To verify whether the
The heteromeric guanine nucleotide-binding proteins (G-proteins) are composed of
In recent literature, this polymorphism has also been associated with neurological and psychic conditions such as depression [
Neuropsychological tests allow standard evaluation of cognitive functions. Memory, language, and executive functions can be assessed and quantified by numeric scores. General cognitive assessment can be performed by means of mini-mental state examination [
It has also been found that poorly educated and elderly persons may show low scores at neuropsychological tests even without developing clinical evidence of dementia [
The aim of the present study was to verify whether, at a population level, the
The study cohort was represented by unselected elderly subjects free from clinical dementia and from neurological and psychiatric diseases, randomly taken from the Italian general population in the frame of the Last Evidences Of Genetic Risk factors in the Aged (LEOGRA) study, whose protocol has been diffusely described elsewhere [
Weight was measured in kg with a mechanical device Astra (GIMA, Gessate, Italy), height in m. Body mass index was calculated in kg/m2 from the weight/squared height ratio.
All subjects underwent a Rose’s questionnaire [
Blood for exams was taken in the morning after overnight fasting. Blood glucose was measured with the colorimetric method at 630 nm, plasma insulin with radioimmunoassay. Low-density-lipoprotein cholesterol was calculated with the Friedlander algorithm [
All subjects underwent blood pressure measurements in triplicate by trained medical doctors by means of an automatic Omron 705-IT device (Omron Europe, Hoofddorp, Netherlands); to minimize the alert reaction, the average of the last two measurements was taken into account for the analysis of data. Subjects also underwent a standard electrocardiogram blindly codified according to the Minnesota code, a 2D-echocardiogram recorded according to the American Society of Echocardiography and the Penn convention (Megas device, Esaote, Firenze, Italy) and a spirometry (Pony Spyrometer class I, type B, Cosmed, Rome, Italy). Murmurs at neck were detected with the auscultatory method.
Genomic DNA was isolated from whole blood collected in ethylenediamine tetraacetic acid tubes using a blood DNA Prep Plus spin-column system, according to the protocol provided by the manufacturer (A&A Biotechnology, Gdansk, Poland). For the determination of the
The evaluation consisted of a battery of validated tests relevant for exploring areas of cognitive functions potentially related to cognitive decline. Fourteen tests were selected in order to assess participant abilities in cognitive processing and grouped according to the function mainly involved: general functioning: mini mental state examination [ memory tests: digit span, immediate and delayed memory, and memory with interference; executive tests involving one or more executive functions: overlapping figures, verbal fluency, trail making tests A and B (TMTs A and B); visuospatial abilities: spontaneous drawing, figure copying, and clock test.
Abstraction was studied by detecting logical abilities looking for a concept overordinating two terms.
Digit span [
Verbal fluency [
In the TMT A subjects were required to connect with line progressive numbers, in the TMT B progressive numbers and letters [
The overlapping figure was composed of 50 objects integrated into one perceptual unit [
In the clock test the participant was instructed to draw a clock indicating 2 : 45, setting the hands and numbers on the face “so that a child could read them”. The instructions could be repeated until they were clearly understood, but once the subject began to draw, no further assistance was allowed.
The entire battery of tests was administered in a single session which took approximately two hours to complete. The results of the neuropsychological battery were compared to the normative sample for Italian subjects aged 60 years or over described by Mondini et al. [
The investigation conformed to the principles outlined in the Declaration of Helsinki and institutional guidelines and was approved by the local Ethics Committee. Before the study and after consulting his/her own general practitioner, each subject accepted and signed an informed consent.
A preliminary power analysis based on previous experience of the same laboratory [
Continuous variables were expressed as mean ± standard deviation and compared between groups with analysis of covariance; 95% confidence intervals were also shown for unadjusted values of the score of the neuropsychological tests across the
The correlation with a continuous dependent variable was performed by stepwise multiple regression analysis, using both continuous and categorical items as independent variables; generating odds ratios and 95% confidence intervals (CI). Regression with categorical variables was performed logistically, also generating relative risks (RR) and 95% CI.
The general characteristics of the cohort are shown in Table
General characteristics of the study cohort. Mean
Items |
| |||
All subjects
|
CC subjects
|
CT subjects
|
TT subjects
|
|
| ||||
Age (years) |
|
|
|
|
Males (%) | 44.4 | 44.1 | 37.9 | 43.8 |
BMI (kg/m2) |
|
|
|
|
LVMI (kg/m2) |
|
|
|
|
LVH (%) | 59.9 | 55.2 | 62.5 | 50.0 |
SBP (mmHg) |
|
|
|
|
DBP (mmHg) |
|
|
|
|
Heart rate (bpm) |
|
|
|
|
Coronary artery disease (%) | 31.6 | 37.1 | 28.6 | 22.2 |
Haematocrit (%) |
|
|
|
|
Sedimentation rate (mm/h) |
|
|
|
|
Blood glucose (mg/dL) |
|
|
|
|
Serum uric acid (mg/dL) |
|
|
|
|
LDL-C (mg/dL) |
|
|
|
|
HDL-C (mg/dL) |
|
|
|
|
TG (mg/dL) |
|
|
|
|
Circulating cortisol ( |
|
|
|
|
Circulating T3 (ng/dL) |
|
|
|
|
Circulating T4 ( |
|
|
|
|
Plasma TSH (mlU/L) |
|
|
|
|
Circulating insulin ( |
|
|
|
|
HOMA-R |
|
|
|
|
Apolipoprotein B/A ratio |
|
|
|
|
Education (years of school) |
|
|
|
|
Hip-to-waist ratio |
|
|
|
|
HOMA-R: homeostasis model assessment index; BMI: body mass index; LVMI: left ventricular mass index; SBP and DBP: systolic and diastolic blood pressure; LDL-C and HDL-C: low-density and high-density-lipoprotein cholesterol, TSH: thyrotropin-stimulating hormone; HOMA: homeostasis model assessment.
Mean scores of the neuropsychological tests recorded in the study cohort. Italian normative scores for the same age and education are also shown [
Tests | Values from the cohort |
Normative scores |
|
---|---|---|---|
Digit span score |
|
|
0.06 (ns) |
Immediate prose memory score |
|
|
<0.001 |
Delayed prose memory score |
|
|
<0.0001 |
MI 10 score |
|
|
<0.0001 |
MI 30 score |
|
|
<0.0001 |
Trail making test A (seconds) |
|
|
0.7 (ns) |
Trail making test B (seconds) |
|
|
<0.001 |
Verbal fluency score |
|
|
<0.0001 |
Abstraction score |
|
|
<0.0001 |
Overlapping figure score |
|
|
<0.0001 |
Figure copying score |
|
|
0.3 (ns) |
Figure drawing score |
|
|
<0.0001 |
Clock drawing task score |
|
|
<0.003 |
MI: memory with interference; ns: nonsignificant difference.
According to the
Multiple regression of the neuropsychological tests with age, education, and
Tests | Age (years) | Education (years) |
| |||
---|---|---|---|---|---|---|
|
|
|
|
|
| |
MMSE | −0.21 (0.04) | <0.0001 | 0.07 (0.09) | 0.4 (ns) | −0.15 (9.24) | 0.5 (ns) |
Digit span | −0.05 (0.01) | <0.001 | 0.04 (0.04) | 0.3 (ns) | −0.30 (0.10) | <0.005 |
IPM | −0.17 (0.05) | <0.0001 | 0.44 (0.12) | <0.0001 | −0.73 (0.32) | 0.02 |
DPM | −0.36 (0.06) | <0.0001 | 0.58 (0.14) | <0.0001 | −0.77 (0.32) | <0.05 |
MI 10 | −0.14 (0.03) | <0.001 | 0.19 (0.08) | 0.02 | −0.18 (0.23) | 0.4 (ns) |
MI 30 | −0.03 (0.04) | 0.3 (ns) | 0.35 (0.07) | <0.0001 | 0.10 (0.19) | 0.3 (ns) |
Verbal fluency | −0.19 (0.04) | <0.0001 | 0.23 (0.11) | <0.05 | −0.80 (0.30) | <0.005 |
TMT A | 1.32 (0.44) | <0.005 | −2.47 (1.04) | <0.03 | 7.96 (3.12) | <0.01 |
TMT B | 2.10 (1.02) | <0.05 | −6.63 (2.47) | <0.01 | 18.80 (9.89) | 0.06 (ns) |
Figure drawing | −0.02 (0.01) | <0.01 | 0.01 (0.02) | 0.9 (ns) | −0.07 (0.05) | 0.1 (ns) |
Figure copying | −0.03 (0.01) | <0.0001 | 0.04 (0.02) | 0.4 (ns) | −0.07 (0.04) | 0.1 (ns) |
Abstraction | −0.09 (0.02) | <0.0001 | 0.22 (0.05) | <0.0001 | 0.01 (0.14) | 0.9 (ns) |
Overlapping figure | −0.58 (0.09) | <0.0001 | 1.00 (0.22) | <0.0001 | −0.59 (0.61) | 0.3 (ns) |
Clock test | −0.15 (0.04) | <0.0001 | 0.16 (0.09) | 0.1 (ns) | -0.46 (0.26) | 0.1 (ns) |
Unadjusted values of the score of the neuropsychological tests across the
Tests | CC |
CT |
C-carriers cumulated |
TT |
---|---|---|---|---|
MMSE score |
|
|
|
|
Digit span score |
|
|
|
|
Immediate prose memory score |
|
|
|
|
Delayed prose memory score |
|
|
|
|
MI 10 score |
|
|
|
|
MI 30 score |
|
|
|
|
Verbal fluency score |
|
|
|
|
TMT A (seconds) |
|
|
|
|
TMT B (seconds) |
|
|
|
|
Figure copying score |
|
|
|
|
Figure drawing score |
|
|
|
|
Abstraction score |
|
|
|
|
Overlapping figure score |
|
|
17.3 |
|
Clock test score |
|
|
|
|
MMSE: mini-mental state examination; MI 10 and MI 30: memory with interference at 10 and 30 seconds; TMTs: trail making tests.
Blood pressure or diagnosis of arterial hypertension, heart rate, body mass index or diagnosis of overweight, blood lipids or diagnosis of hypercholesterolaemia or hypertriglyceridaemia, blood glucose or diagnosis of diabetes, serum uric acid or diagnosis of hyperuricaemia, left ventricular mass index or diagnosis of left ventricular hypertrophy, history of cardiovascular disease, intake of ethanol or caffeine, and smoking did not influence either the response to the neuropsychological tests or their scores across the
MMSE scored in average 26.1 ± 3.9 (CI 25.5–26.7) and was inversely related with age (
Scores of the neuropsychological tests in relation to
The score of the abstraction task was related inversely with age; direct regression with years of school was present both in the whole cohort (Table
In our cohort of elderly subjects, the digit span was inversely related with age, every year of age producing 7% decrease of the score (Table
Relative risk (RR) of performing low digit span in relation to
Regression of age with the memory tests in 220 subjects from general population.
The immediate prose memory score was inversely related with age in the entire cohort (Table
The delayed prose memory score was related inversely with age and directly with years of schooling (Table
The score of MI10 was inversely related with age (−17% for every year). Although the score was not different across the
The score of MI30 was directly related with education in the whole cohort (Table
The overlapping figure test was inversely related with age. After adjusting for age and education, its score was not different in C-carriers (17.4 ± 9.6) and in TT (17.7 ± 10.5,
The score of verbal fluency was inversely related with age, with exclusion of the TT subjects, where no correlation was detectable (Figure
Regression of age with the neupsychological tests in 220 subjects from general population.
The TMTs were directly related with age and—limitedly to the C-carriers—inversely related with years of schooling (
The clock test score was inversely related to age, while no regression with genotype and education was found.
In this cohort of general population, the
All tests of memory but MI30 were inversely related with age, but this effect was not homogenous, being unequally distributed across the
Both short-term and long-term memory functions were
Education limited but did not abolish the effect of TT homozygosis on immediate and delayed prose memory, but not on digit span.
The TMT A and verbal fluency were influenced by the
To our knowledge, no previous data are available in the literature about the interactions between cognitive tests and the
The reason of lower cognitive ability in subjects with the TT homozygosis can only be object of speculation, due to paucity of data in literature. Subjects with the
In our cohort considered as a whole, the cognitive pattern was mildly worse than expected from Italian normative data [
A limitation of the study is represented by the fact that sample sizes were suboptimal, although they are representative of general population and ratified by power analysis.
Mini Mental state examination
Digit Span
Immediate and delayed prose memory
Memory with interference at 10 and 30 seconds
Trail making tests.
None of the authors have any conflicts of interest associated with the work presented in this paper.
All authors had access to the data and played a role in writing this manuscript.
This work was funded by RSF 811-98 and 178-04, Regione Veneto.