Lab Med Online.  2017 Apr;7(2):83-87. 10.3343/lmo.2017.7.2.83.

A Case of Pseudohypoparathyroidism Type Ib Caused by Aberrant Methylation in the GNAS Complex Locus

Affiliations
  • 1Department of Laboratory Medicine, College of Medicine, The Catholic University of Korea, Seoul, Korea. microkim@catholic.ac.kr suhbk@catholic.ac.kr
  • 2Department of Pediatrics, College of Medicine, The Catholic University of Korea, Seoul, Korea. microkim@catholic.ac.kr suhbk@catholic.ac.kr

Abstract

Pseudohypoparathyroidism (PHP) is a rare disorder caused by genetic and epigenetic aberrations in the GNAS complex locus resulting in impaired expression of stimulatory G protein (Gsα). PHP type Ib (PHP-Ib) is characterized by hypocalcemia and hyperphosphatemia due to renal resistance to the parathyroid hormone, and is distinguished from PHP-Ia by the absence of osteodystrophic features. An 11-yr-old boy presented with poor oral intake and cramping lower limb pain after physical activity. Laboratory studies revealed hypocalcemia, hyperphosphatemia, and increased parathyroid hormone levels. The GNAS complex locus was evaluated using the methylation-specific multiplex ligation-dependent probe amplification (MS-MLPA) assay. Gain of methylation in the NESP55 domain and loss of methylation in the antisense (AS) transcript, XL, and A/B domains in the maternal allele were observed. Consequently, we present a case of PHP-Ib diagnosed using MS-MLPA.

Keyword

Pseudohypoparathyroidism; Methylation; GNAS complex locus; MLPA

MeSH Terms

Alleles
Epigenomics
GTP-Binding Proteins
Humans
Hyperphosphatemia
Hypocalcemia
Lower Extremity
Male
Methylation*
Motor Activity
Multiplex Polymerase Chain Reaction
Muscle Cramp
Parathyroid Hormone
Pseudohypoparathyroidism*
GTP-Binding Proteins
Parathyroid Hormone
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