Sandra Bosio

Juvenile Hemochromatosis Locus Maps to Chromosome 1q

Juvenile hemochromatosis (JH) is an autosomal recessive disorder that leads to severe iron loading in the 2d to 3d decade of life. Affected members in families with JH do not show linkage to chromosome 6p and do not have mutations in the HFE gene that lead to the common hereditary hemochromatosis. In this study we performed a genomewide search to map the JH locus in nine families: six consanguineous and three with multiple affected patients. This strategy allowed us to identify the JH locus on the long arm of chromosome 1. A maximum LOD score of 5.75 at a recombination fraction of 0 was detected with marker D1S498, and a LOD score of 5. 16 at a recombination fraction of 0 was detected for marker D1S2344. Homozygosity mapping in consanguineous families defined the limits of the candidate region in an approximately 4-cM interval between markers D1S442 and D1S2347. Analysis of genes mapped in this interval excluded obvious candidates. The JH locus does not correspond to the chromosomal localization of any known gene involved in iron metabolism. These findings provide a means to recognize, at an early age, patients in affected families. They also provide a starting point for the identification of the affected gene by positional cloning.

Haemochromatosis in patients with beta-thalassaemia trait.

Severe iron overload has been reported in patients with the β‐thalassaemia trait. Studies performed before the discovery of the haemochromatosis gene (HFE) have yielded conflicting results: some suggest that iron overload might arise from the interaction of the β‐thalassaemia trait with heterozygosity for haemochromatosis, some with homozygosity for haemochromatosis and others that it was unrelated to haemochromatosis. We have studied the clinical phenotype, iron indices and HFE genotypes of 22 unrelated patients with the β‐thalassaemia trait and haemochromatosis, the inheritance of chromosome 6p and 1q haplotypes in families of non‐homozygous C282Y probands and serum measures of iron status in relatives heterozygous for C282Y with or without the β‐thalassaemia trait. We demonstrate that the β‐thalassaemia trait aggravates the clinical picture of C282Y homozygotes, favouring higher rates of iron accumulation and the development of severe iron‐related complications. We suggest that the coexistence of the β‐thalassaemia trait might also increase the risk of iron overload in patients with HFE genotypes at a mild risk of haemochromatosis. Our findings do not support the hypothesis that the association of the β‐thalassaemia trait with a single C282Y or H63D allele might lead to iron overload and suggest that other non‐HFE‐related inherited factors are present in haemochromatosis patients with incomplete HFE genotypes.

Clinical, biochemical and molecular findings in a series of families with hereditary hyperferritinaemia-cataract syndrome.

Hereditary hyperferritinaemia–cataract syndrome (HHCS) is an autosomal dominant disease caused by mutations in the iron responsive element (IRE) of the l‐ferritin gene. Despite the elucidation of the genetic basis, the overall clinical spectrum of HHCS has been less well studied as, to date, only individual case reports have been described. Therefore, we studied a total of 62 patients in 14 unrelated families, with nine different mutations. No relevant symptoms other than visual impairment were found to be associated with the syndrome. A marked phenotypic variability was observed, particularly with regard to ocular involvement (i.e. age range at which cataract was diagnosed in 16 subjects with the C39T: 6–40 years). Similarly, serum ferritin levels varied substantially also within subjects sharing the same mutation (i.e. range for the A40G: 700–2412 µg/l). We followed an HHCS newborn in whom well‐defined lens opacities were not detectable either at birth or at 1 year. The lens ferritin content was analysed in two subjects who underwent cataract surgery at different ages, with different cataract morphology. Values were similar and about 1500‐fold higher than in controls. These observations suggest that: (i) in HHCS the cataract is not necessarily congenital; (ii) in addition to the IRE genotype, other genetic or environmental factors may modulate the phenotype, especially the severity of the cataract.