translation reading frame of exon 6, introduces a stop codon at amino acid position 174, and thus impairs the activity. A functional expression study of the R217T replacement mutant revealed that the mutant has no steroidogenesis-enhancing activity if the transcript of the R217T mutant allele is ever spliced normally and translated into the protein. From the genetic analysis of 50 healthy subjects, the novel R217T mutation was unlikely to be due to polymorphism. Together, these results indicate that this patient is a compound heterozygote for the mutation in the StAR gene (T217R and A218V) and that these mutations inactivate the StAR function and give rise to clinically manifest CLAH.