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Hereditary hyperferritinemia with congenital cataracts
Hereditary hyperferritinemia with congenital cataracts is characterized by the association of early onset (although generally absent at birth) cataract with persistently raised plasma ferritin concentrations in the absence of iron overload. Prevalence still needs to be precisely determined but is estimated to be at least 1 in 200 000. The syndrome is an autosomal dominant inherited disease. It is caused by a mutation in a translational regulatory element of the gene coding for the L-ferritin subunit, located on 19q13.4-qter. Messenger RNAs for ferritin have a stem-loop structure called an 'iron responsive element' (IRE) in their 5' non-coding region. In the absence of iron, a cytoplasmic protein called the 'iron regulatory protein' (IRP) binds to the IRE and represses ferritin synthesis. As a result of the mutation on the IRE, the IRP no longer recognizes the binding site leading to constitutive L-ferritin expression in tissues and an increase in ferritin levels in the plasma, although there is no iron overload. The mutations that have been identified affect bases on the IRE loop or in the bulge in the middle of the IRE stem. Two partial deletions of either half of the IRE have also been reported. In cases for which no IRE mutations have been detected but the hyperferritinemia persists, hemochromatosis type 4 (which may be caused by ferroportin mutations) should be suspected. There is no treatment for cataract-hyperferritinemia syndrome, but venesections should be avoided as they are not well tolerated. Besides cataracts, there are no other clinical manifestations associated with this syndrome and the prognosis is good.