Endocrine Abstracts

Inactivating PTH/PTHrP signaling disorders (iPPSDs, historically named pseudohypoparathyroidism (PHP)) are primarily characterized by end-organ resistance to parathormone (PTH), which leads to hypocalcemia, hyperphosphatemia and elevated PTH levels. The extent to which bone is responsive to PTH in these patients remains controversial. Until now, variable bone phenotypes have been associated to different subtypes of iPPSDs and increased concentrations of bone turnover markers (BTMs) are described. Persistently elevated PTH levels may cause bone abnormalities similar to what observed in hyperparathyroidism (osteitis fibrosa and rickets). Moreover, data about bone mineral density (BMD) are sparse and report both normal, increased or decreased values. Aim of the present study is to characterize bone metabolism in a cohort of iPPSD patients. We collected data about BMD, vertebral morphometry and BTMs to describe bone abnormalities, aiming to investigate whether there is a relationship with PTH levels or iPPSD subtype. We enrolled 21 patients (62% females, mean age 39.6±11.3 years) diagnosed with iPPSDs and regularly followed-up at our Centre. Six patients were diagnosed with iPPSD2/PHP1A (28.6%), 13 patients with iPPSD3/PHP1B (61.8%), 1 patient with iPPSD4/Acrodysostosis type 1 and 1 patient had no detected mutations. In our cohort PTH levels show significant positive correlation with both CTX and bone alkaline phosphatase (bALP) levels (CTX: r=0.482, P=0.02; bALP: r=0.508, P=0.02). Bone turnover markers were not significantly different between iPPSD2/PHP1A and iPPSD3/PHP1B patients. As for BMD values, mean lumbar, femoral neck and total hip scores were 1.083± 0.18, 0.856±0.18 and 0.968±0.18 g/cm² respectively, with no significant difference between iPPSD2/PHP1A and iPPSD3/PHP1B patients. One patient (5%) was diagnosed with osteoporosis and one patient with osteopenia according to Z and T-scores respectively, as expected for age and sex. Fractures were described in 2 patients with pre-existing comorbidities. As for vertebral morphometry, we described rickets-like signs in 39% (7/18) of patients, with no difference among various iPPSD subtypes. It is worth report one patient affected by iPPSD3/PHP1B, who presented PTH >1000 pg/ml at diagnosis with concomitant cystic bone lesions (compatible with brown tumors/osteitis fibrosa cystica) at multiple sites. In conclusion, our study confirms previous reported data about bone metabolism and phenotypes in iPPSDs. According to BTMs and skeletal remodeling, bone seems to be responsive to PTH in both iPPSD2/PHP1A and iPPSD3/PHP1B. Although these are preliminary data that we are expanding through comparative studies, they could have clinical impact on management, suggesting to control PTH levels on optimal range to avoid negative impact on bone.