Background: Spinal muscular atrophy is a genetically heterogenous disorder, mostly having a recessive inheritance. If the child is diagnosed with this genetic disease, parental screening for spinal muscular atrophy is recommended before planning for future pregnancy as interpreting the results of carrier screening in the context of family history can be challenging. Case: We report the case of a 28-year-old woman with two previous children affected with SMA type 1 succumbed at the age of 6 months; and husband with negative carrier status. Exome sequencing of affected child showed no point mutations. Multiplex ligation probe amplification (MLPA) showed homozygous deletion of both the copies of SMN1 gene. Mother was carrier as her test revealed single copy of SMN1 gene whereas father appeared to be non-carrier with presence of two copies of the same gene. Diagnostic testing for the fetus for SMA showed two copies. Father could be a silent carrier for SMA having cis configuration. Conclusion: Interpretation of carrier screening results could be challenging in case of one of the parents carrying cis configuration and thus behaving as a silent carrier. In these situations, additional genetic testing and genetic counseling are indicated to clarify risk for SMA in pregnancy and guide prenatal diagnosis.
Carrier Screening; Spinal Muscular Atrophy; Prenatal Diagnosis; Genetic Testing