When should a child be tested for Becker and Duchenne muscular dystrophy?

When to Test for Becker and Duchenne Muscular Dystrophy in Children

Testing for Duchenne and Becker muscular dystrophy should be performed in any male child with motor delays, especially those showing signs of weakness, Gowers' sign, or markedly elevated creatine kinase (CK) levels. 1

Clinical Scenarios That Should Prompt Testing

Children with No Family History of DMD/BMD

• Not walking by 16-18 months of age 1
• Presence of Gowers' sign (using hands to "climb up" the legs when rising from floor) at any age, but especially before 5 years old 1
• Frequent falls or difficulty with running and climbing stairs 1
• Delayed motor milestones 1
• Low muscle tone with concomitant weakness 1

Children with Positive Family History of DMD/BMD

• Any suspicion of abnormal muscle function, regardless of age 1
• Lower threshold for testing should be applied even with minimal symptoms 1

Other Clinical Scenarios

• Unexplained elevation of transaminases (AST, ALT) 1
• DMD should be considered before proceeding to liver biopsy in male children with elevated liver enzymes 1
• Unexplained developmental delay, especially motor delays 1

Diagnostic Testing Algorithm

1. Initial Screening Test: Serum creatine kinase (CK) measurement

   • CK is markedly elevated in DMD (usually >1000 U/L) 1
   • This can be performed within the primary care setting 1

2. If CK is elevated:

   • Proceed to genetic testing for DMD mutations 1
   • Begin with dystrophin deletion/duplication testing 1
   • If negative, proceed to complete genetic sequencing of the DMD gene 1

3. If genetic testing is inconclusive but suspicion remains high:

   • Consider muscle biopsy for dystrophin protein analysis 1

Important Clinical Considerations

• The average age of DMD diagnosis is around 5 years, despite symptoms typically appearing by 2.5 years of age 2
• There is an average 2.5-year delay between symptom onset and diagnosis, which has remained unchanged for decades 2
• Early diagnosis is critical for:
  • Timely genetic counseling for family planning 3
  • Earlier initiation of treatments that can improve outcomes 4
  • Eligibility assessment for emerging mutation-specific therapies 3

Key Clinical Distinctions

• Duchenne Muscular Dystrophy (DMD):

  • More severe phenotype
  • Usually presents at 2-4 years of age 1
  • May show early developmental delays in walking and language 1

• Becker Muscular Dystrophy (BMD):

  • Allelic to DMD but with milder phenotype
  • Typically presents in older children 1
  • Later onset of symptoms with less severe course 1

Common Pitfalls to Avoid

• Delayed diagnosis: Don't wait for multiple symptoms to appear before testing. Check CK early in the evaluation of boys with unexplained developmental delay 2
• Missing atypical presentations: In children under 5 years, a normal muscle examination cannot completely exclude DMD 1
• Overlooking DMD in liver enzyme evaluation: Consider DMD before proceeding to liver biopsy in male children with elevated transaminases 1
• Incomplete genetic testing: If initial deletion/duplication testing is negative but clinical suspicion remains high, complete gene sequencing is necessary 1
• Neglecting carrier testing: After diagnosis, genetic counseling should be offered to all at-risk female family members 1

Early identification and diagnosis are crucial for improving long-term outcomes in children with muscular dystrophy, as they allow for timely interventions, appropriate support, and genetic counseling for families.