Autism spectrum disorder (ASD) is a neurodevelopmental condition characterized by challenges in social interaction, communication difficulties, and repetitive behaviors.

While autism is relatively common, affecting approximately 1 in 54 children in the United States alone, there are also rare diseases that display autism-like features. These infrequent disorders pose unique challenges for healthcare professionals and families navigating a complex medical landscape.

1. What is an Infrequent Disease?

Infrequent diseases, also known as rare diseases, are conditions that affect a small portion of the population. In the United States, a disease is considered rare if it affects fewer than 200,000 people.

While individual rare diseases may be uncommon, collectively, they impact a significant number of individuals worldwide.

2. Overlap Between Autism-Like Features and Rare Diseases

Several rare diseases exhibit characteristics similar to autism. Individuals with these disorders often experience difficulties with social interaction, communication, and repetitive behaviors.

However, it is important to note that these features alone do not necessarily indicate the presence of autism, as they can be caused by a range of conditions.

3. Phelan-McDermid Syndrome

Phelan-McDermid Syndrome (PMS) is a rare genetic disorder caused by the deletion or disruption of the SHANK3 gene on chromosome 22.

Individuals with PMS generally have varying degrees of intellectual disability, delayed speech, and a characteristic set of physical features. Alongside these traits, individuals with PMS often exhibit autism-like behaviors, including impairments in social interaction and communication.

4. Rett Syndrome

Rett Syndrome is another rare disorder that predominantly affects females. It is caused by mutations in the MECP2 gene on the X chromosome. Rett Syndrome is characterized by a slowing of development following a period of apparently normal growth.

Individuals with Rett Syndrome frequently display autism-like features, such as social withdrawal, repetitive hand movements, and communication difficulties.

5. Angelman Syndrome

Angelman Syndrome (AS) is a genetic disorder that affects the nervous system, causing neurological and developmental problems. AS is characterized by severe intellectual disability, speech impairment, movement and balance issues, and a happy demeanor.

Many individuals with Angelman Syndrome may exhibit behaviors similar to those seen in individuals with autism, including difficulties in social interactions and communication.

6. Fragile X Syndrome

Fragile X Syndrome (FXS) is the most common inherited cause of intellectual disability and autism. It is caused by a mutation in the FMR1 gene on the X chromosome, leading to a lack of the fragile X mental retardation protein.

Individuals with FXS often display varying degrees of cognitive impairment, delayed speech and language development, social anxiety, and repetitive behaviors, similar to those seen in individuals with autism.

7. Tuberous Sclerosis Complex

Tuberous Sclerosis Complex (TSC) is a rare genetic disorder that causes noncancerous tumors to form in various organs, including the brain, skin, heart, kidneys, and lungs.

Many individuals with TSC experience neurological problems, developmental delays, intellectual disability, and autism-like social and communication difficulties.

8. Dravet Syndrome

Dravet Syndrome is a rare form of epilepsy that begins in infancy. It is caused by mutations in the SCN1A gene, leading to seizures that are often difficult to control with medication.

Individuals with Dravet Syndrome frequently exhibit developmental delays, impaired social skills, repetitive behaviors, and cognitive deficits that may resemble autism.

9. Pitt-Hopkins Syndrome

Pitt-Hopkins Syndrome (PTHS) is a rare genetic disorder caused by mutations in the TCF4 gene. Individuals with PTHS have severe intellectual disability, absent or limited speech, distinctive facial features, and abnormalities in breathing.

Many individuals with PTHS exhibit autistic behaviors, including impaired social communication and repetitive movements.

10. Smith-Magenis Syndrome

Smith-Magenis Syndrome (SMS) is a complex genetic disorder caused by a deletion or disruption of the RAI1 gene.

Individuals with SMS often have intellectual disability, delayed speech and language skills, and distinctive behavioral characteristics such as aggressive outbursts and self-injurious behaviors. While not all individuals with SMS exhibit autism-like features, some display social impairments, communication difficulties, and repetitive behaviors typically associated with autism.