Adults with Prader-Willi syndrome (PWS) have difficulty recognizing facial expressions, which may contribute to their poor social skills, a study reveals.
The researchers found that people with PWS also show atypical, autistic-like features, depending on the specific genetic cause of the disease.
These findings expose the differences in social abilities between subtypes of Prader-Willi, and call attention to the importance of early identification of the disease’s genetic cause for each individual so as to optimize care and improve the social lives of patients and their families.
The study, “Face processing and exploration of social signals in Prader-Willi syndrome: a genetic signature,” was published in the Orphanet Journal of Rare Diseases.
Chromosomes are packed DNA structures that carry the genetic information for each individual. In humans, they are organized in pairs of two similar copies, half inherited from the mother and half from the father.
Three types of defects in a specific region of chromosome 15 — 15q11–13 — can cause PWS. These are paternal microdeletion, which accounts for 65% of cases, maternal uniparental disomy – when both chromosome 15 copies are inherited from the mother, as occurs in 30% of cases — and genomic imprinting errors, which comprise the remaining 5%. Genomic imprint errors occur in the genetic process that marks which copy of the chromosome will be active.
People with PWS often experience autistic-like behaviors, including difficulty in social activities and in understanding others’ emotions.
Together with excessive eating, or hyperphagia, these behaviors may explain these individuals’ poor social interaction and impaired relationships.
Recognizing the mental states, feelings, dispositions, and actions of others is vital for social interactions. This capacity relies on specific brain pathways, collectively known as the social brain.
Earlier studies provided evidence that people with PWS have difficulty in perceiving social clues. For instance, they have trouble in discriminating human voices. Yet, little is known about their skills in recognizing facial expressions and emotions, which also is fundamental for everyday socialization.
Researchers from France addressed this gap, ultimately intending to use the study’s findings to assist in rehabilitation and to improve the daily lives of these patients, their families, and their caregivers.
The study included 39 adults with PWS (mean age 28 years) and 20 controls. Among the patients, the genetic cause of the disease was a deletion in 26 individuals and maternal disomy in 13.
Participants were asked to complete a set of face and emotion discrimination tasks. In face discrimination, they had to recognize either two similar faces or two faces revealing the same emotion, which were displayed on a screen. For the emotion task, participants had to distinguish between faces revealing happiness, sadness, and fear.
During each task, the eye movements of nine patients were recorded to analyze where and for how long the participants fixed their gaze to recognize each face.
The results showed that people with PWS were twice as slow as healthy people in both facial or emotional tasks, reflecting poorer recognition skills. This is “possibly owing to [their] general cognitive processing slowdown,” the researchers said.
In the PWS group, happiness was the easiest emotion to discriminate (26% of the errors), while sadness and fear were both poorly recognized (36-37% of errors).
Patients with maternal disomy showed an atypical pattern of facial exploration, the researchers found. These participants looked preferentially at the mouth region, while both patients whose disease was caused by a deletion and healthy controls were more attracted to the eyes.
These findings reveal a difference between the two main genetic types of PWS. In addition, the atypical facial exploration in people with maternal disomy corresponds to their higher rate of autism spectrum disorder, the scientists said.
“It is therefore crucial to distinguish between the two subtypes as early as possible, so that rehabilitation has the maximum impact on social communication abilities. This, of course, presupposes early determination of the genetic subtype as part of routine diagnosis,” they added.
Noting the small number of participants in the study, the investigators called for further research in a larger group of PWS patients to validate these new findings regarding face exploration.