22q13 deletion syndrome, also known as Phelan-McDermid Syndrome (PMS), is a rare genetic condition that affects various aspects of an individual’s development and health. This syndrome arises from a specific genetic change, leading to a range of characteristics that can impact daily life. Understanding this syndrome provides insight into the challenges and potential support strategies for those affected.
Understanding the 22q13 Deletion
The term “22q13” refers to a specific location on chromosome 22. This syndrome results from a microdeletion, meaning a small piece of genetic material is missing from the long arm (q) of chromosome 22, specifically at the 22q13.3 region. This genetic loss includes the SHANK3 gene, which is considered a major contributor to the syndrome’s characteristics. The SHANK3 gene plays a significant role in the development and function of nerve cells, particularly in forming connections between them.
The absence or alteration of one copy of the SHANK3 gene, known as haploinsufficiency, is believed to be responsible for many of the associated symptoms. Proteins produced by the SHANK3 gene are crucial for maintaining synaptic homeostasis, which is the balance of communication between brain cells. This disruption in nerve cell communication and development leads to the diverse range of symptoms observed in individuals with 22q13 deletion syndrome.
Key Characteristics and Developmental Profile
Individuals with 22q13 deletion syndrome often exhibit a range of physical, developmental, and behavioral characteristics. Intellectual disability, varying from moderate to severe, is a common feature. Delayed or absent speech is also highly prevalent, with many children having limited vocabulary by age three or four, and some may even lose the ability to talk over time. Motor skill delays are frequently observed, along with hypotonia, which is low muscle tone.
Distinctive facial features can include long eyelashes, a pointed chin, and a bulbous nose. Behavioral patterns often resemble aspects of autism spectrum disorder (ASD), including repetitive behaviors and sensory processing differences. Sleep disturbances are also reported in some individuals.
Other potential health issues may accompany the syndrome. These can include seizures, which affect a subset of individuals, and gastrointestinal problems. Kidney issues have also been noted in some cases. While growth is typically within normal limits, the combination of these characteristics creates a unique developmental profile for each individual.
Identifying the Condition and Its Origins
The diagnosis of 22q13 deletion syndrome relies on specific genetic testing methods. Chromosomal microarray (CMA) is a primary tool used to detect the missing pieces of DNA on chromosome 22. Fluorescence in situ hybridization (FISH) is another valuable test, particularly for identifying cases of mosaicism or complex chromosomal rearrangements.
The origins of the 22q13 deletion are predominantly spontaneous. In approximately 75% to 85% of cases, the deletion is de novo, meaning it is a new genetic change not inherited from either parent. These spontaneous deletions occur during the formation of reproductive cells or in the early stages of fetal development. A smaller percentage of cases, however, can be inherited from a parent who carries a balanced chromosomal rearrangement, such as a translocation. In these rare instances, the parent may not show symptoms themselves but can pass on an unbalanced chromosome to their child.
Support and Management Strategies
While there is currently no cure for 22q13 deletion syndrome, management focuses on addressing specific symptoms and maximizing developmental potential. Early intervention therapies include physical therapy to improve motor skills and address hypotonia. Occupational therapy helps individuals develop daily living skills and manage sensory processing differences. Speech therapy is important for addressing communication delays, aiming to improve verbal skills and expand vocabulary.
Behavioral therapy helps manage challenging behaviors, including those that resemble autism spectrum disorder. Medical management is tailored to associated health issues, such as medication for seizures or dietary adjustments for gastrointestinal problems. A multidisciplinary team approach, involving various specialists like neurologists, gastroenterologists, and developmental pediatricians, provides comprehensive care. Family support organizations connect families and provide resources.