transtorno of intellectual development, provisional is assigned when there is evidence of a transtorno of intellectual development but the individual is an infant or child under the age of four or it is not possible to conduct a valid assessment of intellectual functioning and adaptive behaviour because of sensory or physical impairments (e.g., blindness, pre-lingual deafness), motor or communication impairments, grave problem behaviours or co-occurring mental and behavioural transtornos.