pseudohypoparathyroidism type 1B (PHP1B)
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Pathology
- PTH-resistant hypocalcemia & hyperphosphatemia
Genetics
- associated with genetic variations in STX16
- in some cases microdeletions involving STX16 appear to cause loss of methylation at exon A/B of the GNAS gene, resulting in PHP1B
Clinical manifestations
- patients lack developmental defects characteristic of Albright hereditary osteodystrophy
- patients typically show no other endocrine abnormalities besides resistance to PTH
- fear of choking while swallowing[1]
- vomiting[1]
- inspiratory stridor
- Chvostek's sign may be positive
- hypertension may occur due to anxiety
Laboratory
- serum calcium: hypocalcemia
- serum phosphate: hyperphosphatemia
- serum PTH elevated[1]
- serum 25-hydroxyvitamin D may be low
- serum magnesium (may be effects on PTH)[1]
Management
- treatment of hypocalcemia
- infusion of calcium gluconate
- then oral oral calcium supplementation with calcitriol
- calcitriol: start 5 ug/day, then taper
- treatment of hyperphosphatemia
- phosphorus binder sevelamer carbonate
- avoid precipitation of calcium phosphate (calciphylaxis)
- see calcium x phosphate product[1]
More general terms
References
- ↑ 1.0 1.1 1.2 1.3 1.4 Carroll RW, Katz ML, Paul E, Juppner H. Case 17-2017 - A 14-Year-Old Boy with Acute Fear of Choking while Swallowing. N Engl J Med 2017; 376:2266-2275. June 8, 2017 <PubMed> PMID: https://www.ncbi.nlm.nih.gov/pubmed/28591527 <Internet> http://www.nejm.org/doi/full/10.1056/NEJMcpc1616019