Common conditions associated with hereditary haemochromatosis genetic variants: cohort study in UK Biobank
BMJ 2019; 364 doi: https://doi.org/10.1136/bmj.k5222 (Published 16 January 2019) Cite this as: BMJ 2019;364:k5222Linked opinion
Haemochromatosis is linked to more disease than previously thought
All rapid responses
Rapid responses are electronic comments to the editor. They enable our users to debate issues raised in articles published on bmj.com. A rapid response is first posted online. If you need the URL (web address) of an individual response, simply click on the response headline and copy the URL from the browser window. A proportion of responses will, after editing, be published online and in the print journal as letters, which are indexed in PubMed. Rapid responses are not indexed in PubMed and they are not journal articles. The BMJ reserves the right to remove responses which are being wilfully misrepresented as published articles or when it is brought to our attention that a response spreads misinformation.
From March 2022, the word limit for rapid responses will be 600 words not including references and author details. We will no longer post responses that exceed this limit.
The word limit for letters selected from posted responses remains 300 words.
This study demonstrates the power of the UK Biobank to answer questions about disease and genotype. It has been known for decades that “haemochromatosis” is a genetic condition of late onset that was difficult to diagnose before the onset of significant morbidity. Since the discovery of the HFE gene (1) we have realised that p.C282Y homozygosity found in most cases of hereditary haemochromatosis is relatively common in populations of European origin, that evidence of iron accumulation is also common but clinical penetrance is uncertain. This study should answer many questions about the clinical significance of hereditary haemochromatosis.
We are surprised that the authors do not refer to our study of over 10,500 blood donors from South Wales published in 2001 (2). About 97 % were of Northern European Origin. 1 in 147 donors were homozygous for p.C282Y (0.68%) and 1 in 8 (15.1%) were heterozygous for p.C282Y. Mean transferrin saturation and serum ferritin concentration was significantly higher in both men and women who were homozygous for p.C282Y. Of the male p.C282Y homozygotes 86% had a transferrin saturation (TS) > 50% and 34% had a serum ferritin concentration of > 210 µg/l. The figures for women were 45% with TS > 50 % and 22% with serum ferritin > 130 µg/l. Their average ages were 38 and 36 years respectively and they had donated a mean of 2.7 and 2.1 units of blood in the previous three years. None of the p.C282Y homoygotes interviewed showed physical signs of iron overload or were aware of relatives with haemochromatosis.
Based on these gene frequencies a further study showed that only 1% of adult p.C282Y homozygotes in South Wales had a clinical diagnosis of iron overload (3). Iron loading and morbidity was studied in relatives (parents and siblings) of the p.C282Y homozygotes from the blood donor study and in relatives of p.C282Y homozygotes presenting as patients. In both groups p.C282Y homozygosity had a high penetrance for iron accumulation but a low clinical penetrance (4).
The large discrepancy between the present study and some earlier studies of penetrance including that of Beutler et al (5) may be partly due to the inclusion of a “diagnosis of haemochromatosis” in the list of conditions. Since 1996 when the HFE gene was identified the diagnosis of “hereditary haemochromatosis” has increasing been based on a raised transferrin saturation and homozygosity for p.C282Y. In studies of relatives of probands it may only be a genetic diagnosis. Surely, in order to ascertain the overall morbidity associated with homozygosity for pC282Y, diagnosis of haemochromatosis should be excluded as one of the clinical conditions analysed.
Furthermore, as there is a risk of ascertainment bias especially when relying on self-reported illness, individuals with haemochromatosis at diagnosis should be removed and the analysis re-run because:
a. Those with haemochromatosis are likely to have a greater understanding of the condition including potential symptoms/signs and so the risk of over-reporting of disease is high, especially true of non-specific lethargy and arthralgia.
b. Individuals with haemochromatosis at diagnosis are much more likely to undergo more rigorous screening for liver disease than those without and we know there will be a high chance of alcohol-related, fatty and viral liver disease in men over 40 years (the incidence of which has increased dramatically in UK over the reporting period).
c. Relatives of those with known haemochromatosis were also participants – we don’t know the number of relatives of haemochromatosis patients at baseline but they weren’t all excluded. Again there is a risk of ascertainment bias – although this should be a smaller effect. Relatives may also have had liver specific tests as part of screening, particularly liver function tests.
A lack of a precise definition of diagnosis of haemochromatosis, together with lack of iron indices should guard one against statements about penetrance without further analysis/investigation. The presence of minor derangement of liver function tests for instance could presumably be recorded as an “incident diagnosis” and lead to over diagnosis. Thankfully all previous studies to date have found very little significant, serious liver disease in homozygotes. Although the numbers investigated in this study are much larger precise case ascertainment is weaker.
There appears to be no data on BMI and this is potentially a problem. There is a higher prevalence of diabetes in the male p.C282Y homozygotes compared to those without p.C282Y. The vast majority of these individuals at this age are likely to be type 2 diabetics, so adjustment for weight is crucial as one would expect to see a higher prevalence of fatty liver disease and in particular NASH (non-alcohol related steatohepatitis) in this groups as well.
Why was rheumatoid arthritis chosen as an “incident diagnosis” - there is no recognised link nor biological plausibility? The study, by association, implies a link exists and this could cause unnecessary anxiety for homozygotes.
Further study and analysis of the homozygous group with regard to liver disease would be valuable – how many were investigated by liver specialists? What were the iron indices? What reassurances exist there is no coexistent liver disease? What evidence is there for tissue iron overload and/or fibrosis (liver biopsy/MRI/non-invasive fibrosis testing)?
Re-analysis of the data as suggested above will give a more accurate assessment of morbidity in pC282Y homozygotes.
1. Feder JN, Gnirke A, Thomas W, Tsuchihashi Z, Ruddy DA, Basava A, et al. A novel MHC class I-like gene is mutated in patients with hereditary haemochromatosis. Nat Genet. 1996;13:399–408.
2. Jackson HA, Carter K, Darke C, Guttridge MG, Ravine D, Hutton RD, Napier JA and Worwood M. HFE mutations, iron deficiency and overload in 10 500 blood donors. Br J Haematol 2001; 114: 474–484.
3. McCune CA, Al Jader LN, May A, Hayes SL, Jackson HA and Worwood M. Hereditary haemochromatosis: only 1% of adult HFE C282Y homozygotes in South Wales have a clinical diagnosis of iron overload. Hum Genet 2002; 111: 538–543
4. C A McCune, D Ravine, K Carter, H A Jackson, D Hutton, J Hedderich, M Krawczak, M Worwood. Iron loading and morbidity among relatives of HFE C282Y homozygotes identified either by population genetic testing or presenting as patients. Gut; 2006; 55: 554–562.
5. Beutler E, Felitti VJ, Koziol JA, Ho NJ, Gelbart T. Penetrance of the 845G->A (C282Y) HFE hereditary haemochromatosis mutation in the USA. Lancet 2002; 359: 211–218.
Competing interests: No competing interests
Once again we pretend that non-HFE haemochromatosis doesn't exist
Sigh . . . well, they *did* look at some non-HFE genes:
rs8177240 (nearest gene TF)
rs7385804 (nearest gene TRF2)
rs855791 (nearest gene TMPR226)
(the gene assignments in brackets above is from
Unfortunately, Pilling et al did not consider SLC40A1 variants, some of which have been repeatedly shown to produce a type of genetic hemochromatosis in which transferrin doesn't go up until very late in the disease process. More logical jurisidictions that don't ignore SLC40A1 types of iron overload consider these to be the second most common cause of genetic iron overload after HFE-related iron overload.
The standard approach of the Canadian medical system is to ask: Is your transferrin up?
Answer: no.
Canadian medical system: Well, then you don't have hemochromatosis or any sort of iron overload. Go away.
Doctor asks Canadian researcher: what is the prevalence of SLC40A1-related hemochromatosis in Canada?
Canadian researcher: We don't have any.
Doctor: How do you know we don't have any?
Canadian researcher: We did studies looking for people with iron overload and when we found them, we did gene testing on them. People who had genetic iron overload almost all had HFE-related gene variants. We didn't find SLC40A1 iron overload.
Doctor: How do you look for genetic iron overload?
Canadian researcher: We test transferrin saturation. If transferrin saturation is up, then we test the genes. If it isn't, we don't.
Doctor: Transferrin saturation doesn't go up in SLC40A1 iron overload until very late in the disease. You are eliminating people with SLC40A1 before you do any gene testing, which is why you didn't find them.
Canadian researcher: We wouldn't have found them anyhow, because SLC40A1-related iron overload is extremely rare in Canada.
Doctor: How do you know it is extremely rare?
(repeat conversation ad nauseum until doctor gives up and goes back to reading the European (continental) and USA literature . . . . )
Competing interests: No competing interests
As a founder member of the Haemochromatosis Arthropathy Research Initiative (HARI) I welcome these findings.
Patients with genetic haemochromatosis often report an excess of 5 years from first attributable symptoms to diagnosis (1) (and commencement of de-ironing) and our excellent patient society (Haemochromatosis UK) reports widespread frustration caused by the delay in recognition of this disease. As stated, fatigue and joint pain are the most prevalent symptoms at diagnosis (1).
The association of Genetic Haemochromatosis with a characteristic arthropathy is well described, resembling effectively 'accelerated osteoarthritis' whereby affected people develop the clinical characteristics of osteoarthritis (OA) in the absence of predisposing trauma, at an earlier than expected age (often less than 60 years), affecting typical joints (hips, knees, PIP, DIP, 1st CMC) and unusual joints for OA - especially 2nd and 3rd MCPs and ankles. Radiologically there are abundant OA features including osteophytes (termed 'hook like' at ther MCPs), early joint space narrowing and on MRI an excess of bone marrow lesions/subchondral cysts compared to controls (1, 2).
Earlier detection of patients with genetic haemochromatosis could be enhanced with greater primary care awareness that a patient presenting with what superficially looks like 'everyday OA' should be investigated if these unusual features are present - i.e. age less than 60, no predisposing trauma, rapidly progressive joint damage, involvement of the 2nd and 3rd MCPs or ankles. Transferrin saturation and ferritin are inexpensive first line screening tests, and if both are raised, indicating iron overload, then referral for HFE analysis is justified.
I am, however, concerned about the association reported with rheumatoid arthritis. This is a completely different arthropathy to OA, and having seen and examined in excess of 120 patients with genetic haemochromatosis and arthropathy in my specialist clinic, I have only seen 2 cases with co-existent rheumatoid arthritis (matching the expected population prevalence of ~1%) . I would therefore caution interpretation of these findings, and wonder whether diagnostic error, bias or confounding factors have spuriously produced this association? Indeed, I am unsure why rheumatoid arthritis was included in the 11 key outcomes 'implicated in the single shared underlying process of iron overload'. I would be concerned if patients concluded from this work that their homozygous C282Y state meant they were more likely to develop rheumatoid arthritis as well as the characterisitc arthropathy that resembles OA.
Nonetheless, there are many other conundrums associated with the aetiology of haemochromatosis arthropathy, yet scant research directed at unravelling them (3).
References
1. Richardson A, Prideaux A, Kiely PDW. Haemochromatosis: unexplained MCP or ankle arthropathy should prompt diagnostic tests; findings from two UK observational cohort studies. Scand J Rheumatol 2017; 46: 69-74. DOI: 10.3109/03009742.2016.1155645
2. Elstob A, Ejindu V, Heron C, Kiely PDW. Haemochromatosis arthropathy: MRI hindfoot characteristics; a case-control study. Clin Rad 2017 doi:10.1016/j.crad.2017.10.002
3. Kiely PDW. Haemochromatosis arthropathy – a conundrum of the celtic curse. J R Coll Physicians Edinb 2018; 48: 233-8. doi 10.4997/JRCPE.2018.307
Competing interests: No competing interests
Have these conclusions been verified by other researchers? It is surprising when considering the immense significance of these conclusions that others have not made similar conclusions. Let me explain my concerns with the study conclusions.
The biomedical parameters of most, if not all, diabetics is that their condition is accompanied by lower pH (from the normal level of ca 7.35-7.45 to below pH7, perhaps as low as 6.50) ie elevated levels of intercellular acidity which influences the prevailing levels of essential minerals eg Mg, Ca, Zn, Cr; and non-essential heavy metals eg Fe, Al, Hg, etc. As acidity increases the levels and bioavailability of essential minerals declines whilst the levels of nonessential minerals increases (and is associated with the free radical reactions catalysed by heavy metals which accompany pathological onset). This is particularly evident in the diabetic where type 2 diabetes is accompanied by lower levels of magnesium, lower levels and/or biovailability of zinc, elevated levels of iron and heavy metals, etc.
The issue is often observed in long distance runners who can develop anaemia as a result of overexercising ie their blood pH becomes so high as a result of eliminating CO2 and minimising body fat that it is unable to retain adequate levels of iron and hence of haemoglobin. This is basic chemistry. It explains how for example someone who consumes alcoholic and/or acidic beverages would become deficient in essential minerals, why someone who drinks colas would become deficient in magnesium (and perhaps other essential minerals) and why the overweight and diabetic have lower levels of essential minerals and higher levels of iron and other nonessential minerals. The degree of demineralisation of essential minerals depends upon the nature and extent of the acidity e.g. if as phosphoric acid, acetic acid, or other.
Accordingly I question the conclusions made in this study that the genetic indications identified are in fact associated with levels of iron. If considering diabetic patients the study will inevitably note higher levels of iron in the diabetic patients however this does not necessarily mean that the elevated levels of iron have the genetic origins identified in the conclusions of this study.
Ewing GW. Is Metformin a Drug or a Buffer and Why is this Significant? Further evidence that the brain Regulates the Autonomic Nervous System, in particular prevailing levels of Intercellular pH. Endocrinology, Diabetes and Metabolism Journal (EDMJ) 2018;2(4):1-9.
Ewing GW. The Regulation of pH is a Physiological System. Increased Acidity alters Protein Conformation and Cell Morphology and is a Significant Factor in the onset of Diabetes and other common pathologies. The Open Systems Biology Journal 2012;5:1-12.
Competing interests: No competing interests
In 2000, we (1) published an evaluation of a targeted genetic haemochromatosis (GH) screening programme for those with raised alanine aminotransferase (ALT) activity. In one local hospital 35,069 blood samples had ALT measured, unrelated to haemochromatosis, in an eight month period. Samples found to have raised ALT were then tested for transferrin saturation. Patients with raised transferrin saturation were then offered HFE genotyping. Nine were found to be homozygous for the C282Y mutation. This led us to conclude that: "a combination of an initial transferrin saturation screen followed by genetic testing...offer(s) a reliable cost effective algorithm for detecting GH in subjects with liver disease.". After targeted screening was established at that local hospital (2), an analysis of 210,000 blood samples from 100,000 patients, found that 32 patients were homozygous for the C282Y mutation.
Attempts to expand the screening programme beyond that one hospital failed. As the authors of this latest study wrote (3), uptil now: "general population screening is not recommended. This is partly because of the reported low clinical penetration to liver disease and the absence of excess mortality in major studies." Clinicians in hospitals, other than the one where our study was undertaken, felt this applied to targeted as well as population screening. The authors recommend (3) that there should be a "re-examining of options for expanded early case ascertainment and screening". Screening those with raised ALT activity may be the most cost-effective option.
1. Bhavnani M, Lloyd D, Battacharyya A, Marples J, Elton P, Worwood M,. Screening for genetic haemochromatosis in blood samples with raised alanine aminotransferase. Gut 2000;46: 707-710
2. Bhavnani M, Lloyd D, Marples J, Pendry K, Worwood M Targeted screening for genetic haemochromatosis: a combined phenotype/genotype approach J Clin Pathol. 2006;59: 501–504.
3 Pilling Luke C, Tamosauskaite Jone, Jones Garan, Wood Andrew R, Jones Lindsay, Kuo Chai-Ling et al. Common conditions associated with hereditary haemochromatosis genetic variants: cohort study in UK Biobank BMJ 2019; 364 :k5222
Competing interests: No competing interests
Re: Common conditions associated with hereditary haemochromatosis genetic variants: cohort study in UK Biobank
Rapid responses to our paper on HFE p.C282Y associated morbidity in UK Biobank[1] have raised issues that require clarification.
A. Claimed contradictory results to previous community studies
Professor Worwood and Dr McCune highlight their studies of Welsh blood donors and relatives [2-4], which reported similar p.C282Y mutation prevalence to UK Biobank. Their studies also found no excess clinical morbidity in p.C282Y heterozygotes (again similar to UK Biobank): we apologise for not citing these studies.
Worwood and McCune go on to argue that their findings of no excess clinical disease in p.C282Y homozygotes suggest that our UK Biobank findings are invalid. The Welsh studies analysed disease associations in n=72 p.C282Y male and female homozygotes (mean age <40 years) and n=59 p.C282Y homozygous relatives (mean age 52). Samples of this size have low power to detect the expected associations in such relatively young groups, especially if pooling data from men and women. In the eMERGE study across 7 US hospital systems[5], only four of 95 p.C282Y homozygotes with relevant data were diagnosed with haemochromatosis before age 50: most diagnoses were made after the age of 50, with several at age 80 plus. Our paper noted the similar limitations of the Beutler et al[6] study (mean age 50 with n=56 p.C282Y homozygous men), which had only 19% power (at p=0.05) to detect the Biobank p.C282Y male homozygote all ages association with diabetes.
Despite lack of power, these previous studies actually produce broadly similar results to those in younger Biobank participants, which also showed no excess liver disease or diabetes (age 40 to 49 years, n=290 men and n=339 women). An association was present with osteoarthritis in men only, although prevalences in this age-group were low.
It should be noted that the largest previous community study (HIERS) did find significant associations between p.C282Y homozygotes[7] and liver disease in men, and higher prevalence of chronic fatigue and metacarpophalangeal joint swelling in p.C282Y homozygotes with higher serum ferritin levels.
Space does not allow discussion of the many clinical and family studies which support the UK Biobank results of substantial excess morbidity at older ages (50 to 70 at baseline) associated with p.C282Y homozygosity, especially in men. As with other risk factors including high blood pressure or cholesterol levels, lack of association with related disease at mean ages <53 tells us little about the later life excess morbidity, and the true burden of p.C282Y homozygous status would be best assessed on a lifetime basis.
B. Inclusion of (likely misdiagnoses) of rheumatoid arthritis,
Drs Kiely as well as Worwood and McCune question our inclusion of rheumatoid arthritis diagnoses. However, the similarity in presentation of some Hereditary Haemochromatosis arthroses with rheumatoid arthritis is well documented[8]. Our paper noted that “misdiagnoses of iron related pathology has been reported, for example with the iron deposition related arthrosis misdiagnosed as osteoarthritis or rheumatoid”. We apologise that these likely misdiagnosis were insufficiently clear, but do not accept that this result should have been hidden from patients. We hope this finding will contribute to more appropriate treatment for this group in the future.
C. Diabetes and body mass index
Worwood and McCune argue that p.C282Y homozygote associations we reported with diabetes mellitus and liver disease may be explained by obesity. In Biobank, p.C282Y homozygote status was associated with substantially lower rates of obesity (e.g. males OR 0.81, 95% CI 0.69 to 0.95, p=0.01; BMI >30 vs Normal 18.5 to 25), compared to no p.C282Y mutations. When BMI is adjusted for, the p.C282Y homozygous association with prevalent diabetes became stronger (e.g. males OR 1.65, 95% CI 1.26 to 2.15, p=0.0002). Adjustment for BMI had no effect on liver disease associations.
D. Alternative Estimates of associated morbidity
Worwood and McCune speculate that HH diagnoses may be dominated by people with high iron levels and no related morbidity. In UK Biobank 40 to 70 year olds, 48% of the 281 male p.C282Y homozygotes with diagnosed haemochromatosis also had liver disease, diabetes or arthritis diagnoses by the end of follow-up, compared to 15.7% in wild-type males (n=175,539): therefore 32 in 100 p.C282Y homozygotes (95% CI 26.5 to 38.2, p<0.00001) had excess diagnoses. As our paper noted, this is likely a substantial underestimate, as diagnoses after baseline were available from inpatient hospital records only, while most diagnoses of diabetes and arthritis are made in primary care or outpatient settings.
Ignoring diagnoses of haemochromatosis (as requested), e.g. male p.C282Y homozygotes still had substantially more diagnosed liver disease, arthritis or diabetes by end follow-up (mean age only 63 years: 27% in p.C282Y homozygotes versus 16% in wild type: difference 11 (95% CI 9 to 14) additional homozygous patients with diagnosed morbidity per hundred, p<0.00001). Excess morbidity in 40 to 49 year old males by the same measure was small (13% versus 6%, excess 6 CI 3 to 10), and would be very challenging to detect without a large sample.
E. Ascertainment bias and prevalent diagnosis of haemochromatosis
Worwood and McCune suggest that ascertainment bias and self-reported illness with diagnosed haemochromatosis or in family members could explain away our finding. Our paper reported incident associations from hospital inpatient diagnoses only, and found excess morbidity in p.C282Y homozygotes, with a marked gender difference. We also reported such excess morbidity for ‘hard endpoints’ including hip replacements, incident liver cancers and liver cancer deaths. In a sister paper[9] we analysed measured muscle (grip) strength in 60 to 70 year olds. Low measured strengths were more common in male p.C282Y homozygotes (24% versus 15% in wild type: OR 1.69: CI 1.39 to 2.05). Overall therefore it seems implausible that ascertainment bias could explain away all the excess morbidity observed in p.C282Y homozygotes in UK Biobank. It should also be noted that haemochromatosis diagnoses and family histories are likely to lead to early venesection, thus biasing penetrance estimates toward the null.
We look forward to the imminent release of liver enzyme and other data in the UK Biobank cohort, to strengthen the evidence further.
References
1. Pilling LC, Tamosauskaite J, Jones G, et al. Common conditions associated with hereditary haemochromatosis genetic variants: cohort study in UK Biobank. BMJ. 2019;364:k5222. doi:10.1136/bmj.k5222.
2. Jackson HA, Carter K, Darke C, Guttridge MG, Ravine D, Hutton RD, Napier JA and Worwood M. HFE mutations, iron deficiency and overload in 10 500 blood donors. Br J Haematol 2001; 114: 474–484.
3. McCune CA, Al Jader LN, May A, Hayes SL, Jackson HA and Worwood M. Hereditary haemochromatosis: only 1% of adult HFE C282Y homozygotes in South Wales have a clinical diagnosis of iron overload. Hum Genet 2002; 111: 538–543
4. C A McCune, D Ravine, K Carter, H A Jackson, D Hutton, J Hedderich, M Krawczak, M Worwood. Iron loading and morbidity among relatives of HFE C282Y homozygotes identified either by population genetic testing or presenting as patients. Gut; 2006; 55: 554–562.
5. Gallego CJ, Burt A, Sundaresan AS, et al. Penetrance of Hemochromatosis in HFE Genotypes Resulting in p.Cys282Tyr and p.[Cys282Tyr];[His63Asp] in the eMERGE Network. Am J Hum Genet. 2015;97(4):512-520. doi:10.1016/j.ajhg.2015.08.008.
6. Beutler E, Felitti VJ, Koziol JA, Ho NJ, Gelbart T. Penetrance of 845G → A (C282Y) HFE hereditary haemochromatosis mutation in the USA. Lancet. 2002;359(9302):211-218. doi:10.1016/S0140-6736(02)07447-0.
7. McLaren GD, Gordeuk VR. Hereditary hemochromatosis: insights from the Hemochromatosis and Iron Overload Screening (HEIRS) Study. Hematol Am Soc Hematol Educ Progr. 2009;6:195-206. doi:10.1182/asheducation-2009.1.195.
8. Husar-Memmer E, Stadlmayr A, Datz C, Zwerina J. HFE-related hemochromatosis: an update for the rheumatologist. Curr Rheumatol Rep. 2014;16(1):393. doi:10.1007/s11926-013-0393-4.
9. Tamosauskaite J, Atkins JL, Pilling LC, et al. Hereditary Hemochromatosis Associations with Frailty, Sarcopenia and Chronic Pain: Evidence from 200,975 Older UK Biobank Participants. J Gerontol A Biol Sci Med Sci. 2019;In press. doi:10.1093/gerona/gly270.
Competing interests: No competing interests