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Genetic, Metabolic, and Chromosomal Disorders

A syndrome is a medical term that describes individuals who have certain physical, developmental, and/or behavioral characteristics that occur due to a single underlying cause (e.g., a faulty gene or set of genes). An individual who is diagnosed with a certain syndrome may have some or all of the characteristics of that syndrome. There is evidence from research that challenging or problematic behaviors are more common in certain genetic syndromes than might be expected based on the individual’s level of intellectual disability (ID) and other characteristics, such as communication difficulties.

Prader-Willi Syndrome (PWS)

PWS is a genetic disorder involving a defect on chromosome 15. The reported prevalence of PWS has varied widely, but the most commonly cited figure is that PWS affects about 1 in 15,000 births. As with most genetic syndromes, there are common characteristics shared among individuals diagnosed with PWS. For example, early in life they are typically diagnosed with failure to thrive due to poor food intake. However, around 18 months of age, individuals with PWS begin engaging in hyperphagia (the excessive consumption of food) which, if unchecked, can result in morbid obesity and related health problems. Individuals with PWS will often go to great lengths to obtain (or steal) food and may seem to have an obsession with food. Behavior problems are commonly reported in this population. In addition to hyperphagia, food stealing, and tantrums, self-injurious skin picking seems to occur at higher rates in the PWS population relative to the general ID population. Individuals may also engage in aggression, disruptive/destructive behavior, and running away (elopement). Many of these behaviors may occur in an attempt to access food or in response to being denied food.

Down Syndrome

Down syndrome is the most commonly diagnosed chromosomal disorder, which affects 1 in every 691 babies born in the United States. Individuals with Down syndrome have a defect in chromosome 21. The National Down Syndrome Society suggests that individuals with Down syndrome may share some common behavioral concerns including wandering/running off (also called elopement) and stubborn / oppositional behavior (also called noncompliance).

Williams Syndrome

Williams syndrome is a genetic condition that is caused by the deletion of genes from chromosome 7. Williams syndrome affects approximately 1 in every 10,000 people and is found in males and females at equal rates. Most individuals with Williams syndrome have some level of cognitive delay – ranging from mild to moderate. Developmental milestones (e.g., talking, toilet training) often occur somewhat later than what is typical. Young children may have feeding difficulties due to low muscle tone, severe gag reflexes, and poor sucking and swallowing. Infants may also have periods of irritability and difficulty establishing typical sleep patterns. Individuals with Williams syndrome are perhaps best known for their overly social and friendly personalities and cheerful demeanor with strong verbal and social skills; however, they may require help to ensure that there social interactions are appropriate. Further, individuals with Williams syndrome may be more likely to have phobias, which can impact their ability to participate fully in the community. Behavioral interventions may be helpful for phobias and for social skills training (e.g., curbing inappropriate displays of affection towards strangers).

Fragile X Syndrome

Fragile X is the most common known cause of inherited (genetic) intellectual disability. It affects both males and females, but because the affected gene is on the X chromosome, males are more frequently and severely affected than females. The prevalence of Fragile X is approximately 1 in 3,600 to 1 in 4,000 in males and approximately 1 in 4,000 to 1 in 6,000 in females. Males with Fragile X typically have moderate to severe intellectual disabilities; affected females have milder cognitive impairments. Approximately 40 percent of individuals with Fragile X are also diagnosed with autism; these individuals tend to have more significant intellectual impairment than those who are not also diagnosed with autism. Behavioral characteristics can include difficulty with attention and hyperactivity, social anxiety and/or avoidance, poor eye contact, difficulty with transitions, hand biting and/or hand flapping, and aggressive behavior. Although problem behaviors have been shown to occur for a variety of reasons (e.g., to access attention, for sensory stimulation), individuals with Fragile X may be more likely to engage in problem behavior to escape from social interactions because they have a tendency to find those interactions aversive.

Smith-Magenis Syndrome

Smith-Magenis is a genetic disorder most often caused by a deletion of genetic material from chromosome 17. The reported prevalence of Smith-Magenis is 1 in 25,000 individuals; however, researchers believe that the condition is underdiagnosed, and the true prevalence is likely closer to 1 in 15,000 individuals. Individuals with Smith-Magenis have varying levels of intellectual disability from mild to moderate. Although individuals diagnosed with Smith-Magenis have often been described as having endearing/appealing personalities, there are also common behavioral difficulties including speech delay, chronic sleep disturbance, teeth grinding, delayed acquisition of toileting skills, hyperactivity, impulsivity, excessive attention-seeking, distractibility, prolonged tantrums, and aggressive and disruptive behaviors. In addition, specific types of stereotypic and self-injurious behaviors are common. Individuals may engage in arm hugging and/or hand squeezing when excited; they may also do “lick and flip” behavior (e.g., quick flipping of pages of books/magazines with or without licking their finger). Self-injurious behaviors might include head banging, hand biting, skin and/or nail picking, and inserting objects into bodily orifices. Although self-injury may be sensitive to many types of rewards, in some cases, self-injury emitted by individuals with Smith-Magenis has been shown to be more likely under conditions with low levels of adult attention; it has been suggested that the genetic predisposition to enjoy social contact with others may make it more likely that SIB would occur to access attention.

Angelman Syndrome

Angelman syndrome is a genetic disorder that is caused by the loss of a gene located on chromosome 15. Reported prevalence varies, but the most commonly cited estimate is 1 in every 15,000 individuals. It affects males, females, and all racial groups equally. Most affected individuals have recurrent seizures (epilepsy), a small head size (microcephaly), and walking and balance disorders. Many children also have difficulty sleeping and need less sleep than usual, though there is some suggestion that sleep problems may improve with age. Individuals with Angelman syndrome also have profound intellectual disabilities, and although they don’t speak, they typically do understand some language. Despite their challenges, individuals with Angelman often have a happy demeanor and laugh and smile frequently; research has shown that they tend to seek out social interactions, suggesting that they very much enjoy these interactions. Aggressive behavior is common in Angelman syndrome, and there has been some suggestion that for some individuals, these behaviors may occur to initiate, or to prolong, social interaction with adults. Individuals with Angelman can be excitable, which may manifest itself with frequent hand-flapping movements. In addition, hyperactivity, a short attention span, and a fascination with water are common.

Smith-Lemli-Opitz Syndrome

Smith-Lemli-Opitz syndrome (SLOS) is a genetic disorder caused by a defective gene on chromosome 7 that is responsible for the production of cholesterol, which is essential to the cells in the body. Smith-Lemli-Opitz syndrome affects an estimated 1 in 20,000 to 60,000 newborns. This condition is most common in Caucasians (whites) of European ancestry, particularly people from Central European countries such as Slovakia and the Czech Republic. It is very rare among African and Asian populations.

The signs and symptoms of SLOS vary widely. Mildly affected individuals may have only minor physical abnormalities with learning and behavioral problems. Severe cases can be life-threatening and involve profound intellectual disability and major physical abnormalities. One of the common symptoms of SLOS is delayed speech and a difficulty in communicating in general. In addition, individuals with SLOS may have atypical sleep patterns.

One of the more challenging aspects of SLOS is the constant battle with behavior. Almost all of those with SLOS show at least some of the problematic behaviors that are common in those with autism. Behavior can range from screaming, hitting, pinching, and biting, to head banging and self-injury.

Lesch-Nyhan Syndrome

Lesch-Nyhan syndrome is a result of the overproduction of uric acid, a waste product of the body that is found in blood and urine. The gene associated with this condition is located on the X chromosome; as a result, Lesch-Nyhan occurs almost exclusively in males. Lesch-Nyhan occurs in approximately 1 in 380,000 individuals with a similar frequency in all racial/ethnic populations.

Lesch-Nyhan is characterized by involuntary muscle movements including tensing and jerking of muscles and flailing of the limbs. As a result, individuals with Lesch-Nyan are typically wheelchair bound.

Self-injurious behavior is observed in almost all individuals with Lesch-Nyhan. Children begin to bite their fingers, lips, and the insides of their mouths as early as 2 to 3 years old; they may also engage in head banging. The frequency and severity of the self-injury often requires restraints, and some families have had to resort to having the individual’s teeth extracted. In addition, individuals with Lesch-Nyhan may also engage in aggression, such as hitting or spitting at others.

Cornelia de Lange

Cornelia de Lange is caused by a mutation in one of a few different genes located on the X chromosome or chromosomes 5 or 10. In about 35 percent of cases, the cause of Cornelia de Lange syndrome is unknown. Cornelia de Lange occurs in about 1 in every 10,000 to 30,000 newborns. It affects both genders equally and is present at similar rates across racial and ethnic groups. Almost all cases result from new gene mutations and occur in people with no history of the condition in their family.

Individuals with Cornelia de Lange typically have mild to profound intellectual disabilities with the majority of individuals falling in the mild to moderate range. Sleeping and eating patterns are often irregular, and digestive issues can result in challenging behaviors during mealtimes. Both anxiety and difficulty maintaining attention have been noted, and speech may be absent or minimal. Further, individuals with Cornelia de Lange can exhibit behaviors similar to those seen in individuals with autism, such as repetitive behavior and self-injury (for example, eye-directed SIB).

Rett Syndrome

Rett syndrome is caused by mutations to a gene on the X chromosome. It affects approximately 1 in every 10,000 to 1 in every 23,000 female births and appears equally across all racial/ethnic groups. Rett syndrome symptoms appear after an early period of apparently normal or near normal development until six to eighteen months of life, when there is a slowing down or stagnation of skills. A period of regression then follows when the child loses communication skills and purposeful use of her hands.

Although Rett syndrome used to be classified as one of the autism spectrum disorders, it is now considered a distinct disorder that has many autism-like symptoms. Children with autism and children with Rett syndrome both exhibit impaired social interaction, impaired communication, and unusual behavior or movements. The similarity in symptoms is the reason why Rett syndrome is often misdiagnosed as autism. However, as the child with Rett syndrome ages, some of the autism-like symptoms may lessen or even disappear; for example, individuals with Rett syndrome often regain interest in social interactions later in life.

Individuals with Rett syndrome typically fall in the severe to profound range of intellectual disabilities and have limited expressive language abilities. Stereotypic hand movements including hand wringing or “washing” are common as well as biting and/or mouthing of the hands and shoulders. In addition, breath-holding and body rocking may occur.

Cri-du-Chat Syndrome

Cri-du-chat (5P-) syndrome is a genetic disorder that is caused by missing genes on chromosome 5. It affects approximately 1 in every 20,000 to 1 in 50,000 newborns. One of the most distinctive features of infants with Cri-du-chat is their high-pitched, catlike cry.

Individuals with Cri-du-chat typically have severe intellectual disabilities and difficulty communicating with others. Early feeding problems are common as is hyperactivity, obsessive attachments to objects, repetitive movements (e.g., stereotypy), and tantrums, which may include aggression and self-injurious behavior (e.g., head banging, skin picking).

Sotos Syndrome

Sotos syndrome is caused by a defect on chromosome 5 and is reported to occur in 1 in 10,000 to 14,000 newborns. Many cases of this disorder are not diagnosed, however, so the true incidence may be closer to 1 in 5,000. About 95 percent of Sotos syndrome cases occur in people with no history of the disorder in their family.

People with Sotos syndrome often have intellectual impairment; however, for some individuals with Sotos, the syndrome only alters developmental timing, and despite early trends, adults may be within the normal range of intellectual abilities. Most children with Sotos syndrome have behavioral problems. Frequently reported behavioral issues include sleep disturbances, attention deficit hyperactivity disorder (ADHD), phobias, obsessions and compulsions, irritability, impulsive behaviors, and tantrums. Problems with speech and language are also common.

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