PTH and obesity due to melanocortin 4 receptor deficiency: The historical classification of PHP differentiated PHP I from PHP II on the basis of the variation in urinary cAMP levels after exogenous administration of synthetic PTH [15, 16], and further distinguished PHP I in type a, b and c [17], on the basis of hormonal resistances and the presence of the Albright Hereditary Osteodistrophy phenotype [18, 19], which includes peculiar physical features such as short stature, early onset obesity, round face, mental retardation, subcutaneous ectopic ossifications and brachydactyly (Table 1).