The objective of this study was to describe a new mutation in GNAS in a family with pseudohypoparathyroidism type Ia (PHP Ia), a rare osteometabolic disease. An 8-month-old boy was seen by an Endocrinologist due to obesity and low growth velocity. Noteworthy, his mother exhibited typical Albright hereditary osteodystrophy (AHO) phenotype. The clinical diagnosis of PHP Ia was suspected. The GNAS coding region from mother and son was amplified and directly sequenced. A novel heterozygous missense mutation (c.673T>C) was identified in exon 5 in both patients. In this family, the mother's clinical picture was the clue for the son's diagnosis. Molecular analysis of GNAS confirmed the diagnosis of PHP Ia in both patients and the child's early diagnosis was possible. Moreover, this novel missense substitution expands the spectrum of GNAS mutations associated with this disorder and allows for genetic counseling of this family.
