Purpose – During the last few years the prevalence of autism and Autism Spectrum Disorder (ASD) has increased greatly. A recurring issue is the overlap and boundaries between Intellectual Developmental Disorder (IDD), ASD and Schizophrenia Spectrum Disorders (SSD). In clinical practice with people with IDD, the alternative or adjunctive diagnosis of ASD or SSD is particularly challenging. The purpose of this paper is to define the boundaries and overlapping clinical characteristics of IDD, ASD and SSD; highlight the most relevant differences in clinical presentation; and provide a clinical framework within which to recognize the impact of IDD and ASD in the diagnosis of SSD. Design/methodology/approach – A systematic mapping of the international literature was conducted on the basis of the following questions: first, what are considered to be core and overlapping aspects of IDD, ASD and SSD; second, what are the main issues in clinical practice; and third, can key diagnostic flags be identified to assist in differentiating between the three diagnostic categories? Findings – Crucial clinical aspects for the differentiation resulted to be age of onset, interest towards others, main positive symptoms, and anatomical anomalies of the central nervous system. More robust diagnostic criteria and semeiological references are desirable. Originality/value – The present literature mapping provides a comprehensive description of the most relevant differences in the clinical presentation of ASD and SSD in persons with IDD.

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Purpose – Though the very high prevalence of psychiatric disorders (PD) in people with intellectual disability (PwID), the impact of these disorders on adaptive functioning has been minimally investigated. The few contributions present in the literature focussed on children, adolescents, and individual with autism spectrum disorders (ASD). There are no studies concerning the evaluation of any kind of impact on individual skills. Comparison studies between PD and organic disorders, including neurological disorders (ND), was also underexplored. The purpose of this paper is to assess the impact of the presence of a PD on the adaptive functioning of adults with intellectual disability (ID). Design/methodology/approach – In total, 107 adults with ID living in residential facilities or attending day care centers in Tuscany were consecutively assessed with the Psychiatric Instrument for the Intellectually Disabled Adult (SPAID-G), the Diagnostic Manual-Intellectual Disability (DM-ID) criteria, and the Vineland Adaptive Behavior Scales (VABS). The scores were statistically compared and results were controlled for level of ID and other background variables. Findings – The presence of a PD resulted to have a significant negative impact on individual adaptive skills. Participants with PD scored significantly lower than those without PD in communication and socialization areas of VABS. Participants with ND scored significantly lower than people without ND in daily living and motor skills. The average scores of participants with only PD and those of participants with PD and ND showed no significant differences. Significant differences were found between participants with only ND and participants with ND and PD in the interpersonal relationship subscale. Originality/value – As far as the best knowledge, this is the first study on the evaluation of the impact of any kind of PD on the abilities of PwID. This paper suggests that the presence of a PD seems to have a relevant negative impact on functioning of PwID higher than that of ND, particularly in communication and socialization skills.