Wilson Disease (ATP7B) Sequencing

Wilson disease is a rare inherited genetic disorder caused by variants in the ATP7B gene resulting in excessive amounts of copper accumulating in the body, particularly in the liver, brain, and eyes. Signs and symptoms most often appear during the teens but may appear as early as age 6 and as late as the mid-40s. Liver disease is typically the initial feature of Wilson disease in affected children and young adults. Nervous system or psychiatric problems are often the initial features in individuals diagnosed in adulthood and commonly occur in young adults. Neurologic symptoms include clumsiness, tremors, difficulty walking, and speech problem. Psychiatric symptoms include impaired thinking, depression, anxiety, and mood swings. Individuals with Wilson disease may have copper deposits in the cornea that forms a green to brown ring around the iris (Kayser-Fleischer ring). These individuals may demonstrate abnormalities in eye movement, such as the inability to look upward.

Disease Overview

Diagnosis

• Slit-lamp examination of cornea to detect Kayser-Fleisher rings
• Combination of biochemical findings:
  • Serum ceruloplasmin: low
  • Serum copper: low
  • Free copper: high
  • 24-hour urine copper: elevated
• Hepatic copper concentration on liver biopsy: elevated
• Testing ATP7B gene for variants can confirm diagnosis
  • Most reliable method of diagnosis
  • Can help determine if individual is presymptomatic or unaffected carrier

Diagnostic Issues

• Affected individuals occasionally have normal biochemical test results
• Up to 20% of WD carriers have equivocal biochemical findings
• ATP7B gene testing

Treatment

• Disease is fatal if untreated
• Treatment includes use of chelating agents to prevent or reverse symptoms
• Only cure is liver transplant

Genetics

Gene

ATP7B

Inheritance

Autosomal recessive

Penetrance

Age dependent, may be reduced

Test Interpretation

Sensitivity/Specificity

• Clinical sensitivity: 98% 
• Analytical sensitivity/specificity: 99%

Results

• Positive
  • Two pathogenic ATP7B gene variants detected on opposite chromosomes
    • Consistent with a diagnosis of WD
  • One pathogenic ATP7B gene variant detected
    • Individual is at least a carrier of WD
    • May be affected with WD if an undetected variant is present on the opposite chromosome
• Negative
  • No pathogenic ATP7B variants detected
    • Significantly reduces likelihood patient is affected with or a carrier of WD
• Inconclusive
  • Variants of uncertain clinical significance may be identified

Limitations

• Diagnostic errors can occur due to rare sequence variations
• Not determined or evaluated:
  • Regulatory region variants
  • Deep intronic variants
  • Large deletions/duplications
  • Variants in genes other than ATP7B