Rett Syndrome
When to worry about Rett syndrome at 9–12 months
At 9–12 months it is usually too early to confirm Rett syndrome, whose hallmark loss of hand use typically appears between 12 and 18 months. What warrants prompt review now is any genuine loss of skills a baby once had, slowing head growth, or a drop in engagement — none of which confirms Rett syndrome, but all of which deserve a developmental check.
If you've noticed your baby seeming to pause or slip on skills they were reaching for, your watchful love is exactly the right instinct — let's make sense of it together.
In short
At 9–12 months it is usually too early to confirm Rett syndrome — its most recognisable features, including the distinctive loss of purposeful hand use and the appearance of repetitive hand movements, typically emerge a little later, often between 12 and 18 months. What does deserve prompt attention at this age is any genuine loss of skills your baby had clearly gained, a stall in head growth, or a noticeable drop in alertness and engagement. None of these confirms Rett syndrome — but any one of them is a good reason for a developmental check now rather than waiting.What is worth noticing at 9–12 months
Rett syndrome is a rare, genetically based neurodevelopmental condition, recognised far more often in girls. In the first months babies often develop fairly typically, so the most meaningful early flag is regression — losing something already gained. Gentle things to observe:- Hand use — your baby was reaching, grasping or transferring toys, and this fades or is replaced by repetitive hand-to-mouth or wringing movements.
- Engagement — less eye contact, smiling or babbling than before, or seeming to "switch off".
- Head growth — your paediatrician noticing head circumference slowing across visits.
- Movement — losing steadiness in sitting, or unusual stiffness or floppiness.
Most babies who seem briefly behind are simply moving at their own pace — but a real loss of established skills, in any child, is always worth checking sooner rather than later. It is the loss, not a slow start, that matters most.
The Pinnacle way
A clinical AbilityScore® and any diagnosis are formed only at a Pinnacle Blooms Network centre, under qualified clinician care — never from an online description or a single worry at home. Because Rett syndrome can involve a specific genetic change, our clinicians work first to build your baby's own developmental baseline and, where indicated, guide you toward the right medical and genetic review. If movement or daily skills are the concern, our occupational therapy team can begin gentle, strengths-led support while answers are sought. The aim is clarity and a calm way forward — not a label.Trusted sources
WHO ICD-11 framework for developmental disorders; American Academy of Pediatrics developmental surveillance guidance; CDC developmental milestones and "Learn the Signs, Act Early" resources.Next step — Trust what you've seen. Book a developmental assessment so any genuine loss of skills is reviewed promptly by a Pinnacle clinician.
This is general information, not a diagnosis — a clinical AbilityScore® and any diagnosis are formed only at a Pinnacle Blooms Network centre under qualified clinician care.
What to watch
Act sooner if your baby loses skills they clearly had before — fading hand use, less eye contact or babbling, or new repetitive hand movements — or if their head growth is slowing. A real loss of established skills always warrants a prompt developmental check, even though Rett's clearest features usually emerge a little later.
Try this at home
Keep a short weekly note of skills your baby uses well — reaching for toys, transferring them hand to hand, babbling, making eye contact. If any quietly fade over the coming weeks, you'll have a clear, useful record to share with a clinician.
Trusted sources
Developed by SETU Consortium · Pinnacle Blooms Network · Last reviewed 2026-06-10 · reviewed every 365 days
This is general information, not a diagnosis. A clinical AbilityScore® and any diagnosis are formed only at a Pinnacle Blooms Network centre, under qualified clinician care.
Frequently asked
Can Rett syndrome be diagnosed at 9 months old?
It is usually too early to confirm Rett syndrome at this age. Its most recognisable features — especially the loss of purposeful hand use — typically emerge between about 12 and 18 months. At 9–12 months the most meaningful flag is any genuine loss of skills your baby had already gained, which is worth a developmental check now.
What is the earliest sign of Rett syndrome?
In the first months many babies develop fairly typically, so the earliest meaningful sign is often a slowing of head growth or a regression — losing engagement, babbling or hand skills that were already present. Repetitive hand movements such as wringing tend to appear a little later. Any real loss of established skills should be reviewed promptly by a clinician.
Is Rett syndrome more common in boys or girls?
Rett syndrome is recognised far more often in girls. It is linked to a specific genetic change, and only a qualified clinician — with appropriate medical and genetic review where indicated — can assess whether it is present. A developmental assessment is the right first step if you are worried.