Overview
Primary hypomagnesemia with hypercalciuria and nephrocalcinosis with severe ocular involvement (FHHNC with ocular involvement) is a rare autosomal recessive renal tubular disorder caused by mutations in the CLDN19 gene, which encodes claudin-19, a tight junction protein critical for paracellular reabsorption of magnesium and calcium in the thick ascending limb of Henle's loop. This condition is also known as familial hypomagnesemia with hypercalciuria and nephrocalcinosis type 2 (FHHNC2). It is distinguished from the related FHHNC type 1 (caused by CLDN16 mutations) by the presence of severe ocular abnormalities. The disease primarily affects the kidneys and eyes. Renal manifestations include excessive urinary loss of magnesium and calcium, leading to chronic hypomagnesemia, hypercalciuria, and progressive nephrocalcinosis (calcium deposits in the kidneys). Over time, this leads to a decline in kidney function, and many patients progress to chronic kidney disease and end-stage renal disease, often during adolescence or early adulthood. Recurrent urinary tract infections, polyuria, polydipsia, and kidney stones may also occur. The severe ocular involvement includes macular colobomata, significant myopia, horizontal nystagmus, and other visual impairments that can be present from early childhood. Treatment is primarily supportive and aimed at slowing disease progression. Magnesium supplementation is given to correct hypomagnesemia, though oral magnesium may be poorly tolerated due to gastrointestinal side effects and may not fully normalize serum levels. Thiazide diuretics have been used in some cases to reduce urinary calcium excretion. Renal replacement therapy, including dialysis or kidney transplantation, may ultimately be required for patients who develop end-stage renal disease. Notably, the disease does not recur in transplanted kidneys. There is currently no cure, and ocular complications require ophthalmologic monitoring and management.
Also known as:
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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 with severe ocular involvement.
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Specialists
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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
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Common questions about Primary hypomagnesemia with hypercalciuria and nephrocalcinosis with severe ocular involvement
What is Primary hypomagnesemia with hypercalciuria and nephrocalcinosis with severe ocular involvement?
Primary hypomagnesemia with hypercalciuria and nephrocalcinosis with severe ocular involvement (FHHNC with ocular involvement) is a rare autosomal recessive renal tubular disorder caused by mutations in the CLDN19 gene, which encodes claudin-19, a tight junction protein critical for paracellular reabsorption of magnesium and calcium in the thick ascending limb of Henle's loop. This condition is also known as familial hypomagnesemia with hypercalciuria and nephrocalcinosis type 2 (FHHNC2). It is distinguished from the related FHHNC type 1 (caused by CLDN16 mutations) by the presence of severe o
How is Primary hypomagnesemia with hypercalciuria and nephrocalcinosis with severe ocular involvement inherited?
Primary hypomagnesemia with hypercalciuria and nephrocalcinosis with severe ocular involvement 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 with severe ocular involvement typically begin?
Typical onset of Primary hypomagnesemia with hypercalciuria and nephrocalcinosis with severe ocular involvement is childhood. Age of onset can vary across affected individuals.