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What Causes Schizophrenia? (Part 2)

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When does schizophrenia start and who gets it?

Schizophrenia affects men and women equally. It occurs at similar rates in all ethnic groups around the world. Symptoms such as hallucinations and delusions usually start between ages 16 and 30. Men tend to experience symptoms a little earlier than women. Most of the time, people do not get schizophrenia after age 45.3 Schizophrenia rarely occurs in children, but awareness of childhood-onset schizophrenia is increasing.4,5

It can be difficult to diagnose schizophrenia in teens. This is because the first signs can include a change of friends, a drop in grades, sleep problems, and irritability—behaviors that are common among teens. A combination of factors can predict schizophrenia in up to 80 percent of youth who are at high risk of developing the illness. These factors include isolating oneself and withdrawing from others, an increase in unusual thoughts and suspicions, and a family history of psychosis.6 In young people who develop the disease, this stage of the disorder is called the “prodromal” period.

Are people with schizophrenia violent?

People with schizophrenia are not usually violent. In fact, most violent crimes are not committed by people with schizophrenia.7 However, some symptoms are associated with violence, such as delusions of persecution. Substance abuse may also increase the chance a person will become violent.8 If a person with schizophrenia becomes violent, the violence is usually directed at family members and tends to take place at home.

The risk of violence among people with schizophrenia is small. But people with the illness attempt suicide much more often than others. About 10 percent (especially young adult males) die by suicide.9,10 It is hard to predict which people with schizophrenia are prone to suicide. If you know someone who talks about or attempts suicide, help him or her find professional help right away.

People with schizophrenia are not usually violent.

What about substance abuse?

Some people who abuse drugs show symptoms similar to those of schizophrenia. Therefore, people with schizophrenia may be mistaken for people who are affected by drugs. Most researchers do not believe that substance abuse causes schizophrenia. However, people who have schizophrenia are much more likely to have a substance or alcohol abuse problem than the general population.11

Substance abuse can make treatment for schizophrenia less effective. Some drugs, like marijuana and stimulants such as amphetamines or cocaine, may make symptoms worse. In fact, research has found increasing evidence of a link between marijuana and schizophrenia symptoms.12,13 In addition, people who abuse drugs are less likely to follow their treatment plan.

Schizophrenia and smoking

Addiction to nicotine is the most common form of substance abuse in people with schizophrenia. They are addicted to nicotine at three times the rate of the general population (75 to 90 percent vs. 25 to 30 percent).14

The relationship between smoking and schizophrenia is complex. People with schizophrenia seem to be driven to smoke, and researchers are exploring whether there is a biological basis for this need. In addition to its known health hazards, several studies have found that smoking may make antipsychotic drugs less effective.

Quitting smoking may be very difficult for people with schizophrenia because nicotine withdrawal may cause their psychotic symptoms to get worse for a while. Quitting strategies that include nicotine replacement methods may be easier for patients to handle. Doctors who treat people with schizophrenia should watch their patients’ response to antipsychotic medication carefully if the patient decides to start or stop smoking.

 

What causes schizophrenia?

Experts think schizophrenia is caused by several factors.

Genes and environment. Scientists have long known that schizophrenia runs in families. The illness occurs in 1 percent of the general population, but it occurs in 10 percent of people who have a first-degree relative with the disorder, such as a parent, brother, or sister. People who have second-degree relatives (aunts, uncles, grandparents, or cousins) with the disease also develop schizophrenia more often than the general population. The risk is highest for an identical twin of a person with schizophrenia. He or she has a 40 to 65 percent chance of developing the disorder.15

We inherit our genes from both parents. Scientists believe several genes are associated with an increased risk of schizophrenia, but that no gene causes the disease by itself.16 In fact, recent research has found that people with schizophrenia tend to have higher rates of rare genetic mutations. These genetic differences involve hundreds of different genes and probably disrupt brain development.17

Other recent studies suggest that schizophrenia may result in part when a certain gene that is key to making important brain chemicals malfunctions. This problem may affect the part of the brain involved in developing higher functioning skills.18 Research into this gene is ongoing, so it is not yet possible to use the genetic information to predict who will develop the disease.

Despite this, tests that scan a person’s genes can be bought without a prescription or a health professional’s advice. Ads for the tests suggest that with a saliva sample, a company can determine if a client is at risk for developing specific diseases, including schizophrenia. However, scientists don’t yet know all of the gene variations that contribute to schizophrenia. Those that are known raise the risk only by very small amounts. Therefore, these “genome scans” are unlikely to provide a complete picture of a person’s risk for developing a mental disorder like schizophrenia.

In addition, it probably takes more than genes to cause the disorder. Scientists think interactions between genes and the environment are necessary for schizophrenia to develop. Many environmental factors may be involved, such as exposure to viruses or malnutrition before birth, problems during birth, and other not yet known psychosocial factors.

Scientists are learning more about brain chemistry and its link to schizophrenia.

Different brain chemistry and structure. Scientists think that an imbalance in the complex, interrelated chemical reactions of the brain involving the neurotransmitters dopamine and glutamate, and possibly others, plays a role in schizophrenia. Neurotransmitters are substances that allow brain cells to communicate with each other. Scientists are learning more about brain chemistry and its link to schizophrenia.

Also, in small ways the brains of people with schizophrenia look different than those of healthy people. For example, fluid-filled cavities at the center of the brain, called ventricles, are larger in some people with schizophrenia. The brains of people with the illness also tend to have less gray matter, and some areas of the brain may have less or more activity.

Studies of brain tissue after death also have revealed differences in the brains of people with schizophrenia. Scientists found small changes in the distribution or characteristics of brain cells that likely occurred before birth.3 Some experts think problems during brain development before birth may lead to faulty connections. The problem may not show up in a person until puberty. The brain undergoes major changes during puberty, and these changes could trigger psychotic symptoms. Scientists have learned a lot about schizophrenia, but more research is needed to help explain how it develops.

Scientists have learned a lot about schizophrenia, but more research is needed to help explain how it develops.

 

Citations for All Parts

1. Regier DA, Narrow WE, Rae DS, Manderscheid RW, Locke BZ, Goodwin FK. The de facto US mental and addictive disorders service system. Epidemiologic catchment area prospective 1-year prevalence rates of disorders and services. Archives of General Psychiatry. 1993 Feb;50(2):85-94.

2. World Health Organization (WHO). Catatonic Schizophrenia. The ICD-10 Classification of Mental and Behavioural Disorders: Clinical descriptions and diagnostic guidelines.1992.Geneva, Switzerland: World Health Organization.

3. Mueser KT and McGurk SR. Schizophrenia. Lancet. 2004 Jun 19;363(9426):2063-2072.

4. Nicolson R, Lenane M, Hamburger SD, Fernandez T, Bedwell J, Rapoport JL. Lessons from childhood-onset schizophrenia. Brain Research Review. 2000;31(2-3):147-156.

5. Masi G, Mucci M, Pari C. Children with schizophrenia: clinical picture and pharmacological treatment. CNS Drugs. 2006;20(10):841-866.

6. Cannon TD, Cadenhead K, Cornblatt B, Woods SW, Addington J, Walker E, Seidman LJ, Perkins D, Tsuang M, McGlashan T, Heinssen R. Prediction of psychosis in high-risk youth: A Multi-site longitudinal study in North America. Archives of General Psychiatry. 2008 Jan;65(1):28-37.

7. Walsh E, Buchanan A, Fahy T. Violence and schizophrenia: examining the evidence.British Journal of Psychiatry. 2002 Jun;180:490-495.

8. Swanson JW, Swartz MS, Van Dorn RA, Elbogen E, Wager HR, Rosenheck RA, Stroup S, McEvoy JP, Lieberman JA. A national study of violent behavior in persons with schizophrenia. Archives of General Psychiatry. 2006 May;63(5):490-499.

9. Meltzer HY, Alphs L, Green AI, Altamura AC, Anand R, Bertoldi A, Bourgeois M, Chouinard G, Islam MZ, Kane J, Krishnan R, Lindenmayer JP, Potkin S, International Suicide Prevention Trial Study Group. Clozapine treatment for suicidality in schizophrenia: International Suicide Prevention Trial (InterSePT). Archives of General Psychiatry. 2003 Jan;60(1):82-91.

10. Meltzer HY and Baldessarini RJ. Reducing the risk for suicide in schizophrenia and affective disorders. Journal of Clinical Psychiatry. 2003 Sep;64(9):1122-1129.

11. Blanchard JJ, Brown SA, Horan WP, Sherwood AR. Substance use disorders in schizophrenia: Reviews, integration and a proposed model. Clinical Psychological Review. 2000;20:207-234.

12. Zullino DF, Waber L, Khazaal Y. Cannabis and the course of schizophrenia. American Journal of Psychiatry. 2008;165(10):1357-1358.

13. Muller-Vahl KR and Emrich HM. Cannabis and schizophrenia: towards a cannabinoid hypothesis of schizophrenia. Expert Review of Neurotherapeutics. 2008;8(7):1037-1048.

14. Jones RT and Benowitz NL. Therapeutics for Nicotine Addiction. In Davis KL, Charney D, Coyle JT & Nemeroff C (Eds.), Neuropsychopharmacology: The Fifth Generation of Progress (pp1533-1544). 2002. Nashville, TN:American College of Neuropsychopharmacology.

15. Cardno AG and Gottesman II. Twin studies of schizophrenia: from bow-and-arrow concordances to star wars Mx and functional genomics. American Journal of Medical Genetics. 2000 Spring;97(1):12-17.

16. Harrison PJ and Weinberger DR. Schizophrenia genes, gene expression, and neuropathology: on the matter of their convergence. Molecular Psychiatry. 2005;10(1):40-68.

17. Walsh T, McClellan JM, McCarthy SE, Addington AM, Pierce SB, Cooper GM, Nord AS, Kusenda M, Malhotra D, Bhandari A, Stray SM, Rippey CF, Roccanova P, Makarov V, Lakshmi B, Findling RL, Sikich L, Stromberg T, Merriman B, Gogtay N, Butler P, Eckstrand K, Noory L, Gochman P, Long R, Chen Z, Davis S, Baker C, Eichler EE, Meltzer PS, Nelson SF, Singleton AB, Lee MK, Rapoport JL, King MC, Sebat J. Rare structural variants disrupt multiple genes in neurodevelopmental pathways in schizophrenia. Science. 2008 Apr 25;320(5875):539-543.

18. Huang HS, Matevossian A, Whittle C, Kim SY, Schumacher A, Baker SP, Akbarian S. Prefrontal dysfunction in schizophrenia involves missed-lineage leukemia 1-regulated histone methylation at GABAergic gene promoters. Journal of Neuroscience. 2007 Oct 17;27(42):11254-11262.

19. Gogtay N and Rapoport J. Clozapine use in children and adolescents. Expert Opinion on Pharmacotherapy. 2008;9(3):459-465.

20. Lieberman JA, Stroup TS, McEvoy JP, Swartz MS, Rosenheck RA, Perkins DO, Keefe RS, Davis SM, Davis CE, Lebowitz BD, Severe J, Hsiao JK, Clinical Antipsychotic Trials of Intervention Effectiveness (CATIE). Effectiveness of antipsychotic drugs in patients with chronic schizophrenia. New England Journal of Medicine. 2005 Sep 22;353(12):1209-1223.

21. Greig TC, Zito W, Wexler BE, Fiszdon J, Bell MD. Improved cognitive function in schizophrenia after one year of cognitive training and vocational services. Schizophrenia Research. 2007 Nov;96(1-3):156-161.

22. Bell M, Fiszon J, Greig T, Wexler B, Bryson G. Neurocognitive enhancement therapy with work therapy in schizophrenia: 6-month follow-up of neuropsychological performance.Journal of Rehabilitation Research and Development. 2007;44(5):761-770.

23. Hogarty GE, Flesher S, Ulrich R, Carter M, Greenwald D, Poque-Geile M, Kechavan M, Cooley S, DiBarry AL, Garrett A, Parepally H, Zoretich R. Cognitive enhancement therapy for schizophrenia: effects of a 2-year randomized trial on cognition and behavior. Archives of General Psychiatry. 2004 Sep;61(9):866-876.

Source: National Insititute of Mental Health http://www.nimh.nih.gov/health/publications/schizophrenia

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