Condition associated primarily with resistance to the parathyroid hormone

Aetiology

• Genetic defect - dysfunction of Gs alpha subunit (GNAS 1 gene)

Pathophysiology

• End organ resistance to PTH due to mutation of the Gs⍺-protein, which is coupled to the PTH receptor

Clinical features

• Bone abnormalities (McCune Albright)
• Obesity
• Subcutaneous calcification
• Learning disability
• Brachdactyly (shortened 4th metacarpal)

Investigations

• Bloods: calcium will be low but PTH concentrations are elevated due to PTH resistance

Pseudo-pseudohypoparathyroidism

• Describes the phenotypic defects of pseudohypoparathyroidism (Albright's herditary osteodystrophy) but without any abnormalities in calcium metabolism
• Individuals with this condition may share the same gene defect as those with pseudohypoparathyroidism and be members of the same families