This was the first preliminary study in which we demonstrated the prevalence of FH among a population in southern Thailand. The FH prevalence according to the DLCN and the US-MEDPED criteria were 0.47% (1:211) and 0.41% (1:247), respectively. Currently, there are 69.93 million people in Thailand [16]. We assumed that the number of FH cases in Thai subjects may be approximately 286,713 to 328,671. Our results were similar to a previous report that the overall prevalence of FH was 1:200-1:250 in the general population worldwide [3]. However, variations in the prevalence of FH have been observed among various populations. For example, previous prevalence data has demonstrated rates of 1:208 in Japan, 1:323 in China, 1:353 in Australia, 1:250 in the USA, 1:295 in Germany, 1:319 in the Netherlands, and 1:300 in Spain [5]. These differences may be due to the different ethnicities, as well as due to the different criteria applied among various studies. However, in some populations, including Tunisia (1:165), Denmark (1:137), Christian Lebanon (1:85), South Africans Afrikaners (1:72), and Ashkenazi Jews (1:67), the prevalence of FH was higher because of the “founder effect” [3, 17–19].
In this study, subjects with probable FH and definite FH had a Bachelor's degree in education. Most of the subjects also resided in the urban area. A previous study in a Thai population also demonstrated that subjects in urban areas had higher levels of TC and LDL-C than subjects in rural areas [20]. This may be due to the different behavioral lifestyles and sociodemographic data among subjects who resided in urban and rural areas. Nevertheless, education, area of residence, and other cardiovascular risk factors, such as age, sex, diabetes mellitus, hypertension, smoking, physical activity, alcohol consumption, and obesity, were not associated with FH in this study.
In this study, only 1 in 3 to 1 in 5 patients received lipid-lowering therapies. However, most of the individuals never received lipid-lowering therapies. This may be due to the fact that they lost self-awareness for their lipid control. Our results were consistent with those of previous studies [21–22]. In Thailand, 78% and 61.7% of hypercholesterolemic subjects were undiagnosed in 2004 and 2014 national health examination surveys, respectively [21–22]. This may be due to the low number of treatments and controls among Thai subjects. In addition, a previous study showed that only 9.7-19.8% of Thai adults aged ≥ 20 years with high LDL-C were treated [20]. Moreover, data on the prevalence of FH in Thai subjects have not been reported. Although two mutations of LDLR (D151Y and M391T) have been reported in Thai FH patients [12–13], other genetic mutations in Thai FH patients have not yet been elucidated. This suggests that FH subjects in Thailand may be underdiagnosed and undertreated. Similarly, a previous report in the USA, European, and Asian populations among 22 countries showed that most FH patients were underdiagnosed and undertreated in the general population [4]. Moreover, it was found that less than 1% of FH cases were diagnosed in most countries. However, a higher diagnosis rate of FH was observed in some countries (71% in the Netherlands, 43% in Norway, 19% in Iceland, 13% in Switzerland, 12% in the UK, and 6% in Spain) [4].
Studies of FH in Thailand have been rarely conducted. Furthermore, the reasons for the underdiagnosis of FH among Thai subjects are still unknown. However, we hypothesized that this may result from the lack of lipid screening and monitoring among the Thai population. Although district health hospitals have been distributed in all provinces of Thailand, there were no laboratory facilities or manpower for lipid determination. Moreover, the genetic analysis for FH in Thailand was not performed in the routine laboratory tests because of costs. The detection of gene mutations in Thai FH patients is usually conducted under research projects funded by universities or the government. Furthermore, the FH screening program in Thailand has not been set up, and FH awareness and education among physicians and other health care professionals should be considered. A previous study showed that Asian physicians had a lower awareness of FH guidelines than did UK physicians [23]. In addition, a study of the awareness and knowledge of FH among 230 physicians in Japan, Korea, and Taiwan also demonstrated that only 47% were aware of the heritability, 27% of the prevalence, and 13% of the risk of cardiovascular disease relating to FH [24]. However, a small number of Thai subjects had LDL-C > 250-329 mg/dl (0.47%) and LDL-C > 330 mg/dl (0.07%). Many subjects in this study had LDL-C > 190-249 mg/dl (6.15%). It has been found that 2% of the subjects with LDL-C > 190 mg/dl were diagnosed with FH [25]. Moreover, the prevalence rates of FH (as diagnosed by the DLCN and the US MEDPED) were likely similar in this study. The prevalence rates of FH according to the DLCN and the US MEDPED were higher in subjects aged > 40 years than in subjects aged < 40 years. We suggested that subjects who had LDL-C > 190 mg/dl should be referred to lipid specialists or expert physicians to screen for FH. Moreover, subjects aged > 40 years should pay more attention to lipid control.
Our study had some limitations. First, the study subjects were from Nakhon Si Thammarat and Patthalung Provinces in southern Thailand. Therefore, the results may not represent the data from all regions of Thailand. Even though the number of study subjects appeared to be small, the sample size was calculated, and it was representative of the southern Thai population. Moreover, the statistical power for the data analysis was high. Second, data on family history, personal history, tendon xanthomas, and genetic analysis were not collected. We suggest that the prevalence of FH according to the DLCN criteria among these study subjects may be underestimated. Nevertheless, the US MEDPED criteria for the diagnosis of FH used only LDL-C levels according to age in this study. The family history, genetic detection, xanthomas, and history of CVD were not used in the US MEDPED criteria. Therefore, we could imply that the prevalence of FH among southern Thai subjects was approximately 1:247 by using the US MEDPED criteria. This estimated prevalence was not considerably different from the estimated prevalence via the DLCN (1:211). Moreover, the DLCN and the US MEDPED criteria used for the diagnosis of FH were developed from European and US populations. In practice, the lower serum lipid levels among the Asian population [26] may lead to false negative results when using the same LDL-C cutoff. These results suggest that the modified criteria for FH diagnosis among the Thai population should be further developed. Furthermore, other diagnostic criteria for FH in some studies in Hong Kong [27], Cyprus [28], and India [29] have used only serum lipids. Overall, we suggest that the varying FH criteria used in the diagnosis of FH among various populations may lead to a different prevalence of FH and difficulty in determining the true prevalence of FH.
Finally, the exact dosage, duration, and compliance of the lipid-lowering therapies were not recorded. Future studies with larger sample sizes and data collection of all FH diagnosis criteria from all regions of Thailand should be implemented.