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Genetic and Rare Diseases Information Center (GARD)

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Familial hypocalciuric hypercalcemia


Other Names for this Disease
  • Familial benign hypercalcemia
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Your Question

I have this condition. Are there different types? I was told by my doctors I have a double mutation. What does that mean? My doctors don't have any information for me. I have not been told to watch my diet or anything. I find it incredibly hard to lose weight. Is this calcium problem stopping me from losing weight? I was adopted at birth and do not have any genetic information.

Our Answer

We have identified the following information that we hope you find helpful. If you still have questions, please contact us.

Are there different types of familial hypocalciuric hypercalcemia?

In the medical literature, some authors reference different types of familial hypocalciuric hypercalcemia (FHH) - types 1, 2 and 3. These subtypes of FHH are generally used to describe forms of the condition that are genetically distinct (i.e. are caused by mutations in different genes). In more than 65% of families affected by FHH, the condition is due to mutations in the CASR gene, which is located on chromosome 3. In the other families affected by FHH, the exact genetic abnormality that causes the condition has not yet been identified. Researchers have discovered that one of two other genes, located at different parts of chromosome 19, may be responsible for the condition in some of these remaining individuals. These three genetically distinct types of FHH have therefore been designated as FHH type 1 (due to a mutation in the CASR gene at chromosome 3q21.1) and FHH types 2 and 3 (due to genetic abnormalities at chromosome locations 19p and 19q13, respectively).[1] More information about describing the location of genes on chromosomes is available on the following page from Genetics Home Reference: http://ghr.nlm.nih.gov/handbook/howgeneswork/genelocation

These three types of FHH are all characterized by abnormally high blood calcium levels and  low urine calcium excretion. In FHH type 3, affected individuals additionally have increased serum parathyroid hormone (PTH) concentrations as well as occasional, mild hypophosphatemia (low blood phosphorus level) that manifests after 30 years of age.[1]
Last updated: 9/23/2011

How is familial hypocalciuric hypercalcemia inherited?

Familial hypocalciuric hypercalcemia (FHH) is inherited in an autosomal dominant manner. Individuals have two copies of each gene (one inherited from each parent). For a condition with autosomal dominant inheritance, one mutated copy of the gene in each cell is sufficient to cause the condition. An affected individual may inherit the mutated copy of the gene from an affected parent, or the mutation may occur for the first time in the affected individual. An individual with FHH has a 50% (1 in 2) risk to pass on the mutation to each of his/her children.

Although most affected individuals have one mutated copy of the gene, it is possible for an affected individual to have a mutation in both copies of the causative gene. These individuals may have very little (or no) function in the mutated gene and have a more severe variation of the disease called neonatal severe primary hyperparathyroidism (NSHPT). Because two mutated copies of the gene cause NSHPT, this condition is inherited in an autosomal recessive manner. This condition may become evident within the first week of life and can be life-threatening; aggressive medical management is usually needed.[2] It is also technically possible for an individual to have two separate mutations in the same copy of the gene responsible for FHH.

For answers to specific questions about an individual's circumstances, a consultation with a genetics professional is recommended. Genetics pprofessionals can answer questions about the diagnosis, natural history, treatment, mode of inheritance, and genetic risks to other family members.
Last updated: 9/23/2011

How can I find a genetics professional in my area?

Genetics clinics are a source of information for individuals and families regarding genetic conditions, treatment, inheritance, and genetic risks to other family members. More information about genetic consultations is available from Genetics Home Reference. To find a genetics clinic, we recommend that you contact your primary healthcare provider for a referral.

The following online resources can help you find a genetics professional in your community:
Last updated: 10/18/2013

Can familial hypocalciuric hypercalcemia make it difficult to lose weight?

A thorough search of available medical literature does not currently yield information about the effects of familial hypocalciuric hypercalcemia on an individual's ability to lose weight.
Last updated: 9/23/2011

References