Hypoparathyroidism

Inherited condition caused by a lack of parathyroid hormone resulting in hypocalcemia and hyperphosphatemia and their clinical manifestations.

Endocrine disorder of the parathyroid gland as a consequence of primary or secondary lack of parathormone secretion. Primary forms result from many rare diseases.

Primary hypoparathyroidism is rare; fewer than 1000 cases of the idiopathic form, familial or not, have been reported. Rare in children.

• Both autosomal dominant (gene map locus 3q13) and X-linked (also related to a mutation in the parathyroid hormone gene) forms of familial idiopathic hypoparathyroidism have been reported.
• X-Linked Agenesis of Parathyroid Gland: Gene map locus is Xq26-q27.
• Hypoparathyroidism-Retardation-Dysmorphism Syndrome (HRDS): Autosomal recessive.
• Sanjad-Sakati Syndrome (Congenital Hypoparathyroidism with Growth Retardation, Developmental Delay, and Dysmorphism): Gene map location is 1q42-43.

Primary and secondary hypoparathyroidism are conditions in which there is a deficiency of parathyroid hormone. This deficiency induces hypocalcemia and decreases calcium resorption from bone and calcium absorption from gastrointestinal tract by preventing synthesis of vitamin D. The lack of parathyroid hormone stops the osteolytic effect of vitamin D and results in a decrease in bone metabolism. The decreased calcium concentration in the motor plate induces neuromuscular hyperexcitability. A very sensitive extracellular calcium-sensing receptor, coupled to a G protein, has been isolated from parathyroid, kidney, and brain cells. Some autosomal dominant forms of hypocalcemia result from activating mutations of this extracellular calcium-sensing receptor, which inhibits parathyroid hormone exocytosis (mechanism is unknown).

In primary hyperparathyroidism, note hypocalcemia, hypomagnesemia, hyperphosphoremia, and low serum level of parathyroid hormone. Urinary excretion of calcium, phosphorus, and cAMP is decreased. Ellsworth Howard test (infusion of 200 IU of parathyroid hormone) induces an increase of cAMP and phosphaturia. Intracerebral calcifications on CT scan.

In neonates, the symptoms of hyperparathyroidism are respiratory distress, cyanosis, apnea, hypertonia, agitation, and tetany. In infants, the symptoms are seizures and tinnitus crisis with inspiratory stridor, laryngospasm, and unexplained tachycardia. In children, tinnitus is the most frequent sign, with seizures that can be typical or not. Hypocalcemia may be life-threatening and can cause nephrocalcinosis and renal lithiasis.

Primary forms are related to many rare diseases, mostly genetically inherited.

Autoimmune diseases: Type I autoimmune polyglandular syndrome (or HAM syndrome) results in primary hypoparathyroidism by 10 years of age as a result of destruction of the parathyroids. Other types of autoimmune hypoparathyroidism may exist alone, in sporadic or familial forms.

Congenital diseases and syndromeswith agenesis or hypoplasia of the parathyroid glands include the following:

• Isolated primary hypoparathyroidism
• X-linked primary hypoparathyroidism (band Xq26-Xq27)
• X autosomal recessive primary hypoparathyroidism
• Branchial dysgenesis (DiGeorge syndrome)
• Chromosomal defects dup(1q), del(5p), dup(8q), del(10q), del(22q)
• Monogenic hypoparathyroidism
• Isolated autosomal dominant conditions
• Isolated autosomal recessive conditions
• Velocardiofacial syndrome
• Zellweger ...