When to worry about Rett Syndrome at 12–18 months

If your little girl seemed to be growing beautifully and you've now noticed something has shifted, your watchfulness is loving and wise — let's make sense of it together.

In short

Rett Syndrome (ICD-11 LD90.0) is a rare genetic condition that almost always affects girls. Classically, development looks typical for the first 6–18 months, and then a child may slow down, plateau, or lose skills she had already gained — particularly purposeful use of the hands and emerging words. So in the 12–18 month window, the signal to act on is not a single milestone delay but a clear regression — a loss of skills she once had. This is a concern to have gently checked, never a diagnosis you should reach at home.

What would genuinely warrant a check

In this age band, the patterns clinicians take seriously are changes from your child's own earlier ability:

• Loss of purposeful hand use — she used to reach, grasp or point, and now seems unable to
• Repetitive hand movements — wringing, washing, tapping, squeezing or hand-to-mouth movements that replace useful hand skills
• Loss of babble or early words she had previously used
• Slowing head growth — your doctor may notice this on the growth chart
• New unsteadiness in sitting or walking, or walking that doesn't emerge as expected
• Reduced eye contact or social engagement after a period of being connected

A single late milestone, in isolation, is usually not this. It is the picture of regression — going backwards on skills already mastered — that should prompt a prompt medical and developmental review.

When and where to seek help

Because Rett Syndrome has a genetic basis (often involving the MECP2 gene) and can be confirmed with medical testing, any suspected loss of skills deserves a prompt paediatric and developmental review, not a wait-and-see approach. Early review also rules in or out the many gentler explanations for a temporary plateau — illness, a growth spurt, or simply a child's own pace. Your paediatrician can arrange the right medical assessment alongside a developmental check.

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 form or a checklist. Our clinicians map your daughter's whole developmental story, coordinate with medical testing where needed, and build supportive, strengths-based occupational therapy and communication plans that protect her hand function, mobility and connection. Across 70+ centres and 25 million+ therapy sessions, families find a calm, expert team beside them from the very first question.

Trusted sources

WHO ICD-11 (LD90.0, Rett Syndrome); American Academy of Pediatrics developmental surveillance guidance (healthychildren.org); WHO Nurturing Care Framework on early development.

Next step — If you've noticed your daughter losing skills she once had, see your paediatrician promptly and book a developmental check with a Pinnacle clinician.

This is general information, not a diagnosis — individual assessment and diagnosis require an appropriately qualified healthcare professional.