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Familial isolated hyperparathyroidism
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Condition

Familial isolated hyperparathyroidism

Familial isolated hyperparathyroidism is an inherited condition characterized by overactive parathyroid glands, leading to elevated calcium levels in the blood.

Overview

Familial isolated hyperparathyroidism is an inherited condition characterized by overactive parathyroid glands (hyperparathyroidism). The four parathyroid glands, located in the neck, release a hormone called parathyroid hormone that regulates the amount of calcium in the blood.

In people with this condition, the overproduction of parathyroid hormone leads to elevated levels of calcium in the blood (hypercalcemia). This can cause several signs and symptoms, including:

  • Kidney stones
  • Nausea and vomiting
  • High blood pressure (hypertension)
  • Thinning of the bones
  • Weakness and fatigue

Many affected individuals develop one or more noncancerous (benign) tumors called adenomas. While typically only one gland is affected, more than one may develop an adenoma. Rarely, these tumors can become cancerous, known as parathyroid carcinoma.

The condition may not be diagnosed until adulthood. Often, the first indication is the discovery of elevated calcium levels during a routine blood test, even in the absence of symptoms.

Frequency

The prevalence of familial isolated hyperparathyroidism is unknown. It accounts for 1 percent of all cases of primary hyperparathyroidism.

Causes

Familial isolated hyperparathyroidism can be caused by variants (mutations) in the MEN1, CDC73, or CASR genes. Certain variants in the GCM2 gene may also increase the risk of developing the condition.

  • MEN1 and CDC73: These genes provide instructions for making proteins that act as tumor suppressors. Variants in these genes lead to altered proteins that cannot effectively control cell growth, resulting in enlarged glands (hyperplasia) or adenomas.
  • CASR: This gene produces the calcium-sensing receptor (CaSR). Variants associated with this condition cause the production of a version of the CaSR protein that requires higher calcium levels to signal the body to stop producing parathyroid hormone. Consequently, hormone production continues even when calcium levels are already elevated.
  • GCM2: Variants in this gene can lead to the production of a protein that allows for increased parathyroid hormone production, resulting in higher calcium levels.

In many cases, no identified genetic variant is found, suggesting other unknown genes may be involved.

Inheritance

This condition is inherited in an autosomal dominant pattern, meaning one copy of the altered gene in each cell is sufficient to cause the disorder.

Frequently Asked Questions

Elevated calcium prompts measurement of parathyroid hormone (PTH); a high or inappropriately normal PTH with hypercalcemia points to primary hyperparathyroidism. If imaging (ultrasound or sestamibi scan) reveals a single or multiple parathyroid adenomas and there’s a family history of similar findings, clinicians suspect the familial isolated form. Genetic testing for MEN1, CDC73, CASR, or GCM2 variants then confirms the diagnosis.
Surgical removal of the overactive gland(s) is the definitive therapy and often cures hypercalcemia. Minimally invasive parathyroidectomy guided by pre‑operative imaging is preferred. If surgery is not feasible or the patient has mild disease, careful monitoring of calcium, kidney function, and bone density, along with hydration and avoidance of calcium‑rich supplements, may be used.
Chronic hypercalcemia can lead to kidney stones, nephrocalcinosis, reduced kidney function, osteoporosis or fractures, hypertension, and, rarely, parathyroid carcinoma. Early treatment or vigilant monitoring reduces these risks and improves long‑term health.
First‑degree relatives (parents, siblings, children) of a confirmed case should be offered targeted genetic testing for the identified mutation. Even if they are asymptomatic, testing guides surveillance for hypercalcemia and early detection of adenomas. If a mutation is found, extended testing can be offered to cousins or more distant relatives.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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