[Pseudohypoparathyroidism and the concept of hormonal resistance. Diagnosis, classification and therapy].

CLINICAL AND BIOLOGICAL FEATURES: Pseudohypoparathyroidism is a heterogenous group of conditions with variable clinical and biological features and a common resistance to parathormone (PTH) leading to hypocalcemia associated with high levels of PTH. The classification of these conditions depends on the expression of Albright's osteodystrophy and response to exogenous parathormone: urine phosphorus and cyclic AMP excretion. TYPE IA: The characteristic feature is Albright's osteodystrophy associated with a totally negative response to exogenous PTH. Defective protein G is the cause. Pseudopseudohypoparathyroidism is defined by Albright's osteodystrophy without resistance to PTH. This condition occurs in families with type Ia pseudohypoparathyroidism. It is also related to a defect in protein G. TYPE IB: Type Ib corresponds to PTH resistance alone, without Albright's osteodystrophy. This condition is apparently secondary to anomalous regulation of the gene coding the PTH receptor. TYPE II: Type II is defined by the inconstant presence of Albright's osteodystrophy and a dissociated response to PTH: urinary phosphorus does not respond to PTH (hormone resistance) but urine cyclic AMP increases in response to PTH suggesting anomalous signal transduction downstream from adenyl cyclase. TREATMENT: In all types, treatment is based on combining calcium therapy and vitamin D supplementation under rigorously controlled conditions.