Screening for hereditary hemochromatosis: a clinical practice guideline from the American College of Physicians

Genetic diagnosis and testing in clinical practice

Genetic testing is defined as "the analysis of human DNA, RNA, chromosomes, proteins and certain metabolites in order to detect heritable disease-related genotypes, mutations, phenotypes or karyotypes for clinical purposes." This article focuses on diagnostic and predictive genetic testing. The latter includes presymptomatic testing, which identifies individuals who are expected to become ill in the future and predisposition testing, which identifies those who are at increased risk of becoming ill. Decisions regarding genetic testing must be based not only on the analytic accuracy, availability and cost of the test, but on the clinical utility as well, including the sensitivity, specificity and interpretability of results. Clinical information, including the medical and family history and the findings of the physical examination, is vital for the selection of appropriate diagnostic tests, as well as the interpretation of the results. Presymptomatic genetic testing is a very personal choice that should only be made after the patient has had sufficient counseling to develop an understanding of the risks and benefits of the test and is able to make an informed decision. The same principle applies to predisposition testing; however, additional factors, such as the probability of a positive result, the likelihood that the disease will actually develop in those with positive results, the effect on the management of the index patient, the effects on family members, the risk of false reassurance if the result is negative or the potential for loss of hope if it is positive, all contribute to the assessment of risk versus benefit. Clinical evaluation and counseling of the patient who is at risk for a genetic disorder are labor intensive but essential for the selection and interpretation of genetic tests.

Revisiting hereditary hemochromatosis: current concepts and progress

Originally regarded as a rare affliction notable for its distinctive evolution to "bronze diabetes," hereditary hemochromatosis is now recognized as the most common genetic disorder in populations of European ancestry. Recent advances in our understanding of iron metabolism, the identification of the gene responsible for hemochromatosis, and large epidemiologic studies have changed the diagnostic approach toward patients with hereditary hemochromatosis and other forms of iron overload. This article reviews the pathophysiology, epidemiology, clinical features, diagnostic testing, and management of hemochromatosis for the primary care provider.

Hereditary hemochromatosis: genetic complexity and new diagnostic approaches

Since the discovery of the hemochromatosis gene (HFE) in 1996, several novel gene defects have been detected, explaining the mechanism and diversity of iron-overload diseases. At least 4 main types of hereditary hemochromatosis (HH) have been identified. Surprisingly, genes involved in HH encode for proteins that all affect pathways centered around liver hepcidin synthesis and its interaction with ferroportin, an iron exporter in enterocytes and macrophages. Hepcidin concentrations in urine negatively correlate with the severity of HH. Cytokine-mediated increases in hepcidin appear to be an important causative factor in anemia of inflammation, which is characterized by sequestration of iron in the macrophage system. For clinicians, the challenge is now to diagnose HH before irreversible damage develops and, at the same time, to distinguish progressive iron overload from increasingly common diseases with only moderately increased body iron stores, such as the metabolic syndrome. Understanding the molecular regulation of iron homeostasis may be helpful in designing innovative and reliable DNA and protein tests for diagnosis. Subsequently, evidence-based diagnostic strategies must be developed, using both conventional and innovative laboratory tests, to differentiate between the various causes of distortions of iron metabolism. This review describes new insights in mechanisms of iron overload, which are needed to understand new developments in diagnostic medicine.