Abstract: Clinical features of and genetic mutations in two cases of pseudohypoparathyroidism type Ⅰa（PHPⅠa） with early-onset skin nodules were analyzed. Both of the two patients were males, and their ages at onset were 2 and 3 months respectively. They both presented with early-onset skin nodules as the main clinical manifestation, and were clinically characterized by a round face, short neck and early obesity. Histopathological examination of skin lesions showed subcutaneous ectopic osteogenesis in both patients. The first patient had low blood calcium, high blood phosphorus, high parathyroid hormone （PTH）, and gene sequencing showed a heterozygous mutation c.399delT causing a T base deletion at position 399 in exon 5 of the GNAS gene. The second patient had normal blood calcium and phosphorus levels as well as normal PTH levels at early stage, and gene sequencing showed a heterozygous mutation c.939delT causing a T base deletion at position 939 in exon 9 of the GNAS gene. The blood PTH level was found to increase in the second patient after 1-year follow-up. Both the patients were confirmedly diagnosed with PHPⅠa. After treatment with vitamin D3, no new skin nodules occurred, and the blood calcium and phosphorus levels returned to normal.

Key words: Pseudohypoparathyroidism, Cholecalciferol, DNA mutational analysis, Skin manifestations, GNAS gene