This section of Global HD aims to highlight regions within Asia in which the HD populations have been studied, and where history and significance within the HD context have been demonstrated.
The prevalence of HD in the West is estimated at five to ten people per 100,000 people. However, in Asia, the prevalence of HD is approximately one tenth of the HD prevalence in Western population. The prevalence is 0.4 per 100,000 people in Hong Kong and 0.65 per 100,000 in Japan. In India, there are case reports from Punjab and northern India and until 1990, there were 69 case reports of HD in China. In Southeast Asia, the epidemiology data for HD consists mainly of case reports with HD in Singapore being reported from a Chinese family and second-generation Indian families. There is no accurate data obtained from Thailand, Indonesia and Philippines.
The reason for this wide variation in HD prevalence in different ethnic communities is unclear. Some people advocate a European origin for the mutation, suggesting that migration and inter-racial mixture of genes led to a lower prevalence in non-European countries. As mentioned in the HD in Hong Kong section, it has been proposed that the prevalence of HD in Hong Kong maybe attributed to a European origin. This assumption derives from the fact that the ancestors of the families with HD can be connected to coastal provinces with histories of strong colonial presence. Hence, it has been hypothesized that HD in other Chinese related countries may also have originated from a common Caucasian ancestry by ways of migration.
There is limited information on Huntington’s disease in China. However, in 1992, researchers at the Chinese University of Hong Kong published Huntington’s disease in China: A hypothesis of its origin. As with many other non-European populations, HD’s origins in China’s coastal provinces indicate that it likely spread as a result of interactions between European and Chinese traders.
Between 1984 and 1991, the prevalence of HD in Hong Kong was 3 to 7 patients per million. This population appeared to be predominately males who experienced an earlier disease onset. The first instances of HD were noted in 1959 and again in 1962. Historically, war and natural disasters disrupted living patterns and caused mixing of populations that increased the prevalence of HD outside of the original coastal provinces. However, compared to other regions, the spread of HD in China is rather limited and has remained predominately in these coastal regions.
This research is over 20 years old. More comprehensive statistics are needed to understand the true prevalence of the disease, particularly the prevalence of HD in women as this population is most likely underreported due to their status in society in the 1980’s and 1990’s.
Chinese Huntington’s Disease Network
The Chinese Huntington’s Disease Network was launched on December 10, 2011 in Shanghai. This organization seeks to help the estimated 300 affected families in the region by increasing awareness about HD and improving quality of care.
For Further Reading^
Malaysia is a multicultural country with three main ethnic populations. The indigenous Malaysians, Chinese and Indians make up approximately 62 percent, 29 percent and 8 percent of the population respectively. The prevalence of HD is 0.0024 per 10,000 people, based on seven reported cases.
To test the hypothesis that HD in Asia has a Caucasian origin, a HD registry was established in Malaysia in 1995 at the University of Malaya Medical Centre, Kuala Lumpur. Within eighteen months, the registry had identified seven unrelated patients with HD. From these individuals, there were four Chinese, one Malaysian and two Indians. Despite the previous hypothesis set forth that HD in Asian countries originated from Europe; only one Chinese patient, out of selected seven patients, had possible Irish ancestry. Moreover, there are several social and cultural reasons that the hypothesis set forth is likely to be false. The remaining three Chinese participants did not have any relatives with Caucasian features. Culturally, Chinese women were forbidden to have close contact with foreigners. Women did not travel unless they were accompanying their husbands. Prostitution as a profession for women was deeply despised and extramarital sexual contact was strongly forbidden. Hence, it was highly unlikely that female ancestors of these patients would have sexual contact with asymptomatic Caucasian HD men and therefore result in the mixing of genes. In addition, other participants also did not have European origin, since one Malaysian patient was a local while the two Indian patients originated from Tamil Nadu and Punjab in India respectively.
There is also evidence against the European migration hypothesis from the current genetic literature. Although the nature of the abnormal trinucleotide repeats of the HD gene in Chinese patients is similar to that in Caucasian HD patients, a majority of the tested Chinese patients have a small number of excess CAG repeats. Additional genetic evidence show that there are seven CCG repeats adjacent to IT15, or the Huntington Gene, in Asians but ten CCG repeats in Caucasians. The distribution of the CCG repeat adjacent to IT15 is of seven repeats in Asians and 10 repeats in Caucasians. The distribution of the CCG repeats differs among populations of low prevalence and the west. Therefore, mutation of the IT15 gene rather than the European migration hypothesis is likely to be the explanation for the variation in Malaysian prevalence of HD.
The interim results of the Malaysian HD registry have shown that HD exists in all major racial groups in Malaysia, with all cases exhibiting an excess of CCG repeats. The theory that Caucasian migration led to genetic mixing and a resulting low HD prevalence in Malaysia is less plausible according to the data collected by the registry; more likely, cases of HD in Malaysia arose due to a separate mutation of the HD gene. Nevertheless, because only seven HD patients were identified, these conclusions should be considered with caution to avoid errors in assumption and generalization.
The Global HD research and articles received partial support from the Bingham Fund for Innovation in the Program in Human Biology.
Resources in Malaysia^
University of Malaya Medical Centre in Kuala Lumpur
In 1995, a nationwide HD registry was established at the University of Malaya Medical Centre, Kuala Lumpur. The Medical Centre is one of the major public tertiary referral hospitals. It keeps reports of clinical and genetic studies of the patients seen since the setting up of the Registry.
For more information regarding the association, please visit: http://www.ummc.edu.my/view/index.php
Huntington’s disease (HD) is notably rare in Japan, with a prevalence of 1-4 cases per million people – about one-tenth of the prevalence in most European and European-origin populations. Even among those who do not have HD, studies consistently report that the average CAG (Perhaps briefly state around here what CAG repeats are) repeat size in western populations is larger than that found in Japanese populations. Research from Chinese Medical Journal shows that the mean CAG repeat length is 18.4 ± 3.7 in western populations, but only 16.6 ± 1.5 in Japan. It is known that larger CAG counts in the trinucleotide expansion (Perhaps briefly explain the trinucleotide expansion a little more between two commas. Maybe not. That’s a style call.) characteristic of HD diagnosis are associated with the course and severity of illness, such as the progression and magnitude of motor and cognitive decline.
HD populations in Japan experience typical symptom onset. Kageyama et al. reported that, similar to observations in Caucasian populations, adult-onset of HD in Japanese patients presents spasticity (unusual stiffness) and cerebellar ataxia (lack of muscle coordination).
It has been hypothesized that the Huntingtin mutation in Japan has a separate origin from the HD mutation in Europe or Africa. Researchers came to this conclusion after comparing the genetic sequences of the Huntingtin gene (HTT) that there are significant differences between the European, Japanese, and African HTT genes. If one HTT allele were responsible for all the HD cases in the world, there would be strikingly similar HTT alleles in all persons with HD – not the distinct varieties that are actually found. The European, African and Japanese general population chromosomes can be grouped into three different major haplogroups (defined as group of genes within an organism that was inherited together from a single parent). The majority of HD chromosomes in Europe, African and Japanese are found on haplogroup A, B and C respectively. The highest risk HD haplotypes (A1 and A2), are absent from the general and HD populations of Japan, and therefore provide an explanation for why HD prevalence is low in Japan. Such differences, therefore, suggest that the HTT allele originated independently in these three regions.
Resources in Japan^
Japanese Huntington’s Disease Network (JHDN). The main goal of JHDN is to use online activities to provide and share information about the latest HD research and resources. Its more specific aims are: 1) to liaison with other HD societies, such as the World Federation of Neurology and International Huntington Association, to gain access the latest HD research; 2) to translate and distribute documents and publications for Japanese readers; 3) to distribute newsletters to HD families and those who are interested; and 4) to organize HD family meetings for informal talks and discussions. For more information, please visit http://www.jhdn.org/ejhdn.html or e-mail firstname.lastname@example.org
The Movement Disorder Society of Japan (MDSJ). The main goal of MDSJ is to promote clinical and basic studies on movement disorders, including chorea and Huntington’s disease. They host seminars, educational lectures, symposiums, video sessions, forums to discuss controversies and poster presentations about genetic studies, biomarkers, recent advances in drug therapies, and regenerative medicine. For more information, please visit http://mdsj.umin.jp/en/index.html
Xu, M., & Wu, Z.-Y. (2015). Huntington Disease in Asia. Chinese Medical Journal, 128(13), 1815–1819. https://doi.org/10.4103/0366-6999.159359
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