Abstract
This is a review of nature (genetics) vs. nurture (environment in several genetically based conditions of the brain and nervous system. In the medical literature on twins similar symptoms and progression of the diseases are described as concordant. Symptoms that differ among identical twins are described as discordant. If a genetic condition like Huntington's disease is 100 percent influenced by genetics, then one would expect all Huntington's symptoms to be concordant. If some symptoms are discordant then they are attributed to the environment. Ways to describe these environmental factors include: non-genetic factors, epigenetics, nurture, stochastic (patterns that can't be predicted), pre and post-natal environment, lifestyle, and nutrition. These environmental factors are slightly different or hugely different even for identical twins. The environmental factors, especially lifestyle and nutrition are the factors most influenced by brain health coaches and complementary and alternative medicine practitioners. The literature supports the idea that even in Mendelian disorders (conditions that are thought of as primarily influenced by genetics) the environment, lifestyle, and nutrition can make large differences in the symptom picture and quality of life.
Highlights
IntroductionThings that can be different or similar in twins include age at onset, landmarks of the disease process, behavioral abnormalities, severity of chorea or symptoms, mental deficits, clinical expression, motor or muscle related symptoms, attentional impairment, hyperkinetic hypotonic, and more
Things that can be different or similar in twins include age at onset, landmarks of the disease process, behavioral abnormalities, severity of chorea or symptoms, mental deficits, clinical expression, motor or muscle related symptoms, attentional impairment, hyperkinetic hypotonic, and more.Some of the conditions in which discordant symptoms are found in identical twins include: Huntington's disease, Episodic Ataxia Type 1, Spinocerebellar ataxia (SCA1), Machado-Joseph Disease (MJD), Dentatorubro-pallidoluysian Atrophy (DRPLA), Familial forms of Alzheimer's disease, Familiar Amyloidotic Polyneuropathy, Neurofibromatosis type 1, Facioscapulohumeral Muscular Dystrophy, Myotonic Dystrophy, Gerstmann-Straussler-Scheinker disease, Rett Syndrome, and Joubert syndrome
The differences point to differential involvement between twins of discrete regions in the cerebellum and brainstem. These results demonstrate the presence of quantitative differences in the severity, rate of progression, and regional central nervous system involvement in monozygotic twins with spinocerebellar ataxia (SCA) that must be owing to the existence of nongermline or external factors [7]
Summary
Things that can be different or similar in twins include age at onset, landmarks of the disease process, behavioral abnormalities, severity of chorea or symptoms, mental deficits, clinical expression, motor or muscle related symptoms, attentional impairment, hyperkinetic hypotonic, and more. Some of the conditions in which discordant symptoms are found in identical twins include: Huntington's disease, Episodic Ataxia Type 1, Spinocerebellar ataxia (SCA1), Machado-Joseph Disease (MJD), Dentatorubro-pallidoluysian Atrophy (DRPLA), Familial forms of Alzheimer's disease, Familiar Amyloidotic Polyneuropathy, Neurofibromatosis type 1, Facioscapulohumeral Muscular Dystrophy, Myotonic Dystrophy, Gerstmann-Straussler-Scheinker disease, Rett Syndrome, and Joubert syndrome
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