Concurrent diagnosis of spinal muscular atrophy and trisomy 21: Value of comprehensive analysis in prenatal genetic testing.

Co-occurrence of Spinal muscular atrophy and Trisomy 21 in prenatal diagnosis has not been previously described. Amniocentesis was performed at 17 weeks gestation on a 40-year-old woman with two prior SMA-affected offspring. Standard short tandem repeat analysis for maternal cell contamination detection was conducted prior to SMN1/2 copy number assessment via multiplex ligation-dependent probe amplification (MLPA). STR marker analysis revealed tri-allelic patterns in five of six chromosome 21 markers, indicative of Trisomy 21. MLPA confirmed homozygous SMN1 deletion (exons 7-8) and two SMN2 copies. Quantitative fluorescence PCR validated Trisomy 21 and normal chromosomes 13, 18, and sex chromosomes. This case demonstrates the diagnostic utility of STR-based MCC analysis beyond quality control, serving as effective aneuploidy screening. The concurrent identification of SMA and Trisomy 21 emphasizes comprehensive evaluation importance and suggests modifications to genetic counseling protocols in prenatal diagnosis.