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pseudohypoparathyroidism type 1B (PHP1B)
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]
General
pseudohypoparathyroidism
Database Correlations
OMIM 603233
References
- 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
PMID: 28591527
http://www.nejm.org/doi/full/10.1056/NEJMcpc1616019