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Think of ATP7B as the liver's copper 'exit door' into bile. When that door is jammed, copper backs up in the liver first, then spills over into the brain's basal gangliaA group of deep brain structures that help control movement and are affected in Parkinson's disease and by antipsychotic drugs.Read more → and the eye, producing the classic liver-brain-eye triad of Wilson's disease.

• Wilson's disease (hepatolenticular degeneration) is an autosomal recessive disorder caused by mutation of the ATP7B gene on chromosome 13, which encodes a copper-transporting ATPase in hepatocytes.
• Loss of ATP7B function impairs incorporation of copper into caeruloplasmin and biliary copper excretion, causing toxic copper accumulation, first in the liver and then in the basal gangliaA group of deep brain structures that help control movement and are affected in Parkinson's disease and by antipsychotic drugs.Read more → (especially the lentiform nucleus), cornea and other tissues.
• Hepatic accumulation causes liver dysfunction, ranging from asymptomatic transaminitis to fulminant liver failure.
• Basal gangliaA group of deep brain structures that help control movement and are affected in Parkinson's disease and by antipsychotic drugs.Read more → (lentiform nucleus) accumulation produces the movement disorder features: tremor, dystoniaInvoluntary muscle contractions causing abnormal, sometimes painful, postures or movements.Read more →, dysarthria and parkinsonism.
• Corneal copper deposition in Descemet's membrane produces the Kayser-Fleischer ring, especially visible with neurological involvement.

• A 19-year-old woman with personality change, clumsiness, slurred speech, tremor, dystoniaInvoluntary muscle contractions causing abnormal, sometimes painful, postures or movements.Read more →, a golden-brown corneal ring and low serum caeruloplasmin.
• Questions on the ATP7B gene mutation encoding a copper-transporting ATPase.
• A slit-lamp examination showing a Kayser-Fleischer ring from copper deposition in Descemet's membrane.
• A 24-year-old man with new psychiatric symptoms plus liver dysfunction, low caeruloplasmin, raised urinary copper, and basal gangliaA group of deep brain structures that help control movement and are affected in Parkinson's disease and by antipsychotic drugs.Read more → changes on MRI.

• Wilson's disease vs haemochromatosis — Wilson's disease is a copper-overload disorder (ATP7B mutation, low caeruloplasmin, Kayser-Fleischer ring), whereas haemochromatosis is an iron-overload disorder (HFE mutation, raised ferritin and transferrin saturation).
• Wilson's disease vs Huntington's disease — Wilson's disease is a treatable, autosomal recessive copper-storage disorder presenting young with hepatic plus basal gangliaA group of deep brain structures that help control movement and are affected in Parkinson's disease and by antipsychotic drugs.Read more → features, whereas Huntington's disease is an autosomal dominant CAG-repeat disorder with striatal GABAergic neuron loss and chorea.
• Kayser-Fleischer ring vs Lisch nodules — the ring is corneal copper deposition seen in Wilson's disease, whereas Lisch nodules are iris hamartomas seen in neurofibromatosis type 1.
• Wilson's disease vs Parkinson's disease — Wilson's disease occurs in young patients with hepatic involvement and low caeruloplasmin, whereas Parkinson's disease is a disorder of older adults from nigrostriatal dopaminergicRelating to dopamine, a brain chemical involved in reward, motivation and movement.Read more → loss without copper abnormality.

• Overlooking Wilson's disease in a young patient (under 40) presenting with 'psychiatric' symptoms plus abnormal liver function tests — always consider it in unexplained young-onset neuropsychiatric plus hepatic disease.
• Assuming a normal serum caeruloplasmin excludes Wilson's disease — caeruloplasmin can occasionally be normal, especially early or in an acute-phase response, so urinary copper and clinical findings still matter.
• Confusing the Kayser-Fleischer ring's location (cornea) with a retinal sign.
• Mixing up copper-overload (Wilson's) and iron-overload (haemochromatosis) biochemistry and gene names.

• Localise the clue to the relevant anatomical level, cell type, pathway or molecular process.
• Map that structure or process to its normal function.
• Predict the deficit or clinical sign produced when it is disrupted.
• Reject options that belong to a neighbouring structure, pathway or level of explanation.