The presence of an additional X or Y chromosome (sex chromosome trisomies, SCT) is associated with an increased risk for neurodevelopmental difficulties, including socio-emotional problems, across the life span. Studying emotion regulation in young children with SCT could signal deviations in emotional development that serve as risk markers to guide clinical care. This study explored the presence and variety of emotion regulation strategies in 75 SCT children and 81 population-based controls, aged 1–7 years, during a frustration-inducing event in which physiological (heart rate) and observational data (behavioral responses) were collected. Children with SCT were equally physiologically aroused by the event as compared to controls. However, they showed more emotion regulation difficulties in terms of behavior compared to controls that were not explicable in terms of differences in general intellectual functioning. Specifically, they had a more limited range of behavioral alternatives and tended to rely longer on inefficient strategies with increasing age. The field of practice should be made aware of these early risk findings regarding emotion regulation in SCT, which may potentially lay the foundation for later socio-emotional problems, given the significant impact of emotion regulation on child and adult mental health outcomes. The current results may help to design tailored interventions to reduce the impact of the additional sex chromosome on adaptive functioning, psychopathology, and quality of life.

Investigating sex chromosome trisomies (SCTs) may help in understanding neurodevelopmental pathways underlying the risk for neurobehavioral problems and psychopathology. Knowledge about the neurobehavioral phenotype is needed to improve clinical care and early intervention for children with SCT. This is especially relevant considering the increasing number of early diagnosed children with the recent introduction of noninvasive prenatal screening. The TRIXY Early Childhood Study is a longitudinal study designed to identify early neurodevelopmental risks in children with SCT, aged 1–7 years. This review summarizes the results from the TRIXY Early Childhood Study, focusing on early behavioral symptoms in areas of autism spectrum disorder, attention-deficit hyperactivity disorder, and communication disorders, and underlying neurocognitive mechanisms in domains of language, emotion regulation, executive functioning, and social cognition. Behavioral symptoms were assessed through structured behavior observation and parental questionnaires. Neurocognition was measured using performance tests, eyetracking, and psychophysiological measures of arousal. In total, 209 children aged 1–7 years were included: 107 children with SCT (33 XXX, 50 XXY, and 24 XYY) and 102 age-matched population controls. Study outcomes showed early behavioral symptoms in young children with SCT, and neurocognitive vulnerabilities, already from an early age onward. Neurobehavioral and neurocognitive difficulties tended to become more pronounced with increasing age and were rather robust, independent of specific karyotype, pre/postnatal diagnosis, or ascertainment strategy. A more longitudinal perspective on neurodevelopmental ‘at-risk’ pathways is warranted, also including studies assessing the effectiveness of targeted early interventions. Neurocognitive markers that signal differences in neurodevelopment may prove to be helpful in this. Focusing on early development of language, social cognition, emotion regulation, and executive functioning may help in uncovering early essential mechanisms of (later) neurobehavioral outcome, allowing for more targeted support and early intervention.

The 3rd International Workshop on Klinefelter Syndrome, Trisomy X, and 47,XYY syndrome was held in Leiden, the Netherlands, on September 12–14, 2022.

Here, we review new data presented at the workshop and discuss scientific and clinical trajectories. We focus on shortcomings in knowledge and therefore point out future areas for research.

We focus on the genetics and genomics of supernumerary sex chromosome syndromes with new data being presented. Most knowledge centre specifically on Klinefelter syndrome, where aspects on testosterone deficiency and the relation to bone, muscle and fat were discussed, as was infertility and the treatment thereof. Both trisomy X and 47,XYY syndrome are frequently affected by infertility.

Transitioning of males with Klinefelter syndrome was addressed, as this seemingly simple process in practise is often difficult.

It is now realized that neurocognitive changes are pervasive in all supernumerary sex chromosome syndromes, which were extensively discussed. New intervention projects were also described, and exciting new data concerning these were presented.

Advocacy organizations were present, describing the enormous burden carried by parents when having to explain their child’s specific syndrome to most professionals whenever in contact with health care and education systems. It was also pointed out that most countries do not have health care systems that diagnose patients with supernumerary sex chromosome syndromes, thus pinpointing a clear deficiency in the current genetic testing and care models.

At the end of the workshop, a roadmap towards the development of new international clinical care guidelines for Klinefelter syndrome was decided.