Abstract
This thesis explores how proband (older sibling) autism and ADHD traits associate with their infant sibling’s development across the first three years of life using the prospective longitudinal infant sibling design. The aim is to better understand the complex developmental models of neurodevelopmental conditions by looking at the distinct roles that familial factors play in their development. Structural equation modelling is used to study the association of the proband autism/ADHD traits and the infant sibling’s 1) temperament development at 8-, 14-and 24-months of age, and 2) adaptive behaviour development during the first three years of life, and 3) later manifestation of autism/ADHD traits at the age of three. Participants were from the British Autism Study of Infant Siblings (BASIS) and from the Studying Autism and ADHD Risks (STAARS) cohorts that included infants with family history of autism (n = 250), ADHD (n = 31), both (n = 21) or neither (n = 106). Parent ratings were used for all measures of infant temperament and adaptive behaviour and infant and proband autism and ADHD trait measures. In addition, this thesis looks at the genetic and environmental influences on adaptive behaviour in 5-month-old infants (n = 622) from Babytwins Study Sweden (BATSS).Results show that proband autism and ADHD traits associate distinctively with the infant sibling’s temperament development. Proband autism traits associate with infant fear/shyness, while ADHD traits associate with infant activity level and attentional measures (Chapter 2). Looking at infant adaptive behaviour development (Chapter 3), high autism traits in proband associated with lower communication and socialization skills in infant siblings. Meanwhile proband ADHD did not associate with infant adaptive behaviour development. Chapter 4 examines how proband autism and ADHD traits associate with the same traits in the infant sibling at 36-months of age. Proband autism traits and inattention associated with higher infant sibling autism traits, while proband inattention associated with higher ADHD traits. Finally, the results of the twin study of adaptive behaviour indicate that most of motor and social-communication skills at 5 months of age are explained by shared environment with some genetic and non-shared environmental influences (Chapter 5), suggesting that early home environment plays an important role in the development of these skills in infancy.
Autism and ADHD are highly heritable neurodevelopmental conditions that often co-occur. Prospective longitudinal studies offer an opportunity to study the associations between familial factors and the associations with the development of autism and ADHD traits, before the emergence of the symptoms. Understanding how familial factors contribute to the complex developmental pathways of these conditions is important, for this helps with building a more complete picture of all the factors in play in their development and thus offers better opportunities for individualistic support for families with history of these neurodevelopmental conditions.
| Date of Award | 1 Jan 2025 |
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| Original language | English |
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| Supervisor | Tony Charman (Supervisor) & Emily Jones (Supervisor) |