Hemochromatosis: new insights in pathogenesis and diagnosis following the discovery of the gene

EMQN best practice guidelines for the molecular genetic diagnosis of hereditary hemochromatosis (HH)

Molecular genetic testing for hereditary hemochromatosis (HH) is recognized as a reference test to confirm the diagnosis of suspected HH or to predict its risk. The vast majority (typically >90%) of patients with clinically characterized HH are homozygous for the p.C282Y variant in the HFE gene, referred to as HFE-related HH. Since 1996, HFE genotyping was implemented in diagnostic algorithms for suspected HH, allowing its early diagnosis and prevention. However, the penetrance of disease in p.C282Y homozygotes is incomplete. Hence, homozygosity for p.C282Y is not sufficient to diagnose HH. Neither is p.C282Y homozygosity required for diagnosis as other rare forms of HH exist, generally referred to as non-HFE-related HH. These pose significant challenges when defining criteria for referral, testing protocols, interpretation of test results and reporting practices. We present best practice guidelines for the molecular genetic diagnosis of HH where recommendations are classified, as far as possible, according to the level and strength of evidence. For clarification, the guidelines' recommendations are preceded by a detailed description of the methodology and results obtained with a series of actions taken in order to achieve a wide expert consensus, namely: (i) a survey on the current practices followed by laboratories offering molecular diagnosis of HH; (ii) a systematic literature search focused on some identified controversial topics; (iii) an expert Best Practice Workshop convened to achieve consensus on the practical recommendations included in the guidelines.

Analysis of HFE gene mutations and HLA-A alleles in Brazilian patients with iron overload

CONTEXT AND OBJECTIVE

Hemochromatosis is a common inherited disorder of iron metabolism and one of the most important causes of iron overload. The objective was to analyze the presence of C282Y, H63D and S65C mutations in the HFE gene and HLA-A alleles for a group of Brazilian patients with iron overload, and to correlate genotype with clinical and laboratory variables.

DESIGN AND SETTING

Prospective study, in Discipline of Hematology and Oncology, Faculdade de Ciências Médicas da Santa Casa de Misericórdia de São Paulo.

METHODS

We studied 35 patients with iron overload seen at our outpatient unit between January 2001 and December 2003. Fasting levels of serum iron and ferritin, and total iron-binding capacity, were assayed using standard techniques. Determinations of C282Y, H63D and S65C mutations in the HFE gene and of HLA-A alleles were performed by polymerase chain reaction (PCR).

RESULTS

Twenty-six out of 35 patients (74%) presented at least one of the HFE gene mutations analyzed. Among these, five (14%) were C282Y/C282Y, four (11%) C282Y/H63D, one (3%) H63D/H63D, six (17%) C282Y/WT and ten (29%) H63D/WT. No patients had the S65C mutation and nine (25%) did not present any of the three HFE mutations. Four out of five patients with C282Y/C282Y genotype (80%) and three out of four patients with C282Y/H63D genotype (75%) were HLA A*03.

CONCLUSION

Analysis of HFE gene mutations constitutes an important procedure in identifying patients with hereditary hemochromatosis, particularly for patients with iron overload.

Role of liver biopsy in the diagnosis of hepatic iron overload in the era of genetic testing

We studied hepatic iron overload (HIOL) patterns in 32 patients who underwent liver biopsies and testing for HFE mutations (C282Y, H63D). Iron-stained biopsy specimens were examined for patterns of iron deposits: hereditary hemochromatosis (HH) pattern or non-HH pattern. Visual iron grade based on amount of cellular and lobular iron was evaluated. We found the HH pattern in 17 biopsy specimens (53%) and the non-HH pattern in 6 specimens (19%). HH with superimposed non-HH was noted in 9 cases (28%). In 25 patients with HFE mutations, HH alone and combined with non-HH patterns was noted in 22 specimens (88%). Visual iron grade correlated approximately with the hepatic iron index. Heavy HIOL was noted in C282Y homozygotes and 1 patient with cirrhosis without either HFE mutation. Mild steatohepatitis was found in 21 specimens (66%); it was associated with the non-HH pattern in 80% (12/15) and the HH pattern in 62% (16/26) of cases. Liver biopsy can identify pattern and grade of HIOL and associated pathology for diagnosis and management of patients with abnormal iron studies and elevated liver function test results. Genetic tests for HFE mutations and liver biopsies are complementary in the workup of these patients.