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Background Down syndrome (DS) is one of the most common genetic causes of intellectual disability, and it is associated with an increased incidence of numerous co-occurring conditions. Autism spectrum disorder (ASD) is common in persons with DS, with rates reported as high as 39%. However, little is known regarding co-occurring conditions in children with both DS and ASD. Methods A single-center retrospective review of prospective longitudinally collected clinical data was performed. Any patient with a confirmed diagnosis of DS evaluated at a large, specialized Down Syndrome Program in a tertiary pediatric medical center between March 2018 and March 2022 was included. A standardized survey which included demographic and clinical questions was administered during each clinical evaluation. Results In total, 562 individuals with DS were included. The median age was 10 years (IQR: 6.18–13.92). Of this group, 72 (13%) had a co-occurring diagnosis of ASD (DS+ASD). Individuals with DS+ASD were more likely to be male (OR 2.23, CI 1.29–3.84) and had higher odds of a current or prior diagnosis of constipation (OR 2.19, CI 1.31–3.65), gastroesophageal reflux (OR 1.91, CI 1.14–3.21), behavioral feeding difficulties (OR 2.71, CI 1.02–7.19), infantile spasms (OR 6.03, CI 1.79–20.34) and scoliosis (OR 2.73, CI 1.16–6.40). There were lower odds of congenital heart disease in the DS+ASD group (OR 0.56, CI 0.34–0.93). There was no observed difference in prematurity or Neonatal Intensive Care Unit complications between groups. Individuals with DS+ASD had similar odds of having a history of congenital heart defect requiring surgery to those with DS only. Furthermore, there was no difference in rates of autoimmune thyroiditis or celiac disease. There was also no difference in rates of diagnosed co-occurring neurodevelopmental or mental health conditions in this cohort, including anxiety disorders and attention-deficit/hyperactivity disorder. Conclusions This study identifies a variety of medical conditions which are more frequent in children with DS+ASD than DS alone, providing important information for the clinical management of these patients. Future research should investigate the role of some of these medical conditions in the development of ASD phenotypes, and whether there may be distinct genetic and metabolic contributions towards these conditions.

This study aimed to learn about the experiences of families of individuals with a dual diagnosis of Down syndrome (DS) and autism spectrum disorder (ASD) (DS-ASD), and to document the journey from early concerns to diagnosis and intervention. Caregivers completed an online survey describing their journey raising a child with DS-ASD. Survey responses were analyzed qualitatively and coded into categories to highlight common themes. Stereotypy, severe communication impairments, and behavioral difficulties prompted caregivers to pursue further evaluation. There was a mean 4.65-year gap between first noticing symptoms and receiving an ASD diagnosis. Several therapeutic interventions were identified as beneficial, including behavioral and communication support. Caregivers expressed frustration and described high levels of stress and social isolation. The diagnosis of ASD in children with DS is often delayed, and caregivers’ initial concerns are frequently dismissed. Raising a child with DS-ASD can lead to social isolation and elevated caregiver stress. More research is needed to tailor diagnostic algorithms and therapeutic interventions to the unique needs of this patient population. Caregivers yearn for improved understanding of DS-ASD, more targeted therapies and educational programs, and more overall support.