（源自：Medlineplus）

　　在日常生活中，人们似乎可以注意到精神病患者具有家族聚集性。那么，精神病会遗传或有遗传倾向吗？目前看来“有”，但概率不想人们所认为的那么大。日前，著名的医学杂志～柳叶刀（The Lancet）发表来自瑞士和德国学者联合研究的报告指出“多数精神病，特别是严重的智力异常（severe intellectual disability）并非因为遗传，而是源自随机的基因突变（random genetic mutations）。”

　　如何解释这一结果？彭博认为至少有2个方面的意义：一是“避免超量的电离辐射和/或辐射防护（特别是在妊娠期），及增补抗辐射损伤之食品”等措施似有预防精神病之功效；二是当一对夫妇已经生育了一个患有孤独症或严重智力异常的孩子，并不意味着他们所生育的其它孩子也会存在或出现智力缺陷等精神异常。

More Than Half of Severe Mental Disability Cases Not Inherited: Study

Finding may encourage parents to have more children, researcher says

THURSDAY, Sept. 27 (HealthDay News) -- More than half of the cases of severe intellectual disability are the result of random genetic mutations that are not passed down from parents, researchers from Switzerland and Germany report.

Severe intellectual disability, also known as nonsyndromic mental retardation, is the most common form of mental retardation. Children or adults with the condition have no physical abnormalities, but have IQs of less than 50. It affects up to 2 percent of kids worldwide.

The new study, which appears online Sept. 27 in The Lancet, suggests that many of the gene variants associated with the condition show up for the first time in the affected children.

"The majority of patients with severe intellectual disability are due to gene mutations that are not present in the parents," said study author Dr. Anita Rauch, a researcher at the Institute of Medical Genetics in Zurich. "In the majority of cases, the recurrence risk within the family is low, which is usually a big relief for the parents and encourages them to have further children."

Researchers from the German Mental Retardation Network used a new gene sequencing technique to look for mutations in 51 children with unexplained intellectual disability and their unaffected parents. According to the report, children with intellectual disability carried a significantly higher number of potentially disease-causing genes than those without the disorder. New mutations in 11 known and six new candidate genes were estimated to cause intellectual disability in up to 55 percent of the children, the study authors reported.

In the future, Rauch said, "identification of subgroups of patients with a certain defect may soon lead to a better understanding of the respective natural course, which may then lead to a better disease management by earlier recognition of accompanying complications." As it stands, children and adults with nonsyndromic mental retardation are treated only with "supportive education and supportive treatment of complications such as epilepsy," she added.

Commenting on the findings, Dr. Marshall Summar, chief of genetics and metabolism at Children's National Medical Center in Washington, D.C., said: "This study drills down even deeper into our understanding of nonsyndromic mental retardation. This doesn't change how you treat the child, but it gives us a few more clues into what is involved."

The findings are reassuring for parents concerned that future children will also be affected, Summar noted. However, "the chance is not zero, the genes may be in the parents' testes or ovaries, so there is still a chance that it is passed down from parents and may affect other children in the family," he said. "The risk is low, but it's not zero."

Dr. Andrew Adesman, chief of developmental and behavioral pediatrics at Steven and Alexandra Cohen Children's Medical Center of New York in New Hyde Park, pointed out that the new genetic screening tests and technologies are more sophisticated than older versions. "We can't rely upon physical signs of a genetic disorder to suggest gene testing," he said. "We should implement universal genetic testing for all kids with unexplained intellectual disability and/or severe forms of autism," he suggested.

"The fact that the genes do not seem to be passed down from parents may prove reassuring," Adesman said. "When families have a child with severe intellectual disability or autism, they may have concerns about the recurrence risk or whether it was caused by something that they did during the pregnancy, but this is reassuring that they can have other children and not be worried about increased risk for another similarly affected child."

Doctors were unable to give parents this type of reassurance before the advent of new gene testing technologies, Adesman explained.

SOURCES: Marshall Summar, M.D., chief, genetics and metabolism, Children's National Medical Center, Washington, D.C.; Andrew Adesman, M.D., chief, developmental and behavioral pediatrics, Steven and Alexandra Cohen Children's Medical Center of New York, New Hyde Park, N.Y.; Anita Rauch, M.D., researcher, Institute of Medical Genetics, Zurich, Switzerland; Sept. 27, 2012, The Lancet, online