February 2026 Research Update

This month adds a clearer, more concrete picture of early childhood development in Kleefstra syndrome, based on information from a larger group of families. The overall pattern is that early motor milestones and early language tend to be reached later than in typical development, with wide variation between children. Having specific milestone ages reported can help families put their child's progress into a Kleefstra syndrome context, even though it does not predict an individual child's future development. [1]

In a review of 100 people with molecularly confirmed Kleefstra syndrome, the median age for rolling was 6 months and for sitting was 10 months. Independent walking was reached at a median of 1.96 years, and first words at a median of 24 months. These numbers describe what was recorded across this group and help anchor expectations around the timing of early skills in Kleefstra syndrome. [1]

In a smaller subset of 24 participants who had more formal early testing, average developmental quotients for visual-motor skills and language were both in the 50s (with receptive and expressive language also around this range). In plain language, that means many children in this subset were developing these skills more slowly than expected for age, rather than losing skills. Because only some families had this testing documented, it gives a partial but still helpful snapshot of early abilities in Kleefstra syndrome. [1]

For families, this mainly adds better reference points for what early development can look like in Kleefstra syndrome, especially for sitting, walking, and early words. It may matter now as a way to frame conversations and track progress over time, but it does not set a "normal" timeline for any one child. What remains uncertain is how well these early milestone patterns predict later communication, learning, or independence, because the report was based on past records and did not follow children forward in a consistent way. [1]

This month includes an additional signal that heart rhythm changes can occur in Kleefstra syndrome, including changes that may only show up under stress. The report describes a child with Kleefstra syndrome whose resting heart tracing looked normal, but whose QT interval became prolonged with exercise. Because this is a single patient, it mainly expands awareness of what can happen rather than showing how common it is. [2]

In this case, testing did not find a known disease-causing variant in common long QT syndrome genes, while an EHMT1 change confirming Kleefstra syndrome was identified. Heart imaging did not show a structural heart problem, and the QT prolongation was seen with exercise monitoring rather than on a baseline ECG. The authors also discussed a possible link between EHMT1 (a gene involved in epigenetic regulation) and heart rhythm control, but this mechanism remains a hypothesis. [2]

For patients and caregivers, this is most relevant as a reminder that some health issues in Kleefstra syndrome may be missed by only looking at one resting test, because this case involved exercise-related changes. This finding may matter now mainly as background understanding, since it comes from a single case and does not show how often this occurs in Kleefstra syndrome. What remains uncertain is how frequently long QT patterns happen in Kleefstra syndrome and whether they are directly caused by EHMT1 changes or by other factors. [2]