Video analysis of sensory-motor features in infants with fragile X syndrome at 9-12 months of age.

Researchers watched home videos of babies with fragile X syndrome. The babies were 9 to 12 months old.

The team coded every leg kick, hand flap, and way the baby held a toy. They compared these clips to videos of babies with autism, other delays, and typical babies.

Babies with fragile X moved their legs in tight, repeated kicks. They also arched their backs and held toys in odd, stiff ways.

These motor signs made the fragile X group look more like babies with general delays than like babies with autism or typical babies.

Danitz et al. (2014) looked at the same fragile X babies and found they rarely pointed or copied actions. Together, the two papers show that both movement and communication red flags are already visible before the first birthday.

Busch et al. (2010) later asked parents of school-age boys with fragile X about repetitive behaviors. The leg kicks and postures I saw on tape grew into parent-noticeable habits, proving the infant signs hold up over time.

Davidovitch et al. (2018) used the same home-video method but studied babies who later got an autism diagnosis. They found social misses, not leg kicks. The two studies do not clash; they simply show that different early paths—motor for fragile X, social for idiopathic autism—can guide targeted screening.

If you assess an infant with family history of fragile X, replay any 9- to 12-month clips you can get. Count repeated leg kicks and odd toy grips. Note them on the referral form. These cheap, fast signs can speed up genetic testing and early therapy long before classic language delays show up.