Can Type B interrupted aortic arch (IAA) occur without DiGeorge syndrome?

Type B Interrupted Aortic Arch Can Occur Without DiGeorge Syndrome

Yes, Type B interrupted aortic arch (IAA) can occur without DiGeorge syndrome, although there is a strong association between the two conditions.

Association Between Type B IAA and DiGeorge Syndrome

Type B IAA has a significant but not absolute association with DiGeorge syndrome (22q11.2 deletion):

• According to ACC/AHA guidelines, DiGeorge syndrome is commonly associated with IAA type B, aortic arch anomalies, truncus arteriosus, and tetralogy of Fallot 1
• Studies show that many patients with Type B IAA have DiGeorge syndrome, but not all 2, 3
• In one long-term outcomes study, the presence of DiGeorge syndrome was not associated with increased mortality risk in patients with IAA who survived initial repair 2

Epidemiology and Genetics

• Approximately 50-75% of patients with Type B IAA have DiGeorge syndrome 1, 4
• DiGeorge syndrome (22q11.2 deletion) is an autosomal dominant condition 1
• An underlying chromosomal abnormality exists in at least 10% of infants with congenital heart disease (CHD) 1

Clinical Implications

For Patients with Type B IAA:

• Genetic testing for 22q11.2 deletion is recommended regardless of the presence of extracardiac features 1
• The American Heart Association recommends that all infants with interrupted aortic arch type B be tested for 22q11.2 deletion 1
• In clinical practice, infants with Type B IAA are often treated as if they have DiGeorge syndrome while awaiting genetic test results, especially during surgical interventions 1

For Patients with DiGeorge Syndrome:

• Clinical features include thymic and parathyroid hypoplasia, immunodeficiency, low-set ears, hypocalcemia, speech and learning disorders, renal anomalies, and psychiatric disease 1
• Regular screening for associated conditions is necessary 1

Surgical Management Considerations

• Type B IAA (vs Type A) is associated with higher long-term mortality risk (adjusted hazard ratio 3.32) 2
• Staged repair approaches for Type B IAA are associated with higher mortality risk 2
• The need for left ventricular outflow tract obstruction interventions during initial hospitalization is a significant risk factor 2
• Survival outcomes for IAA repair have improved over time 2, 3

Diagnostic Approach

For patients with Type B IAA:

1. Perform complete cardiac evaluation with echocardiography
2. Genetic testing for 22q11.2 deletion regardless of extracardiac features
3. If DiGeorge syndrome is confirmed, evaluate for associated conditions:
   • Immune function assessment
   • Calcium levels
   • Thyroid function
   • Developmental assessment
   • Renal imaging

Conclusion

While Type B IAA and DiGeorge syndrome frequently co-occur, Type B IAA can definitely occur in the absence of DiGeorge syndrome. The strong association warrants genetic testing in all patients with Type B IAA, but clinicians should recognize that a significant minority of these patients will not have DiGeorge syndrome.