Separation of pseudohypoparathyroidism into types I and II using only basal nephrogenous cAMP determinations

The separation of pseudohypoparathyroidism (PHP) into Type I (non responders, usually with signs of Allright's hereditary osteodystrophy--AHO--and resistance to other hormones secretion) and Type II (responders) is classically done with the parathyroid hormone (PTH) infusion test using as criterion of cellular response total urinary cAMP determinations. But since total urinary cAMP is not an accurate index of intracellular cAMP production from the renal tubular cells--as is nephrogenous cAMP (NcAMP)--it was considered worthwhile to examine the diagnostic value of NcAMP in this case. A total of 12 PHP patients were studied along with 19 controls of corresponding age and sex. All 31 persons underwent--inter alia--to a 2 hrs I.V. PTH infusion test with 500 I.U. of human 1-34 PTH. Using as criterion total urinary cAMP, the PHP patients were separated into Type I (7 patients, of whom 5 with AHO) and Type II (5 patients). The same results were obtained when the NcAMP stimulation values were used instead, although in PHP Type II patients the mean increase of NcAMP at the end of PTH infusion was 2 fold than the corresponding increase of total urinary cAMP. But the most impressing finding was that the separation of PHP patients to the Types I or II was possible by using the basal NcAMP values only (NcAMP basal values ranged from 0.35 to 0.56 nmols/100 ml GFR in Type I and from 0.93 to 1.75 in Type II PHP). These results render possible the use of NcAMP basal values as a screening test for the separation of PHP patients into Types I and II.