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Familial glucocorticoid deficiency (FGD) is an autosomal recessive disorder characterized by a glucocorticoid adrenal insufficiency without mineralocorticoid deficiency. Mutations of the ACTH receptor (MC2-R) gene have been reported in some FGD cases, but only a few of them have been functionally studied. We reported clinical features and MC2-R gene analysis in three families. For each proband, an homozygous mutation was identified after amplification and sequencing of the whole intronless MC2-R gene. One mutation converted Val-142 located in the second intracellular loop to Leu. Another mutation in the sixth transmembrane domain converted Ala-233 to Pro. The last mutation converted the negatively charged Asp-103 in the first extracellular loop to an uncharged Asn. Functional studies of these mutations as well as the S120R mutation were performed after stable transfection of M3 cells and measurement of ACTH-induced cAMP production. For the S120R, V142L, and A233P mutated MC2-R, cAMP production curves were similar to that obtained with M3 parental cells, confirming that these mutations are responsible for the FGD in the affected patients. The D103N-mutated MC2-R had an impaired cAMP response to physiological doses of ACTH, but the maximal response at very high concentrations of ACTH was similar to that obtained for the wild-type MC2-R. All these results demonstrated clear relationships based on functional studies between MC2-R homozygous mutations and FGD phenotype.

Familial glucocorticoid deficiency (FGD) is a rare autosomal recessive disease resulting from resistance to the action of adrenocorticotropic hormone (ACTH) on the adrenal cortex, which leads to isolated glucocorticoid deficiency with normal mineralocorticoid secretion. It may present in infancy or early childhood with hyperpigmentation, failure to thrive, recurrent infections, hypoglycemic attacks and convulsions that may result in coma or death. Laboratory investigations reveal low cortisol and androgen levels with high ACTH associated with normal reninaldosterone axis. The disorder may be caused by mutations in the gene of ACTH receptor (MC2R), or mutations in the newly described melanocortin- 2 receptor accessory protein (MRAP) namely, FGD type 1 and FGD type 2, respectively. Twenty five percent of FGD cases are due to the mutations of the ACTH receptor, while FGD type 2 accounts for approximately 15-20% of FGD cases. Here, we report a six-month-old male infant, who presented with recurrent hypoglycemic convulsions. Serum hormone analysis showed low cortisol and androgen levels associated with a high ACTH concentration. No mutation was found in the NR0B1 and MC2R genes excluding congenital adrenal hypoplasia and FGD type 1. We found a homozygous deletion (c. 106+1delG) in intron 3 of MRAP gene. To our knowledge, this is the first Turkish patient reported with FGD type 2 due to a known MRAP mutation.