Characterization of Alzheimer’s Disease and Mild Cognitive Impairment in Older Adults in Panama

INTRODUCTION

Latin America and the Caribbean (LAC) region is experiencing rapid population aging 1 with prevalence rates of dementia [1, 2] and cognitive impairment [3] similar to those in more developed regions. To date, there is only one published study reporting cognitive impairment among the elderly population in Panama [4], an upper middle income country in Central America. Despite its economic classification, the health status of elderly individuals is significantly affected by low income levels, poor education, and early childhood exposure to health risks [5].

Here we report the results of a cross-sectional analysis of demographic, clinical and genetic factors associated with Alzheimer’s disease (AD), mild cognitive impairment (MCI), or no cognitive impairment. The main objective was to describe the risk factors associated with AD, including the frequency of the apolipoprotein E (ApoE) genotypes, in older adults in Panama. Various clinical, community, and postmortem studies have pointed to the ApoE gene and the presence of the ɛ4 allele as the strongest genetic risk factor for sporadic AD, but this association has not been consistent for Hispanics [6–9]. Thus, to our knowledge, this is the first report of the associated risk between the ApoE ɛ4 allele and AD among Hispanics in Panama.

METHODS

RESULTS

Groups did not differ in gender, relationship status, monthly household income, or chronic conditions. Controls were significantly younger than AD (p = 0.001) and MCI groups (p = 0.015) and more educated (ps < 0.05). AD and MCI groups did not differ in either age or education. Highly significant differences in cognitive performance were noted among the groups: (ps < 0.001). The AD group reported greater BADL and IADL difficulties than control and MCI groups (ps < 0.001), which did not differ from each other. The MCI group endorsed more depressive symptoms (GDS-30) than AD and control groups (ps < 0.05), which did not differ from one another. BMI in AD subjects was significantly lower than controls (p < 0.05). At least half of AD (57%) and MCI (50%) groups expressed one or two copies of the ApoE ɛ4 allele. Table 1 summarizes the frequencies for the five ApoE genotypes observed. The logistic regression analysis (Table 2) indicated that age (OR = 2.53, 95% CI = 1.03–6.17, p = 0.042) and ApoE ɛ4 expression (OR = 5.14, 95% CI = 2.11–12.52, p < 0.001) were significant predictors of cognitive impairment, whereas educational level was marginally associated with cognitive impairment.

DISCUSSION

This study suggests that the ApoE ɛ4 allele is a significant factor associated with AD and MCI in elderly individuals in Panama. The frequency of ApoE ɛ4 expression as well as the strength of the association between ApoE ɛ4 expression and risk for AD in Hispanics has varied across studies [6–9, 21]. Among Mexican Americans, there is a lower frequency of ApoE ɛ4 expression [6, 21] that may explain the difference in etiology of dementia in this population. Moreover, the strength of the association between ApoE ɛ4 expression and risk for AD in Hispanics also has varied across studies within and outside the U.S. [6–9, 22]. To our knowledge, our study shows one of the highest ApoE ɛ4 allele frequencies among Hispanics diagnosed with AD, and underscores the association between AD and the ApoE ɛ4 allele in Panamanian older adults. The only study reporting a similarly high frequency was conducted in Hispanics in Colombia [7]. In that study, 51% of individuals with AD expressed ApoE ɛ4, and the odds of expressing at least one copy of ApoE ɛ4 among subjects diagnosed with sporadic AD was also comparable to our results (6.8, 95% CI 2.1–21.5). The variation among studies is likely due to the fact that Hispanics are a mixture of Amerindian, African, and European descent with relative compositions varying by country [23]. In light of this, the genetic admixture of Panamanians is likely very different from other Hispanic populations and this is a line of investigation we are beginning to examine.

An important limitation to the present study is its sample size, particularly in regard to ApoE genotyping. In addition to being able to analyze the association between ApoE ɛ4 expression and AD and MCI groups separately, an increased sample size will allow us to determine whether there is a correlation between the number of copies of ApoE ɛ4 allele and the severity of cognitive impairment. Also, the study is cross-sectional so we cannot draw causal inference about the variables measured and cognitive function. Despite these limitations, the current study adds to the debate regarding ApoE risk and AD among Hispanics. Little is known about the factors associated to cognitive health at old age in Central American populations. In Panama, cognitive impairment is seen as a normal part of the aging process. Affected individuals do not seek formal medical services until advanced stages of impairment, and care for the elderly is typically carried out at home by family members, factors that increase the burden of aging on healthcare services and individuals. In U.S. population studies, compared with non-Hispanics, Hispanics are more burdened with dementia risk factors and there is less awareness, treatment and control of risk factors [24, 25]. Thus, our study adds to the effort to document the cognitive status of older adults in Central America and constitutes a contribution to our understanding of the risk factors of cognitive outcomes among Hispanics both within and outside LAC. Our results underscore also the potential of genetic screening for the identification of those at highest risk for dementia.