Genetic Disorders
Genetic disorders are disorders that are caused by an abnormal gene an extra gene in a group, a mutated gene or a variation in a gene. Other genetic disorders are caused by chromosomal abnormalities such as the malformation, deletion, addition and/or dislocation of chromosomal material during the development of the oocyte or spermatocyte or during conception and germination of the egg (Zillmer, 2008). Genetic and chromosomal disorders can cause things to go wrong in brain development and examples include Turner’s syndrome, Williams syndrome and Down’s syndrome.
Turner’s syndrome (TS) is caused by a sex chromosome abnormality in females that only have one X on the 45th chromosome. Turner’s syndrome is characterized by failure to develop secondary sexual characteristics, having a short stature (often born premature), webbed neck and “cubitus valgus”, which is an increased carrying angle at the elbow (Zillmer, 2008). Evidence that Turner’s syndrome is often comorbid with ADHD and learning disorders suggests that TS affects the brain’s executive functioning and processing abilities. Typically children with TS have intact verbal abilities but deficits in visuospatial, visuomotor and arithmetic abilities. These cognitive impairments are a result of abnormalities in the posterior area of the right hemisphere and problems with executive functioning are due to abnormalities in the frontal lobes (Zillmer, 2008). Treatment for Turner’s syndrome includes treating any learning disabilities or ADHD that may be present, estrogen supplements during adolescence and occasionally growth hormones.
Williams syndrome (WS) is also a chromosomal disorder due to submicroscopic genetic deletion on chromosome 7. Williams syndrome is a neurodevelopment disorder characterized by unusual facial features, cardiovascular problems, hypercalcemia, poorly developed joints and mental retardation (Zillmer, 2008). Children are identified as having WS because they have characteristic physical abnormalities and low IQ scores. They also fit a specific cognitive profile and have distinctive personality traits for example they are usually very sociable and have an extraordinary interest in music. Structural abnormalities found in brains of individuals with WS include decreased volume in white matter with greater posterior volume loss versus anterior volume loss and significant gray loss matter in the right occipital lobe. Their density of their auditory cells is also abnormal and they have smaller neurons in the temporal lobe (Zillmer, 2008). The brain abnormalities associated with WS cause intellectual impairment but relatively preserved language skills, an increased attention to facial processing and weak visuoconstructive skills.
Down’s syndrome is a result of a trisomy of chromosome 21 rather than two. It is typically not an inherited trisomy but rather due to an error in cell division when the sperm and egg joined together. Infants with Down’s syndrome have poor muscle tone from birth and recognizable facial characteristics such as a flattened face. As they get older, mental retardation and learning disabilities become apparent. Neurofibrillary tangles and neuritic plaques accumulate in the brains of people with Down’s syndrome similar to the way they do in the brains of people with Alzheimer’s disease.
It is important for potential parents to be aware of genes that they might be carrying. Additionally, it is important for parents to understand symptom profiles of children with genetic disorders, disorders that are frequently comorbid with genetic disorders and the neurological underpinnings of genetic disorders. This brief overview is meant to help people understand the basic neuropsychology of these three genetic disorders and not meant to provide any sort of medical definition or be an ultimate resource. Refer to a medical professional or certified genetic counselor for more information.
This information is based on an advanced college neuropsychology course and references the following textbook:
Zillmer, Eric A., Mary V. Spiers, William Culbertson (2008). Principles of
Neuropsychology. Wadsworth Publishing.
