Wilson Disease (ATP7B) Sequencing

Biochemical or genetic testing may be used in evaluating individual for WD.

  • Biochemical testing is more cost effective
  • Genetic testing has higher sensitivity and specificity
  • Combination of both is useful for diagnosis

Most reliable testing method for genetic confirmation of WD or determination of carrier status

May be used as initial screening test in WD or copper transport disorders

Useful in the assessment of deficiency or overload

May be useful in the assessment of overload or response to copper-reducing therapies

Useful in the assessment of overload

Useful in the assessment of overload

May be useful when related serum or urine assessments are inconclusive

Useful when a pathogenic familial variant identifiable by sequencing is known

 

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

Prevalence

1/30,000-50,000

Age of Onset

Early childhood through late adulthood

Symptoms

Caused by toxic accumulation of copper in tissue

  • Ophthalmologic disease
    • Kayser-Fleisher rings caused by copper deposits in the cornea
    • Liver disease
    • Hepatomegaly
    • Jaundice
    • Hepatitis
    • Cirrhosis
    • Chronic liver disease
    • Acute or end-stage liver failure
  • Neurologic disease
    • Progressive rigidity or abnormal movements (tremors, dystonia, dysarthria)
    • Difficulty with gross and fine motor tasks
  • Psychiatric disease
    • Mood disturbance (anxiety, depression, personality or behavioral changes)
    • Cognitive decline or memory problems

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

Diagnostic Issues

  • Affected individuals occasionally have normal biochemical test results
  • Up to 20% of WD carriers have equivocal biochemical findings
  • ATP7B gene testing
    • Most reliable method of diagnosis
    • Can help determine if individual is presymptomatic or unaffected carrier

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

References