Diagnosis of Wilson disease in a patient with chronic liver disease, tremor or dystonia, and Kayser-Fleischer rings is readily made, but it is very rare to find all three of these at the same time. For most patients the diagnosis therefore has to step far beyond the clinical ground and rest on biochemical testing, and each test has its own pitfalls.
Serum ceruloplasmin
Serum ceruloplasmin is typically reduced in Wilson disease, because ATP7B is needed to load copper onto the protein: without that activation the protein is unstable and is not secreted into the circulation in its normal form. A level below 50 mg/L (5 mg/dL) is strong evidence of the disease. The test has to be read with care for three reasons.
- A technical problem in laboratory measurement: the most common assays detect both apo- and holo-ceruloplasmin, so they over-estimate the amount of functional, copper-carrying protein.
- Ceruloplasmin is not decreased in all patients: in children it can even be increased, and because ceruloplasmin is an inflammatory biomarker, liver inflammation raises its production.
- A decreased serum ceruloplasmin is not specific for Wilson disease: it can also be seen in other liver diseases, nephrotic syndrome, malabsorption and malnutrition.
A normal ceruloplasmin therefore does not exclude the diagnosis.
Hereditary aceruloplasminemia
There is a rare hereditary condition, inherited in an autosomal recessive pattern, in which no ceruloplasmin is detectable in the serum; it is called hereditary aceruloplasminemia. In this condition iron accumulates in the liver, retina and pancreas, leading to degeneration of these organs. It illustrates the physiological role of ceruloplasmin in the oxidation of iron, which is needed to transport iron from ferritin to transferrin.
Serum copper
Most of the copper in the serum is bound to ceruloplasmin, and the smaller non-ceruloplasmin-bound fraction is the free copper that damages tissue and that the tests for Wilson disease follow. Because ceruloplasmin is low in Wilson disease, the amount of serum copper it carries is decreased. In most cases, except the very severe cases with acute liver failure (ALF), this fall in ceruloplasmin-bound copper lowers the total serum copper. In severe Wilson disease with ALF, damage to the hepatocyte releases the copper inside it into the general circulation, so the non-ceruloplasmin-bound copper increases and the total serum copper can even rise.
24-hour urinary copper
The urinary excretion of copper in 24 hours reflects the amount of non-ceruloplasmin-bound copper in the circulation. In untreated symptomatic patients it is typically above 100 µg per 24 hours, and a value above 40 µg per 24 hours, the upper limit of normal in many laboratories, already warrants further investigation, although other liver diseases can also raise it. When basal excretion is below 100 µg in a symptomatic child, a penicillamine challenge test can be added: 500 mg of penicillamine is given at the start and again 12 hours into the collection, and a rise above 1600 µg of copper per 24 hours supports the diagnosis.
Liver biopsy and genetic testing
Measurement of hepatic parenchymal copper above 250 µg/g dry weight remains the best biochemical evidence for Wilson disease, and normal liver copper, below about 40–50 µg/g dry weight, makes the diagnosis very unlikely; intermediate values of 70–250 µg/g need further testing. The main problem with the measurement is that copper is distributed unevenly in advanced disease, so sampling error can underestimate it.
Because no single test is decisive and patients are usually compound heterozygotes, genetic testing by whole-gene sequencing of ATP7B is used when the biochemical picture is difficult. The Leipzig score, which combines the clinical, biochemical and genetic findings into a single diagnostic score, and the newer measurement of relative exchangeable copper are both recommended to support diagnosis. Once the variants in an index patient are known, mutation or haplotype testing can screen the family.
Screening of relatives
First-degree relatives of any patient newly diagnosed with Wilson disease must be screened, because disease found before symptoms appear is treatable. Where molecular testing is available it is the most efficient route; otherwise screening uses the history and examination, serum copper, ceruloplasmin, liver tests, slit-lamp examination for Kayser-Fleischer rings, and a basal 24-hour urinary copper.