Theophylline Treatment for Pseudohypoparathyroidism

Pseudohypoparathyroidism (PHP) is a rare, genetic disorder caused by impaired stimulatory G protein (Gsα) signaling through downregulation of the gene, GNAS. The resultant hormone abnormalities can be treated with hormone replacement therapy, but other aspects of the disorder such as early-onset obesity and premature epiphyseal closure are without effective treatment options. Gsα signaling is essential for the normal hormonal function of the pituitary, thyroid, gonads, renal proximal tubules and hypothalamus. While many of the resulting hormone deficiencies can be treated with hormone replacement therapy (HRT), HRT is not an effective therapy for the severe early-onset obesity and short stature which are major features of the PHP phenotype. Therefore, the goal of this proposal is to test the efficacy of upstream therapy aimed at correcting the function of two Gsα-dependent receptors responsible for the obesity (melanocortin-4 receptor, MC4R) and short stature (parathyroid hormone, PTH, receptor) phenotype in children with PHP. Gsα-coupled receptor signaling cascade begins with an increase in cyclic adenosine monophosphate (cAMP) which is rapidly degraded by the enzyme phosphodiesterase (PDE). PDE inhibitors act by prolonging cAMP signaling by decreasing the rate of degradation. Given that patients with PHP have reduced, but not completely absent, cAMP production, the investigators seek to test the hypothesis that the PDE inhibitor theophylline will reduce BMI, glucose intolerance, and hormone resistance in children and young adults with PHP through improved Gsα-coupled receptor signaling. The investigators will conduct a 52-week randomized, placebo controlled clinical trial of theophylline in children and young adults with PHP. Theophylline is a non-selective PDE inhibitor that is generically available and has a long history of use in pediatric patients, making it an ideal drug for re-purposing in youth with PHP. Furthermore, the pharmacokinetics of theophylline are well understood and serum drug levels are easily measured. The investigators primary outcome is change in body mass index. Secondary outcome measures include change in glucose tolerance and HRT dose. Anticipating a 10% dropout rate, the investigators will enroll 34 patients and expect that 30 patients will complete the study.