Evidence of hormone resistance in a pseudo-pseudohypoparathyroidism patient with a novel paternal mutation in GNAS.

CONTEXT

Loss-of-function GNAS mutations lead to hormone resistance and Albright's hereditary osteodystrophy (AHO) when maternally inherited, i.e. pseudohypoparathyroidism-Ia (PHPIa), but cause AHO alone when located on the paternal allele, i.e. pseudoPHP (PPHP).

OBJECTIVE

We aimed to establish the molecular diagnosis in a patient with AHO and evidence of hormone resistance.

CASE

The patient is a female who presented at the age of 13.5years with short stature and multiple AHO features. No evidence for TSH or gonadotropin-resistance was present. Serum calcium and vitamin D levels were normal. However, serum PTH was elevated on multiple occasions (64-178pg/mL, normal: 9-52) and growth hormone response to clonidine or L-DOPA was blunted, suggesting hormone resistance and PHP-Ia. The patient had diminished erythrocyte Gsα activity and a novel heterozygous GNAS mutation (c.328 G>C; p.A109P). The mother lacked the mutation, and the father's DNA was not available. Hence, a diagnosis of PPHP also appeared possible, supported by low birth weight and a lack of AHO features associated predominantly with PHP-Ia, i.e. obesity and cognitive impairment. To determine the parental origin of the mutation, we amplified the paternally expressed A/B and biallelically expressed Gsα transcripts from the patient's peripheral blood RNA. While both wild-type and mutant nucleotides were detected in the Gsα amplicon, only the mutant nucleotide was present in the A/B amplicon, indicating that the mutation was paternal.

CONCLUSION

These findings suggest that PTH and other hormone resistance may not be an exclusive feature of PHP-Ia and could also be observed in patients with PPHP.