The genetics of ACTH resistance syndromes (original) (raw)
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Molecular Genetics and Metabolism, 1998
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.
Familial Glucocorticoid Deficiency: Advances in the Molecular Understanding of ACTH Action
Hormone Research, 2008
Familial glucocorticoid deficiency (FGD), otherwise known as hereditary unresponsiveness to ACTH, is a rare autosomal recessive disease characterized by glucocorticoid deficiency in the absence of mineralocorticoid deficiency. Mutations of the ACTH receptor, also known as the melanocortin-2 receptor (MC2R), account for approximately 25% of FGD cases. More recently a second gene, MRAP (melanocortin-2 receptor accessory protein), was identified and found to account for a further 15-20%. MRAP encodes a small single transmembrane domain protein, which is essential in the trafficking of the MC2R to the cell surface. In this review, we will firstly summarize the clinical presentation and genetic aetiology of this condition. Secondly, we will discuss how the discovery of MRAP has enhanced our understanding of the mechanisms of ACTH/MC2R action. Finally, we will explore future developments in this field.
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 Clinical Investigation, 1993
Isolated glucocorticoid deficiency (IGD) is an autosomal recessive disorder characterized by progressive primary adrenal insufficiency, without mineralocorticoid deficiency. The cDNA and gene of the human ACTH receptor were recently cloned. The gene encodes a 297-amino acid protein that belongs to the G protein-coupled superfamily of membrane receptors. We hypothesized that the ACIH receptor gene might be defective in IGD. To examine this, we studied its genomic structure by PCR and direct sequencing in a 5-yr-old proband with the disease, his parents, and grandparents. The proband was a compound heterozygote for two different point mutations, one in each allele: (a) a substitution (C --T), also found in one allele of the mother and maternal grandmother, which introduced a premature stop codon (TGA) at position 201 of the protein; this mutant receptor lacks its entire carboxy-terminal third and, if expressed, should be unable to transduce the signal; and (b) a substitution (C -G), also found in one of the paternal alleles, which changed neutral serine " in the apolar third transmembrane domain of the receptor to a positively charged arginine, probably disrupting the ligand-binding site. Standard ovine corticotropin releasing hormone (oCRH) test in the heterozygote parents and maternal grandmother revealed exaggerated and prolonged ACTH responses, suggestive of subclinical resistance to ACTH. We conclude that IGD in this family appears to be due to defects of the ACTH receptor gene. The oCRH test appears to be useful in ascertaining heterozygosity in this syndrome. (
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...
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.
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.