Laboratory for Molecular Diagnostics
Center for Nephrology and Metabolic Disorders

Hypomagnesemia with hypercalciuria and nephrocalcinosis with ocular involvement

FHHNC with ocular involvement is an autosomal recessive disorder with hypomagnesemia, hypercalciuria, nephrocalcinosis and coloboma often complicated by progressive chronic renal failure during childhood or adolescence. Loss of function mutations in the CLDN19 gene are the underlying genetic cause.

Historical Aspects

The first family as described by Michelis exhibited renal magnesium wasting and a distal renal tubular acidosis.[Error: Macro 'ref' doesn't exist]

Clinical Findings

Signs and Symptoms

The first typical symptom is nephrocalcinosis, which becomes apparent in childhood or adolescence. if not a sibling is affected or consanguinity present family history is not instructice as with all recessive disorders. Although the prevailing symptoms are renal and every so often end-stage renal failure develops, it is an multiorgan disorder. Ocular symptoms are pathognomonic of this disorder, and findings are myopia, nystagmus and chorioretinitis. Other organ's involvement includes tetany, seizures, hypertension, gout, deafness, chondrocalcinosis, and rickets.

Laboratory Findings

Plasma magnesium is 0.59 ± 0.06 mmol/l. Renal magnesium excretion is inaprpriatly high 2.07 ± 0.073mmol/d. The same holds true for fractional magnesium excretion 12.5 ± 4.7%. Of note, trenal calcium excretion is also elevated. Urinary calcium creatinin ratio is 1.88 ± 0.67.

Diagnosis

Often the patients present with urinary tract infections and carful sultrasound examination then reveals nephrocalcinosis. The diagnosis is further confirmed by laboratory findings and finally proved by molecular genetic tests of CLDN19.

Management

It is only a symptomatic therapy available for this disorder, which includes substitution of renal mineral losses, the complex care for recurrent kidney stones, and antibiotics if urinary tract infections occur. Unfortunately these measures exert minimal effect on the progression of renal failure and ocular symptoms.

Symptoms

Hypomagnesaemia
Hypomagnesemia is a cardinal symptom of FHHNC with ocular involvement. Typical of this disorder is further hypocalcemia, due to excessive renal losses of divalent cations; nephrocalcinosis; recurrent kidney stones; progressive renal failure; and macular coloboma.
Hypocalcemia
Hypocalcemia is typical of FHHNC with ocular involvement though hypomagnesemia is essential. Other crucial symptoms are nephrocalcinosis, recurrent kidney stones, progressive renal failure, and macular coloboma.
Nephrocalcinosis
Nephrocalcinosis in FHHNC with ocular involvement is accompanied by hypomagnesemia and hypocalemia due to excessive renal losses. By contrast to other diseases with nephrocalcinosis, progressive renal failure is typical. Also ocular invovment is essential for the diagnosis.
Hypercalciuria
Hypercalciuria in FHHNC is accompanied by hypomagnesemia and nephrocalcinosis.

Systematic

Hypomagnesemia
EGFR
Gitelman syndrome
Hereditary myokymia type 1
Hypomagnesemia with hypercalciuria and nephrocalcinosis
Hypomagnesemia with hypercalciuria and nephrocalcinosis with ocular involvement
CLDN19
Hypomagnesemia with normocalciuria
Intestinal hypomagnesemia with secondary hypocalcemia
Isolated dominant hypomagnesemia
Renal cysts and diabetes (RCAD)
Renal hypomagnesemia 6
TRPM7

References:

1.

Vezzoli G et al. (2008) Hypercalciuria revisited: one or many conditions?

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2.

Hou J et al. (2008) Claudin-16 and claudin-19 interact and form a cation-selective tight junction complex.

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3.

Vezzoli G et al. (2008) Update on primary hypercalciuria from a genetic perspective.

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4.

Alexander RT et al. (2008) Molecular determinants of magnesium homeostasis: insights from human disease.

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5.

Günzel D et al. (2009) Function and regulation of claudins in the thick ascending limb of Henle.

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6.

Michelis MF et al. (1972) Decreased bicarbonate threshold and renal magnesium wasting in a sibship with distal renal tubular acidosis. (Evaluation of the pathophysiological role of parathyroid hormone).

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Update: Sept. 26, 2018