There have been dramatic improvements in our ability to more accurately diagnose the underlying genetic causes of developmental delay/intellectual disability; however, there is less known about the treatment trajectory and whether or not patient management and outcomes have changed due to the information gained from genetic testing. Here we report a case study of a 20-month-old male first referred to the genetics clinic in 2008 for interhemispheric cysts, agenesis of the corpus callosum, left cortical dysplasia, and developmental delay of unknown etiology. The diagnostic work-up for this patient included chromosomal microarray which detected >20% mosaicism for monosomy 7, which raised concern for a possible myelodysplastic syndrome. The clone was not detected in stimulated peripheral blood cultures and his karyotype was reported as a normal male. Because of this microarray finding, he was referred to pediatric hematology/oncology where he was confirmed to have a pre-symptomatic diagnosis of myelodysplastic syndrome and was treated with chemotherapy and a bone-marrow transplant. This case illustrates the clinical utility of microarray testing and the importance of long-term follow-up to assess patient outcomes.