A novel GNAS mutation inherited from probable maternal mosaicism causes two siblings with pseudohypoparathyroidism type 1A.

Objectives Objectives Pseudohypoparathyroidism type 1A (PHP1A) is caused by maternal inheritance of GNAS mutations. It is characterized by the resistance to several hormones, primarily the parathyroid hormone (PTH), and the features of Albright's hereditary osteodystrophy. Case presentation Here, we present a family comprised two affected brothers with PHP1A and identify a novel mutation (c.277C>T) in the GNAS gene. The siblings developed a slightly different presentation in the same clinical condition. Although both patients presented with PTH resistance, which is the hallmark of PHP, the proband showed the thyroid-stimulating hormone resistance with the progression of heterotopic ossification from skin and subcutaneous tissue into deep connective tissue, while the younger brother with normocalcemia did not show the resistance to other hormones. The patients may inherit the mutation from their mother who presumably carries the mutation as a mosaicism. Conclusions Our case highlights the significance of considering mosaicism as an explanation for apparent de novo cases of pseudohypoparathyroidism.