Familial isolated hypoparathyroidism due to impaired PTH secretion

Familial isolated hypoparathyroidism due to impaired PTH secretion is a rare inherited endocrine disorder characterized by low or absent parathyroid hormone (PTH) secretion in the absence of other associated developmental or autoimmune abnormalities. Unlike syndromic forms of hypoparathyroidism (such as DiGeorge syndrome or autoimmune polyendocrinopathy), this condition affects the parathyroid glands in isolation, resulting in deficient PTH production or release despite structurally present parathyroid tissue. PTH is essential for maintaining calcium and phosphorus balance in the body, and its deficiency leads to hypocalcemia (low blood calcium) and hyperphosphatemia (high blood phosphorus). The condition primarily affects the endocrine and neuromuscular systems. Key clinical features include muscle cramps, tingling and numbness in the hands, feet, and around the mouth (paresthesias), muscle spasms (tetany), and in severe cases, seizures due to critically low calcium levels. Chronic hypocalcemia can also lead to calcification of the basal ganglia in the brain, cataracts, dental abnormalities, and cardiac rhythm disturbances. Symptoms may present in infancy, childhood, or later in life depending on the specific genetic cause and severity of the PTH secretion defect. Several genetic causes have been identified, including mutations in the PTH gene itself, the GCM2 (GCMB) gene which is a transcription factor critical for parathyroid gland development and function, and gain-of-function mutations in the calcium-sensing receptor (CASR) gene that cause the parathyroid glands to inappropriately suppress PTH secretion at normal or low calcium levels. Treatment consists of lifelong supplementation with oral calcium and active vitamin D analogs (such as calcitriol or alfacalcidol) to maintain serum calcium levels within an acceptable range. Recombinant PTH (such as teriparatide or PTH 1-84) may be considered in refractory cases. Regular monitoring of serum calcium, phosphorus, renal function, and urinary calcium excretion is essential to prevent complications such as nephrocalcinosis and kidney stones.

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