[The symptoms of autism spectrum disorders in the first two years of life: a review of longitudinal prospective studies].

The prospective longitudinal studies of infant siblings of children with Autism Spectrum Disorders (ASD) are revolutionising our understanding of the disorder, offering us the opportunity to examine its development in detail from birth. In this paper we will present a detailed summary of the early symptoms that characterise children with autism from birth to two years of age. The description of the symptoms description will be based on the data from longitudinal prospective studies of children with ASD published to date. The review will conclude with research employing retrospective methodologies. We will discuss the ASD symptoms reviewing those in the first and second year separately, as well as the onset patterns of the disorder. We will highlight those symptoms that allow us to differentiate ASD from other developmental disabilities. ASD are defined by a constellation of symptoms. Studies did not find any differences between ASD and typical development at 6 months of age. The data show that the earliest specific manifestations of ASD are not seen until the end of the first year of life and involve a decreased interest in social stimuli. Other social, communicative, symbolic and in some cases, repetitive and stereotyped interests and behaviours gradually appear in the second year of life, as well as atypical sensorial behaviours. In the second year of life the difficulties in sharing interests with others are noticeable. We will conclude by commenting on the relevance of the data reviewed for the theoretical models explaining autism.