Phelan-McDermid Syndrome

Phelan-McDermid syndrome is a very rare genetic condition. It is caused by a mutation or deletion of chromosome 22 or a disease-causing variant of the SHANK3 gene. In most cases, the condition occurs at random, however, it can also be inherited from a parent. Phelan-McDermid syndrome is present at birth and most children with the condition show signs in early childhood, and as early as the first 6 months of life. First signs and symptoms often include low muscle tone and developmental delays (e.g., late rolling, sitting, walking, talking). 

Phelan-McDermid syndrome affects development, behavior, cognition, and physical appearance, as well as medical challenges. Symptoms can vary by individual. Phelan-McDermid syndrome can cause developmental delays, delayed or absent speech, and intellectual disabilities. Many individuals with the condition also present with autism spectrum disorder (ASD). An individual with Phelan-McDermid syndrome may demonstrate repetitive behaviors (e.g., hand flapping), anxiety/nervousness, lower ability to sweat (which can lead to overheating), and/or high pain tolerance. Sleep disorders and seizure disorders can occur with Phelan-McDermid syndrome. Difficulties with toilet training and eating are also common. Individuals with Phelan-McDermid syndrome may present with certain physical traits, including low muscle tone (especially during infancy), long head shape, full or puffy cheeks, puffy or droopy eyelids, long eyelashes, wide, flat nose or face, pointed chin, large hands, and underdeveloped toenails. Medically, individuals with Phelan-McDermid syndrome can have gastrointestinal, renal, and cardiac problems. To date, there is no cure or treatment specifically for Phelan-McDermid syndrome, however, the symptoms can be managed by therapies and medications. The team of doctors and therapists may include a pediatrician, neurologist, nephrologist, gastroenterologist, immunologist, orthopedist, physical therapist, occupational therapist, speech-language pathologist, or behavior therapist, depending on the symptoms and medical needs of the individual. Researchers are working to better understand the condition and to develop drugs and therapies to improve the quality of life for those affected.

Phelan-McDermid syndrome is estimated to occur in 2.5-10 per million births, however, this may be an underestimate, as diagnosis can be difficult. It affects males and females equally. Phelan-McDermid syndrome is diagnosed through genetic testing. Genetic testing and a diagnosis of Phelan-McDermid syndrome should be discussed with a child's pediatrician for those with an intellectual disability, severe speech delay, or hypotonia as a newborn (with unknown cause). Talk to your pediatrician if you are concerned.

Sources: https://www.massgeneral.org/children/phelan-mcdermid-syndrome/ , https://rarediseases.org/rare-diseases/phelan-mcdermid-syndrome/ , https://pmsf.org