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Pseudohypoparathyroidism Type Ia/Ib

Genetic disorders of PTH-receptor signaling causing target-organ resistance to parathyroid hormone.

Written by: Saygı Hospital Health Guide Editorial Board
Published:

This content is for general information; please consult your physician for diagnosis and treatment.

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What is Pseudohypoparathyroidism Type Ia/Ib?

Pseudohypoparathyroidism type Ia (PHP-Ia) results from heterozygous loss-of-function mutations on the maternal GNAS allele, reducing Gs-alpha activity. Patients show resistance to PTH, TSH, gonadotropins, and GHRH, plus the somatic features of Albright hereditary osteodystrophy (AHO).

Pseudohypoparathyroidism type Ib (PHP-Ib) is caused by epigenetic defects (loss of methylation) at the GNAS locus restricted to renal expression, producing isolated PTH resistance without AHO features.

Diagnosis combines characteristic biochemistry (low calcium, high phosphate, elevated PTH, normal 25-OH vitamin D) with confirmatory GNAS sequencing and methylation analysis.

Symptoms

PHP-Ia: short stature, round face, brachydactyly (especially short 4th–5th metacarpals), subcutaneous ossifications, obesity, intellectual disability
Hypocalcemia: paresthesia, muscle cramps, tetany, Chvostek/Trousseau signs, seizures
Hyperphosphatemia and basal ganglia calcifications (chronic)
PHP-Ia additional resistance: hypothyroidism, hypogonadism, growth hormone deficiency
PHP-Ib: hypocalcemic symptoms only, normal stature and appearance

Risk Factors

Maternal inheritance of GNAS mutation (PHP-Ia)
Imprinting defects at GNAS locus (PHP-Ib, sporadic or familial)
Family history of AHO or unexplained hypocalcemia
Consanguinity (autosomal recessive familial PHP-Ib variants)

When to See a Doctor?

If you experience any of the following symptoms, seek medical attention promptly:

  • Recurrent hypocalcemic symptoms with elevated PTH and high phosphate
  • Childhood with short metacarpals, round face, and short stature
  • Family member diagnosed with AHO or PHP
  • Tetany or seizures triggered by hypocalcemia

Treatment Methods

01
Calcium supplementation (1000–2000 mg elemental/day)
02
Active vitamin D analog (calcitriol 0.25–1 μg/day, titrated to normal-low calcium)
03
Avoid hypercalciuria — monitor 24-hour urinary calcium and renal ultrasound
04
Treat associated hormone resistances (levothyroxine for hypothyroidism, sex hormone replacement for hypogonadism)
05
Phosphate-restricted diet, possible phosphate binders if hyperphosphatemia persists
06
Genetic counseling and family screening (parent-of-origin matters)
07
Multidisciplinary follow-up: endocrinology, genetics, orthopedics for AHO

Which Department to Visit?

You can visit our Endokrinoloji department for these complaints. Our specialist physicians will create the most suitable treatment plan for you.

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Health Disclaimer: The information on this page is prepared for general informational purposes only. It does not replace medical diagnosis and treatment. Please consult your physician for your complaints. Saygı Hospital does not accept responsibility for actions taken based on the information on this page.