Clinical research: Autism-related syndrome changes with age

Many characteristics of Phelan-McDermid syndrome — an autism-linked disorder arising from abnormalities at the tip of chromosome 22q13 — change as individuals age, reports a study published in January in Human Genetics­¹.

People with the syndrome show a wide variety of symptoms, including developmental delay, speech delay, intellectual disability, low muscle tone and, frequently, autism. Mutations in the SHANK3 gene, which is linked to autism, are associated with many of the neurological traits of the syndrome.

Only about 600 people worldwide are diagnosed with Phelan-McDermid syndrome. A few studies have suggested that the disorder’s features may change with age and may include a progressive loss of skills. However, given the syndrome’s rarity and relatively recent recognition, the frequency of those changes was unclear.

In the new study, the researchers examined 201 individuals diagnosed with the syndrome and analyzed the results by age. Participants older than 18 years tend to have fewer behavioral problems and better developmental abilities, and fewer of them show the unusual physical features associated with the disorder: full or puffy eyelids, large or fleshy hands, low muscle tone, lax ligaments and overly mobile joints.

However, more individuals in the older age groups reported seizures and diagnoses of autism. This may be because of neurological deterioration over time or because they have had more time to receive a diagnosis. Trauma, infection and other triggers may also be involved.

Seizures affect 11 percent of children younger than 5 years but 60 percent of adults. A higher proportion of adults also have abnormal reflexes, connective tissue inflammation and fluid retention in lymph nodes.

When the researchers analyzed the 22q13 abnormalities in 120 participants, they found that 89 percent had lost the tip of the chromosome, 2 percent had lost an inner section and 11 percent carry both duplications and deletions. The study confirmed previous findings that the larger the deletion, the more severe the symptoms. The researchers also found that seizures are more common in individuals who inherited the affected chromosome from their mother.

Some age-related changes — such as learning not to chew non-food items — might simply be delayed aspects of normal development, the researchers suggest.

The study underscores the diversity of symptoms in individuals with Phelan-McDermid syndrome. It also suggests that as screening methods and diagnoses improve, more people, including those with mild symptoms, may be diagnosed.

References:

1. Sarasua S.M. et al. Hum. Genet. Epub ahead of print (2014) PubMed