Many parents first notice something subtle, like a newborn who seems unusually quiet, has trouble feeding, or feels a bit “floppy” because of low muscle tone; these early clues often prompt the first check-ups. Doctors may then see features such as a small head size, distinctive facial traits, or heart findings on exam or ultrasound, which lead to genetic testing that confirms 1p36 deletion syndrome. So the first signs of 1p36 deletion syndrome are usually recognized in infancy through feeding difficulties, low muscle tone, developmental delays, and medical features that bring families and clinicians to ask how 1p36 deletion syndrome is first noticed.