In summary, the new variant c.166A > T (p.Ile56Phe) on exon 2 of GNAS gene, originated on maternal allele, has been described in a young girl as likely causative of a new multisystemic disorder characterized by hyponatremia, subclinical hyperthyroidism, subclinical hypercortisolism, precocious thelarche and pubarche and congenital bone abnormalities. This evidence concerns the gene GNAS and Hyponatremia.