BACKGROUND: Although linkage studies strongly suggest that proopiomelanocortin (POMC) alterations could play a role in the genetic predisposition to obesity, systematic POMC mutational analysis did not completely confirm this hypothesis.

OBJECTIVES: To verify the presence of mutations of the POMC coding region in Italian children with very early onset obesity.

SUBJECTS AND METHODS: Eighty seven unrelated Italian obese children and adolescents were studied. Mean age at obesity onset was 4.7±2.5 y. The POMC gene coding region was screened using single-strand conformation polymorphism (SSCP) analysis. Bi-directional automatic sequencing of PCR products was performed for all individuals who showed an aberrant SSCP pattern.

RESULTS: Three new mutations have been identified in the heterozygous state in three patients:(a) G3834C, resulting in the substitution of Ser with Thr at codon 7 within the POMC signal peptide;(b) C3840T, resulting in the substitution of Ser with Leu at codon 9 of the pre-proopiomelanocortin signal peptide; and (c) C7406G, producing the substitution of Arg with Gly at codon 236 within the β-endorphin peptide. A polymorphism consisting of a 9 bp insertion, AGC AGC CGC, between position 6997 and 6998 has been found at the heterozygous state in nine patients. They showed leptin levels adjusted for BMI, gender and pubertal stage significantly higher than obese subjects homozyous for the POMC wild-type allele.

CONCLUSIONS: Mutations in codons 7 and 9 of the signal peptide may alter the translocation of the pre-proopiomelanocortin into the endoplasmic reticulum and, therefore, can be implicated in obesity. Although further studies are required, the polymorphism between position 6997 and 6998 may represent one of the genetic variations that explain the linkage between obesity and POMC.