Clinical And Genetic Analysis Of Patients With Pseudohypoparathyroidism

Background:The term pseudohypoparathyroidism(PHP) indicates a group of heterogeneous and rare disorders whose common feature is represented by impaired signaling of various hormones, primarily PTH. The two main subtypes of PHP are PHP type la and Ib(PHP-Ia, PHP-Ib). PHP-la is characterized by multi-hormone resistance and typical Albright’s hereditary osteodystrophy(AHO), while PHP-Ib only involves PTH resistance. PHP is caused by molecular alterations within or upstream of the imprinted GNAS gene, which encodes alpha-subunit of the stimulatory G protein(Gsa) and other products, leading to abnormal signaling of cAMP-dependent pathways. Recent studies have suggested clinical overlaps between the two subtypes, so the genetic analysis becomes more crucial to the diagnosis and classification. Meanwhile, it can be applied to prenatal diagnosis. So the aim of this study was to investigate the clinical and genetic characteristics in PHP patients, and provide further insight for the diagnosis and management of patients with this disease.Methods:Two patients with clinically diagnosed PHP from Sir Run Run Shaw Hospital were recruited for this study, as well as their kindred. Clinical manifestations and lab examinations were retrospectively analyzed. Diagnosis and management of pseudohypoparathyroidism were discussed referring to literature. Genomic DNA was collected from the blood samples of these patients and their kindred (altogether eight samples). The 1-13 exons were detected by PCR and direct sequencing, while the methylation status of GNAS gene was detected by methylation-specific PCR technique(MSP).Results:1. This study diagnosed two patients with PHP according to their clinical manifestations and lab tests. Because of hypocalcemia, hyperphosphatemia, elevated serum PTH and TSH, as well as AHO phenotype, two cases were classified into PHP-Ia clinically. The mother of one patient presented with short stature in the absence of PTH resistance. By detecting the 1-13 exons and the methylation status of GNAS, one case was confirmed as PHP-Ia and her mother as PPHP.2. A1-base pair deletion of exon 4 in GNAS gene was detected in one patient and her mother, i.e. c.310de1G (p.Glu104Lysfs*7), resulting in frameshift and truncated gene products. The mutation is first reported. However, mutations of exon 1-13 were not found in the other patient with PHP-Ia or her kindred.3. No abnormal methylation of DMRs in the GNAS gene was detected in two PHP-Ia patients or their kindred.Conclusion:1. The onset of PHP-Ia could happen at an early age by epileptic seizure or tetany. Patients with PHP-Ia have AHO phenotype and multi-hormone resistance in addition to PTH. Intracranial calcification is a common complication.2. The detection of the GNAS exons revealed a novel mutation c.310delG (p.Glu104Lysfs*7), which might lead to a premature stop codon in the new frame, thus producing truncated gene products and impaired Gsa. However, patients diagnosed with PHP-1a by clinical manifestions do not always have mutation of GNAS exons.3. The analysis of the three DMR regions suggested normal imprinting of the GNAS gene, thus excluding the patients from PHP-Ib.4. To determine the subtypes of PHP depends largely on the molecular diagnosis.