Methylation-specific multiplex-ligation-dependent probe amplification as a rapid molecular diagnostic tool for pseudohypoparathyroidism type 1b.

Pseudohypoparathyroidism type 1b (PHP1b) is a rare metabolic bone disorder characterized by isolated renal parathyroid hormone resistance. The disorder is almost always associated with an imprinting defect or deletions in the differentially methylated region of the GNAS locus located on chromosome 20q13. In addition to the epigenetic and genetic aberrations of the differentially methylated region, PHP1b can also result from a deletion of STX16, a long-range control element of methylation at the GNAS locus located centromeric of GNAS. This report describes the utilization of a recently described methylation-specific multiplex-ligation-dependent probe amplification assay for high-throughput molecular analysis of a patient with the clinical diagnosis of PHP1b. Although more patients will need to be tested to confirm this, methylation-specific multiplex-ligation-dependent probe amplification in our hands proved to be a rapid, sensitive, and fairly easy-to-interpret assay that can be used in lieu of Southern blot analysis to diagnose PHP1b.