3.3.2. Module 3 Items

Between-group comparisons were also conducted for algorithm items on Module 3 of the ADOS-2 (see Figure 4). Group differences were found in the mean ranks for the five SA algorithm items measuring: (1) reporting of events (U = 75.500; *p* = 0.016); (2) unusual eye contact (U = 76.00; *p* = 0.005); (3) quality of social overtures (U = 54.50; *p* = 0.001); (4) quality of social response (U = 76.00; *p* = 0.017); (5) amount of reciprocal social communication (U = 38.00; *p* < 0.001); (6) overall quality of rapport (U = 43.00; *p* < 0.001). These differences remained significant even after applying the FDR corrections. One algorithm item from the RRB subdomain, measuring unusually repetitive interests or stereotyped behaviors, emerged as significantly different between participants who met classification from those who did not (U = 86.50; *p* = 0.034); however, this finding did not remain significant after applying the FDR correction.

**Figure 3.** Mean Rank comparisons for Module 2 algorithm items; (**a**) Mean Rank comparisons for Module 2 SA items; (**b**) Mean Rank comparisons for Module 2 RRB items. Note: JA = Joint attention. \* *p* < 0.05; \*\* *p* < 0.01; \*\*\* *p* < 0.001. **Figure 3.** Mean Rank comparisons for Module 2 algorithm items; (**a**) Mean Rank comparisons for Module 2 SA items; (**b**) Mean Rank comparisons for Module 2 RRB items. Note: JA = Joint attention. \* *p* < 0.05; \*\* *p* < 0.01; \*\*\* *p* < 0.001.

**Figure 4.** Mean Rank comparisons for Module 3 algorithm items; (**a**) Mean Rank comparisons for Module 3 SA items; (**b**) Mean Rank comparisons for Module 3 RRB items. Note: \* *p* < 0.05; \*\* *p* < 0.01; \*\*\* *p* < 0.001; + signifies no longer significant after FDR correction. **Figure 4.** Mean Rank comparisons for Module 3 algorithm items; (**a**) Mean Rank comparisons for Module 3 SA items; (**b**) Mean Rank comparisons for Module 3 RRB items. Note: \* *p* < 0.05; \*\* *p* < 0.01; \*\*\* *p* < 0.001; + signifies no longer significant after FDR correction.

### **4. Discussion 4. Discussion**

*4.1. ASD Classification*

The detection of co-occurring ASD among individuals with ID associated with known genetic conditions, such as DS, poses many challenges [32,33]. It is becoming increasingly apparent that individuals with DS are at increased risk for presenting with the symptoms ASD relative to the general population [5,6]; moreover, due to the developmental delays associated with the DS phenotype may influence the presentation of ASD symptomatology in this population [10–12]. Studies that clarify the nature of social communication skills and restricted and repetitive interests and behaviors in DS, and other populations with ID, can provide important information for understanding the The detection of co-occurring ASD among individuals with ID associated with known genetic conditions, such as DS, poses many challenges [32,33]. It is becoming increasingly apparent that individuals with DS are at increased risk for presenting with the symptoms ASD relative to the general population [5,6]; moreover, due to the developmental delays associated with the DS phenotype may influence the presentation of ASD symptomatology in this population [10–12]. Studies that clarify the nature of social communication skills and restricted and repetitive interests and behaviors in DS, and other populations with ID, can provide important information for understanding the unique way in which ASD presents

unique way in which ASD presents among individuals. The goal of the present study was

symptomatology in a large sample of individuals with DS using the ADOS-2, a gold

Several key findings emerged from the present study. First, we explored the prevalence of ASD in a sample of 83 individuals with DS and found that 37.3% of the sample met overall classification criteria for ASD on the ADOS-2, which falls within the range of prevalence rates presented in several previous publications on DS [13–15]. This similarity in prevalence rates suggests that the specific measures used may not differ significantly in their utility in detecting ASD in individuals with DS. Individuals in the sample who had overall scores that met classification cutoff for ASD (DS + ASD) had significantly higher SA-CSS and RRB-CSS scores than individuals who did not (DS-only). This finding is consistent with prior research finding of both more challenges in social communication and increased rigidity and repetitive behaviors when comparing individuals classified as having DS-only and those classified as having DS + ASD [18–22]. It should be noted that studies have found that individuals with DS who were at low risk for ASD nonetheless presented with challenges in social communication and restricted and repetitive interests and behaviors relative to normative expectations for their chronological ages, indicating that these symptoms and behaviors may also be phenotypic to DS [5,6]. This is further underscored by findings in the current study that a number of

standard direct-assessment diagnostic instrument.

among individuals. The goal of the present study was to elucidate the prevalence and the factors shaping the presentation of ASD symptomatology in a large sample of individuals with DS using the ADOS-2, a gold standard direct-assessment diagnostic instrument.
