A Rare Genetic Intersection: Down Syndrome With Coexisting Spinal Muscular Atrophy.

Down syndrome (DS), characterized by trisomy of chromosome 21, and spinal muscular atrophy (SMA), an autosomal recessive neuromuscular disorder, are individually recognized distinct entities. Their co-occurrence in clinical practice is rare and has not been extensively reported. We present a case of a three-month-old, female child who presented with respiratory failure necessitating intubation. Due to typical facial features and congenital heart disease, DS was confirmed with chromosomal analysis. However, subsequent recurrent chest and bloodstream infections, failure to extubate, and laboratory abnormalities raised the suspicion of accompanying immune disorder with DS. To investigate this, whole exome sequencing analysis was sent, and it revealed a homozygous pathogenic mutation in the SMA type 1 gene in the patient. This rare intersection of two unique genetic conditions presents diagnostic challenges due to overlapping clinical features like hypotonia and delay in motor skills, which can be progressive in both situations. Additionally, the clinical trajectory, therapeutic interventions, and outcomes are variable for both conditions and a lack of guidelines for the management of two concurrent genetic conditions, such as in our patient, can pose a challenge for clinicians. Hence, this case report underscores the importance of comprehensive clinical and diagnostic evaluation in individuals with syndromic features and the need for heightened vigilance for concurrent rare genetic conditions that add to the complexity of the disease and may impact clinical outcomes, management, and counseling for the family.