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To date, approximately 72 cases have been described in the literature.

FHHNCOI has a childhood onset. The initial symptoms may include recurrent urinary tract infections, polyuria and polydipsia. Additional features include nephrocalcinosis, nephrolithiasis, enuresis, abdominal pain, muscular twitches and failure to thrive. The clinical hallmark of this disorder is an ocular abnormality involving severe bilateral myopia with divergent squint, nystagmus, keratoconus, corneal calcifications, cataract, chorioretinitis, pigmentary retinitis, pigmentary maculopathy, macular coloboma, strabismus or visual loss. Renal function generally declines progressively in most patients and patients may reach end stage renal disease in their adolescence or young adulthood. 50% of patients require renal replacement therapy in the second decade of life.

FHHNCOI is caused by mutations in CLDN19 (1p34.2) which encodes claudin-19, a protein member of the claudin family which is highly expressed in the tight junctions of the thick ascending limb of Henle's loop, as well as in the retinal epithelium.

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% risk of having an affected child.