Many families first notice something is different when a baby has low muscle tone that makes them feel “floppy,” feeding or sucking difficulties, or slower-than-expected early milestones like rolling or sitting. Doctors may first suspect 21q22.11q22.12 microdeletion syndrome after a prenatal ultrasound shows growth differences or heart findings, or later when a newborn exam notes distinctive facial features, congenital heart defects, or poor weight gain. If development doesn’t follow the usual pace or medical issues cluster, genetic testing is often done to confirm the first signs of 21q22.11q22.12 microdeletion syndrome.