Not so long ago, physicians believed that psychiatric disorders were exclusionary and claims of a dual diagnosis were doubted or not accepted.  According to this way of thinking, patients with Down syndrome could not exhibit signs of autism or vice versa.  Each of these conditions, autism and Down syndrome, therefore stood on their own.  To this day, some physicians still resist the idea of a dual diagnosis, believing that atypical behaviors may represent a more severe form of Down syndrome.  Similarly, some parents may resist the idea of comorbidity as it would mean having another label attached to their son or daughter.

It is well known that individuals with Down syndrome are at increased risk for congenital heart disease, leukemia, deafness, serious otitis media, gastrointestinal atresia, eye disease, acquired hip dislocation, and thyroid disease.  We also know that patients with Down syndrome can have comorbid attention deficit disorder, autism, or both.  According to a recent study about 19% of Down syndrome patients fall into the autism spectrum (Moss et al., 2013). Depending on the prevalence statistic that you care to cite, this is about 15 times more common than in the general population.  The commonality may be partly due to the way we diagnose autism; one based on behavioral observations, all of which are ultimately subjective. It does not necessarily mean that patients with Down syndrome bear the same pathology as autism.

Localization attempts in Neurology rely on correlating symptoms with the known functions of different parts of the brain.  A person with paralysis of a limb, for example, could have a lesion mapped to the motor cortex.  In the case of autism, communication and socialization deficits point towards generalized findings.  It may be that for some Down syndrome patients the more affected the brain may be, the lower the threshold to exhibit autism-like symptoms.  This observation may bear prognostic value, but we lack the necessary longitudinal studies to draw any conclusions.  What we do know is that a dual diagnosis confers those affected with an increased risk for stereotyped behaviors, repetitive language, hyperactivity, self-injury, and diminished mental functions.

The Down Syndrome-Autism Connection (DS-AC) meets on a yearly basis along with the annual convention of the National Down Syndrome Congress where they offer a track of sessions on the topic.  According to the DS-AC your child with Down syndrome may have autism if he or she:

• Does not orient to people
• Is nonverbal, makes unusual vocalizations, says words without actual communicative intent, repetitive speech
• Stops using speech, signs or other means of communication
• Seems happiest playing alone
• Exhibits inappropriate laughing or giggling
• Lacks imaginative play, prefers repetitive play with objects
• Insists on sameness and routine, has great difficulty with transitions
• Has difficulty understanding gestures and does not use gestures to communicate, e.g. pointing
• Shows no real fear of dangers
• Appears to be insensitive to pain
• May not want to cuddle or hug
• Has eating problems– limited foods, textures, etc.
• Has sleep problems
• Exhibits repetitive motions – flapping, twirling, tics, rocking, head shaking, spinning, twisting the hands at the wrist
• Exhibits sustained odd play and inappropriate attachment to objects
• Exhibits self-stimulating behaviors («stimming»)
• Has meltdowns

Establishing a diagnosis of autism in Down syndrome is complicated because affected individuals already live with challenges that complicate behavioral observations.  In the end, children and adults with DS-ASD are underserved, parents are overwhelmed, and educators are frustrated.  However, establishing a proper diagnosis may help in both obtaining needed school/community services and in better explaining some of the patient’s behaviors.  A list of helpful resources are cited in the reference section.

References

Moss J, Richards C, Nelson L, Oliver C. Prevalence of autism spectrum disorder symptomatology and related beavioural characteristics  in individuals with Down syndrome. Autism 17(4):390-404, 2013.

Support link: Down syndrome-autism connection http://www.ds-asd-connection.org/

Margaret Froehlike. When Down syndrome and autism intersect: a guide to DS-ASD for parents and professionals. Woodbine House, 2012.