Neurodevelopmental

• Severe or moderate developmental delay (little or no speech, limited motor skills)
• Intellectual disability 
• Microcephaly (small head size), often developing after birth
• Low muscle tone (hypotonia) early on, sometimes progressing to stiffness or spasticity

Movement & Motor Control

• Abnormal involuntary movements (jerky, twisting, or writhing motions)
• Poor coordination and balance
• Limited ability to sit, stand, or walk independently 

Seizures

• Epilepsy is very common
• Seizures often begin in infancy and can be difficult to control. (A few children have no seizures)

Feeding & Growth

• Feeding difficulties (poor sucking, swallowing issues)
• Gastroesophageal reflux
• Slow weight gain; some require feeding tubes

Behavior & Communication

• Minimal or absent speech (some individuals have some speech but nearly all will need speech, language and communication support)
• Limited eye contact in some individuals, cortical visual impairment.
• Features that can resemble autism spectrum disorder, though FOXG1 is distinct

Sleep & autonomic issues

• Severe sleep disturbances
• Episodes of unexplained crying or irritability
• Temperature regulation or breathing irregularities (in some cases)