What Is Known/What Is New
What Is Known
- Wilson disease can be accompanied by subclinical zinc deficiency.
- Wilson disease has a multitude of clinical disguises, making diagnosis sometimes difficult.
- Genetic testing can reveal clinically unsuspected diagnoses.
- What Is New
- Clinical zinc deficiency can be a first symptom of Wilson disease.
- Association to mutations in the zinc pathway can aggravate the clinical picture.
See “Wilson Disease: A Matter of Copper, But Also of Zinc” by Iorio and Ranucci on page 423.
Wilson disease (MIM #277900) is a rare autosomal recessive disorder (1/30.000–1/100.000 individuals) of the copper metabolism caused by homozygous or compound heterozygous mutations in the ATP-ase Cu(2+) transporting polypeptide (ATP7B) gene (1,2). Copper accumulation in liver, brain, cornea, and kidneys leads to the most frequent presenting symptoms of progressive liver degeneration (40% of cases), neurological symptoms (35%), Kayser-Fleischer rings, sunflower cataract, and psychiatric problems (10%). Children (>3 years of age) are more likely to present with hepatic symptoms, whereas young adults will more frequently present with neurological symptoms (3). The remaining 15% to 20% of patients have symptoms attributable to involvement of other organs such as the kidney (Fanconi syndrome, renal failure), the heart (cardiac failure), the pancreas (pancreatitis), red blood cells (haemolytic anaemia), and skin (nail, skin discoloration) (4–8).
Seven years ago, a 2.5-year-old white boy was referred for a periocular, perioral, and perineal skin eruption since the age of 12 months, which was resistant to local steroids, antifungal and, antibacterial therapy as well as oral antibiotic therapy; he also complained of frequent episodes of diarrhoea. He displayed a sharp-edged scaly eruption on the above-mentioned locations with an angular cheilitis (Fig. 1). The lesions were infected with Streptococcus pneumoniae. Because the clinical picture was consistent with acrodermatitis enteropathica (AEZ, MIM #201100), a rare autosomal recessive form of severe zinc deficiency, serum zinc levels were measured and found decreased (41.1 μg/dL [normal values 65–150 μg/dL]). The child having a typical Western diet, rich in meat and low in cereals, had a normal zinc intake as calculated by the dietician, which excluded a nutritional zinc deficiency. Familial history was negative. No aetiology which could lead to secondary zinc deficiency because of maldigestion and malabsorption was found, as the sweat test was normal (chloride 29 mmol/L [normal values 0–40 mmol/L]), coeliac serology was negative, and faecal elastase was normal (>500). Duodenal biopsies collected during gastroduodenoscopy were normal. There was no parasitic infestation. Abdominal ultrasound was normal. Rast tests, total IgE, and skin-prick tests for common food allergens were negative, and no association to the intake could be found using an intake-symptom diary.
A zinc acetate supplementation was then started (initially dosed at 4.5 mg elemental zinc/kg body weight a day, tapered until 1 mg · kg−1 · day−1 based on clinical complaints and serum zinc levels), which normalised serum zinc levels and fully resolved the cutaneous symptoms, although our patient remained susceptible for prolonged gastrointestinal infections, such as rotavirus, giardia lamblia, and adenovirus. An immunological screening including B- and T-lymphocyte, leukocyte transformation test, CD11 and CD8 identification, chemotaxis, immunoglobulins, and reaction on pneumococcal vaccination were all normal. He grew along the 10th percentile for height and the 25th percentile for weight, which was within the expected growth channel based on the parents’ height. During follow-up the serum zinc levels, liver enzymes, serum copper, and ceruloplasmin remained normal. To verify the hypothesis of an AEZ, genomic DNA extracted from the child's venous blood samples was screened by Sanger sequencing for mutations of SLC39A4, a major intestinal zinc transporter. As this initial testing was negative, the search was expanded to the high-throughput sequencing (using a custom Sureselect library (Santa Clara, CA) on a Genetic Analyzer (Illumina, San Diego, CA) of 50 genes directly involved in cellular zinc ion homeostasis according to the Gene Ontology database AMIGO 2 (http://amigo.geneontology.org/amigo/term/GO:0006882). This approach revealed, 7 years after the initial presentation, the presence of 2 compound heterozygous mutations in the Wilson disease gene ATP7B (NM_000053.3): c.1995G>A (p.Met665Ile) in exon 7 inherited from the father, and c.2804C>T (p.Thr935Met) in exon 12 inherited from the mother; validation and segregation analysis of both mutations were done by Sanger sequencing. The mutation c.1995G>A (p.Met665Ile) is referenced as rs72552259 in the variant public database dbSNP, and it is reported with a minor allele frequency of 0.26% in the white American population of European descent from the Exome Variant Server (National Heart, Lung, and Blood Institute Exome Sequencing Project, Seattle, WA; http://evs.gs.washington.edu/EVS, April 23, 2014). By contrast, the mutation c.2804C>T (p.Thr935Met) is absent from any public variant database. In addition, a third rare heterozygous variant, inherited from the father, was found in the child's metallothionein gene MT1X (NM_005952.3): c.29–2A>T, reported as rs112485803 in database single-nucleotide polymorphism with a 0.05% minor allele frequency in European American individuals from Exome Variant Server (National Heart, Lung, and Blood Institute Exome Sequencing Project, http://evs.gs.washington.edu/EVS, April 23, 2014). The screening tests for Wilson disease were performed at the age of 10 years during low-dose zinc supplementation (1 mg · kg−1 · day−1, 22.5 mg elemental zinc). The 24-hour urinary collection for copper revealed an increased excretion (217 μg/24 h (normal value: <40 μg/24 h (9)) before D-penicillamine; however, it did not increase significantly after D-penicillamine (352 μg/24 h). There were no Kayser-Fleicher rings and a brain MRI scan did not demonstrate any copper accumulation. The treatment with zinc was then augmented again to 67.5 mg/day (=2.5 mg · kg−1 · day−1). With the treatment urinary copper excretion measured 6 months later revealed a normalisation of the copper excretion (8 μg/24 h).
More than 500 different mutations associated with Wilson disease have been described (http://www.wilsondisease.med.ualberta.ca). The 2 heterozygous missense variants of ATP7B observed in this child were both described as causative mutations (10,11). The exon 12 mutation, which leads to an amino acid change from threonine to methionine (p.Thr935Met), was mainly described in the Chinese population (12) and in an Italian patient with Wilson disease (13). The exon 7 mutation, which leads to the change of methionine to isoleucine (p.Met665Ile), was described in an Albanian patient with Wilson disease (11). Although our patient did not display symptoms or signs of Wilson disease, which was not abnormal because the patient was only 2.5 years old, the basal copper excretion was significantly increased even in the absence of liver disease and within the range of patients reported with presymptomatic Wilson disease (14). The absence of an increased excretion after D-penicillamine could be the result of the zinc supplements he received during 7 years since the age of 2.5 years. Also in untreated presymptomatic children with Wilson disease, the D-penicillamine test has, however, been shown to be less sensitive for the diagnosis of Wilson disease (14).
This unusual clinical presentation of Wilson disease has never been described before. Although we found one letter reporting significantly lower plasma zinc, the reported values are only mildly decreased as the mean plasma zinc value was 60.6 μg/dL (15). The exact mechanism of this presentation is not yet understood as literature is virtually nonexistent. The potentially pathogenic variant identified in MT1X in this case could be responsible for the clinical presentation of this patient. Taking into account the ability of metallothioneins to bind to both copper and zinc, MT1X appears as a good candidate in the hypothesis of a digenic mechanism. The regulations of zinc and copper are indeed tightly interconnected if we refer to the mechanism of action of zinc therapy in Wilson disease. Thus, zinc supplements induce the expression of intestinal copper-binding metalloproteins that inhibit copper absorption into the bloodstream (16). This leads to the hypothesis of the reverse effect in case of a copper overload. On the contrary, the copper overload could influence expression of zinc transporters. An argument in favour of this hypothesis is the unpublished observation of Lutsenko et al (Johns Hopkins University, Baltimore, MD), which is a significant decrease in the expression of 2 zinc uptake hZip transporters (hZip5: 2-fold decrease; hZip8: 2.5-fold decrease), using gene arrays in liver biopsy samples from patients with Wilson disease.
In the case of our patient, the supposed diagnosis of AEZ led to a treatment based on zinc acetate, which is also used in asymptomatic cases of Wilson. The doses used (1–4.5 mg · kg−1 · day−1; 22.5–67.5 mg elemental zinc/day) were initially within the advised treatment doses for Wilson disease in young children (50 mg/day for <6 years) (17) but then tapered to suboptimal doses at the time of diagnosis (60–150 mg elemental zinc for >6 years) (16).
This case demonstrates the possible clinical disguise of Wilson disease. It is important for the clinician to be aware of the multitude of atypical subtle presentations because early recognition can prevent severe complications. The association with the pathogenic MT1X variant could be responsible for this unexpected clinical presentation.
The authors thank Svetlana Lutsenko, PhD, Professor of Physiology at the Johns Hopkins University, Baltimore, Maryland, for sharing with us unpublished data that sustain our pathomechanistic hypothesis.
1. Frydman M, Bonné-Tamir B, Farrer LA, et al. Assignment of the gene for Wilson's disease to chromosome 13: linkage to the esterase D locus. Proc Natl Acad Sci U S A
2. Olivarez L, Caggana M, Pass KA, et al. Estimate of the frequency of Wilson's disease in US Caucasian population: a mutation analysis approach. Ann Hum Genet
3. Gow PJ, Smallwood RA, Angus PW, et al. Diagnosis of Wilson's disease: an experience over three decades. Gut
4. Di Stefano V, Lionetti E, Rotolo N, et al. Hypercalciuria and nephrocalcinosis as early feature of Wilson disease onset: description of a pediatric case and literature review. Hepat Mon
5. Nandi M, Sarkar S, Mondal R. Generalized hyperpigmentation in Wilson's disease: an unusual association. J Neurosci Rural Pract
6. Hlubocka Z, Maracek Z, Linhart A, et al. Cardiac involvement in Wilson disease. J Inherit Metab Dis
7. Weizman Z, Picard E, Barki Y, et al. Wilson's disease associated with pancreatitis. J Pediatr Gastroenterol Nutr
8. Michel M, Lafaurie M, Noel V, et al. Hemolytic anemia disclosing Wilson's disease. Report of 2 cases. Rev Med Interne
9. European Association for Study of Liver. EASL Clinical Practice Guidelines: Wilson's disease. J Hepatol
10. Lepori MB, Lovicu M, Dessi V, et al. Twenty-four novel mutations in Wilson disease patients of predominantly Italian origin. Genetic Testing
11. Loudianos G, Dessi V, Lovicu M, et al. Further delineation of the molecular pathology of Wilson disease in the Mediterranean population. Hum Mutat
12. Gu Y-H, Kodama H, Du S-L, et al. Mutation spectrum and polymorphisms in ATP7B identified on direct sequencing of all exons in Chinese Han and Hui ethnic patients with Wilson's disease. Clin Genet
13. Lepori MB, Lovicu M, Dessi V, et al. Twenty-four novel mutations in Wilson disease patients of predominantly Italian origin. Genet Test
14. Nicastro E, Ranucci G, Vajro P, et al. Re-evaluation of the diagnostic criteria for Wilson disease in children with mild liver disease. Hepatology
15. Geetha A, Jeyachristy SA, Selvamathy SM, et al. A study on the concentrations of serum zinc, non-ceruloplasmin copper, reactive oxygen and nitrogen species in children with Wilson's disease. Clin Chim Acta
16. Ala A, Walker AP, Ashkan K, et al. Wilson's disease. Lancet
17. Ranucci G, Di Dato F, Spagnuolo MI, et al. Zinc monotherapy is effective in Wilson's disease patients with mild liver disease diagnosed in childhood: a retrospective study. Orphanet J Rare Dis