A single gene mutation can cause multiple diseases 同一基因缺陷 可能引發不同疾病

Wed, Nov 27, 2013 - Page 11

Can a single gene defect cause two different diseases? When one 45-year-old woman started suffering from dementia, Chang Gung Memorial Hospital conducted tests and discovered that she also had two collateral blood relatives and one direct blood relative who had dementia. Genetic testing showed evidence of abnormalities in C9orf72 (chromosome 9 open reading frame 72), which was the cause of this familial frontotemporal dementia (FTD).

In another case of a person with amyotrophic lateral sclerosis (ALS), commonly known as Lou Gehrig’s disease, Chang Gung Memorial Hospital discovered the same gene mutation in the patient’s hereditary history. The patient was also 40-something when he started suffering from muscular dystrophy, but he showed no signs of dementia, exhibiting how the same genetic mutation in C9orf72 can cause two distinct degenerative neurological diseases.

Yeh Tu-hsueh, a neurologist at Chang Gung Memorial Hospital’s Taipei Branch, says that in 2011 researchers from the US National Institutes of Health discovered that disease-causing mutations in the gene C9orf72 could cause dementia, as well as the motor neuron disease ALS. The hospital subsequently joined this research team in conducting related international research.

This disease-causing gene mutation can be found in around 25.1 percent of patients with early-onset familial FTD, Yeh says, adding that 37.6 percent of patients with familial ALS also exhibit the mutation.

The female patient, for example, was only 45 years old when she started suffering memory loss and physical impairment. At the time, her family discovered that she had lost interest in daily life. These changes in cognitive ability and personality made it difficult for her to maintain amicable relations with coworkers. By the age of 49, she suffered muscular dystrophy and joint contractures in her limbs, so that she had to rely entirely upon others to take care of her. Aside from her, one of her parents and two of her collateral relatives had the same disease. In the other family, four out of six siblings exhibited symptoms such as dementia and personality changes.

Chen Jou-hsien, director of movement disorders in the Division of Neurology at the hospital, says that 65 is the average age when dementia usually occurs. The patient who started suffering from dementia in her 40s, for example, or even someone in their 50s, would be considered to have early-onset dementia, Chen says, adding that he recommends getting tested for genetic abnormalities in such cases.

Aside from clinical genetic testing, Chen says that with degenerative nerve diseases, including dementia, Parkinson’s disease and ALS, now that it is known that one gene can cause two different diseases, it means that a new research avenue is available and shows that in the future it might be possible to find a mechanism explaining the degenerative process in humans.

(Liberty Times, Translated by Kyle Jeffcoat)

同一基因缺陷,竟可能導致兩種不同疾病?一名女性年僅四十五歲即罹患失智症,長庚醫院進一步調查發現,原來她的兩名同輩親屬以及一名直系血親也有失智症狀,經基因篩檢證實是「C9orf72」基因變異,導致家族遺傳性額顳葉失智症。

長庚醫院在另一個漸凍人遺傳家族也發現此一基因變異,患者也是四十多歲就開始進行性全身肌肉萎縮,但卻沒有失智症狀;由此顯示,同樣是C9orf72基因變異,臨床卻可能引起兩種不同的神經退化疾病。

台北長庚醫院神經內科副教授葉篤學指出,二0一一年美國國衛院研究人員即發現「C9orf72」基因變異可能引起失智症,也可能造成俗稱「漸凍人症」的運動神經元疾病。長庚後續也加入該團隊的跨國研究。

他指出,在早發型家族性「額顳葉」失智症中,約百分之二十五點一可以找到這個致病基因;有家族史的漸凍人中,更有百分之三十七點六有此基因變異。

以該名女性患者為例,年僅四十五歲就開始有記憶減退與動作變慢的情形。當時家人發現,她變得對日常生活失去興趣。這些認知能力及個性的改變,甚至讓她變得與同事難以和睦相處。四十九歲後就漸漸四肢肌肉萎縮,關節攣縮,需完全仰賴他人照顧。除了她之外,她的雙親之一,以及兩名同輩親屬也有同樣疾病;另一家族則是一家六個兄弟姊妹有四人出現失智、個性改變等症狀。

長庚醫院神經內科系動作障礙科主任陳柔賢指出,一般失智症平均發生年齡在六十五歲後,像該名患者四十多歲就發病,或是五十多歲發病者,都屬於早發型失智症,建議應檢查是否有基因上的變異。

除了臨床上的基因篩檢外,陳柔賢指出,失智症、帕金森氏症、漸凍人症都是神經退化的疾病,如今知道其中兩種可由同一個基因引起,就如同打開一個研究入口,顯示未來或許有機會找到一個解釋人類退化過程的機制。

(自由時報記者洪素卿)