"FISHed" out the diagnosis: A case of DiGeorge syndrome

Diagnosis of 22q11.2 deletion syndrome in children with congenital heart diseases and facial dysmorphisms

Background

Congenital heart diseases (CHDs) are the leading cause of birth defects. Approximately, 30% of CHDs are related to genetic syndromes accompanied by extracardiac anomalies. Aneuploidies and 22q11.2 deletions account for majority of cases. 22q11.2 deletion involves deletion of 30-40 genes, and varying deletions in this region lead to different phenotypes. Fluorescent in situ hybridization probes span a narrow region on chromosome 22 as compared to other recent techniques like multiplex ligation probe amplification assay (MLPA) which may also identify any gene duplications if present.

Methods

Present study was a cross-sectional descriptive study. In total, 350 children with CHD reported to pediatric cardiology clinic during the study period. Of these, 60 children had associated facial dysmorphism. Out of these 60 children, 18 children had clinical phenotype characteristic of Down syndrome and hence these children were excluded from the study. Forty-two children with CHDs (conotruncal and other defects) and craniofacial features (subtle or obvious) suggestive of 22q11.2 deletion spectrum disorder were included in this study.

Results

Nineteen percent of children presenting with CHDs and facial dysmorphisms had 22q11.2 deletion syndrome. All the samples were subjected to karyotyping.

Conclusion

Metaphase FISH has been the method of choice for microdeletions. However, apart from technical challenges and longer turnaround time, FISH probes span a very narrow region in 22q11.2 chromosome (LCR22 D) and provide information about DiGeorge syndrome (DGS) only. Take home message is that patients of CHDs with facial dysmorphism should be investigated in an approach-based manner.