Pro-opiomelanocortin Deficiency
Synonyms
2
Overview
Pro-opiomelanocortin (POMC) deficiency is a form of monogenic obesity resulting in severe early-onset obesity, adrenal insufficiency, red hair and pale skin. It is has been described in less than 10 patients.
Symptoms
Patients with POMC deficiency usually present in the neonatal period with hypoglycaemic seizures, hyperbilirubinaemia and cholestasis to due to secondary congenital hypocortisolism. Hyperphagia is noted from the first weeks of life leading to severe obesity before one year of age. Subclinical hypothyroidism was also reported.
Causes
Complete POMC deficiency is transmitted as an autosomal recessive trait and is caused by homozygous or compound heterozygous loss-of-function mutations in the POMC gene (chromosome 2p23.3). POMC is regulated by leptin and is cleaved by prohormone convertases to produce the melanocortin receptor (MC-R) ligands adrenocorticotrophin (ACTH) and melanocyte-stimulating hormones (MSH) alpha, beta and gamma. The red hair pigmentation, adrenal insufficiency and obesity are caused by deficiencies in the ligands and subsequent lack of activation of the MC1, MC2, and MC4 receptors, respectively. In addition to complete POMC deficiency, a few individuals with isolated deficiency of the MC4-R POMC-derived ligand, beta-MSH, have also been described. These individuals carry a distinctPOMC mutation in the region encoding beta-MSH. This isolated deficiency of beta-MSH leads to a clinical phenotype similar to that observed in MC4-R deficiency (childhood obesity, hyperphagia and increased linear growth) but is not associated with red hair or adrenal insufficiency.
Diagnosis
Diagnosis of complete POMC deficiency may be suspected on the basis of the clinical manifestations of the disease and can be confirmed by identification of mutations in the POMC gene. Analysis of the serum reveals an absence of pituitary-derived POMC peptides, even after stimulation. Differential diagnosis includes combined pituitary hormone deficiencies, which can be excludedby multiple pituitary hormone stimulation tests.
Treatment
At present, there is no specific treatment. The neonatal complications of POMC deficiency may lead to lethal hepatic failure if left untreated, with patients requiring prompt and long-term hydrocortisone substitution therapy. Advances in melanocortin peptide therapy may lead to the development of MC4R agonists capable of improving melanocortin function in these patients. However, an initial 3-month trail with intranasal administration the ACTH 4-10 melancortin fragment did not lead to a reduction in body weight. Administration of thyroid hormone was also found to have no effect on the obesity. Although the specific prognosis for this disease has not yet been defined, it is likely these patients are at increased risk of complications (cardiovascular disease, cancer and type 2 diabetes) present in other obese patients.