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Understanding Your High Calcium: An Introduction to FHH1

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Familial Hypocalciuric Hypercalcemia Type 1 (FHH1) is a benign, lifelong genetic condition that causes mildly elevated blood calcium. It occurs when a mutation alters the body's calcium thermostat. FHH1 is not cancer, rarely causes symptoms, and generally does not require surgery.

Key Takeaways

  • • FHH1 is a benign, lifelong genetic condition that causes mildly elevated blood calcium levels.
  • • It is caused by a change in the CASR gene, which makes the body's internal calcium thermostat less sensitive.
  • • People with FHH1 typically have high calcium in their blood but low calcium in their urine.
  • • FHH1 is not a parathyroid tumor or cancer, and it generally does not require surgery or medical intervention.
  • • Most individuals with FHH1 are completely asymptomatic and live a normal, healthy lifespan.

Discovering you have high blood calcium (hypercalcemia, meaning excess calcium in the blood) on a routine blood test can be a startling experience. Many patients worry that it indicates a serious illness, such as a tumor or cancer [1]. However, Familial Hypocalciuric Hypercalcemia Type 1 (FHH1) is a benign, lifelong genetic condition that is often discovered by accident [2][3].

If you have FHH1, your body is not “sick” in the traditional sense; rather, it is simply operating with a different internal setting for calcium [1].

Your Body’s Calcium ‘Thermostat’

To understand FHH1, it helps to think of your body having a calcium “thermostat” located in your parathyroid glands and kidneys [4]. This thermostat is controlled by a protein called the Calcium-Sensing Receptor (CaSR), which measures the amount of calcium in your blood [4].

In FHH1, a genetic change in the CASR gene makes this thermostat slightly less sensitive [1]. Because the sensor doesn’t “see” calcium as easily, it tells the body to keep more calcium in the blood to reach what it perceives as a normal level [1][4]. As a result:

  • Blood calcium stays mildly elevated for your entire life [5][3].
  • Urinary calcium is usually low (hypocalciuria, meaning not enough calcium is passed into the urine) because your kidneys are instructed to hold onto calcium rather than flushing it out [4][6].
  • Parathyroid Hormone (PTH) levels are often “inappropriately” normal or slightly high, because the parathyroid glands think the high calcium level is actually correct [4][7].

How Common is FHH1?

FHH1 is more common than once thought. A large study of over 50,000 people found an incidence rate of approximately 74.1 per 100,000 individuals [8]. This is similar to the frequency of more well-known conditions like Primary Hyperparathyroidism (PHPT), which is the most common cause of high calcium [8][3].

What FHH1 Is and Is Not

It is important to clarify what this diagnosis means for your health:

  • It is NOT cancer: Unlike Hypercalcemia of Malignancy (HCM), which is caused by advanced cancers and usually results in very low PTH levels, FHH1 is a stable, non-cancerous genetic trait [9][4].
  • It is usually NOT a parathyroid tumor: In Primary Hyperparathyroidism (PHPT), a small non-cancerous tumor on the parathyroid gland usually causes the high calcium. In FHH1, the glands themselves are typically healthy but are following “wrong” instructions from the genetic thermostat [1][6].
  • Surgery is generally not the answer: Because FHH1 affects every calcium-sensing cell in your body, removing a parathyroid gland (a common treatment for PHPT) will not “fix” the calcium level and is usually not recommended [1][10][11].

Symptoms: What to Expect

The vast majority of people with FHH1 are asymptomatic, meaning they feel completely normal and only learn they have the condition through blood work [1][2].

While most people feel fine, some individuals may experience mild symptoms that are common to many conditions, such as:

  • Fatigue or general tiredness [12].
  • Joint stiffness or “achiness” (which can be related to calcium crystal deposits in the joints, a condition called chondrocalcinosis) [2][13].
  • Brain fog or mild difficulty concentrating [14].

In very rare cases, FHH1 has been associated with more distinct issues like pancreatitis (inflammation of the pancreas), but these are the exception rather than the rule [12][15]. Most people with FHH1 live a normal, healthy lifespan without needing any medical intervention for their calcium levels [1][2].

Explore This Guide:

Frequently Asked Questions

What is FHH1 and why is my blood calcium high?
FHH1 is a genetic condition that alters your body's calcium thermostat, making it less sensitive to calcium in the blood. As a result, your body naturally holds onto more calcium to reach what it incorrectly believes is a normal level. It is a benign trait and is not caused by cancer or tumors.
Do I need parathyroid surgery for FHH1?
No, surgery is generally not recommended for FHH1. Because the condition is caused by a genetic trait that affects every calcium-sensing cell in your body, removing a parathyroid gland will not correct your calcium levels.
What are the symptoms of FHH1?
The vast majority of people with FHH1 feel completely normal and never develop symptoms. When mild symptoms do occur, they can include generalized fatigue, brain fog, and joint stiffness caused by calcium deposits.
Should my family members be tested for high calcium?
Because FHH1 is passed down through families, it is a good idea to discuss your diagnosis with your relatives. Your doctor may recommend that your biological children, siblings, or parents have a simple blood test to check their calcium levels.

Questions for Your Doctor

  • • Am I part of the group that is likely to remain asymptomatic, or should I be watching for specific long-term symptoms?
  • • What was my Calcium-to-Creatinine Clearance Ratio (CCCR), and does it clearly point toward FHH1 or is it in a 'gray zone'?
  • • Now that we suspect FHH1, should my children or siblings also have their calcium levels checked?
  • • Does this diagnosis change how I should monitor my bone density or kidney health compared to someone without FHH1?
  • • Can we confirm this with genetic testing for the CASR gene to avoid any future confusion with other calcium conditions?

Questions for You

  • • How did I feel before I knew about my high calcium levels? (Many people feel perfectly fine until the 'high' number creates anxiety).
  • • Do I have any biological relatives who were told they had high calcium or who had parathyroid surgery that didn't seem to work?
  • • Am I currently experiencing symptoms like fatigue or joint stiffness that I previously ignored, or am I feeling mostly normal?

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References

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    Hormones (Athens, Greece) 2024; (23(1)):3-14 doi:10.1007/s42000-023-00508-9.

    PMID: 38038882
  2. 2

    Severe Symptomatic Hypercalcemia in a Patient With Familial Hypocalciuric Hypercalcemia.

    Kurian R, Madegowda Chandrashekar G, Antony MA, et al.

    Cureus 2021; (13(11)):e20057 doi:10.7759/cureus.20057.

    PMID: 34993031
  3. 3

    [Syndrome of hypocalсiuric hypercalcemia. Is it rare? Two clinical cases in an outpatient clinic].

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    Problemy endokrinologii 2022; (68(5)):24-31 doi:10.14341/probl13125.

    PMID: 36337015
  4. 4

    A novel mouse model for familial hypocalciuric hypercalcemia (FHH1) reveals PTH-dependent and independent CaSR defects.

    Küng CJ, Daryadel A, Fuente R, et al.

    Pflugers Archiv : European journal of physiology 2024; (476(5)):833-845 doi:10.1007/s00424-024-02927-y.

    PMID: 38386045
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    Familial Hyperparathyroidism - Disorders of Growth and Secretion in Hormone-Secretory Tissue.

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    PMID: 29136674
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    Parathyroid hormone-dependent familial hypercalcemia with low measured PTH levels and a presumptive novel pathogenic mutation in CaSR.

    Mahajan A, Buse J, Kline G

    Osteoporosis international : a journal established as result of cooperation between the European Foundation for Osteoporosis and the National Osteoporosis Foundation of the USA 2020; (31(1)):203-207 doi:10.1007/s00198-019-05170-9.

    PMID: 31641801
  7. 7

    Generation of an induced pluripotent stem cell line CSSi015-A (9553), carrying a point mutation c.2915C > T in the human calcium sensing receptor (CasR) gene.

    Rotundo G, Turco EM, Ruotolo G, et al.

    Stem cell research 2023; (67()):103023 doi:10.1016/j.scr.2023.103023.

    PMID: 36638628
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    Familial Hypocalciuric Hypercalcemia Type 1 and Autosomal-Dominant Hypocalcemia Type 1: Prevalence in a Large Healthcare Population.

    Dershem R, Gorvin CM, Metpally RPR, et al.

    American journal of human genetics 2020; (106(6)):734-747 doi:10.1016/j.ajhg.2020.04.006.

    PMID: 32386559
  9. 9

    Primary Hyperparathyroidism With Undetectable Intact Parathyroid Hormone.

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    Clinical medicine insights. Endocrinology and diabetes 2024; (17()):11795514241290125 doi:10.1177/11795514241290125.

    PMID: 39381434
  10. 10

    Novel mutations of the calcium-sensing receptor impede differential diagnosis of primary hyperparathyroidism and familial hypocalciuric hypercalcemia.

    Bhangu JS, Baumgartner-Parzer S, Hargitai L, et al.

    Gland surgery 2022; (11(1)):12-22 doi:10.21037/gs-21-577.

    PMID: 35242665
  11. 11

    Case report: familial hypocalciuric hypercalcemia.

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    AME case reports 2024; (8()):55 doi:10.21037/acr-23-132.

    PMID: 38711891
  12. 12

    Neonatal Hypocalcemic Seizures in Offspring of a Mother With Familial Hypocalciuric Hypercalcemia Type 1 (FHH1).

    Dharmaraj P, Gorvin CM, Soni A, et al.

    The Journal of clinical endocrinology and metabolism 2020; (105(5)) doi:10.1210/clinem/dgaa111.

    PMID: 32150253
  13. 13

    Case Report: Familial hypocalciuric hypercalcemia type 1 with a novel mutation combined with Gitelman syndrome and a review of the literature.

    He T, Li X, Li G, et al.

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    PMID: 40070587
  14. 14

    Stepwise CaSR, AP2S1, and GNA11 sequencing in patients with suspected familial hypocalciuric hypercalcemia.

    Szalat A, Shpitzen S, Tsur A, et al.

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    PMID: 28176280
  15. 15

    Nephrotic Syndrome Complicated with Familial Hypocalciuric Hypercalcemia in an Infant: A Case Report and Comprehensive Literature Review.

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    PMID: 38702153

This page provides an educational overview of FHH1 and high blood calcium. It is not a substitute for professional medical advice or diagnosis from your endocrinologist.

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