Familial Hypercalciuric Hypomagnesemia and Nephrocalcinosis (FHHNC) is a rare autosomal recessive disorder of magnesium re-absorption by the thick ascending loop of Henle (tALH), which manifests itself during childhood. This re-absorption defect results in severe renal magnesium wasting, hypercalciuria, bilateral nephrocalcinosis, and progressive renal failure. Other features of the condition include recurrent urinary tract infections, polyuria, nephrolithiasis, incomplete distal tubular acidosis, growth retardation, rickets, convulsions, and abdominal colics. Like all magnesium deficiency diseases, FHHNC is also associated with tetanic convulsions, muscle weakness and cramps. Interestingly, unlike other hypomagnesic conditions, patients with FHHNC do not readily develop hypocalcemia, as the excess urinary excretion of calcium is compensated for by increased intestinal absorption and release from the bone.
Dudin and Teebi, 1987, described primary hypomagnesemia with secondary hypocalcemia as a cause of infantile tetany and convulsions in an Arab girl of consanguineous parentage.
Bhasker et al, 1999, were the first to report the development of reversible external hydrocephalus (increased collection of cerebrospinal fluid in the subarachnoid space with normal or minimal ventricular dilatation) in two siblings with primary hypomagnesemia, who were born to consanguineous parents.
Al-Elq, 2008, described two Saudi sisters with FHHNC born to consanguineous parents.