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Genetics of Developmental Disabilities

Introduction

Developmental disabilities (DDs) comprise a group of chronic conditions associated with physical or mental impairments. A complex mix of factors causes these conditions in early stages of the human development. These factors include genes, complications during birth, exposure to environmental toxins, parental behaviours during pregnancy, and infections. Genetic defects account for many disorders producing DDs such as intellectual disabilities, Down’s syndrome, autism, dyslexia, and foetal alcohol syndrome (Vorstman & Ophoff 2013). Parents transfer genetic defects to their children through the chromosomal pattern of inheritance, which involves the transfer of one or two defective genes to their children. Thus, the aim of the essay is to explore genetic causes of DDs, especially dyslexia, and the effectiveness of DNA modification in the treatment of these disorders.

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Genetic Causes of Developmental Disabilities

DDs caused by genetic factors involve a significant number of birth defects. The prevalence rate of DDs is more than 15% in children aged between 3 and 17 years (Centres for Disease Control and Prevention 2018)). The common causes of these abnormalities are monosomies and trisomies that occur as nondisjunction during meiosis (Paracchini, Diaz & Stein 2016). Other malformations encompass abnormalities of chromosome structure due to genetic mutations. These genetic mutations affect the capacity of both human cells and body organs to conduct normal cell functions. The developmental disabilities caused by genetic abnormalities fall into four major groups, according to diagnosis. These groups include the nervous system, sensory-related, metabolic, and degenerative disorders.

Nervous System-Related Developmental Disability

This group of gene-related disability impairs the network of nerve cells responsible for coordinating nerve impulses between different parts of the body such as the spinal cord, the brain, and the nervous system. Chiurazzi and Pirozzi (2016) report that damaging cell network influences intelligence and causes behavioural conditions such as language difficulties, movement disorders, and convulsions. The most common forms of disability under this category are intellectual and developmental disabilities (IDDs), which result from Down’s syndrome and fragile X syndrome (Chiurazzi & Pirozzi 2016). Down’s syndrome occurs when the DNA structure acquires an extra copy of chromosome 21, while Fragile X syndrome results from a gene mutation that causes the expansion of fragile gene on chromosome X (Schoen, Miller & Sullivan 2016). These mutations lead to the production of low levels of proteins necessary for optimum functioning of the brain. Autism is another common nervous system-related disorder under this category, which emanates from nucleotide alterations on chromosome X causing the brain abnormality. This condition affects intellectual, social, and communication skills of an individual.

Sensory-Related Disability

This group of genetic disability interferes with the normal body’s ability to exercise effective sense functionality within its immediate environment. Sensory-related conditions occur as part of a complex genetic defect of altered chromosome pattern such as in children with William’s syndrome who have trouble in determining distances between objects (Hubbard et al. 2015). In some other cases, children inherit deleted chromosomes from parents suffering from the condition. Visual and hearing problems are other disabilities in this group that have a close association with nervous system disabilities and may occur concurrently (Schoen, Miller & Sullivan 2016). An example is Fragile X syndrome and sensitivity to loud sounds. Overall, children with sensory-related disabilities have problems processing and using basic sensory information, namely, perception, smell, touch, sight, and taste.

Metabolic-Related Disability

A birth defect in this group affects metabolic processes in the body of an individual. For instance, phenylketonuria (PKU) occurs due to the mutation in the gene responsible for the production of phenylalanine hydroxylase. In the metabolic process, this enzyme converts phenylalanine to tyrosine. Inadequate production of this enzyme owing to genetic defects causes a build-up of phenylalanine in the body. Another disorder of this groups is hypothyroidism, which is a hormonal condition where genetic defect leads to the production of antibodies that destroy own tissues in the body. Generally, metabolic-related conditions occur when genetic disorders impair chemical processes in the body.

Degenerative Disability

This type of disability makes people lose normal functional capacity. In most cases, the genetic defect causes mental, sensory, and physical problems as individuals advance in age (Feng, Egan & Wang 2016). An example of this birth defect is Rett syndrome in girls, which results from genetic mutation of the methyl CpG-binding protein 2 (mecp2), which is essential for normal functioning of cells. The generative disability retards physical and mental growth, causes the loss of communication abilities, restricts normal body movements, and triggers breathing problems.

DNA Modification in Treatment and Prevention

Advancements in genetic engineering have led to the introduction of new diagnosis and gene correction technologies making it possible to determine and modify gene defects. Diagnostic techniques include chorionic villus sampling, imaging techniques, karyotyping and sex chromosome analysis, as well as biochemical and molecular analysis of cells from amniotic fluid. In gene correction, Transcription Activator-Like Effector Nucleases (TALENs), Zinc Finger Nucleases (ZFNs), and Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) technologies facilitate the modification of defective genes. According to Hubbard et al. (2015), gene correction technologies allow scientists to combine RNA sequences that match a specific stretch of DNA in a targeted genome. The method facilitates targeting of faulty genes, cutting out the damaged sequence, and replacing with healthy DNA. CRISPR associated protein 9 (Cas9) is an enzyme that significantly improves the ability to edit targeted strands of DNA locus, leading to an effective modification of selected sequences.

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This rapid technology in genetic engineering facilitates tailoring of cell development during pregnancy. The process enables the establishment of novel DNA structures and the transfer of health genetic material from one organism to another. Additionally, in already disabled individuals, genetic modelling facilitates reprogramming of defective DNA and the development of healthy gene structures. The insertion of a replacement copy of the gene using the edit tools fixes the damage on an individual’s DNA helix. Thus, by introducing the corrective technology early enough to the embryo and applying CRISPR-Cas9 to DNA repair system effectively fixes the mutated gene and corrects the associated genetic development disabilities. Generally, genetic engineering is significantly effective for the treatment of genetic associated abnormalities.

Genetic Causes of Dyslexia

Dyslexia is a neurobiological condition of genetic origin that affects the performance of the neurological system in parts of the brain responsible for learning to read. A genetic mutation involving loci on chromosomes 6 and 18 show strong and replicable effects on reading abilities. Becker et al. (2017) argue that since the two genomic regions contain several candidate genes, an abnormal gene modification along the two regions impairs brain development. KIAA0319 is a transmembrane protein associated with neuronal migration in the early development stage of the brain. This gene regulates the synthesis of the signature molecule on the surface of the nerve cells. Under-expression of the KIAA0319 gene leads to failure of nerve cells to migrate to their correct positions in the brain. In dyslexic individuals, a genetic defect on chromosome 6 and 18 impairs the synthesis of the KIAA0319 gene, leading to the misplaced location of nerve cells in the cerebral cortex impairing visual input and causing the brain to lose the ability to process symbols.

Genetics and Environmental Factors of Dyslexia

Over the recent past, researchers from various medical sectors and universities have tried to explain causes of dyslexia. The focus of their research hinges on the complexities that the condition demonstrates and on whether it is preventable. Notably, it is evident that the genetic development and environmental factors have a significant contribution to contraction and severity of dyslexia among susceptible individuals. While studies reveal that conditions like dyslexia are hereditary, it is important to note that with the right interventions at early stages of child development, the severity of the condition reduces considerably.

Dyslexia and Genetic Relationship

Fundamentally, dyslexia has a close relationship with the genetic development of individuals. The relationship is what explains the hereditary nature of the condition. Studies by scholars such as Paracchini, Diaz, and Stein (2016) indicate that if a family member suffers from dyslexia it is likely to have a child with the condition within the same lineage. Moreover, if a twin has the condition, then the other twin is likely to experience reading challenges frequently, an explanation that compounds the relationship between dyslexia and genetic development. The cases of dyslexia, which have gradually perplexed several scholars, relates to the increasing demand for education and the need to read (Peterson & Pennington 2015). Therefore, the perception that the cases of dyslexia are on the rise may be untrue because in the past identification of people suffering from the condition and other reading impairments were complex due to the little demand to read and learn. However, modern societies require learning and extensive reading, a scenario that makes the identification of the condition easy.

Some of the genes associated with dyslexia include those responsible for the migration of cells to the brain, specifically to the nerve cells in Chromosome 6. During the early stages of child development, KIAA0319 gene facilitates the movement of nerve cells to the brain. However, in the case of dyslexics, the gene fails to facilitate the migration effectively, but instead, inhibits the process. As such, the neurones responsible for reading and learning fail to reach the required parts of the brain, a factor that is evident even during post-mortem results of dyslexia victims (Jiménez-Bravo, Marrero & Benítez-Burraco 2017). Importantly, impaired movement of these neurones responsible for learning and coordinating numbers and letters with sounds implies that people become dyslexics. Unlike in other scenarios where the neurones move even when impaired, neurones associated with learning stop moving when impaired.

Therefore, it becomes complex to successfully treat the condition after diagnosis, especially at late stages of an individual’s development. Recent studies reveal that the rate of dyslexia infections is high in individuals who do not have definite handedness. Since handedness is a hereditary condition that runs down family lines, it is evident that the connection between weak lateralisation and dyslexia is also genetic. The main chromosome linked to the issue of lateralisation is Chromosome 2, which runs paternal lineage. According to Dyslexia Research Trust (2017), children may inherit Chromosome 2 from their paternal parents and suffer from dyslexia and other conditions, which include schizophrenia. Chromosome 2, dyslexia, and family lineage have an intricate link that explains the strong relationship between dyslexia and genetic development of individuals. It is important to allude that children, who have parents suffering from dyslexia, are vulnerable to the condition as compared to their counterparts whose parents are healthy.

Environmental Relationship

Although some children are born with perfect neurological systems, the environment can trigger dyslexia. For instance, if a society does not help children to learn properly, the children may end up as dyslexics. Learning institutions, caregivers, and religious associations play a role in ensuring that children get the right insights on learning and reading. However, if these entities do not assist children, then the likelihood of having dyslexic adults is high. Bishop (2015) elucidates that the relationship between the environmental factors and dyslexia is more than 50%. Therefore, while some cases of dyslexia result from genetic development, others are outcomes of poor parenting by caregivers, schools, and religious associations.

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Dyslexia Treatment

Therapy and training programs hinged on prolonged retention of information are the major existing treatment measures used on children suffering from dyslexia. It is important to understand that treatment is successful if the condition is identified at its early stages, particularly among young individuals. As such, the management of the condition in children has higher rates of success as compared to adults. Fundamentally, the management of the disorder involves a range of programs that enhance the reading skills of the affected children (Sehic 2017). Programs such as multisensory structured language education (MSLE) and Orton Gillingham (OG) approach are vital in elevating the memory of children suffering from the condition and helping them to lead successful lives at adulthood (Bishop 2015). To manage the disorder, caregivers and trainers need to work together with professionals, for instance, speech-language pathologists (SLPs), who review the rate at which a child connects letters and numbers with sounds.

Although there is little information on the effectiveness of DNA modification in treatment and prevention of dyslexia, continued research is expected to provide positive results. Identification of KIAA0319 as the gene that causes brain imbalance and triggers dyslexia is a milestone towards the use of DNA to modify and possibly prevent the condition among the unborn children. It is vital to elaborate that DNA modification has a range of pros, which include a reduced rate of infection owing to the high prevention rates. By interfering with KIAA0319 gene and ensuring that it does not inhibit the movement of neurones to the cerebral cortex or triggering fresh neurone movement even impairment, the rate of prevention augments significantly (Dyslexia Research Trust 2017). However, mutations and new complications may arise from the modifications. Past research has proved that while DNA modifications provide positive results that address various situations, they have a number of unforeseen cons that can trigger serious repercussions. As such, researchers need to continue working on the issue of DNA modifications so that they weed out any demerit that can occur in the aftermath of implementation.

Conclusion

Dyslexia is a disorder that affects the learning ability of individuals. The disorder usually manifests at the tender stages of child development, especially when they come across activities that require reading and relating words and numbers with sounds. Presently, few medical interventions can be useful in managing the condition. Research continues with the purpose of identifying the various solutions that can help in preventing or treating the condition. However, early diagnosis of the condition minimises its effects. With the use of right interventions and programs, which help the children to grasp information and retain them in their minds, caregivers and trainers can manage the condition and support the children to lead successful lives.

Reference List

Becker, N, Vasconcelos, M, Oliveira, V, Santos, F, Bizarro, L, Almeida, R, Salles, J & Carvalho, M 2017, ‘Genetic and environmental risk factors for developmental dyslexia in children: systematic review of the last decade’, Developmental Neuropsychology, vol. 42, no. 7, pp. 423-445.

Bishop, D 2015, ‘The interface between genetics and psychology: lessons from developmental dyslexia’, Proceedings of the Royal Society B: Biological Sciences, vol. 282, no. 1, pp.1-8.

Centres for Disease Control and Prevention 2018, Helping children live to the fullest by understanding developmental disabilities, Web.

Chiurazzi, P & Pirozzi, F 2016, ‘Advances in understanding genetic basis of intellectual disability’, F1000Research, vol. 5, no. 1, p. 599.

Dyslexia Research Trust 2017, Genetics of dyslexia, Web.

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Feng, Y, Egan, B & Wang, J 2016, ‘Genetic factors in intervertebral disc degeneration’, Genes & Diseases, vol. 3, no. 3, pp. 178-185.

Hubbard, B, Badran, A, Zuris, J, Guilinger, J, Davis, K, Chen, L, Tsai, S, Sander, J, Joung, J & Liu, D 2015, ‘Continuous directed evolution of DNA-binding proteins to improve TALEN specificity’, Nature Methods, vol. 12, no. 10, pp. 939-942.

Jiménez-Bravo, M, Marrero, V & Benítez-Burraco, A 2017, ‘An oscillopathic approach to developmental dyslexia: from genes to speech processing’, Behavioral Brain Research, vol. 329, no. 1, pp. 84-95.

Paracchini, S, Diaz, R & Stein, J 2016, ‘Advances in dyslexia genetics-new insights into the role of brain asymmetries’, Advances in Genetics, vol. 96, no. 1, pp. 53-97.

Peterson, R & Pennington, B 2015, ‘Developmental dyslexia’, Annual Review of Clinical Psychology, vol. 11, no. 1, pp. 283-307.

Schoen, S, Miller, L & Sullivan, J 2016, ‘The development and psychometric properties of the Sensory Processing Scale Inventory: a report measure of sensory modulation’, Journal of Intellectual & Developmental Disability, vol. 42, no. 1, pp.12-21.

Sehic, S 2017, ‘Learning methodologies for learners with dyslexia’, International Journal of Educational Technology and Learning, vol. 1, no. 1, pp. 28-36.

Vorstman, J & Ophoff, R 2013, ‘Genetic causes of developmental disorders’, Current Opinion in Neurology, vol. 26, no. 2, pp.128-136.

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