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Adult onset

A growing number of reports of adult-onset symptoms in Phelan-McDermid syndrome underline the need to follow people with the disorder throughout their lives, says Katy Phelan.

By Katy Phelan
5 February 2013 | 3 min read
This article is more than five years old.
Neuroscience—and science in general—is constantly evolving, so older articles may contain information or theories that have been reevaluated since their original publication date.

In our early studies in the 1990s of Phelan-McDermid syndrome, a genetic disorder linked to mild to severe intellectual disability, delayed speech and autism, very few adults were diagnosed. As a result, we knew little of the health issues associated with advancing age in people with this disorder.

But that’s changing as a growing number of reports in the literature detail a loss of cognitive, behavioral and motor skills in adults with this and similar disorders. Researchers have published findings on at least eight adults with the syndrome, ranging in age from 20 to 70 years1-5.

Motor decline, such as the loss of the ability to stand or walk, is one of the most common problems, observed in five of these individuals. Loss of speech skills, worsening eye contact and social skills, and late-onset seizures have also been noted. Three of the adults have bipolar disorder, complicated by major depressive episodes in two of them4, 5.

Adding to concerns about age-related regression, at the Phelan-McDermid Syndrome Foundation family conference last July, a number of parents of adults described deterioration in speech, loss of physical activity, unexplained weight loss and increased muscle weakness.

One way for parents and caregivers to better track health issues in adults with the syndrome is to maintain a diary of changes in behavior, sleep habits, activity level, and cognitive and communication skills, as well as physical attributes — is there weight loss, lymphedema, unusual joint movement?

They must also carefully watch for side effects of medication. Drugs given for behavior management are particularly problematic and their side effects may mask or intensify other behaviors, making it difficult to track signs of regression.

The lack of verbal expression in adults with the syndrome can also complicate efforts to detect depression and mood fluctuations associated with atypical bipolar disorders (unstable mood disorders)4. That may in turn delay appropriate treatment.

From the research perspective, long-term studies are the best way to learn how the features of Phelan-McDermid syndrome or other disorders associated with autism change with age. By following individuals at different intervals as they move into adulthood, we will learn how the syndrome evolves.

We may identify predictors of disease or uncover symptoms that will help us diagnose and treat people earlier. This information is invaluable to parents of these adults, and to parents who are planning for the future needs of their young children with the syndrome.

Katy Phelan is director of cytogenetics at Tulane University School of Medicine in New Orleans.


1: Anderlid B.M. et al. Hum. Genet. 110, 439-443 (2002) PubMed

2: Bonaglia M.C. et al. PLoS Genet. 7, e1002173 (2011) PubMed

3: Verhoeven W.M. et al. Am. J. Med. Genet. Part A 161, 158-161 (2013)PubMed

4: Verhoeven W.M. et al. Neuropsych. Dis. Treat. 8, 175-179 (2012) PubMed

5: Willemsen M.H. et al. Mol. Syndromol. 2, 217-234 (2012) PubMed