Comorbidity is the presence of one or more additional diseases or disorders co-occurring with (that is, concomitant or concurrent with) a primary disease or disorder; in the countable sense of the term, a comorbidity (plural comorbidities) is each additional disorder or disease.

 

So, what about Williams syndrome? Does it co-occur with other disorders?

Although Williams syndrome (WS) mostly occurs on its own, some studies have stated that as high as 67% of children meet the criteria for another developmental disorder: Autism spectrum disorders (ASD) and ADHD being the most common ones. However, establishing whether your child has a comorbidity or many comorbidities is not easy for professionals, mainly because very few of them have experience with WS as well as these other developmental disorders.

There are a number of symptoms that overlap between different disorders (see table below that shows the overlap between symptoms in WS, ASD and ADHD). Seeing the overlap between the symptoms, the question is whether these symptoms are part of the same or different neurodevelopmental disorder. In order for a child to be diagnosed with a co-morbid disorder, there should be evidence that the child has two separate disorders. For example, children with WS can sometimes show restrictive behaviours and can have social communication difficulties, just like those with ASD. However, in contrast to children with ASD, those with WS usually make a lot of eye contact and like looking at faces. Therefore, only when children with WS show all of the features that overlap with ASD as well as avoidance of eye contact or looking at people’s faces, it may be possible that this child with WS meets the diagnostic criteria for comorbid ASD and an ASD assessment would be appropriate.

Secondly, comobordity means that the child has two different disorders and thus it needs to be ruled out that WS alone can explain some of the behaviours that overlap between the disorders. For example, children with WS and those with ADHD find it difficult to concentrate and are highly inattentive. However, in many cases the inattention in WS is caused by distraction or avoidance behaviour due to sensory needs issues, in contrast to those with ADHD. In addition, children with WS can often pay attention for long time when it is their favourite show, relates to music or something else that they like. A child with ADHD, on the other hand, will find it very difficult to concentrate regardless of the task. Finally, although about 50% of children with WS may qualify for the diagnosis of inattentiveness, very few make the diagnosis for other types of ADHD such as hyperactivity or impulsivity. Thus, the cause of inattentiveness in WS often differs from those with ADHD. 

Thirdly, both ASD and ADHD are on a continuum and are diagnosed only when a specific number of symptoms are present. For example, some children with WS might have communication difficulties, avoid eye contact, or like spinning wheels but that doesn’t mean that they have ASD. ASD is diagnosed when there is a dyad of symptoms present: including social communication and social interaction across multiple contexts as well as restrictive behaviours. These difficulties persist over time. However, in WS whilst many children show a language delay and very restrictive repetitive behaviours when younger, most will develop language at some point and, as mentioned before, show a strong interest in other people and faces. The same is true for ADHD, although children with WS will show some of the symptoms that overlap with ADHD, most do not meet every criterion of a particular ADHD type.

In sum, diagnosing a comorbid disorder in WS is very tricky because we do not always know what causes the problems in the different disorders and without knowing the cause of a difficulty, we cannot say whether that the child has just WS or WS with a comorbid disorder. Still, there is lots of overlap between the different disorders and consequently therapies and educational programmes that have been shown to help children with ADHD or ASD may also benefit those with WS.

 

Table 1. Behavioural and cognitive overlap between Williams syndrome, Autism spectrum disorders (ASD) and ADHD (this list is not exhaustive).

 

Symptom

Williams syndrome

ASD

ADHD

Language delay

v

v

 

Likes routine

v

v

 

Hand flapping/rocking

v

v

 

Limited peers

v

v

v

Lack of social awareness

v

v

v

Attention to detail

v

v

 

Attention difficulties

v

 

v

Sensory needs

v

v

 

Inflexibility

v

v

 

Distractibility

v

 

v

Working memory difficulties

v

 

v

Planning difficulties

v

 

v

Difficulties taking turns

v

 

V

 

 

Further reading:

Klein-Tasman, B. P., Phillips, K. D., Lord, C. E., Mervis, C. B., & Gallo, F. (2009). Overlap with the Autism Spectrum in Young Children with Williams Syndrome. Journal of Developmental and Behavioral Pediatrics30(4), 289–299. http://doi.org/10.1097/DBP.0b013e3181ad1f9a 

Rhodes, S. M., Riby, D. M., Matthews, K. & Coghill, D. R. (2011). Attention-deficit/hyperactivity disorder and Williams syndrome: Shared behavioral and neuropsychological profiles. Journal of Clinical and Experimental Neuropsychology, 33(1), 147-156.

ADHD: http://adhd-institute.com/assessment-diagnosis/diagnosis/dsm-5/

ASD: https://www.autismspeaks.org/what-autism/diagnosis/dsm-5-diagnostic-criteria