Rare Rheumatology News

Disease Profile

Familial primary hypomagnesemia with hypercalciuria and nephrocalcinosis

Prevalence
Prevalence estimates on Rare Medical Network websites are calculated based on data available from numerous sources, including US and European government statistics, the NIH, Orphanet, and published epidemiologic studies. Rare disease population data is recognized to be highly variable, and based on a wide variety of source data and methodologies, so the prevalence data on this site should be assumed to be estimated and cannot be considered to be absolutely correct.

Unknown

Age of onset

#N/A

ICD-10

#N/A

Inheritance

Autosomal dominant A pathogenic variant in only one gene copy in each cell is sufficient to cause an autosomal dominant disease

no.svg

Autosomal recessive Pathogenic variants in both copies of each gene of the chromosome are needed to cause an autosomal recessive disease and observe the mutant phenotype

no.svg

X-linked
dominant X-linked dominant inheritance, sometimes referred to as X-linked dominance, is a mode of genetic inheritance by which a dominant gene is carried on the X chromosome.

no.svg

X-linked
recessive Pathogenic variants in both copies of a gene on the X chromosome cause an X-linked recessive disorder

no.svg

Mitochondrial or multigenic Mitochondrial genetic disorders can be caused by changes (mutations) in either the mitochondrial DNA or nuclear DNA that lead to dysfunction of the mitochondria and inadequate production of energy.

no.svg

Multigenic or multifactor Inheritance involving many factors, of which at least one is genetic but none is of overwhelming importance, as in the causation of a disease by multiple genetic and environmental factors.

no.svg

Not applicable

no.svg

Other names (AKA)

FHHNC; Michellis-Castrillo syndrome

Summary

The following summary is from Orphanet, a European reference portal for information on rare diseases and orphan drugs.
orphanet

Orpha Number: 306516

Definition
Familial primary hypomagnesemia with hypercalciuria and nephrocalcinosis (FHHNC) is a form of familial primary hypomagnesemia (FPH, see this term), characterized by renal magnesium (Mg) and calcium (Ca) wasting, nephrocalcinosis, kidney failure and, in some cases, severe ocular impairment. Two subtypes of FHHNC are described: FHHNC with severe ocular involvement (FHHNCOI) and without severe ocular involvement (FHHN) (see these terms).

Epidemiology
To date, approximately 200 cases have been reported in the literature.

Clinical description
The median age of onset ranges from 1 to 8 years. The most common presenting features are recurrent urinary tract infections, nephrolithiasis, nephrocalcinosis, polyuria, polydipsia, enuresis, hematuria and pyuria. Additional manifestations include failure to thrive, seizures, abdominal pain, muscular tetany and, rarely, rickets. Patients develop chronic kidney disease (CKD) that progresses to end-stage renal disease (ESRD). Two subtypes of FHHNC have been described: FHHNCOI and FHHN. Both forms share identical renal manifestations. By contrast, severe ocular involvement (macular coloboma, pigmentary retinitis, nystagmus, or visual loss) has been described in FHHNCOI, while mild nonspecific ocular involvement (myopia, astigmatism, hypermetropia, or strabismus) has been reported in some cases of FHHN.

Etiology
The disease is caused by mutations in the genes CLDN16 (3q28) and CLDN19 (1p34.2), encoding claudin-16 and claudin-19 respectively. Both proteins are expressed in the thick ascending limb of Henle's loop where they interact to form heteromultimers and play a role in the paracellular reabsorption of Mg and Ca. Inactivating mutations in either gene results in urinary loss of Mg and Ca. Ocular involvement occurs in patients with the CLDN19 mutation as claudin-19 is expressed in retinal pigment epithelium.

Diagnostic methods
Diagnosis is based on the triad of hypomagnesemia, hypercalciuria and nephrocalcinosis. Hypocalcemia, hyperuricemia, incomplete distal renal tubular acidosis and hypocitraturia are supportive findings. Parathyroid hormone levels are high before onset of CKD. High fractional urinary excretion of Mg is found while serum level is inappropriately low. Ocular abnormalities are detected by fundoscopy and optical coherence tomography (OCT). Diagnosis is confirmed by genetic screening of CLDN16 and CLDN19.

Differential diagnosis
Differential diagnosis includes Bartter syndrome, autosomal dominant hypocalcemia, Dent disease, hereditary hypophosphatemic rickets with hypercalciuria, distal renal tubular acidosis and other tubular disorders causing early nephrocalcinosis (like primary hyperoxaluria) (see these terms).

Genetic counseling
Transmission is autosomal recessive. Genetic counseling should be offered to at-risk couples (both individuals are carriers of a disease-causing mutation) informing them of the 25% chance of having an affected child.

Management and treatment
Management is mainly supportive and includes administration of Mg supplements in high doses and thiazide diuretics to reduce urinary Ca excretion and the progression of nephrocalcinosis. Indomethacin may be used to increase Ca reabsorption. Therapies aimed at delaying progression of CKD should be provided as well as conventional management strategies for kidney stones. Renal transplantation is the optimal treatment for ESRD. Lens implantation can be proposed to patients suffering from severe ocular abnormalities.

Prognosis
Progression to ESRD is frequent (50% of patients at 20 years). Follow-up data in one of the described cohorts suggested that patients harboring CLDN19 mutations have a higher risk of progression to CKD than patients with CLDN16 mutations.

Visit the Orphanet disease page for more resources.

Learn more

These resources provide more information about this condition or associated symptoms. The in-depth resources contain medical and scientific language that may be hard to understand. You may want to review these resources with a medical professional.

In-Depth Information

  • The Monarch Initiative brings together data about this condition from humans and other species to help physicians and biomedical researchers. Monarch’s tools are designed to make it easier to compare the signs and symptoms (phenotypes) of different diseases and discover common features. This initiative is a collaboration between several academic institutions across the world and is funded by the National Institutes of Health. Visit the website to explore the biology of this condition.
  • Orphanet is a European reference portal for information on rare diseases and orphan drugs. Access to this database is free of charge.
  • PubMed is a searchable database of medical literature and lists journal articles that discuss Familial primary hypomagnesemia with hypercalciuria and nephrocalcinosis. Click on the link to view a sample search on this topic.