Overview
Primary hypomagnesemia with hypercalciuria and nephrocalcinosis (often called FHHNC, which stands for Familial Hypomagnesemia with Hypercalciuria and Nephrocalcinosis) is a rare inherited kidney disorder. In this condition, the kidneys lose their ability to properly reabsorb magnesium and calcium from the urine back into the blood. This leads to abnormally low magnesium levels in the blood (hypomagnesemia), too much calcium in the urine (hypercalciuria), and a buildup of calcium deposits in the kidneys (nephrocalcinosis). Over time, these calcium deposits can damage the kidneys and lead to progressive kidney failure. Symptoms often begin in childhood and can include frequent urinary tract infections, excessive thirst and urination, kidney stones, muscle cramps, seizures, and fatigue. Some patients also develop eye problems, particularly abnormalities of the cornea or lens. The disease tends to progress over years, and many affected individuals eventually develop chronic kidney disease that may require dialysis or kidney transplantation. Treatment focuses on replacing magnesium through oral or intravenous supplements and managing complications. Unfortunately, magnesium supplementation often cannot fully correct the blood levels because the kidneys continue to waste magnesium. Thiazide diuretics are sometimes used to try to reduce calcium loss in the urine. Close monitoring of kidney function is essential, and some patients will need kidney replacement therapy. There is currently no cure for this condition, and research continues to find better ways to slow kidney damage.
Also known as:
Key symptoms:
Low magnesium levels in the bloodExcessive calcium in the urineCalcium deposits in the kidneys (nephrocalcinosis)Kidney stonesFrequent urinary tract infectionsExcessive thirstFrequent urinationMuscle cramps and spasmsSeizuresFatigue and weaknessFailure to thrive or poor growth in childrenEye problems such as severe nearsightedness or corneal abnormalitiesProgressive kidney failureBone pain or rickets-like bone changesTingling or numbness in hands and feet
Autosomal recessive
Passed on when both parents carry the same gene change; often skips generations
Childhood
Begins in childhood, roughly ages 1 to 12
Treatments
No FDA-approved treatments are currently listed for Primary hypomagnesemia with hypercalciuria and nephrocalcinosis.
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Specialists
View all specialists →No specialists are currently listed for Primary hypomagnesemia with hypercalciuria and nephrocalcinosis.
Treatment Centers
8 centersBaylor College of Medicine Rare Disease Center ↗
Baylor College of Medicine
📍 Houston, TX
🏥 NORDStanford Medicine Rare Disease Center ↗
Stanford Medicine
📍 Stanford, CA
🔬 UDNNIH Clinical Center Undiagnosed Diseases Program ↗
National Institutes of Health
📍 Bethesda, MD
🔬 UDNUCLA UDN Clinical Site ↗
UCLA Health
📍 Los Angeles, CA
🔬 UDNBaylor College of Medicine UDN Clinical Site ↗
Baylor College of Medicine
📍 Houston, TX
🔬 UDNHarvard/MGH UDN Clinical Site ↗
Massachusetts General Hospital
📍 Boston, MA
🏥 NORDMayo Clinic Center for Individualized Medicine ↗
Mayo Clinic
📍 Rochester, MN
👤 Mayo Clinic Center for Individualized Medicine
🏥 NORDUCLA Rare Disease Day Program ↗
UCLA Health
📍 Los Angeles, CA
Travel Grants
No travel grants are currently matched to Primary hypomagnesemia with hypercalciuria and nephrocalcinosis.
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Caregiver Resources
NORD Caregiver Resources
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Mental Health Support
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Family & Caregiver Grants
Financial assistance programs specifically for caregivers of rare disease patients.
Social Security Disability
Learn how rare disease patients may qualify for SSDI/SSI benefits.
Questions for your doctor
Bring these to your next appointment
- Q1.What is my (or my child's) current kidney function, and how quickly is it expected to change?,Which gene mutation is causing this condition, and does it affect the eyes as well?,What is the best magnesium supplement and dosing schedule for this condition?,How often should blood tests, urine tests, and kidney imaging be done?,At what point should we start planning for dialysis or kidney transplantation?,Are there any clinical trials or new treatments being studied for this disease?,Should other family members be tested for this condition or carrier status?
Common questions about Primary hypomagnesemia with hypercalciuria and nephrocalcinosis
What is Primary hypomagnesemia with hypercalciuria and nephrocalcinosis?
Primary hypomagnesemia with hypercalciuria and nephrocalcinosis (often called FHHNC, which stands for Familial Hypomagnesemia with Hypercalciuria and Nephrocalcinosis) is a rare inherited kidney disorder. In this condition, the kidneys lose their ability to properly reabsorb magnesium and calcium from the urine back into the blood. This leads to abnormally low magnesium levels in the blood (hypomagnesemia), too much calcium in the urine (hypercalciuria), and a buildup of calcium deposits in the kidneys (nephrocalcinosis). Over time, these calcium deposits can damage the kidneys and lead to pro
How is Primary hypomagnesemia with hypercalciuria and nephrocalcinosis inherited?
Primary hypomagnesemia with hypercalciuria and nephrocalcinosis follows a autosomal recessive inheritance pattern. Genetic counseling can help families understand recurrence risk and testing options.
At what age does Primary hypomagnesemia with hypercalciuria and nephrocalcinosis typically begin?
Typical onset of Primary hypomagnesemia with hypercalciuria and nephrocalcinosis is childhood. Age of onset can vary across affected individuals.