Developmental and environmental differences in infants with family history of autism and ADHD during the first year of life in Brazil

• Family history (FH): Having a biological parent or older sibling with autism and/or ADHD (suspected or diagnosed).

• Autism: A neurodevelopmental condition involving differences in social communication and sensory processing, plus repetitive or restricted behaviours.

• ADHD (attention-deficit/hyperactivity disorder): A neurodevelopmental condition marked by persistent inattention, hyperactivity, and impulsivity.

• Neurodevelopmental condition: A condition affecting how the brain develops, usually showing up in childhood.

• Temperament: An infant’s inborn style of reacting and self-calming, such as activity level or fussiness.

• Adaptive behaviour (daily living skills): Practical skills for everyday life, such as feeding and self-care.

• Perceptual sensitivity: How readily an infant notices faint sights, sounds, or other environmental changes.

• Vocal reactivity: How much an infant vocalises during everyday activities.

• Recovery from distress: How quickly an infant calms down after peak upset or excitement.

• Soothability: How much an infant’s fussing or crying decreases when a caregiver soothes them.

• Self-regulation: The ability to manage emotions, attention, and arousal.

• Household chaos: Noise, confusion, and disorder in the home.

• Low-and middle-income country (LMIC) / high-income country (HIC): World Bank-style economic groupings. Most earlier research came from HICs.

• Global South: A term for regions, often LMICs, with marked economic inequality and limited services.

• Preemptive intervention: Support offered early, before a diagnosis, to help infants considered more likely to develop a condition.

• Cross-sectional: Data collected at a single point in time.

• Factorial ANOVA: A statistical test that compares groups on two factors at once and checks whether the factors interact.

• False discovery rate correction: An adjustment that reduces false positives when many statistical tests are run.

• Clinically significant: A difference large enough to matter in practice, not only statistically.

Most research on infants with a family history of autism or ADHD comes from wealthy countries, rarely compares the two family histories directly, and rarely considers the home environment. The authors therefore asked:

1. Do infants aged 6–11 months with FH of autism and/or ADHD in Brazil differ from infants without FH across a broad range of development? The domains were cognitive, motor, and language skills, adaptive behaviour, and temperament.

2. Do FH of autism and FH of ADHD show distinct (non-overlapping) developmental profiles?

3. Are FH of autism and/or ADHD linked to environmental factors, namely caregiver mental health (stress, anxiety, depression) and household chaos?

Hypotheses:

• FH of autism would be linked to difficulties in language, motor skills, adaptive functioning, and temperamental sensory sensitivity.

• FH of ADHD would be linked to higher activity, more negative affect, and weaker self-regulation.

• Household chaos would be linked to FH of ADHD only, while poorer caregiver mental health would be linked to both FH of autism and FH of ADHD.

Sample and design: 252 infants (mean age 8.7 months) from the Floreah cohort in Brazil, mostly from the Southeast. Groups were FH autism only (n = 36), FH ADHD only (n = 66), FH autism + ADHD (n = 84), and no FH controls (n = 66). Groups were similar on most sociodemographic characteristics. Infants in the FH autism group were slightly younger at birth than controls. Infants were assessed with the Bayley-III, the MacArthur-Bates vocabulary inventory, the Vineland-3, and a temperament questionnaire (IBQ-R). Caregivers completed the DASS-21 (mental health) and CHAOS (household chaos) scales. The analysis was a 2 × 2 factorial ANOVA, so each FH factor was tested across groups, with a multiple-testing correction.

Cognitive, language, and motor development: No significant effects of FH of autism or ADHD.

FH of autism:

• Lower adaptive daily living skills. However, all group means stayed above the population average of 100, so this was not clinically significant.

• Lower temperamental perceptual sensitivity (more so in infants assigned male at birth).

• Lower vocal reactivity (fewer vocalisations).

FH of ADHD:

• Higher temperamental activity levels.

• Slower recovery from distress.

Overlap: The developmental profiles were only partly overlapping. The autism-related differences did not appear in the ADHD group, and the reverse was also true.

Differences that did not survive correction: The following were nominally significant (before correction for multiple tests) but not after: lower motor skills (Bayley and Vineland) and lower communication (Vineland) for FH of autism, and lower soothability for FH of ADHD. They should be treated as non-significant.

Environment (shared across both FH types):

• Caregivers of infants with FH of autism and/or ADHD reported significantly higher stress, anxiety, and depression symptoms (DASS-21).

• Their homes had higher household chaos (CHAOS).

• Effects were larger than for the developmental differences (for example, partial η² of about .09 for ADHD on caregiver mental health, versus about .02–.05 for developmental measures).

• Results held after adjusting for age, gestational age, sex, and socioeconomic level, and in non-parametric checks.

• Household chaos was also linked to FH of autism, contrary to the hypothesis that it would be specific to ADHD.

Interpretation: This is, to the authors' knowledge, the first study of its kind in an LMIC. Despite Brazil’s different cultural and socioeconomic context, many findings match research from wealthy countries. This suggests the early patterns generalise.

• Autism FH: Reduced vocalisation is an early sign linked in past research to later autism outcomes and is a key target of caregiver-mediated early interventions. The findings support exploring communication-focused preemptive interventions in Brazil. The lower perceptual sensitivity fits some prior reports of sensory under-responsiveness in infancy, though other studies found no difference.

• ADHD FH: Higher activity and weaker recovery from distress replicate earlier work and support interventions that build self-regulation.

• Null cognitive, language, and motor results: These contrast with some previous studies. They are group-level averages, so some individual infants may still struggle. The authors suggest future latent class analysis to identify subgroups of infants with distinct profiles beyond family-history labels.

• Environment: Caregiver mental health difficulties and household chaos are known to predict long-term developmental problems. Their presence in these families is essential context, and interventions should also support caregiver wellbeing and household organisation.

Limitations:

• Few infants had FH of autism without ADHD, which biases the sample toward ADHD.

• Parental ADHD was identified by self-report questionnaires, without clinical interviews.

• Few families were non-university-educated, low-income, Black, Asian, or Indigenous, and most lived in the wealthier Southeast.

• The Bayley and Vineland norms come from the USA, complicating interpretation.

• Caregiver mental health was measured as one total score rather than as separate stress, anxiety, and depression scores.

• Many outcomes were parent-reported, and the design was cross-sectional.

Recommendations:

• Provide early support to infants with FH of autism and ADHD and to their families in Brazil.

• Tailor preemptive interventions to each profile: communication for autism FH, and activity and self-regulation for ADHD FH.

• Integrate caregiver mental health and household support into these interventions.

• Follow these infants longitudinally to see how early differences and the home environment relate to later diagnoses and outcomes. Separate depression, anxiety, and stress in future work.