The correlation between epilepsy and autism spectrum disorder (ASD) has already been established,1 and several studies have reported an ASD diagnosis in 25.0–46.2 % of patients with infantile epileptic spasms syndrome (IESS).2-5

The new ILEA classification proposes the use of the term IESS to encompass West syndrome and epileptic spasms that do not fulfill all criteria of a West syndrome. West syndrome is defined as the presence of epileptic spasms, hypsarrhythmia and developmental stagnation or regression. It starts between 1 and 24 months of age and peaks at approximately 3–12 months of age. Before IESS onset, development can be normal; however, a history of abnormal development is often found. This is the most frequent form of epileptic encephalopathy in the first year of life, with an estimated incidence of 30/100,000 live-born infants.6

ASD is a complex neurodevelopment condition in which genetic and environmental factors contribute to its etiology.7 The prevalence of ASD among infants with IESS exceeds the prevalence of ASD in the general population, which is approximately 1:36 according to the Centers for Disease Control and Prevention (CDC).8

Emerging evidence suggests a neuropathological link between IESS and ASD, particularly in patients with a known genetic cause; genetic abnormalities might play a role in the child's neurodevelopment outcomes. Furthermore, epileptic encephalopathy, a potential consequence of IESS, disrupts brain development through alterations in neurotransmitter systems and abnormal electrical activity, potentially contributing to ASD in some children.9 Common comorbidities of IESS like tuberous sclerosis or cerebral palsy might be important for understanding ASD etiology in these patients.1,10 Although previous studies have reported an association between IESS and ASD,2-5 data from developing countries such as Brazil are lacking.

Therefore, this study aimed to determine the prevalence of ASD among children with IESS in a single center in Brazil. Additionally, the authors aimed to delineate the characteristics of children with IESS and the potential mediators underlying the correlation between IESS and ASD.

Of the 53 participants diagnosed with IESS, 29 (55 %) were female, and 24 (45 %) were male. The mean age at the time of data collection was 49.06 ± 10.06 months, ranging from 28 to 72 months. Regarding comorbidities, five (9.4 %) participants had tuberous sclerosis, seven (13.2 %) had Down's syndrome, 15 (28.3 %) had cerebral palsy, 13 (24.5 %) had cortical malformation, 10 (18.7 %) had mild magnetic resonance imaging abnormalities due to prematurity and three (5.6 %) were classified as having idiopathic IESS.

The age at the first seizure ranged from 3 to 15 months (mean, 6.65 ± 2.71 months), and treatment was initiated after the diagnosis of IESS. The first-line medications included vigabatrin (86.6 %) and adrenocorticotropic hormone (ACTH; 13.2 %), whereas a second-line drug was either added or substituted in 38 patients (71.7 %). Persistence of spasms or evolution to other types of seizures one year after diagnosis was observed in 24 patients. Moreover, hypsarrhythmia on EEG persisted two years after diagnosis in 16 patients.

In the study population, 12 (23 %) of the 53 participants were diagnosed with ASD. Table 1 shows the clinical and demographic data of the participants with ASD. The RR of an ASD diagnosis in children with IESS was 0.293 (95 % CI 0.174–0.492).

The study population was divided into two groups: those with ASD (Group 1) and those without ASD (Group 2). A comparison of the clinical variables is presented in Table 2. None of the children with idiopathic IESS were subsequently diagnosed with ASD.

The median (minimum-maximum range) age of spasm onset was significantly different between the two groups: 10.58 (8–15) months in Group 1 and 5.43 (3–8) months in Group 2 (p < 0.001). None of the participants with spasm onset before the age of six months had an ASD diagnosis.

This retrospective cross-sectional study showed that, of the 53 enrolled patients with IESS, 12 (23 %) were diagnosed with ASD, resulting in an RR of 0.29 (95 % CI 0.174–0.492). These findings are consistent with the results of similar studies from France and Iceland [2–5] and show a substantially higher ASD prevalence compared with the latest prevalence rate in the general population reported by the CDC.8 To the best of our knowledge, the current study is the first to report the prevalence of ASD among children with IESS in South America.

Another interesting finding of this study was that children with later-onset spasms (approximately at 10 months of age) were more likely to receive an ASD diagnosis, whereas none of the children diagnosed with IESS before 6 months of age were diagnosed with ASD. This is an unexpected result since prior studies typically reported greater neurodevelopmental deterioration in patients with earlier-onset spasms.12,13

Previous studies have suggested that epileptic seizures can trigger maladaptive synaptic plasticity, leading to imbalances between excitatory and inhibitory neurotransmitter systems, thereby contributing to neurodevelopmental impairments.14 The pruning process occurs primarily during the first year of life, with sensory and motor areas particularly vulnerable between ages 6 and 12 months,15 and abnormalities in these processes have already been associated with ASD diagnosis.16 The authors therefore hypothesize that the emergence of severe electrophysiological dysfunction, as hypsarrhythmia, involving cortical and subcortical regions during this critical period may substantially increase the risk of ASD development in children with IESS.

Another possible explanation for our findings is the fact that the age of onset is based on the date of referral by the parents. Since infantile spasms may appear as subtle movements, they can be easily missed or misinterpreted as a colic or irritation leading to a later diagnosis and treatment.17,18 This delay might be particularly critical as the persistence of spasms beyond 90 days has been linked to poorer developmental outcomes.19

In the present study, the persistence of spasms or hypsarrhythmia and the evolution to another type of seizure in the second year of life did not lead to a subsequent ASD diagnosis. In contrast, another study in children with IESS showed significant persistent hypsarrhythimia in children with ASD at or after one year of age.20

This study also explored potential links to pre-existing structural brain abnormalities or the presence of genetic disorders, known risk factors for ASD in patients with IESS.10,21-23 While the presence of these comorbidities did not significantly differ between children with and without ASD, it is noteworthy that none of the children diagnosed with idiopathic IESS developed ASD later. A recent systematic review of autism and epilepsy demonstrated that individuals with secondary epilepsy have a higher risk of ASD than those with idiopathic epilepsy, and this association may be the result of a mutual underlying neurological condition.1

Regarding the treatment, no association was found between the choice of first-line medication or the use of additional medications and the development of ASD. This aligns with previous findings from a randomized controlled trial, which showed that early and effective treatment of IESS does not necessarily reduce the risk of ASD.24 However, a study in Iran reported that over half of the children with IESS experienced significant developmental delays, particularly those with persistent seizures or symptomatic IESS.22

The present study has some limitations. Although the sample size might be sufficient for exploratory studies, it poses several challenges for drawing valid conclusions about a broader population due to reduced statistical power, limited generalizability, and the possibility of an increased sampling error. The generalizability of these findings is limited by two factors. First, the symptom severity of the enrolled participants may not be representative of the entire IESS population. Second, all participants had intellectual disability as a comorbid condition. Finally, the authors acknowledge that the gold-standard diagnostic instruments, ADOS-2 and ADI-R, were not employed due to the lack of appropriate validation for the Brazilian population.25-27 Nonetheless, this study has some strengths. First, it represents the largest sample size investigated to date regarding ASD prevalence in children with IESS. Second, all patients were examined in a neurological pediatric center by specialists in epileptology and neurodevelopmental disorders.

In conclusion, the present data contribute to the sparse knowledge regarding the link between IESS and ASD. The authors found a higher prevalence of ASD among children with IESS compared to that among the general population. Notably, these findings suggest a potential link between a later age of spasm onset (approximately 10.58 months) and the risk of an ASD diagnosis. Neurodevelopment is influenced by multiple factors, and future research with larger, more generalizable cohorts is needed to confirm the present study's findings, identify risk factors, and better elucidate the underlying mechanisms.

The authors suggest that after the diagnosis of IESS, these children should be screened and assessed for ASD to enable earlier detection and a better prognosis. The nature of this association, whether spasms contribute to its etiology or whether a common genetic basis is present, is not yet completely understood. Further longitudinal studies with a larger population and inclusion of control groups should be performed to better understand this important association.