Families often first notice something is different when a baby has low muscle tone that makes them feel “floppy,” feeding difficulties, or slower-than-expected milestones like rolling or sitting; some babies have distinctive facial features or a small head size that prompt a checkup. During pregnancy, an ultrasound may show growth restriction or certain structural differences, and chromosomal microarray or other genetic tests can confirm the diagnosis, capturing the first signs of 1q41q42 microdeletion syndrome. In early childhood, developmental delays, seizures, or congenital differences such as heart, brain, or kidney anomalies may be how 1q41q42 microdeletion syndrome is first noticed.