Biallelic expression of the Gsalpha gene in human bone and adipose tissue

Mutations of the Gsα gene inherited from the mother lead to pseudohypoparathyroidism (PHP) type Ia (PHP Ia), in which Albright's hereditary osteodistrophy is associated to resistance to the action of different hormones, whereas the same mutations inherited from the father lead to isolated Albright's hereditary osteodistrophy [pseudo-PHP (PPHP)]. Accordingly, it has been suggested that Gsα is under tissue-specific imprinting control, and recent studies provided evidence for a predominant maternal origin of Gsα transcripts in different endocrine organs involved in the PHP Ia phenotype. To establish whether Gsα is imprinted also in tissues that are site of alteration both in PHP Ia and PPHP, we selected 20 bone and 10 adipose tissue samples, which were heterozygous for a known polymorphism in exon 5. Expression from both parental alleles was evaluated by RT-PCR and enzymatic digestion of the resulting fragments. By this approach, the great majority of the samples analyzed showed an equal expression of the two alleles. Our results provide evidence for the absence of Gsα imprinting in human bone and fat and suggest that the clinical finding of osteodystrophy and obesity in PHP Ia and PPHP patients despite the presence of a normal Gsα allele is likely due to Gsα haploinsufficiency in these tissues.