What is McDonald's syndrome? Exploring the Misnomer for Phelan-McDermid Syndrome

September 30, 2025 •

4 min read

Over 75% of children with the rare genetic disorder known as Phelan-McDermid syndrome are also diagnosed with an autism spectrum disorder. For those asking what is McDonald's syndrome, it is crucial to clarify that no formal medical condition uses this name; it is a widespread misnomer for Phelan-McDermid syndrome (PMS). This article clarifies this misconception and details the true condition.

Quick Summary

The term 'McDonald's syndrome' is a common misnomer for Phelan-McDermid syndrome, a rare genetic disorder caused by a deletion on chromosome 22 or a mutation in the SHANK3 gene, leading to developmental delays, intellectual disability, and other symptoms.

Key Points

Misnomer Clarified: "McDonald's syndrome" is not a recognized medical condition; it is a common mistake for Phelan-McDermid syndrome (PMS).
Genetic Basis: Phelan-McDermid syndrome results from a deletion on chromosome 22 (22q13) or a mutation in the SHANK3 gene.
Developmental Delays: A hallmark feature is global developmental delay, including severe speech and motor skill delays.
Associated with Autism: There is a high co-occurrence of Phelan-McDermid syndrome and autism spectrum disorder.
Multifaceted Care: Management involves a team of specialists addressing symptoms like hypotonia, behavioral issues, seizures, and feeding problems.
Diagnosis by Genetic Testing: The diagnosis of PMS is confirmed through genetic testing, such as a chromosomal microarray.
Variable Severity: Symptoms range from mild to severe, affecting individuals differently.

What is Phelan-McDermid syndrome? The correct diagnosis

The phrase “McDonald’s syndrome” does not refer to a recognized medical condition, but rather is a common misunderstanding or misspelling of Phelan-McDermid syndrome (PMS). Named after the researchers who discovered it, PMS is a rare genetic disorder resulting from a deletion or mutation on the 22nd chromosome. A correct understanding of this condition is vital for affected individuals and their families to receive proper medical care and support.

The genetic basis of Phelan-McDermid syndrome

Phelan-McDermid syndrome is caused by a genetic alteration in the 22q13 region of chromosome 22. The specific genetic changes include:

Simple deletion: The most common cause, where a piece of chromosome 22 is missing.
SHANK3 gene mutation: A pathogenic variant in the SHANK3 gene can also cause the syndrome. This gene is vital for proper brain functioning and communication between brain cells.
Ring chromosome: A rare cause where the ends of chromosome 22 break off and form a circular structure.
Unbalanced translocation: In some cases, a parent carries a balanced translocation, which can result in a child with an unbalanced translocation and a missing piece of chromosome 22.

Most cases of PMS are spontaneous and are not inherited from parents. Genetic testing is the primary method for confirming a diagnosis.

Common symptoms and characteristics

The symptoms of Phelan-McDermid syndrome can vary widely in severity, and not all individuals will have every symptom. The condition is typically characterized by developmental delays that often become noticeable in early childhood.

Neurological and developmental concerns:

Developmental and speech delays: Delays in reaching milestones like sitting, crawling, and walking are common. Many individuals are nonverbal or have severely delayed speech, although receptive language skills may be more developed.
Intellectual disability: Ranging from moderate to severe.
Low muscle tone (hypotonia): Often present at birth and can affect feeding and motor skills.
Autism spectrum disorder (ASD): A high percentage of individuals with PMS are also diagnosed with ASD.
Behavioral problems: These can include repetitive behaviors and anxiety.
Seizures: Approximately 40% of individuals with PMS experience seizures.

Physical features:

Distinctive facial features: Can include deep-set eyes, droopy eyelids (ptosis), full cheeks, and a pointed chin.
Large hands or feet: Often described as large and fleshy.

Medical issues:

Decreased pain sensitivity: Individuals may have a high tolerance for pain, making it difficult to detect medical issues.
Sleep disturbances: Problems with sleep are common.
Gastrointestinal issues: Constipation and gastroesophageal reflux are frequently reported.
Renal and heart problems: Some individuals may have congenital heart defects and kidney abnormalities.

Comparing Phelan-McDermid with other "McDonald" related terms

To further clarify the term "McDonald's syndrome," it is helpful to distinguish Phelan-McDermid syndrome from other medical terms involving the name McDonald.


Feature	Phelan-McDermid Syndrome (PMS)	McDonald Criteria for Multiple Sclerosis (MS)	Hunter-MacDonald Syndrome (HMS)
Classification	Rare genetic disorder	Diagnostic tool for Multiple Sclerosis	Rare skeletal dysplasia
Cause	Chromosome 22 deletion or SHANK3 gene mutation	A set of criteria based on clinical findings and MRI scans	Autosomal dominant genetic cause
Associated Condition	Developmental delay, intellectual disability, and autism	An autoimmune disease affecting the central nervous system	Skeletal abnormalities and malformations
Primary Symptoms	Hypotonia, speech delay, behavioral issues, seizures	Fatigue, numbness, vision problems, muscle weakness	Short stature, scoliosis, joint issues, distinctive facial features
Relevance to "McDonald's syndrome"	The actual syndrome people are likely searching for due to phonetic similarity.	A completely different diagnostic tool, not a syndrome, that uses the name McDonald.	Another distinct and unrelated rare genetic syndrome with a similar name.

Diagnosis and management of PMS

Diagnosis of Phelan-McDermid syndrome typically involves genetic testing, such as a chromosomal microarray, after a careful physical exam and medical history. Given the complexity and variability of symptoms, management requires a comprehensive, multi-specialty approach. This team may include:

Developmental specialists and neurologists: To address developmental delays, hypotonia, and seizures.
Genetic counselors: To help families understand the condition and potential risks.
Speech and occupational therapists: To improve communication and motor skills.
Gastroenterologists: To manage feeding difficulties and reflux.

Early intervention is key to managing symptoms and improving outcomes. While there is no cure for the underlying genetic cause, treating the individual symptoms can significantly improve quality of life.

Conclusion

In summary, the term McDonald's syndrome is not a real medical diagnosis, but rather a misnomer for Phelan-McDermid syndrome. This rare genetic disorder, caused by a deletion on chromosome 22 or a SHANK3 gene mutation, leads to developmental delays, intellectual disability, and is often associated with autism. Distinguishing PMS from other similarly named medical terms, such as the McDonald criteria for multiple sclerosis, is essential for accurate communication and care. For those seeking information, focusing on the correct medical term—Phelan-McDermid syndrome—is the best path to understanding the condition and accessing necessary support.

A note on other 'McDonald' terms

It is important to be aware of other medical terms that can cause confusion. The McDonald Criteria are a set of guidelines used by neurologists to diagnose Multiple Sclerosis (MS). Additionally, Hunter-MacDonald syndrome is a rare condition involving skeletal abnormalities and is unrelated to PMS. By being specific with terminology, patients and caregivers can ensure they are researching and receiving treatment for the correct condition.

An authoritative link for more information

For more comprehensive and up-to-date information on Phelan-McDermid syndrome, visit the Phelan-McDermid Syndrome Foundation website, a leading resource for the global PMS community. Phelan-McDermid Syndrome Foundation.

Frequently Asked Questions

No, 'McDonald's syndrome' is not a real medical condition. It is a common misnomer, and the term is likely used in error when referring to Phelan-McDermid syndrome (PMS), a rare genetic disorder.

Phelan-McDermid syndrome is caused by a genetic alteration, specifically a deletion of a segment on chromosome 22 (the 22q13 region) or a mutation in the SHANK3 gene, which is critical for brain function.

While the core condition is PMS, its genetic cause can vary, including a simple chromosome 22 deletion, a SHANK3 gene mutation, or more complex changes like a ring chromosome or unbalanced translocation. These differences can influence symptom severity.

There is a strong association between PMS and autism spectrum disorder (ASD). Many individuals with PMS are also diagnosed with ASD, and research suggests that a variant in the SHANK3 gene is highly linked with autism traits.

Treatment for PMS focuses on managing the individual symptoms, as there is no cure for the underlying genetic cause. Care plans are tailored to each person and may include therapies, medications, and support from various specialists.

A diagnosis is confirmed through genetic testing, typically a chromosomal microarray. The test can detect the deletion or mutation on chromosome 22 or the SHANK3 gene that causes the syndrome.

Life expectancy can vary depending on the individual and the severity of associated medical issues. Some individuals may have life-threatening complications, such as severe epilepsy or gastrointestinal problems, that can affect lifespan.