Genetic heterogeneity of adrenocorticotropin (ACTH) resistance syndromes: Identification of a novel mutation of the ACTH receptor gene in hereditary glucocorticoid deficiency

Abstract

Hereditary primary adrenal insufficiency syndromes due to ACTH resistance include hereditary glucocorticoid deficiency (HGD) and Allgrove's syndrome (AS). Patients with both conditions present in childhood with failure to thrive, weakness, and fatigue or adrenal crisis; patients with AS in addition have alacrima and achalasia (triple A syndrome). We studied four kindreds with HGD and four kindreds with AS for abnormalities of the ACTH receptor (ACTHR) gene. The ACTHR coding sequence in all AS kindreds and two HGD kindreds was normal. Analysis of the ACTHR gene of the proband in one of the HGD kindreds showed him to be homozygous for the previously described G221T transition causing a Ser74Ile substitution of the protein, which has been shown to inactivate the ACTHR in signal transduction. The proband in another HGD kindred was found to be a compound heterozygote with the G221T transition in one allele and a novel C818A transition in the other allele of ACTHR. The C818A transition caused the substitution of the highly conserved Pro273 by His in the receptor protein. In vitro expression of the mutated ACTHR in mouse melanoma M3 cells showed that at a medium ACTH concentration of 3 nM, cells transfected with the wild-type ACTHR produced twofold and threefold, respectively, of the amount of intracellular cAMP when compared to cells transfected with the ACTHR carrying the Pro273His and the Ser74Ile mutation, respectively, confirming that HGD in this kindred is caused by loss-of-function mutations of the ACTHR. These results showed that the genetic cause of the ACTH-resistant syndromes is heterogeneous.