Diagnostic Stability of Autism Spectrum Disorders Among Children and Siblings of Children with An Autism Spectrum Disorder Diagnosis

Background: The stability of ASD diagnoses between 24 and 48 months was investigated in two groups of children at the University of Connecticut: the younger siblings of children with ASD and children with no family history of ASD.

Objectives: Children in this study failed the M-CHAT or M-CHAT-R and follow-up phone interview, and received two diagnostic evaluations. Children received an initial evaluation (time 1) between 16 and 30 months of age, and received ASD diagnoses based on Clinical Best Estimate using DSM-IV Autistic Disorder criteria. At approximately 48 months, children received a follow-up evaluation (time 2), as well as a diagnosis that best reflected their current symptomatology and level of functioning, independent of previous diagnoses.

            Methods: The general sample (GEN) consisted of 146 children, and the younger sibling sample (SIBLING) consisted of 26 children. Chi-square analysis was conducted to determine if there were significant differences in diagnostic stability between GEN and SIBLING.  We analyzed the groups for the proportion who retained their specific diagnosis (i.e., Autistic Disorder, PDD-NOS, and ASD-Low Mental Age) and for the proportion who retained ASD diagnoses (e.g., Autistic Disorder at time 1, PDD-NOS at time 2).  

Results: There were few differences between the groups regarding diagnostic stability.  Children in the GEN and SIBLING samples were equally likely to retain Autistic Disorder and ASD-Low MA diagnoses, and equally likely to retain ASD diagnoses as a whole.  The only significant difference between the two groups was that SIBLING children who received PDD-NOS diagnoses at time 1 were more likely to retain an ASD diagnosis at time 2 than GEN children. In the SIBLING group, 83.3% of children with PDD-NOS at time 1 retained an ASD diagnosis at time 2; 72.7% of the GEN group with PDD-NOS at time 1 retained an ASD diagnosis at time 2 [x² (1, N = 67 = 4.788, p = .029]. All children in both groups who received ASD-Low MA diagnoses at time 1 continued to have ASD diagnoses at time 2.

            Conclusions: These results indicate a relatively high level of diagnostic stability for ASD diagnoses in the both GEN and SIBLING groups, with rates of ASD diagnostic stability for each group of 83.5% and 84.6%, respectively. Children who receive an ASD diagnosis at time 1 are likely to retain that diagnosis, regardless of whether or not they have an older sibling with ASD.  However, younger siblings do have a higher rate of ASD diagnosis retention at age 4 when they receive a PDD-NOS diagnosis at age 2.  Therefore, younger siblings who present with mild ASD symptoms at age 2, as reflected in a PDD-NOS diagnosis, are more likely to continue to exhibit clinical ASD symptomatology as they age than their counterparts with no family history of ASD.  This finding may suggest that mild autistic symptoms in multiply affected families present differently from mild autism in simplex families, and that mild symptoms in multiplex families may not be as readily remediated as in simplex families.