Schizophrenia is a brain disorder classified as a psychosis, meaning that it affects an individual’s thinking, behavior, perceptions, and loss of reality testing. This disease generally becomes evident during late adolescence or early adulthood.
The incidence of schizophrenia worldwide is between 15–20 per 100,000 per year; while the prevalence is about 0.5–1% with a lifetime risk of 0.9%. The bulk of those affected will develop chronicity with frequent relapse and admission, while a number of them will suffer for their whole life. It imposes a burden not only on the patient but also on carers, the health service, and wider society and is certainly a pricey illness to be treated.
Signs and symptoms
It includes false perceptions called hallucinations. Auditory hallucinations of voices are the foremost common hallucinations in schizophrenia, but affected individuals may also experience hallucinations of visions, smells, and tactile sensations. Delusions are a feature of schizophrenia.
People with schizophrenia often have decreased ability to function at schools, colleges, at work, and in social settings. Disordered thinking and concentration, inappropriate emotional responses, erratic speech and behavior, and difficulty with personal hygiene and everyday tasks may occur. They’ll have diminished facial expression and animation, and in some cases they become catatonic. Drug abuse and suicidal thoughts and actions are common in people with schizophrenia.
Tremors, facial tics, rigidity, and bradykinesia or akinesia are common in people with schizophrenia. In most cases, these are side effects of medicines prescribed to assist control the disorder. However, some affected parties exhibit movement abnormalities before beginning treatment with medication. Individuals who exhibit solid features of both schizophrenia and mood disorders are often given the diagnosis of schizoaffective disorder.
Variations in many genes likely contribute to the probability of developing schizophrenia. In most cases, multiple genetic changes each with a tiny low effect combine to extend the chance of developing the disorder. The genetic changes may interact with environmental factors that are related to increased schizophrenia risk, such as exposure to infections before birth or severe stress during childhood.
Genetics of schizophrenia
Schizophrenia aggregates in families with unknown familial subtypes. Twin and adoption studies have shown that this familiarity is explained predominantly by genetic factors, with estimates of genetic contribution starting from 60 to 80%. These data don’t follow a straightforward recessive or dominant pattern. If it were simple recessive, the frequency in children of two schizophrenic parents would be 100%, but is truly under 40%; if it were simply dominant, 50% of the offspring of one schizophrenic parent would be affected (actually 8–15%) and every person with schizophrenia would have one ill parent (actually in many cases both parents are well). Moreover, the prevalence in offspring is simply too low to be in step with the high monozygotic twin concordance rate.
Pre-molecular and molecular genetic studies have demonstrated that genetics form a robust risk factor for schizophrenia. Many findings from schizophrenia GWAS are replicated and several other of those findings have reached meta-analytic genome-wide significance. The robust associations between schizophrenia and the >100 susceptibility loci, the identified CNVs and SNVs, respectively, seem promising on several scores. Also, the importance of the thousands of common alleles of only an awfully small effect, which don’t individually achieve significance but which collectively form a considerable polygenic component of schizophrenia risk, shouldn’t be underestimated.
The associations between common (SNPs) or uncommon (CNVs, SNVs) genetic variants and schizophrenia, though statistical facts, are not necessarily indexes of causal pathways and many of the explored associations are non-specific to schizophrenia but indicative of a genetic vulnerability to several mental disorders.
The genetic effect isn’t completely penetrant, i.e. 100% phenotype expression rate, indicating that several relatives of individuals with schizophrenia may carry silent genetic susceptibility. An additional complication in epidemiology showed that, while a high population prevalence has been maintained, the reproductive rate of individuals with schizophrenia is low. Currently, the foremost plausible hypothesis is that almost all cases of schizophrenia result from polygenic mechanisms probably interacting with a spread of non-genetic factors which can include in-utero viral infection, subtle birth trauma, and drug abuse.
Overall, the main points of the etiopathogenesis of schizophrenia and therefore the genotype-environment interactions remain to large extent unknown. Therefore caution remains warranted when concluding the scale of the genetic contribution within the etiology of the disorder.