If the other parent does not have the same type of genes, the children would inherit only one copy and thus not get the "schizophrenia". They find that regardless of multiple other environmental risk factors they may have, none of them get the illness.
Notes that we are not talking about a single gene, but a whole constellation of genes, which together, still does not mean the person WILL get schizophrenia, but rather, they increase risk. Also remember, Schizophrenia is not one single illness, but rather, a label from the DSM for communication purposes (as are all the diagnoses in the DSM). The label means the person has some of a large set of possible symptoms of that label (for more on medical vs non-medical aspects of the label, see here:    . And, Schizophrenia, schizoaffective, and bipolar (all considered to be on the same "spectrum") are not just genetic, but EPIGENTIC. This means environmental factors affect the functioning of the genes (see  ) and some of these epigentic are seen to be passed down to the developing fetus as well. In fact, some of these epigenetic changes HAPPEN en-utero.
Yet, the "schizophrenia" seems to appear among the children of some of those siblings or other family members, even though they may be exposed to less environmental risk factors than the generation before them.
The astounding research article below is about just the large array of genes involved and how THAT can raise... or LOWER.. the risk of schizophrenia. Why the RISK of schizophrenia often does NOT get passed down to the next generation. A leading schizophrenia research organization, NARSAD, may have come up with an explanation for such families -- an explanation for a subset of patients with "schizophrenia".
NARSAD has found recessively inherited genes which greatly increase the risk of a person developing a "subtype" or "variant" of "schizophrenia" when a child inherits the same copy from both parents.
Here is their press release:
Genes Inherited From Both Parents Could Trigger Schizophrenia
(Great Neck, NY -January 06, 2008) — A research team led by a 2001 NARSAD Young Investigator has identified nine genetic markers that can increase a person’s risk for schizophrenia.
In a study published in December in the Proceedings of the National Academy of Sciences, Todd Lencz, Ph.D., associate director of research at The Feinstein Institute for Medical Research in Manhasset, N.Y., and colleagues, reported evidence that schizophrenia can be inherited in a recessive manner.
A recessive trait is one that is inherited from both parents. “If a person inherits identical copies of these markers from each parent, his or her risk for schizophrenia increases substantially,” said Dr. Lencz, who was the paper’s lead author. One in every 100 people suffers from schizophrenia, a condition marked by episodes of hallucinations, delusions and disordered thinking.
The scientists developed a complex mathematical approach called whole genome homozygosity association (WGHA) that provides a new way of analyzing genetic information. It enables scientists simultaneously to look at genetic information derived from a patient’s mother and father, and identify pieces of chromosomes that are identical.
They tested genetic material from 178 patients and 144 controls. It has been the prevailing view in psychiatric genetics that there are probably dozens, if not hundreds, of genetic variations that could lead to schizophrenia, but that each gene has a small effect. It is the wrong mix of many genes, plus unknown environmental stressors, that trigger the onset of symptoms, according to the theory.
The new findings suggest another scenario, at least for a subset of patients. Dr. Lencz and his colleagues identified nine regions along the chromosomes that might play a large role in triggering the disease when two identical variants are inherited. Four of these regions contain genes that have been previously associated with schizophrenia. This can be interpreted as validation for the technique. The remaining five regions provide an additional set of newly discovered genetic risk factors.
Many of the genes located in these “high-risk” regions are involved with the structure and survival of neurons. In genetic parlance, several of the markers demonstrated high penetrance, meaning that their effect on disease risk was large. In the study, 81 percent of the schizophrenia patients had at least one of these recessive markers, compared to only 45 percent of the normal control group. Nearly half of the patients had two or more, compared to 11 percent of the controls. And while no one in the healthy group had identical chunks of chromosomes in four or more of these risk regions, subjects with more than three demonstrated a 24-fold increased risk of developing schizophrenia.
“This type of analysis could greatly improve our ability to diagnose schizophrenia and clarify specific subtypes of patients,” Dr. Lencz said. “The critical next step is confirming these results in independent datasets.”
“What is most exciting is that the study implicates new genes in schizophrenia,” said David Goldman, M.D., chief of laboratory of neurogenetics at the National Institute on Alcohol Abuse and Alcoholism. “Now, they have to trace down the genes that mediate this vulnerability.”
Here is the abstract of the actual research article:
Runs of homozygosity reveal highly penetrant recessive loci in schizophrenia.
And here is the link to the full scientific research article in PDF format:
Runs of homozygosity reveal highly penetrant recessive loci in schizophrenia. Lencz T, Lambert C, DeRosse P, Burdick KE, Morgan TV, Kane JM, Kucherlapati R, Malhotra AK Proc Natl Acad Sci U S A. 2007 Dec 11; 104(50): 19942-7
And something about the genetic overlap between Schizophrenia, Bipolar Disorder, and Depression -- also from NARSAD:
NARSAD Researchers Identify Specific Genes And Family Traits Linked To Schizophrenia, Bipolar Disorder And Depression
Genetics and Epigenetics:
- Specific Genes Inherited from Both Parents May Lead to Type of "Schizophrenia" (How schizophrenia can skip a generation)
- What are some genetic causes of psychosis?
- What is Epigenetics
- Brain Health: Nutrition and Epigenetics
- Mitochondrial Dysfunction and Psychiatric Symptoms
- Nutrition, genes, and brain dysfunctions: Folate
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Last Updated: 25 November 2012