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What is Phelan-McDermid Syndrome?
Written by richard lomas
Phelan-McDermid Syndrome -- also known as 22q13 Deletion Syndrome -- is caused by the absence / loss of genes at the tip of the 22nd chromosome, with lack of the Shank3 / ProSAP2 gene suspected as the primary cause of the symptoms associated with the syndrome. This gene plays a pivotal role in development of the human nervous system, including the brain, and loss of this genetic component prevents proper nervous system construction during fetal development.
There is a wide range of severity of symptoms observed in people with the deletion, but most exhibit moderate to severe developmental delays, physically and intellectually, but especially in speaking and communicating. Very low muscle tone is a common trait of the syndrome, and many have problems with eating, sleeping and emotional stability.
There are currently just over 450 members in our database worldwide (as of September 2009), this number includes children and adults. The large majority of these cases are small children due to the recent (1998) development of a reliable test called the Fluorescence In Situ Hybridization Test (aka, FISH) for the deletion. The actual number of people with the deletion is certainly much larger. Outreach to find and help these families with older children is one of the objectives of the support group.
Most, but not all, children with this syndrome will have a number of characteristic features:
Newborns usually have floppy muscle tone (hypotonia) Delayed in sitting up, rolling over, crawling and walking - Newborns/Infants have a difficult time drinking from the bottle/breast - fluids tend to leak out of their mouths making for a messy and wet meals
- Delayed or absent speech
- Normal growth or may be tall for age
- Facial features are fairly subtle and may not be recognized by your doctor: long head shape (dolicocephaly), puffiness around the eyes, long eyelashes, droopy eyelids, puffy cheeks and large ears.
- Physical features: large, fleshy hands, underdeveloped toenails that may peel off effortlessly and the inability to perspire, causing overheating readily.
Developmental
There is a large range of mental and physical abilities among individuals who have the 22q13 Deletion Syndrome. The developmental delays experienced by the population are often not apparent the first 12 months of life. Many infants with 22q13 Deletion reach their developmental milestones at the appropriate times when they are younger than 1 year old. This is true even of babbling and cooing.
Of individuals studied with 22q13 Deletion Syndrome, we know that 100 percent have global developmental delay and nearly 100 percent have absent or severely delayed speech. There are moderate to profound delays in all areas and significant delays in speech. Physical issues such as immature muscles, hypotonia, and visual perception cause some delays. Other delays seem to have more to do with neurological issues such as nerve control or mental processing time. Still other delays appear to be caused by physical and neurological problems.
As mentioned above, for some, early milestones come at an appropriate time. There is a large range for all developmental milestones. Delays are seen in fine motor and gross motor.
For example:
Sitting up:
Average 18 months
Crawling:
Range 10 months to never (some skip the step and creep, others may never develop that skill)
Walking:
Average 27 months, range 16 months to never (some children have started walking as late as 6 years old)
Individuals who do walk, tend to have an unsteady gate. They do slowly progress in the gross motor development learning to run, jump, throw and catch among other things. Fine motor skills progress slowly also. Some individuals make progress in many fine motor skills including page turning, coloring and even writing.
Many coordination delays are easy to spot, but just as many affecting the population are a challenge to see. While it is easy to see that your child is not yet standing, you might be unaware that their swallowing skills are not developing. Muscles affect more than the gross motor and fine motor movements for which we usually look. They also affect lungs, digestion, swallowing, and more. This is caused by physical abnormalities (hypotonia) and developmental delays.
Speech and language is the developmental area that is the most problematic for individuals with 22q13 Deletion. The receptive vocabulary of this group is constantly and considerably ahead of the expressive vocabulary level. Individuals understand much more of what is being said to them than they are able to say. Receptive vocabulary may be well above developmental delays in other areas also. Augmentative Communication is key. This is proven in many cases where given the opportunity to communicate either with gestures, pictures, or sign language, individuals are communicating far beyond what they would ever be able to verbally say. Some individuals are also able to follow directions, respond when told to do tasks, and help out in many nonverbal ways.
There have been some studies done in the area of IQ on people with 22q13 Deletion. The results have ranged from moderate to severe mental retardation. The Vineland Adaptive Behavior Scales (VABS) and the Battelle Developmental Inventory showed severe to profound mental retardation in 75 percent of children assessed. The other 25 percent were in the mild to moderate mental retardation range, but they were also the youngest members of the group. It appears as children with 22q13 Deletion age and more skills are expected, they fall further behind resulting in a more severe category of mental retardation. There is anecdotal evidence that some older children's developmental range is from significantly delayed with few or no words and limited understanding to only moderately delayed with conversational vocabulary and some basic math and reading skills.
There are two other areas involving developmental skills that seem to be unique to people with 22q13 Deletion Syndrome. One is that the population seems to have difficulty in skills of daily living that is beyond what is explained by their developmental delays. These skills include eating, dressing, and toilet training. This does not mean these skills are unattainable for all children with the deletion. They do require more time and learning opportunities than one would expect.
The other area that is unique and is still being studied is that of skill loss. This is very different from global skill loss where the individual would be regressing in many areas simultaneously. What is seen with this population is loss of one specific skill while the individual continues to make development growth in other areas. The specific skill loss is seen while there is no evidence of seizures, neurodegeneratic disorders, or inborn errors of metabolism to explain it. Skill loss has been seen with speech including all speech or just specific words and the ability to repeat certain sounds or words. Skill loss has also been seen in other areas such as toilet training.
It is important to acknowledge this characteristic among people with 22q13 Deletion because we often try to discover why the skill was lost. Is the individual no longer trying or being stubborn? Did the therapist not do a proper job of teaching the skill? Did the parent not spend enough time practicing the skill with their child? The answers to all of these questions might be no. Everyone did the right things and still the skill disappeared. It can be a huge frustration, but blame and guilt are not the answer.
There is a large range of mental and physical abilities among individuals who have the 22q13 Deletion Syndrome. The developmental delays experienced by the population are often not apparent the first 12 months of life. Many infants with 22q13 Deletion reach their developmental milestones at the appropriate times when they are younger than 1 year old. This is true even of babbling and cooing.
Of individuals studied with 22q13 Deletion Syndrome, we know that 100 percent have global developmental delay and nearly 100 percent have absent or severely delayed speech. There are moderate to profound delays in all areas and significant delays in speech. Physical issues such as immature muscles, hypotonia, and visual perception cause some delays. Other delays seem to have more to do with neurological issues such as nerve control or mental processing time. Still other delays appear to be caused by physical and neurological problems.
As mentioned above, for some, early milestones come at an appropriate time. There is a large range for all developmental milestones. Delays are seen in fine motor and gross motor.
For example:
Sitting up:
Average 18 months
Crawling:
Range 10 months to never (some skip the step and creep, others may never develop that skill)
Walking:
Average 27 months, range 16 months to never (some children have started walking as late as 6 years old)
Individuals who do walk, tend to have an unsteady gate. They do slowly progress in the gross motor development learning to run, jump, throw and catch among other things. Fine motor skills progress slowly also. Some individuals make progress in many fine motor skills including page turning, coloring and even writing.
Many coordination delays are easy to spot, but just as many affecting the population are a challenge to see. While it is easy to see that your child is not yet standing, you might be unaware that their swallowing skills are not developing. Muscles affect more than the gross motor and fine motor movements for which we usually look. They also affect lungs, digestion, swallowing, and more. This is caused by physical abnormalities (hypotonia) and developmental delays.
Speech and language is the developmental area that is the most problematic for individuals with 22q13 Deletion. The receptive vocabulary of this group is constantly and considerably ahead of the expressive vocabulary level. Individuals understand much more of what is being said to them than they are able to say. Receptive vocabulary may be well above developmental delays in other areas also. Augmentative Communication is key. This is proven in many cases where given the opportunity to communicate either with gestures, pictures, or sign language, individuals are communicating far beyond what they would ever be able to verbally say. Some individuals are also able to follow directions, respond when told to do tasks, and help out in many nonverbal ways.
There have been some studies done in the area of IQ on people with 22q13 Deletion. The results have ranged from moderate to severe mental retardation. The Vineland Adaptive Behavior Scales (VABS) and the Battelle Developmental Inventory showed severe to profound mental retardation in 75 percent of children assessed. The other 25 percent were in the mild to moderate mental retardation range, but they were also the youngest members of the group. It appears as children with 22q13 Deletion age and more skills are expected, they fall further behind resulting in a more severe category of mental retardation. There is anecdotal evidence that some older children's developmental range is from significantly delayed with few or no words and limited understanding to only moderately delayed with conversational vocabulary and some basic math and reading skills.
There are two other areas involving developmental skills that seem to be unique to people with 22q13 Deletion Syndrome. One is that the population seems to have difficulty in skills of daily living that is beyond what is explained by their developmental delays. These skills include eating, dressing, and toilet training. This does not mean these skills are unattainable for all children with the deletion. They do require more time and learning opportunities than one would expect.
The other area that is unique and is still being studied is that of skill loss. This is very different from global skill loss where the individual would be regressing in many areas simultaneously. What is seen with this population is loss of one specific skill while the individual continues to make development growth in other areas. The specific skill loss is seen while there is no evidence of seizures, neurodegeneratic disorders, or inborn errors of metabolism to explain it. Skill loss has been seen with speech including all speech or just specific words and the ability to repeat certain sounds or words. Skill loss has also been seen in other areas such as toilet training.
It is important to acknowledge this characteristic among people with 22q13 Deletion because we often try to discover why the skill was lost. Is the individual no longer trying or being stubborn? Did the therapist not do a proper job of teaching the skill? Did the parent not spend enough time practicing the skill with their child? The answers to all of these questions might be no. Everyone did the right things and still the skill disappeared. It can be a huge frustration, but blame and guilt are not the answer.