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The most commonly known genetic disorders diagnosed during childhood and adolescence are developmental delay and autism, although a host of inherited conditions can involve any organ system with onset after the newborn period. Often dubbed “diagnostic dilemmas” because of the difficulty in recognizing them as genetic diseases, these conditions often result in a struggle to establish a diagnosis and effective treatment regimen. Genomic medicine is dramatically impacting genetic disease diagnosis in children, and in some cases leading to life-altering treatment.
A great deal of research in genomics has focused on understanding the genetic pathways that lead to proper or dysfunctional brain development and function. Progress has been made, and much remains to be learned.
As with many childhood genetic diseases, children with autism or developmental delay can be divided into those where the behavioral/cognitive feature is the only symptom, and those that also include other medical problems (e.g., birth defects, dysmorphic/unusual features, abnormal muscle tone). The presence of epilepsy straddles this distinction, as epilepsy is both a component of syndromic causes of autism as well as idiopathic autism. Practitioners who interact with autistic children play a huge role in identifying any other medical concerns, determining the course of intellectual and/or social disability (late onset, regressive, progressive, static), and defining the areas of cognitive function that are impacted (social, spatial, language, etc.).
Role of genetics in autism
A review of the considerable progress in understanding the genetics of autism is beyond the scope of this text. Briefly, twin studies demonstrate that a considerable portion of risk for autism is genetic (possibly >50%), though some environmental contribution must exist. Genetic variation associated with autism currently is understood to consist of:
Common variants in genes that confer a small risk of autism individually, and must be combined to cause disease. This class of common-but-small-effect variant may contribute relatively less to autism compared to other common disorders (e.g., type II diabetes), or may be too complex in relation to autism to be detected by current techniques. Testing for this type of variant is not yet clinically useful in the diagnosis or management of autism.
Known genetic syndromes that affect multiple organ systems and include autism, such as Fragile X, tuberous sclerosis, Cowden syndrome, single-gene disorders affecting the Ras pathway (Noonan, Costello, neurofibromatosis type I, cardio-facio-cutaneous syndrome), and others. Identifying this type of cause of autism is particularly important because other health care maintenance may be necessary (e.g., cancer screening).
Copy number variants CNVs involving deleted or duplicated chromosomal material, usually too small to be detected by karyotype but readily detectable by microarray technology. These may account for approximately 15% of cases of autism and can be diagnosed readily by ...