Familial glucocorticoid deficiency is a rare autosomal recessive genetic disorder which belongs to a group of primary adrenal insufficiency (PAI) and is mainly caused by mutations in the
Familial glucocorticoid deficiency (FGD) (OMIM #202200), a type of primary adrenal insufficiency (PAI), is an autosomal recessive disorder, known as isolated glucocorticoid deficiency or hereditary unresponsiveness to adrenocorticotropic hormone (ACTH) occur during early childhood and neonatal periods [
ACTH regulates the adrenal cortex. Adrenocorticotropic hormone receptor (MC2R) is mostly in the zona fasciculata which controls the glucocorticoid and cortisol synthesis [
FGD is a genetically heterogeneous disorder consisting of more than two subtypes including FGD type 1 (OMIM 607397) caused by mutations in the
Different types of
Here, the spectrum of the
A 5-month-old infant girl who was born with cesarean section due to breach presentation with normal Apgar score was the first child of a healthy family with consanguineous marriage. Other family members did not have history of any disease. Her height, weight, and head circumference were 50 cm, 3300 g, and 37 cm at birth, respectively; all were within the normal range.
At 17th day of birth, she was admitted to the newborn intensive care unit (NICU) due to hypoglycemia and seizure. Her blood glucose was 2 mmol/L (normal range: 2.5–5.5 mmol/L). Biochemical investigations showed high thyroid-stimulating hormone (TSH) level of 14.2 U/L (normal range: 0.5–5 U/L), growth hormone (GH) level of 13 ng/ml (normal range: > 10 ng/ml), insulin level of 1.43 mU/L (normal range: < 2 mU/L), and cortisol level of 495 nmol/L (normal range: > 497 nmol/L). Autoimmune analysis was not performed for the patient since she was a newborn. Physical examination showed mild skin pigmentation and normal female external genitalia. She was discharged from the hospital with levothyroxine (10 mg/kg/day), and blood glucose was stabilized.
By 4th month of age checkup, weight was 5.3 kg (25th percentile), height was 61.5 cm (50th percentile), and head circumference was 41.5 cm (50th percentile). There was no documentation on recurrent infection. Biochemical investigations showed a very low cortisol level of <0.054
At six‐month‐old, biochemical assays showed 17OHP < 0.1 ng/mL (normal range: <1 ng/mL) and TSH 5.3 U/L. She was 5.9 kg (3rd percentile), with height 64.3 cm (15th percentile). She underwent genetic testing to confirm FGD diagnosis.
At the age of 15 months, (9th month of treatment), her weight was 14 kg (97th percentile), height was 80 cm (80th percentile), and head circumference was 47 cm (85th percentile); TSH level was 0.61 U/L (normal range: 0.5–5 U/L), and ACTH level was 1310 pg/ml (normal range: <50 pg/mL). She was in good condition.
A 2-year-old boy who was born from a first-cousin couple referred for genetic testing of congenital adrenal hypoplasia and FGD. He had hypoglycemia when he was 14 months old. Other family members did not have history of any disease. His brother, aunts, and uncles did not show the disease; they were analyzed for genetic variants.
His blood glucose was 2.2 (normal range: 2.5–5.5 mmol/L). Biochemical investigations showed a high TSH level of 12 U/L (normal range: 0.5–5 U/L), GH level of 4 ng/ml (normal range: > 10 ng/ml), insulin level of 1.5 mU/L (normal range: < 2 mU/L), ACTH level of 118 pg/mL (normal range: <50 pg/mL), aldosterone level of 900 pg/mL (normal range: 20–1100 pg/mL), 17-OHP level of 1.3 ng/mL (normal range: <1 ng/mL), and cortisol level of 250 nmol/L (normal range: >497 nmol/L). Autoimmune analysis was not performed for the patient since he was young. Physical examinations showed mild skin pigmentation. He had hypothyroidism and congenital adrenal hypoplasia. He underwent hydrocortisone treatment. He had responded well to the conventional treatment.
A 15-year-old girl born from a first-cousin couple was referred to confirm genetic diagnosis of FGD. Her parents mentioned the history of hypoglycemia at the 3rd day of birth and hospitalization. Other family members did not have history of any disease. Her brother was also healthy and had no sign. At the 2nd year of life, physical examination showed skin pigmentation and normal female external genitalia.
Her blood glucose was 2.5 (normal range: 2.5–5.5 mmol/L). Biochemical investigations showed a GH level of 6 ng/ml (normal range: > 10 ng/ml), insulin level of 1.5 mU/L (normal range: < 2 mU/L), ACTH level of 282 pg/mL (normal range: <50 pg/mL), aldosterone level of 700 pg/mL (normal range: 20–1100 pg/mL), 17-OHP level of 3 ng/mL (normal range: < 1 ng/mL), and cortisol level of 200 nmol/L (normal range: >497 nmol/L). No autoimmune analysis was performed for the patient. She was clinically diagnosed as FGD. She underwent hydrocortisone treatment and did well until the genetic testing. She underwent molecular testing to confirm the diagnosis at later ages.
Informed consent was obtained from patients and the parents or guardian of the minors for genetic testing. DNA was extracted according to the standard methods. In brief, PCR amplification was performed using routine protocols; direct sequencing was performed by the sequencing analyzer (ABI3130XL, Biosystems, US) for coding regions of
A comprehensive search was conducted on published variants in PubMed using keywords including “MC2R gene mutations [ti/abs]” and “Familial glucocorticoid deficiency AND MC2R.” MRAP variants were identified based on keywords including “MRAP gene mutations [ti/abs]” and “Familial glucocorticoid deficiency AND MRAP.”
Articles including functional studies, animal studies, and mechanism of disease were excluded from our study. According to our inclusion criteria, articles having FGD patients with defined
All variants were named based on the human genome variation (HGVS) nomenclature, and the type of mutation, positional effect, and functional effect were used for further study.
The pathogenic significance of selected mutations was analyzed based on reference sequence NM_000529 and NP_000520.1 (
A multiple sequence alignment was carried out in UniProtKB for the MC2R protein to demonstrate the conservation in different paralogs and orthologs within the position of the studied cases.
Human MC2R protein, known as adrenocorticotropic hormone receptor, is a member of G-protein melanocortin receptor. There is no experimentally structured model for MC2R. We conducted protein modeling based on SWISS-model (
The structural analysis was performed based on Phyre2 and DynaMut [
Interaction of the encoded protein of MC2R and MRAP with other proteins was predicted by STRING-10, a protein-protein interaction system analysis (V10.5) [
Data were analyzed by Statistical Package for Social Sciences (SPSS version 22.0, SPSS, Inc., Chicago, Ill, USA).
Three homozygous mutations including two novel mutations (c.128T > G and c.251T > A) were found in the studied patients (Figure
(a) Electropherogram of the patients having novel variants shows homozygote variants at positions c.128T > G and c.251T > A in the
Alignment of the MC2R protein at positions 43 and 84 showed conservation in different species (Figure
The modeling was based on structural experiment 6jzh (adenosine receptor A2a, soluble cytochrome b562) with coverage of amino acids 20 to 295 and identity of 27.82% for position Ile84. No structural damage was detected based on isoleucine (hydrophobic) to asparagine (hydrophilic) substitution which does not trigger any change; both amino acids are exposed to uncharged amino acid replacement. Only the interactions are influenced by the substitution (Figure
(a) Substitution of p.Ile84Asn in the
The modeling for Leu43 was based on 5tgz (cannabinoid receptor 1, flavodoxin) with the identity of 29.07% and coverage of amino acids of 26 to 291.
Based on the free Gibbs energy (ΔΔG) prediction, it was 1.42 kcal/mol and showed a stabilizing structure for Ile84Asn but decrease of molecule flexibility. The structural change based on ΔΔG for Leu43Arg was 0.711 kcal/mol which showed a stabilizing structure. It also decreased the molecule flexibility. Also, structure interaction changes were influenced by amino acid change (Figure
Our search strategy yielded 84 articles including original, case reports, and reviews. After exclusion, 33 articles were related to the
The clinical phenotype and presentation were available for 93 of the patients. About 80% of MC2R-related cases were presented at the age of <2 years (data not shown). All these patients had high levels of ACTH, and 79% of patients (73) had hyperpigmentation as the major sign of FGD; 77% showed hypoglycemia (72), 20% had seizures (19), 30% had jaundice (28), 14% had vomiting (13), 10% had respiratory stress (9), and 12% had recurrent infection (11) (Figure
Frequency of the phenotypic characterization of the reported variants in the literature.
107 of FGD patients had
Totally, 59 variants were found in the
(a) MC2R receptor has 297 amino acids and consists of 7 transmembrane domains from positions 24–49 (TM helix 1, 26–52), 59–79 (TM helix 2, 59–85), 105–126 (TM helix 3, 103–133), 148–168 (TM helix 4, 145–165), 181–199 (TM helix 5, 170–199), 218–244 (TM helix 6, 212–242), and 257–278 (TM helix 7, 255–280). This receptor consists of four cytoplasmic domains expanded in positions 50–58, 127–147, 200–217, and 279–297 and four extracellular domains 1–23, 80–104, 169–180, and 245–256. (b) MRAP consists of 172 amino acids, and positions 38–58 are located in the transmembrane domain. Reported variants of each domain and region are shown.
MC2R and MRAP proteins predicted to associate with nine proteins as follows: POMC: proopiomelanocortin, MC2R: melanocortin-2 receptor, CRH: corticotropin-releasing hormone, GNAS: GNAS complex locus, CRHR2: corticotropin-releasing hormone receptor 2, NPS: neuropeptide S, LHCGR: luteinizing hormone/choriogonadotropin receptor, CRHR1: corticotropin-releasing hormone receptor 1, and MRAP: melanocortin-2 receptor accessory protein (Figure
Interactome analysis by STRING (V10.5). Protein-protein interaction network; predicted functional partners are as follows: POMC: proopiomelanocortin, MC2R: melanocortin-2 receptor, CRH: corticotropin-releasing hormone, GNAS: GNAS complex locus, CRHR2: corticotropin-releasing hormone receptor 2, NPS: neuropeptide S, LHCGR: luteinizing hormone/choriogonadotropin receptor, CRHR1: corticotropin-releasing hormone receptor 1, and MRAP: melanocortin-2 receptor accessory protein.
The genes interacting with the adrenocorticoid receptor are shown in Figure
The genetic study of FGD is of importance. FGD is a clinical heterogeneous disorder which could lead to death if remains untreated; for example, recurrent hypoglycemia leads to mental disability which is categorized as lethal [
Mutations in
In brief, our systematic analysis showed that
Interestingly, our literature review revealed no splice or intronic variant, found to cause FGD1, while more than half of FGD2 patients (44 of 78) were due to these types of mutations. c.221G > T (p.Ser74Ile) and c.560delT (p.Val187Alafs
In addition, 2 novel mutations in 2 Iranian families are reported for the first time in patients with different age of onset. Our studied patients had hypothyroidism and hyperpigmentation. Based on prediction analysis, these variants do not make significant structural changes in the protein. The mutations p.Leu43Arg and p.Ile84Asn are located in TM1 and TM2, respectively. They may result in loss of signal transduction rather than structural disruption or ligand binding on the transmembrane protein. Regarding
Our results determined that the rate of homozygosity is high (85 of 107). Also, the study indicated that 46%
In 2014, Meimaridou et al. conducted a review article on genetics of FGD and collected mutations in different genes involved in FGD including
The enzymes and proteins shown in the interactome analysis may be a plausible explanation that patients show variable phenotypes. This makes genotype-phenotype correlation difficult to explain. As observed in the studied cases, different presentations might be due to different interactions, modifier genes, and variable expressions at different stages of life compared to other reported patients. Also, type of the variant may complicate the phenotype. Various overlapping phenotypes could be expected due to interactions of different proteins.
Our study was limited to a small number of studies in the genetics of FGD. FGD is a rare disorder according to Orphanet (
In conclusion, four
No other data were used to support this study.
All the experiments were carried out according to the Declaration of Helsinki. This study was approved by Tehran University of Medical Sciences, no: 87-02-80-7383.
The authors declare that they have no conflicts of interest.
Katayoun Heshmatzad contributed to genetic analysis of the variants, data extraction, data validation, reviewing, and editing. Nejat Mahdieh contributed to writing, reviewing, editing, and data validation. Ali Rabbani contributed to clinical analysis, reviewing, and editing. Abdolah Didban contributed to clinical analysis. Bahareh Rabbani contributed to writing, reviewing, editing, and structural and modeling analyses. Katayoun Heshmatzad and Nejat Mahdieh equally contributed to this work. All authors read and approved the final manuscript.
The authors would like to thank Shahab Aghaei for the support in providing Figure
Supplementary Materials: information on genetic characterization of the reported