Polymorphism of methylenetetrahydrofolate reductase as disease modifier – A déjà-vu in Wilson disease?
Authors: Peter Ferenci
Journal: Journal of Hepatology (2011)

Genetic variability in the methylenetetrahydrofolate reductase gene (MTHFR) affects clinical expression of Wilson's diseaseJournal of HepatologyVol. 55Issue 4PreviewWilson's disease (WND) is an autosomal recessive disorder of copper (Cu) transport, resulting from pathogenic mutations in the ATP7B gene. The reason for the high variability in phenotypic expressions of WND is unknown. Hepatotoxic and neurotoxic effects of homocysteine (Hcy), as well as interrelationships between Hcy and Cu toxicity, were documented. Full-Text PDF Wilson disease (WD) is a genetic disorder found worldwide. The most common presentations are with liver disease or neuropsychiatric disturbance. Although the primary defect is impaired biliary copper excretion resulting in hepatic copper accumulation, the liver is not always affected [[1]Ferenci P. Steindl-Munda P. Vogel W. et al.Diagnostic value of quantitative hepatic copper determination in patients with Wilson disease.Clin Gastroenterol Hepatol. 2005; 3: 811-818Abstract Full Text Full Text PDF PubMed Scopus (194) Google Scholar]. Presenting symptoms of liver disease can be highly variable, ranging from asymptomatic, with only biochemical abnormalities, to overt cirrhosis, with all its complications, or acute liver failure associated with Coomb's negative hemolytic anemia. On the other hand, patients with chronic liver disease may not have any neurologic symptoms or brain MRI abnormalities. Clinically evident liver disease may precede neurologic manifestations by as much as 10 years. Wilson disease may present symptomatically at any age, although the majority present between ages 5 and 35. The youngest patient reported with cirrhosis due to Wilson disease was 3 years old [[2]Wilson D.C. Phillips M.J. Cox D.W. Roberts E.A. Severe hepatic Wilson's disease in preschool-aged children.J Pediatr. 2000; 137: 719-722Abstract Full Text Full Text PDF PubMed Scopus (103) Google Scholar]. About 3% of patients present beyond the fourth decade, either as hepatic or neurologic disease [[3]Ferenci P. Członkowska A. Merle U. Szalay F. Gromadzka G. Yurdaydin C. et al.Late onset Wilson disease.Gastroenterology. 2007; 132: 1294-1298Abstract Full Text Full Text PDF PubMed Scopus (195) Google Scholar]. The oldest patients were two siblings diagnosed in their eighth decade [4Ala A. Borjigin J. Rochwarger A. Michael Schilsky M. Wilson disease in septuagenarian siblings: raising the bar for diagnosis.Hepatology. 2005; 41: 668-670Crossref PubMed Scopus (166) Google Scholar, 5Członkowska A. Rodo M. Gromadzka G. Late onset Wilson's disease therapeutic implication.Mov Dis. 2008; 23: 897-899Crossref Scopus (60) Google Scholar]. WD can manifest with an impressive spectrum of neurological, behavioral, or psychiatric disorders, which may be its first clinical manifestation, appearing simultaneously with hepatic signs, or some years later. Neurological presentation can be extremely subtle, and intermitted for many years, but may also develop very rapidly leading to complete disability in a few months. The clinical hallmark of Wilson disease is the Kayser–Fleischer ring, which is present in 95% of patients with neurologic symptoms but only in half of patients with Wilsonian liver disease [6Steindl P. Ferenci P. Dienes H.P. Grimm G. Pabinger I. Madl Ch. et al.Wilson's disease in patients presenting with liver disease: a diagnostic challenge.Gastroenterology. 1997; 113: 212-218Abstract Full Text PDF PubMed Scopus (332) Google Scholar, 7Gow P.J. Smallwood R.A. Angus P.W. Smith A.L. Wall A.J. Sewell R.B. Diagnosis of Wilson's disease: an experience over three decades.Gut. 2000; 46: 415-419Crossref PubMed Scopus (209) Google Scholar]. In children presenting with liver disease, Kayser–Fleischer rings are usually absent [[8]Sanchez-Albisua I. Garde T. Hierro L. Camarena C. Frauca E. de la Vega A. et al.A high index of suspicion: the key to an early diagnosis of Wilson's disease in childhood.J Pediatr Gastroenterol Nutr. 1999; 28: 186-190Crossref PubMed Scopus (81) Google Scholar]. The reasons for the highly variable clinical manifestations are unknown. The so far reported disease modifiers are summarized in Table 1. There is a wide range of mutations in the Wilson disease (APT7B) gene, with most of the over 500 described mutations being very rare. Not all mutations have the same pathophysiologic consequence at the cellular level. The most prevalent mutation in European patients is the H1069Q point mutation. H1069Q homozygotes (accounting for 25% of Wilson disease patients in Europe) present more frequently at an older age with neurologic symptoms [[9]Stapelbroek J.M. Bollen C.W. van Amstel J.K. van Erpecum K.J. van Hattum J. van den Berg L.H. et al.The H1069Q mutation in ATP7B is associated with late and neurologic presentation in Wilson disease: results of a meta-analysis.J Hepatol. 2004; 41: 758-763Abstract Full Text Full Text PDF PubMed Scopus (129) Google Scholar]. A truncating mutation may be associated with early onset of disease [[10]Merle U. Weiss K.H. Eisenbach C. Tuma S. Ferenci P. Stremmel W. Truncating mutations in the Wilson disease gene ATP7B are associated with very low serum ceruloplasmin oxidase activity and an early onset of Wilson disease.BMC Gastroenterol. 2010; 10: 8Crossref PubMed Scopus (74) Google Scholar]. Beyond that, further phenotype–genotype correlations were not found in databases with more than 1000 patients, possibly because all other mutations are far less common. Environmental, epigenetic, and other genetic factors may probably play a role. There is clear evidence that female gender (mediated by estrogens) has an impact on the course of disease. More than 2/3 of patients with fulminant Wilson disease are female and overall more females present with hepatic disease than males [[11]Ferenci P. Merle U. Czlonkowska A. Bruha R. Houwen R. Szalay F. et al.Impact of gender on the clinical presentation of Wilson disease.J Hepatol. 2010; 52: S31-S32Abstract Full Text PDF Google Scholar].Table 1Disease 12Schiefermeier M. Kollegger H. Madl C. Polli C. Oder W. Kühn H.J. et al.The impact of apolipoprotein E genotypes on phenotypic expression of Wilson's disease.Brain. 2000; 123: 585-590Crossref PubMed Scopus (125) Google Scholar, 19Arredondo M. Núñez H. López G. Pizarro F. Ayala M. Araya M. Influence of estrogens on copper indicators: in vivo and in vitro studies.Biol Trace Elem Res. 2010; 134: 252-264Crossref PubMed Scopus (34) Google Scholar, 20Ferenci P. Wilson's disease.Clin Gastroenterol Hepatol. 2005; 3: 726-733Abstract Full Text Full Text PDF PubMed Scopus (102) Google Scholar, 21de Bie P. van de Sluis B. Burstein E. van de Berghe P.V. Muller P. Berger R. et al.Distinct Wilson's disease mutations in ATP7B are associated with enhanced binding to COMMD1 and reduced stability of ATP7B.Gastroenterology. 2007; 133: 1316-1326Abstract Full Text Full Text PDF PubMed Scopus (118) Google Scholar in Wilson disease.∗COMMD1:copper metabolism Murr1 domain region 1. Murr1 is the gene responsible for the copper storage disease in Bedlington terriers. Open table in a new tab ∗COMMD1:copper metabolism Murr1 domain region 1. Murr1 is the gene responsible for the copper storage disease in Bedlington terriers. Variations of some genes were reported to be linked to the clinical presentation, like apolipoprotein E [[12]Schiefermeier M. Kollegger H. Madl C. Polli C. Oder W. Kühn H.J. et al.The impact of apolipoprotein E genotypes on phenotypic expression of Wilson's disease.Brain. 2000; 123: 585-590Crossref PubMed Scopus (125) Google Scholar] or human prion gene [[13]Merle U. Stremmel W. Gessner R. Influence of homozygosity for methionine at codon 129 of the human prion gene on the onset of neurological and hepatic symptoms in Wilson disease.Arch Neurol. 2006; 63: 982-985Crossref PubMed Scopus (37) Google Scholar]. The data were obtained in small cohorts and some were not reproduced by others. So far, the overall contribution of other genetic factors to the disease heterogeneity is minimal. This raises several important questions regarding the natural history of Wilson disease and the long term management of patients. In this issue of the Journal, a further association is reported [[14]Gromadzka G. Rudnicka M. Chabik G. Przybylkowski A. Czlonkowska A. Genetic variability in the methylenetetrahydrofolate reductase gene (MTHFR) affects clinical expression of Wilson's Disease.J Hepatol. 2011; 55: 913-919Abstract Full Text Full Text PDF PubMed Scopus (47) Google Scholar]. Gromadzka et al. genotyped the two 5,10-methylenetetrahydrofolate reductase (one of the key folate/homocysteine pathway enzymes) gene (MTHFR) polymorphisms: C677T and A1298C in a relative small cohort (for the purpose of the study), 245 WD patients. Patients with the MTHFR 1298C allele were 4 years younger at symptoms onset than those without this allele. Carriers of MTHFR "high activity" diplotype (double wild-type homozygotes 677CC/1298AA) manifested WD at older age than non-carriers (33.5 vs. 25.0 years, p = 0.0009). Patients with the MTHFR 677T allele less frequently exhibited the neurological WD phenotype (29.5% vs. 48.0%), and more frequently presented with hepatic WD (41.9% vs. 29.3%), compared with subjects MTHFR 677T(−). Polymorphisms of 5,10-methylenetetrahydrofolate reductase are linked to hundreds of diseases including coronary heart disease, colorectal cancer, acute lymphoblastic leukemia, cerebral ischemia, inflammatory bowel diseases, schizophrenia, just to name a few. Thus, the first question is what are the underlying mechanisms of all this disease associations? The authors argue that homocysteine is involved in copper metabolism and is also neurotoxic. This may well be the case, but multiple other consequences have been described, including effects on DNA synthesis or oxidative stress, common factors associated with cancer development and chronic inflammation. One key factor for increasing homocysteine levels is folate intake. Unfortunately most of the studies, including the present one, did not collect data on nutritional habits. As also addressed by the authors, there is a geographic and ethnic variation in the population frequency of the T allele. US Hispanics and Southern Europeans have a high frequency of the variant allele (>40%), whereas other European populations (e.g., British, Irish) and US whites have frequencies between 30% and 36%. US blacks have a low frequency of the variant allele (14%), while Asian populations have a frequency of 11% [[15]Botto L.D. Yang Q. 5,10-Methylenetetrahydrofolate reductase gene variants and congenital anomalies: a HuGE review.Am J Epidemiol. 2000; 151: 862-877Crossref PubMed Scopus (888) Google Scholar]. The fact that hepatic disease at young age is more frequent in Asian population (with a low frequency of MTHFR 677T) does not support the observation in Polish patients. There are many problems in the interpretation of genetic association studies [[16]Attia J. Ioannidis J.P. Thakkinstian A. McEvoy M. Scott R.J. Minelli C. et al.How to use an article about genetic association: B: are the results of the study valid?.JAMA. 2009; 301: 181-195Google Scholar]. One of the basic requirements is to define the phenotype as accurately as possible, ideally by somebody not involved in the study. The authors correctly point out the difficulty in defining the time and type of symptomatic presentation. In clear cut cases, it is fairly straightforward to identify patients with neurologic or hepatic symptoms. However, if somebody presents with neurologic symptoms, how can one exclude that the patient already had an asymptomatic liver disease for decades? If liver disease is accidentally found at a routine blood test – how can one discard the possibility that this patient would have developed the neurologic disease at a later time? We described a case of an 18-year-old asymptomatic woman with the accidental finding of a Kayser–Fleischer ring, who received no treatment and developed neurologic symptoms 27 years later [[3]Ferenci P. Członkowska A. Merle U. Szalay F. Gromadzka G. Yurdaydin C. et al.Late onset Wilson disease.Gastroenterology. 2007; 132: 1294-1298Abstract Full Text Full Text PDF PubMed Scopus (195) Google Scholar]. Many chronic liver diseases including chronic viral hepatitis are asymptomatic and will be diagnosed when the end stage liver disease produces symptoms. A delay in diagnosing WD for those patients with neuropsychiatric presentations is frequent and was in one case as long as 12 years [[17]Merle U. Schaefer M. Ferenci P. Stremmel W. Clinical Presentation, diagnosis and long-term outcome of Wilson disease – a cohort study.Gut. 2007; 56: 115-120Crossref PubMed Scopus (460) Google Scholar]. Patients presenting with neuropsychiatric symptoms may have concurrent symptomatic liver disease, but in most patients, liver disease can only be detected by laboratory evaluation, imaging of the liver, or liver biopsy. Some patients presenting with neurologic symptoms report that they have previously experienced transient episodes of jaundice, probably due to hemolysis [[18]Członkowska A. A study of haemolysis in Wilson's disease.J Neurol Sci. 1972; 16: 303-314Abstract Full Text PDF PubMed Scopus (11) Google Scholar]. About half of the patients have advanced fibrosis or frank cirrhosis [[1]Ferenci P. Steindl-Munda P. Vogel W. et al.Diagnostic value of quantitative hepatic copper determination in patients with Wilson disease.Clin Gastroenterol Hepatol. 2005; 3: 811-818Abstract Full Text Full Text PDF PubMed Scopus (194) Google Scholar]. On the other hand, signs of liver disease may be even completely absent at biopsy [[1]Ferenci P. Steindl-Munda P. Vogel W. et al.Diagnostic value of quantitative hepatic copper determination in patients with Wilson disease.Clin Gastroenterol Hepatol. 2005; 3: 811-818Abstract Full Text Full Text PDF PubMed Scopus (194) Google Scholar]. Thus, the question is how one can define the phenotype. Obviously, diagnosis of liver disease is complex in asymptomatic patients. Cirrhosis can be diagnosed quite reliably by noninvasive techniques, while for milder forms, liver histology is still the "gold standard". The authors cite many reasons why they have not done liver biopsies. This is acceptable for the clinical management of patients, but in a study which compares neurologic with hepatic presentation it is a necessity. Without a biopsy, the conclusion that that MTHFR polymorphism contributes to the phenotypic variability of WD is not sustainable. The study should be repeated in cooperation with centers where liver biopsies are done routinely. Second, there is a major selection bias. The authors work at a well recognized adult neuropsychiatric facility, as a result the median age of their patients was 28 years. About 40% of patients with WD present below the age of 15 [[11]Ferenci P. Merle U. Czlonkowska A. Bruha R. Houwen R. Szalay F. et al.Impact of gender on the clinical presentation of Wilson disease.J Hepatol. 2010; 52: S31-S32Abstract Full Text PDF Google Scholar], thus, apparently children and young adults with WD were not investigated. If the association of MTHFR mutations is valid, this group of patients may have a low frequency of this "protective" mutation and a statistical significance may be lost. Finally, the study included asymptomatic siblings; thereby the frequency of the studied mutation may have been influenced. In summary, the results of the study are not conclusive but should encourage a worldwide cooperation to identify factors associated with the phenotypic presentation in a sufficiently large, well defined group of WD patients. The difficulties to define the phenotype in WD patients call for a study about the natural history of WD. Furthermore, MTHFR polymorphisms are common and have been associated with many diseases. So the finding of an association with WD phenotypes is neither unique nor specific. The author declared that he does not have anything to disclose regarding funding or conflict of interest with respect to this manuscript.