Familial Glucocorticoid Deficiency: Advances in the Molecular Understanding of ACTH Action (original) (raw)
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Context: There are at least twenty-four missense, non-conservative mutations found in the ACTH receptor (Melanocortin 2 receptor, MC2R) which have been associated with the autosomal recessive disease Familial Glucocorticoid Deficiency (FGD) type 1. The characterization of these mutations has been hindered by difficulties in establishing a functional heterologous cell transfection system for MC2R. Recently the melanocortin 2 receptor accessory protein (MRAP) was identified as essential for trafficking of MC2R to the cell surface; therefore a functional characterization of MC2R mutations is now possible. Objective: To elucidate the molecular mechanisms responsible for defective MC2R function in FGD. Methods: Stable cell lines expressing human MRAPα were established and transiently transfected with wild-type or mutant MC2R. Functional characterization of mutant MC2R was performed using a cell surface expression assay, a cAMP reporter assay, confocal microscopy and co- immunoprecipitati...
Endocrine Reviews, 2010
Background: Familial glucocorticoid deficiency (FGD) is an autosomal recessive disorder characterized by isolated glucocorticoid deficiency. Mutations in the ACTH receptor [melanocortin 2 receptor (MC2R)] or the MC2R accessory protein (MRAP) cause FGD types 1 and 2, respectively. Typically, type 2 patients present early (median age, 0.1 yr), and no patient reported to date has presented after 1.6 yr. Aim: The aim of this study was to investigate the cause of disease in two families with late-onset FGD. Patients: The proband in family 1 was diagnosed at age 4 yr. Family review revealed two older siblings with undiagnosed FGD. One sibling was well, whereas the second had cerebral palsy secondary to hypoglycemic seizures. The proband in family 2 was diagnosed at age 18 yr with symptoms of fatigue, weight loss, and depression. Methods: The coding exons of MC2R and MRAP were sequenced. ACTH dose-response curves were generated for MC2R when transfected with wild-type or mutant MRAP constructs using HEK293 cells. MC2R trafficking with both mutant MRAPs was investigated using immunocytochemistry. Results: MRAP gene analysis identified two novel homozygous missense mutations, c.175TϾG (pY59D) in family 1 and c.76TϾC (p.V26A) in family 2. In vitro analysis showed that the Y59D mutant had significant impairment of cAMP generation, and both mutants caused a shift in the dose-response curve to the right when compared to wild type. Immunocytochemistry showed normal trafficking of MC2R when transfected with both mutant MRAPs, indicating a probable signaling defect. Conclusion: These results indicate that missense MRAP mutations present with a variable phenotype of ACTH resistance and can present late in life. (J Clin Endocrinol Metab 95: 3497-3501, 2010) F amilial glucocorticoid deficiency (FGD) is a rare genetically heterogeneous autosomal recessive disorder. It is characterized by resistance of the adrenal cortex to ACTH resulting in adrenal failure with isolated glu-cocorticoid deficiency. Mineralocorticoid production by the adrenal gland remains near normal.
Journal of Molecular Medicine, 2002
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.
European Journal of Endocrinology, 2011
Background: Familial glucocorticoid deficiency (FGD) is a rare autosomal recessive disorder characterised by isolated glucocorticoid deficiency. Mutations in the ACTH receptor/melanocortin 2 receptor (MC2R), the MC2R accessory protein (MRAP) or the STAR protein (STAR) cause FGD types 1, 2 and 3, respectively, accounting for w50% of all cases. Patient and methods: We report a neonate of Indian origin, who was diagnosed with FGD in the first few days of life. He presented with hypoglycaemic seizures and was noted to have generalised intense hyperpigmentation and normal male genitalia. Biochemical investigations revealed hypocortisolaemia (cortisol 0.223 mg/dl; NR 1-23 mg/dl) and elevated plasma ACTH (170 pg/ml). Serum electrolytes, aldosterone and plasma renin activity were normal. Peak cortisol following a standard synacthen test was 0.018 mg/dl. He responded to hydrocortisone treatment and continues on replacement. Patient DNA was analysed by direct sequencing. The effect of the novel mutation was assessed by an in vitro splicing assay using wild type and mutant heterologous minigenes. Results: A novel homozygous mutation c.106C2_3dupTAwas found in the MRAP gene. Both parents were heterozygous for the mutation. In an in vitro splicing assay, the mutation resulted in the skipping of exon 3. Conclusion: We have identified a novel MRAP mutation where disruption of the intron 3 splice-site results in a prematurely terminated translation product. This protein (if produced) would lack the transmembrane domain that is essential for MC2R interaction. We predict that this would cause complete lack of ACTH response thus explaining the early presentation in this case.
Familial glucocorticoid deficiency due to compound heterozygosity of two novel MC2R mutations
Journal of Pediatric Endocrinology and Metabolism, 2000
Familial glucocorticoid defi ciency (FGD) is a rare autosomal recessive disorder characterized by isolated glucocorticoid defi ciency. Mutations in the ACTH receptor (melanocortin 2 receptor, MC2R ) or the MC2R accessory protein ( MRAP ) cause FGD types 1 and 2, respectively. A 2-year-old adopted Chinese girl presented with hypertonic seizures associated with hypoglycemia, skin hyperpigmentation, muscle weakness and mild jaundice. Hormonal analyses revealed high ACTH, low serum cortisol along with normal blood electrolytes. On hydrocortisone supplementation, the disease symptoms disappeared and the child recovered, although further episodes occurred with infection. To date, her physical and neurocognitive development progress is normal. A clinical diagnosis of FGD was given. We undertook MC2R and MRAP mutation screening. Two novel MC2R mutations were identifi ed: p.D107G localized in the transmembrane region, predicted to be traffi cking-competent but is unable to bind to ACTH, and p.R145C, situated in the second intracellular loop, predicted to be traffi cking-defective.
Mutations of the ACTH Receptor Gene in a New Family with Isolated Glucocorticoid Deficiency
Molecular Genetics and Metabolism, 2000
Isolated glucocorticoid deficiency (IGD) is an autosomal recessive disorder characterized by primary adrenocortical insufficiency, without mineralocorticoid deficiency. Mutations of the ACTH receptor gene have been reported in several families with IGD. We have amplified and directly sequenced the entire intronless ACTH receptor gene in a new family with IGD. The proband was found to be compound heterozygote for two different point mutations, one in each allele: (a) a substitution (360C>G) which changed neutral serine at position 120 in the apolar third transmembrane domain of the receptor to a positively charged arginine (S120R), probably disrupting the ligand-binding site; and (b) a substitution (761A>G) changing tyrosine at position 254 to cysteine (Y254C) in the third extracellular loop of the receptor protein, that also likely disrupts its structure and interferes with ligand binding. Each of the two mutations in the proband has previously been described in a different family, S120R in compound heterozygosity with a stop codon (R201X) and Y254C in homozygote form. Thus, in the absence of in vitro functional studies, our findings confirm the pathogenetic role of the S120R and Y254C mutants in the development of resistance to ACTH.
Familial glucocorticoid deficiency with a point mutation in the ACTH receptor: a case report
Journal of Korean medical science, 2009
Familial glucocorticoid deficiency (FGD) is a rare autosomal recessive disorder characterized by severe glucocorticoid deficiency associated with failure of adrenal responsiveness to ACTH but no mineralocorticoid deficiency. We report a 2 month-old boy of nonconsanguineous parents, presented with hyperpigmentation. Physical examination showed diffuse dark skin of body including, oral mucosa, gum, hands, nails and scrotum. Laboratory evaluation revealed low serum cortisol (0.3 microg/dL), with very high plasma ACTH level (18,000 pg/mL), and serum cortisol level did not increase after ACTH stimulation test. Serum sodium, potassium, plasma renin activity, aldosterone and 17-hydroxyprogesterone were normal. Sequence analysis of the ACTH receptor (MC2R) gene showed a homozygous mutation of D103N. Diagnosis of FGD was made and treatment started with oral hydrocortisone.