Due to this problem, clinicians have shifted to combining dimensional approach with existing categorical approaches. With this approach, clinicians can quantify a characteristic of disease based on using numerical values in different scales during disease assessment. The benefits of this approach lies in the fact that that it not only helps in identifying the presence of particular disorder but also aids in evaluating the degree of the condition a patient is suffering from (Shedler & Westen, 2014). A clinicians can evaluate this by the question ‘how much?’ to determine the level of severity of the disorder. Thus, in addition to categorical approach, it also takes into account various factors to get access to detailed information on each symptom. Instead of just labeling a disease, dimensional approach facilitates creation of a disease profile for specific patients. However, in relation to disease sensitivity and comorbidity analysis, much more time is consumed in getting each score. Dimensional approach aims to enhance diagnostic precision of psychiatric illness. Dimensional scale measurement will allow better conceptualization and assessment of etiology and psychiatric syndrome. Challenges in user acceptability may occur with this approach because of interpreting underlying mechanism of disease (Cuthbert & Insel, 2013).2. Autism spectrum disorder is a neurophysiological disorder that impairs social interaction, communication and cognitive development of affected person. Other diagnostic features are poor social development, reduced interest and repetitive behavior. This disease may be caused by genetic or hormonal factors. According to mind blindness theory of autism, children with autism syndrome have delayed development of feelings and thought. Hence, a degree of mind blindness is present in affected person. They find it difficult to interpret others behavior and reduced rate of joint attention. Just et al., (2013) has suggested that this inability to identify mental states of self and other individual occurs because of brain abnormality and it occurs due to weak connection between medial prefrontal region and the posterior superior temporal region. Thus minblindness theory highlighted the social impairment in patients with autistic spectrum but it did not described about non-social characteristics of autism. Another limitation is that this theory is not specific to autism only.
Another advanced theory called the emphathising-systemising (E-S) theory explains the combination of both social and non-social characteristics are present in people with autism spectrum disorder. It states that neurological disorder occurs not just because of lower empathy (E), but also because of below-average psychological factor (systemizing-S). Thus, inconsistency between E and S determines whether a person has autism spectrum disorder or not. Sabet et al., (2015) suggest that autistic people have exaggerated form of connectivity in each hemisphere and decreased inter-hemispheric connectivity due to small corpus callosum. Thus, increased interconnectivity disorder is found in specific area of brain in individual with the illness.
The E-S theory was further developed by the extreme male brain theory of autism (EMB) which states that females perform better in emphasizing activities and males perform better in systemizing activities. Wen & Wen, (2014) demonstrated that 54% males have systemizing brain while 44% females have brain with empathy activity. People with autism have smaller brain regions like thalamus, prefrontal cortex and superior gyrus compared to normal males. Besides this, normally size of male brain is larger than females, but in people with autism condition have even more larger brain than males. Thus this theory is useful in explaining why increases number of males develops the diseases compared to females.
Psychological changes take place prior to onset of symptoms of schizophrenia. This occurs due to changes in brain structure particularly prefrontal lobes of the brain. Prefrontal lobe is extremely responsive to environmental stress. This leads to the manifestation of psychological changes such as memory impairment, hallucinations, delusions, inattentiveness and many others (Kahn & Keefe, 2013).
After the manifestation of schizophrenia, neurological changes take place due to abnormal brain chemistry. Brain structure impairs in patients with schizophrenia and it is mainly associated with enlarged brain ventricle leading to decrease in brain tissue volume. The frontal lobe is the region which is associated with decision making and reasoning property in people, but in people with the condition, low function is seen in the frontal lobe (Hirjak et al., 2014). Psychological changes are associated with loss of emotional function reduced ability to express and plan things in life. People struggle in sustaining to activities (Frith, 2014).5. Endophenotypes are the term used to classify behavioral symptoms on the basis of clear phenotypes and identification of possible genetic connection. It helps to different between symptoms for diseases like ADHD, Alzheimer’s and many others. In case of people with schizophrenia, the most visible symptoms is psychosis which is associated with personality changes, abnormal behavior and low level of social interaction. However the distinct phenotype of the illness is overload of stimuli and impaired memory. As these phenotypes have clear genetic connections too, that is why they have been identified as endophenotypes of schizophrenia. These phenotypes reflect the neurobiological mechanism of the disease that represents the most overt symptoms of schizophrenia. The genes involved in endophenotypic traits in schizophrenia include RELN, FABP7 and CHRNA7. They are linked to schizophrenia phenotype of prepulse inhibition. It is a phenomenon which weak prestimulus inhibits the reaction of individual to stronger stimulus. The criteria involve in assessment of endophenotypes of psychiatric disorder is that the endophenotype should be associated with specific illness; it should be heritable and present in individuals despites their clinical status. Other criterion is it should be separated from other symptoms of illness (Ross, & Freedman, 2015). As psychiatric illness is mostly associated with multiple risk factors, one endophenotypes related to the mechanism of illness most frequently develops. In schizophrenia brain changes occurs throughout the life span. One endophenotype that is useful to detect the risk of schizophrenia is sensory gating which is a process of filtering out unnecessary stimuli from other environmental stimuli (Ripke et al., 2013).
People with Down syndrome above 40 years develop numerous plaques and neurofibrillary tangles and there is maximum chance of pathophysiology of Alzheimers disease. These plaques contain beta-amyloid peptide from APP genes. In Down syndrome, over expression of APP takes place and amyloid-beta is major factor in the pathogenesis of Alzheimer’s disease. Amyloid-beta is neuronal in origin and localized in endosomes. People with Down syndrome also have increased oxidative stress compared to normal people (Elizabeth Head, 2012).7. Neural development is the process that provides insight into the cellular and molecular mechanism involved in nervous system development. Neurotrophins are group of protein that facilitates the development and function of neurons. These protein molecules regulate cell division and overgrowth of neurite. The neurotrophins binds to particular tyrosine kinases receptor that induces dimerization and auto-phophorylation of receptors. It leads to the formation of a complex of receptor and neurotrophin which is endocytosed. This complex is then transported to the soma (Neural migration). In between the process, it initiates signal transduction cascade that inhibits the apoptosis of genes and thus neural cell survives eventually. Other examples of neurotrophin factors that promote survival of neuron include nerve growth factor (NGF), neurtrophin-3, fibroblast growth factor and many others (Park & Poo, 2013).
Another type of neurotrophin is the brain-derived neurotrophic factors that play an important role in synapse plasticity and development of brain. A recent study demonstrated its role in synapse formation and plasticity. Synapse formation is promoted by regulating the axon morphology and increasing the number of excitable synapse and inhibitory synapse. It also enhances the number of functional synapses by the facilitating the maturation of those cellular components that triggers the release of neurotransmitter. This long term modification will be crucial in providing synaptic plasticity to an individual (Harrington & Ginty, 2013).
Neurulation is the process of development of neural tube (embryo’s central nervous system) from the embryo. The human brain development initiates from the third week of gestation period and it progressed to differentiation of neural progenitor cells. Neurotrophic factors play a role in this development by acting against the apoptosis cascade. It target distinct neurons at synaptic connection and makes connection with target cells. These factors are present in embryo during gastrulation and neurulation process. Neurotrophin-3 is expressed in the neural tube and tyrosine kinase C (TrkC) is present in the neural plate. A neural tube differentiates TrkC gets localized in specific region of the tube. Thus neurotrophic factors and TrkC plays a role in early neural development (Davis, 2014).8. Meiosis is a type of cell division that divides the chromosome number by half and enables sexual recombination in organisms. It produces four gamete cells and the number of orginal chromosome is restored back in the offspring. The diploid parent cell consists of two chromosome copies. It divides to form four haploid cells which have half the number of original chromosome. The first meiotic division is called meiosis I. The first stage in this case is the prophase I where the chromatin fibre condenses to form sister chromatids. It is then followed by condensation of chromosome into tetrad structure in the prophase I. This pair of chromosome exchanges their DNA by recombination process. During Metaphase I the chromosome pair aligns at the centre of the cell and the centriole moves towards the poles. The spindle fibre is formed which attaches to the chromosome. In the next stage which is the anaphase I, the spindle fibres pull each chromosome towards the poles. During Teleophase I the chromosomes are arranged in nuclei and cytokinesis takes place which leads to formation of two separate daughter cells. This phase is followed by meiotic division of haploid cells called Meiosis II. In prophase II new set of spindle fibres are formed and they align the equatorial plate in Metaphase II. In the Anaphase II, sister chromatids are pulled apart and chromosomes are enclosed in nuclear membrane in telophase II. This is followed by cytokinesis and results in formation of four haploid daughter cells that develop into a sperm or egg cells (Wang et al., 2015).
There are key steps in meiosis where there is chance of spontaneous mistakes. The genetic constitution is altered and the and unexpected crossing over leads to increased genetic variability in a population. The crossing over of sister chromatids occurs during metaphase I and random alignment of chromosomes gives rise different gene combination in the offspring. In rare cases, failure to separate homologous chromosomes lead over accumulation of chromosome in one cell and lack of chromosome in another cell. This process of non-disjunction of chromosomes leads to production of gametes with odd number of chromosomes. It may give rise to variety of syndromes like Kleinfelter’s syndrome, Turner’s syndrome, and other syndrome (Marchett et al., 2015).
Mitosis is a multi-step process during which chromosome is divided into two daughter cells. The first phase is called karyokinesis where nuclear division takes place. It consist of five phases mainly prophase, metaphase, anaphase and telophase. The second phase is called cytokinesis wherein cytoplasmic components separate into two daughter cells. Due to error in mitosis, two types of errors occur and it has benign or deadly consequences. Silent mutation can occur where no change in DNA sequence is found or missense mutation may occur when DNA sequence are changed. This type of mutations may lead massive disruption in cell cycle and formation of tumours. Chromsomal abnormalities may also take place when chromosomes fail to attach to spindle fibres and the daughter cell either has one extra or one missing copy of chromosome after division. It leads to disorders like Down syndrome, Alzheimer disease and may other condition (Yoshida et al., 2013).
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