Familial Hypomagnesemia with Hypercalciuria and Nephrocalcinosis (FHHNC)
What is Familial Hypomagnesemia with Hypercalciuria and Nephrocalcinosis (FHHNC)?
Familial hypomagnesemia with hypercalciuria and nephrocalcinosis is a rare genetic disorder. It causes your kidneys to lose too much magnesium and calcium in your urine. Over time, calcium deposits build up in your kidneys. This buildup is called nephrocalcinosis.
FHHNC usually starts in infancy or early childhood. The condition is inherited, meaning it passes from parents to children through genes. Children inherit one faulty gene copy from each parent. Without treatment, FHHNC can lead to chronic kidney disease or kidney failure before age 20.
The main problem is that your kidneys cannot hold onto magnesium properly. Your body needs magnesium for hundreds of functions including muscle and nerve work. When magnesium stays too low, it affects calcium balance too. This creates a cycle that damages kidney tissue over time.
Symptoms
- Muscle cramps or spasms
- Seizures in infancy or childhood
- Excessive thirst and urination
- Kidney stones, sometimes recurring
- Fatigue and weakness
- Abnormal heart rhythms
- Slowed growth in children
- Eye problems including cloudy lenses
- Bone pain or fractures
Some children show symptoms in the first few months of life. Others may not have obvious signs until school age. Blood tests often reveal the problem before severe symptoms appear.
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Causes and risk factors
FHHNC is caused by mutations in specific genes that control how kidneys handle magnesium. The most common faulty genes are CLDN16 and CLDN19. These genes make proteins that help your kidney tubules reabsorb magnesium and calcium. When the genes do not work correctly, magnesium and calcium leak into urine instead of staying in your blood.
This is an autosomal recessive condition. Both parents must carry one copy of the faulty gene. Each child has a 25% chance of inheriting both copies and developing FHHNC. Parents who are carriers typically have no symptoms. Family history of early kidney disease or consanguinity increases risk. There are no lifestyle factors that cause this condition because it is purely genetic.
How it's diagnosed
Doctors diagnose FHHNC by measuring magnesium levels in blood and urine. Serum magnesium tests show persistently low blood levels. Urine tests reveal high calcium and magnesium loss. Imaging tests like kidney ultrasounds can show calcium deposits in kidney tissue. Genetic testing confirms the diagnosis by identifying mutations in CLDN16 or CLDN19 genes.
Rite Aid offers serum magnesium testing as part of our preventive health panel. You can get tested at over 2,000 Quest Diagnostics locations nationwide. Early detection helps slow kidney damage. Regular monitoring tracks how well treatment is working. If your magnesium stays low despite normal diet, talk to a kidney specialist about FHHNC.
Treatment options
- High-dose magnesium supplements, often several times daily
- Potassium-sparing diuretics like amiloride to reduce calcium loss
- Thiazide diuretics to lower urine calcium in some cases
- High fluid intake to prevent kidney stones
- Regular kidney function monitoring with blood tests
- Salt restriction to reduce calcium excretion
- Vitamin D management to protect bones
- Dialysis or kidney transplant if kidney failure develops
Treatment focuses on slowing kidney damage because there is no cure. Many patients need lifelong magnesium replacement. Even with high doses, blood magnesium may stay below normal. Early treatment in childhood offers the best chance to preserve kidney function. Work with a nephrologist who specializes in rare kidney diseases.
Concerned about Familial Hypomagnesemia with Hypercalciuria and Nephrocalcinosis (FHHNC)? Get tested at Rite Aid.
- Simple blood draw at your nearest lab
- Results in days, not weeks
- Share results with your doctor
Frequently asked questions
Life expectancy depends on how early the condition is diagnosed and treated. Without treatment, many patients develop kidney failure before age 20. Early diagnosis and consistent magnesium replacement can slow kidney damage significantly. Some patients maintain kidney function into adulthood with proper care.
There is no cure for FHHNC because it is a genetic condition. Treatment focuses on managing symptoms and slowing kidney damage. Kidney transplant can replace damaged kidneys but does not fix the genetic problem. Gene therapy research is ongoing but not yet available.
Regular low magnesium usually responds to oral supplements and dietary changes. FHHNC causes severe magnesium wasting that does not fully correct with supplements. Blood levels often stay low despite high-dose magnesium replacement. FHHNC also involves calcium loss and kidney deposits that simple magnesium deficiency does not cause.
Each child of two carrier parents has a 25% chance of having FHHNC. Siblings have a 50% chance of being carriers like the parents. Genetic counseling and testing can determine carrier status. Early screening helps catch the condition before severe kidney damage occurs.
Normal serum magnesium ranges from 1.7 to 2.2 mg/dL. In FHHNC, levels typically fall below 1.5 mg/dL and often drop below 1.0 mg/dL. The levels stay low despite oral supplementation. High urine magnesium loss confirms that kidneys are wasting magnesium.
Diet alone cannot manage FHHNC because the problem is genetic kidney wasting. Even magnesium-rich foods like spinach, nuts, and whole grains cannot overcome the kidney loss. High-dose supplements are always needed. Diet can support overall kidney health but cannot replace medical treatment.
Newly diagnosed patients need testing every few weeks to find the right supplement dose. Once stable, testing every 3 to 6 months helps monitor kidney function. More frequent testing is needed if symptoms worsen or kidney function declines. Regular monitoring catches problems early.
Nephrocalcinosis means calcium deposits in kidney tissue. You cannot see these deposits from the outside. Kidney ultrasound or CT scan reveals the deposits. Symptoms like kidney stones, pain, or declining kidney function may indicate worsening deposits.
Potassium-sparing diuretics like amiloride help reduce calcium loss in urine. This slows calcium deposit formation in kidneys. Thiazide diuretics may also lower urine calcium in some patients. Magnesium supplements remain the cornerstone of treatment even though they cannot fully correct blood levels.
FHHNC is present from birth because it is genetic. Most cases are diagnosed in infancy or childhood when symptoms appear. Some milder cases may not be recognized until teenage years or early adulthood. Adults do not suddenly develop FHHNC, but late diagnosis can occur if symptoms were previously missed.