From OMIM
Familial isolated primary hyperparathyroidism is an autosomal dominant hypercalcemic disorder caused by inappropriate oversecretion of parathyroid hormone (PTH) from parathyroid adenomas, hyperplasia, and carcinomas (summary by Shibata et al., 2015). Genetic Heterogeneity of Familial Hyperparathyroidism Hyperparathyroidism-2 with jaw tumors (HRPT2; 145001), also known as the hyperparathyroidism-jaw tumor syndrome (HPT-JT), is also caused by mutation in the CDC73 gene. A locus for HRPT (HRPT3; 610071) has been mapped to chromosome 2p14-p13.3. HRPT4 (617343) is caused by mutation in the GCM2 gene (603716) on chromosome 6p24. Neonatal severe hyperparathyroidism (NSHPT; 239200) is caused by mutation in the CASR gene (601199) on chromosome 3q. Familial isolated primary hyperparathyroidism occasionally results from incomplete expression of multiple endocrine neoplasia (see MEN1, 131100). Familial hypocalciuric hypercalcemia (see 145980) can be confused with familial primary hyperparathyroidism.  http://www.omim.org/entry/145000

From MedlinePlus Genetics
Familial isolated hyperparathyroidism is an inherited condition characterized by overactivity of the parathyroid glands (hyperparathyroidism). The four parathyroid glands are located in the neck, and they release a hormone called parathyroid hormone that regulates the amount of calcium in the blood. In familial isolated hyperparathyroidism, one or more overactive parathyroid glands release excess parathyroid hormone, which causes the levels of calcium in the blood to rise (hypercalcemia). Parathyroid hormone stimulates the removal of calcium from bone and the absorption of calcium from the diet, and the mineral is then released into the bloodstream.

In people with familial isolated hyperparathyroidism, the production of excess parathyroid hormone is caused by tumors that involve the parathyroid glands. Typically only one of the four parathyroid glands is affected, but in some people, more than one gland develops a tumor. The tumors are usually noncancerous (benign), in which case they are called adenomas. Rarely, people with familial isolated hyperparathyroidism develop a cancerous tumor called parathyroid carcinoma. Because the production of excess parathyroid hormone is caused by abnormalities of the parathyroid glands, familial isolated hyperparathyroidism is considered a form of primary hyperparathyroidism.

Disruption of the normal calcium balance resulting from overactive parathyroid glands causes many of the common signs and symptoms of familial isolated hyperparathyroidism, such as kidney stones, nausea, vomiting, high blood pressure (hypertension), weakness, and fatigue. Because calcium is removed from bones to be released into the bloodstream, hyperparathyroidism often causes thinning of the bones (osteoporosis). The age at which familial isolated hyperparathyroidism is diagnosed varies from childhood to adulthood. Often, the first indication of the condition is elevated calcium levels identified through a routine blood test, even though the affected individual may not yet have signs or symptoms of hyperparathyroidism or hypercalcemia.  https://medlineplus.gov/genetics/condition/familial-isolated-hyperparathyroidism