Missense Mutations in the Melanocortin 2 Receptor Accessory Protein That Lead to Late Onset Familial Glucocorticoid Deficiency Type 2

• Published in: The journal of clinical endocrinology and metabolism 2010-07, Vol.95 (7), p.3497-3501
• Main Authors: Hughes, C. R., Chung, T. T., Habeb, A. M., Kelestimur, F., Clark, A. J. L., Metherell, L. A.
• Format: Article
• Language: English
• Subjects: Adrenal Gland Diseases - genetics; Adult; Biological and medical sciences; Child; Endocrinopathies; Feeding. Feeding behavior; Female; Fluorescent Antibody Technique; Fundamental and applied biological sciences. Psychology; Glucocorticoids - deficiency; Glucocorticoids - genetics; Humans; Male; Medical sciences; Membrane Proteins - genetics; Microscopy, Confocal; Mutation, Missense - genetics; Pedigree; Vertebrates: anatomy and physiology, studies on body, several organs or systems; Vertebrates: endocrinology
• ISSN: 0021-972X; 1945-7197
• DOI: 10.1210/jc.2009-2731

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.175T>G (pY59D) in family 1 and c.76T>C (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. Two novel mutations in MRAP are described that lead to late onset FGD2; appropriately functional characterization confirms these mutations have reduced but not absent function.