Tuberous sclerosis complex (TSC) may have significant effects on intelligence and other abilities critical to learning. As in all aspects of TSC, however, this can vary widely from one individual to the next.
In the past, mental retardation was considered a characteristic sign of TSC, along with facial angiofibromas and intractable seizures. This view reflected the fact that mildly affected individuals were less likely to be diagnosed than individuals whose cognitive abilities were severely affected. As knowledge of TSC has increased, specialists have learned that approximately 60 percent of people with TSC have broadly defined normal intelligence (an IQ score of 70 or higher), while the remaining 40 percent fall below what psychologists consider to be the lower limit for normal intelligence.
Research has found that people with TSC are more likely than the general public to experience difficulty with language acquisition, memory, information processing, attention, and organization. Deficits in any of these areas typically affect an individual's ability to master higher-order skills involved in reading, writing, mathematics, problem solving, and concept formation. As a result, people with TSC may struggle in school and in jobs where these skills are required.
Although experts aren't certain how or why TSC affects the cognitive abilities of people who have it, they are exploring two likely possibilities. One suggests that seizures disrupt the orderly electrical activity responsible for transmitting signals involved in all neurological functions. This hypothesis is supported by the fact that the majority of people with TSC who have significant cognitive impairment also have a long history of seizures, especially infantile spasms. Preliminary studies also show that reducing or eliminating infantile spasms with medication seems to have a long-term positive effect on cognitive ability.
However, it is also possible that seizures and cognitive disabilities may result from the same underlying brain dysfunction. The most likely cause of this dysfunction is the presence of cortical tubers. Both the number of seizures and the severity of cognitive impairment have been positively correlated to the number of cortical tubers and the volume of brain space occupied by these tubers. Still, the studies exploring these connections have involved only a small number of individuals, and it is too early to make strong conclusions based on them.
Diagnosing cognitive and learning problems early can make a dramatic difference in the lives of people with TSC. Certainly, those who have significant cognitive impairment benefit from special educational programs and appropriate school settings. However, those with TSC who are of normal intelligence may have issues that are not so easily identified. And unfortunately, studies show that even this group is at greater risk than the general population for specific cognitive deficits that can affect their progress in reading, writing, spelling, and arithmetic. Thus, it is important that all individuals diagnosed with TSC undergo thorough cognitive assessments that can identify problems as early as possible. This will enable all people with TSC to access the help they need in order to succeed.
TSC affects four main cognitive areas that are central to an individual's ability to learn:
- Intelligence—Studies have shown that the majority of people with TSC fall into one of two relatively distinct groups: those with very low intelligence (an IQ lower than 21), and those whose intelligence is roughly comparable to the distribution of the general population.
- Language—Those with TSC who have significant cognitive impairment may achieve little more than single-word expression. These individuals often require visual prompts to assist in comprehension. Those with TSC who have normal intelligence may experience delays in language acquisition, as well as problems with verbal fluency and expressive vocabulary, abstract language and conceptualization, and organization of language. All of these affect development of reading and writing skills.
- Executive Functioning—This represents a major area of weakness for individuals with TSC. Individuals who struggle with executive functioning have poor organizational skills and have difficulty developing a logical plan with which to address a challenge. This may be seen as an inability to complete assignments on time, or as difficulty with managing changes in routine. People with TSC may also make poor choices due to impulsivity and inability to anticipate consequences of behavior.
- Attention—Mental health and behavioral problems inevitably stand in the way of learning. Approximately 20 to 30 percent of people with TSC experience these problems—such as poor attention, impulsivity, hyperactivity, aggression, and other disruptive behaviors—as compared to 5 to 10 percent of the general population.
Often, diagnoses of such cognitive and learning problems begin with parents, teachers, caregivers, relatives, or acquaintances who notice that an individual with TSC is struggling. Still, the importance of having a qualified neuropsychologist, developmental pediatrician, or psychologist conduct a formal, objective cognitive assessment cannot be stressed enough. It is these assessments that ultimately lead to adequate assistance for those individuals who are struggling.