Many families first notice 15q13.3 microdeletion syndrome when a baby or toddler seems slower to reach milestones like sitting, talking, or walking, or when speech is limited compared with peers. As children grow, doctors are often alerted by learning differences, attention or behavior challenges, or, in some, seizures that prompt genetic testing. For many, the first signs of 15q13.3 microdeletion syndrome are recognized in early childhood during developmental checkups, though it can also be picked up earlier with prenatal testing or after birth when newborn hearing tests or feeding difficulties raise questions.