Reference
Complete the bibliographic reference for the article according to AJE format.

Ellervik C, Mandrup-Poulsen T, Nordestgaard BG, et al.  Prevalence of hereditary hemochromatosis in late-onset type 1 diabetes mellitus:  a retrospective study. Lancet 2001 October;358:1405-9.

Category of HuGE information
Specify the types of information (from the list below) available in the article:

1. Prevalence of gene variant
2. Gene-disease association
3. Gene-environment interaction
4. Gene-gene interaction
5. Genetic test evaluation/monitoring

1. Prevalence of gene variant
2. Gene-disease association

Study hypotheses or purpose
The authors study hypotheses or main purpose for conducting the study

Gene(s)
Identification of the following:

1. Gene name
2. Chromosome location
3. Gene product/function
4. Alleles
5. OMIM #

1. Gene: HFE 
2. Chromosome location:  6p
3. Gene product/function: Iron absorption and storage
4. Alleles:  C282Y and H63D
5. OMIM #: 23520

Environmental factor(s)
Identification of the major environmental factors studied (infectious, chemical, physical, nutritional, and behavioral)

N/A

Health outcome(s)
Identification of the major health outcome(s) studied

Intervention
Identification of the intervention  studied

1. Case-control
2. Cohort 
3. Cross-sectional
4. Descriptive or case-series
5. Clinical trial
6. Population screening

1. Case-control

Cohort definition
For study designs 2, 3, and 6, the following are defined, where available:

1. Cohort selection criteria
2. Exclusion criteria
3. Gender
4. Race/ethnicity
5. Age
6. Time period
7. Geographic location
8. Number of participants

1. Cohort selection criteria: Potential cases were selected from patients who had attended the Steno Diabetes Center on referral from their primary physician.  Each had late-onset type 1 diabetes mellitus diagnosed according to WHO criteria.
2. Exclusion criteria: People less than 30 years of age
3. Gender:  male and female
4. Race/ethnicity: 99% Danish descent
5. Age: > 30 years of age
6. Time period:  April 1999 – November 1999
7. Geographic location:  Copenhagen
8. Number of participants: 716 (792 asked to participate, 90% agreed)

Control definition 
For study design 1, the following are defined, if available.  

1. control selection criteria
2. matching variables
3. exclusion criteria 
4. gender
5. race/ethnicity
6. age
7. time period
8. geographic location
9. number of participants

1. Control selection criteria: Controls were selected from a cross-section of Danish adults who had taken part in a previous study (Copenhagen City Heart Study.  Note:  These individuals were considered to be representative of the general population). 
2. Matching variables: Selected at random after stratification for sex and age in 10-year age groups
3. Exclusion criteria: People who did not agree to give blood
4. Gender:  male and female
5. Race/ethnicity: 99% Danish descent
6. Age: > 30 years of age
7. Time period:  1976-1978, and followed up again in 1981-1983
8. Geographic location:  Copenhagen
9. Number of participants: 9,260 (17,180 asked to participate, 54% agreed)

1. Environmental factor
2. Exposure assessment
3. Exposure definition
4. Number of participants with exposure data (% of total eligible)

N/A

Assessment of intervention
For studies that include the following:

1. Intervention
2. Intervention definition
3. Number of participants with exposure data (% of total eligible)

1. Environmental factor: Prophylactic mastectomy
2. Intervention definition: Individuals who selected prophylactic mastectomy
3. Number of individuals from cohort who selected intervention: 76/139

1. Gene
2. DNA source
3. Methodology
4. Number of participants genotyped (% of total eligible)  

1. Gene: HFE
2. DNA source:  Blood
3. Methodology: Two PCR assays with allele specific amplification were used to determine non-carriers, heterozygotes, and homozygotes for C282Y and H63D mutations.  To confirm diagnosis, followed with arestriction enzyme digest.  
4. Participants genotyped: 716 cases (99% genotyped), 9,174 controls (99% genotyped)

Note:  Phenotypic expressions of iron overload:  plasma concentrations of iron, transferrin saturation, and ferritin were also measured.

1. Prevalence of gene variant
2. Gene-disease association
3. Gene-environment interaction
4. Gene-gene interaction
5. Genetic test evaluation

1. Prevalence of gene variant:

Genotype frequencies in controls did not differ from those predicted by the Hardy-Weinberg equilibrium (P=0.58); however, among the diabetes group they did (P=0.002).  The prevalence of the homozygous C282Y/C282Y geneotype among patients with type-1 diabetes was1.26% (95% CI = 0.58-2.37) compared to 0.25% (0.16-0.38) of controls, resulting in an OR = 4.6 (95% CI = 2.1-10.1).  There was no significant interaction between genotype and sex or age on risk of hemochromatosis.

2. Gene-disease association:

* Adjusted for sex and age 

There was no statistically significant difference for genotype frequencies between the cases and controls except for C282Y/C282Y.  The diabetes patients had unrecognized signs of hemochromatosis.

3. Gene-environment interaction: Transferrin saturation (TS) values for diabetes mellitus patients by genotype were calculated.  TS values in C282Y/C282Y patients were higher than for all other genotypes. The Anova for all six genotype levels was P=0.01.  There was not significant interaction between genotype and sex or age in relation to TS. 

5. Genetic test evaluation: Compared TS values (> or < 50%) by genotype (C282Y/C282Y vs. other) and demonstrated positive predictive value of 0.26, negative predictive value of 1.0%, sensitivity of 100% and specificity of 100%.

Conclusion
The author’s overall conclusions from the study

The representativeness of the controls pulled from the heart study cohort is not clear.  No information was provided about their health status.  However, 43 of the controls were receiving insulin and 2/23 C282Y/C282Y controls had been reported to have type-2 diabetes. 

The potential for response bias, mentioned briefly by the authors, may actually be an important bias - the response rate in controls was 54% and among cases was 90%. 

All 4 C282Y/C282Y females had no iron overload (ferritin levels were for all below 300) and the onset of diabetes was years before the study. It is not clear how diabetes can be caused by hereditary hemochromatosis without signs of organ overload.  Therefore, the AR% may be lower than reported. 

Also, the researchers did not analyze serum iron measures in the controls; 23 were C282Y/C282Y.  It would be of interest to examine if these genetically predisposed patients, as well as the healthy controls, had undiagnosed iron overload. 

CDC currently recommends serum iron testing of people with 1) a close blood relative with hereditary hemochromatosis, 2) the unexplained symptoms compatible with hemochromatosis (severe weakness, fatigue, arthralgia, or abdominal pain), or 3) signs of diabetes, liver disease, heart problems, impotence, infertility, or amenorrhea.