doi:10.1093/brain/awh296 Brain (2004), 127, 2621–2628

Six-month recovery from mild to moderateTraumatic Brain Injury: the role of APOE-e4 allele

Laury Chamelian,1,2 Marciano Reis1,3 and Anthony Feinstein1,2

Correspondence to: Dr Anthony Feinstein, Department of

Psychiatry, FG08, Sunnybrook and Women’s College

Health Sciences Centre, 2075 Bayview Avenue,

Toronto, ON M4N 3M5, Canada

E-mail: loricham@yahoo.com, antfeinstein@aol.com

1University of Toronto, 2Department of Psychiatry,

Traumatic Brain Injury Clinic, Sunnybrook and Women’s

College Health Sciences Centre and 3Department of

Clinical Pathology, Sunnybrook and Women’s College

Health Sciences Centre, Toronto, ON, Canada

SummaryThe possession of at least one APOE-e4 allele may be

linked to poor outcome in patients with predominantlysevere traumatic brain injury (TBI). In mild TBI, which

accounts for approximately 85%of all cases, the role of the

APOE-«4 allele is less clear. Studies completed to date

have relied on brief cognitive assessments or coarse meas-

ures of global functioning, thereby limiting their conclu-

sions. Our study investigated the influence of the APOE-«4allele in a prospective sample of 90 adults with mild to

moderate TBI in whom neuropsychiatric outcome 6months after injury was assessed as follows: (i) a detailed

neuropsychological battery; (ii) an index of emotional dis-

tress (General Health Questionnaire); (iii) a diagnosis of

major depression (Structured Clinical Interview for

DSM-IV); (iv) a measure of global functioning (GlasgowOutcome Scale); (v) an index of psychosocial outcome

(Rivermead Head Injury Follow-up Questionnaire); and

(vi) symptoms of persistent post-concussion disorder

(Rivermead Post-Concussion Symptoms Questionnaire).

No association was found between the presence of the

APOE-«4 allele and poor outcome across all measures.

Given the homogeneous nature of our sample (mild to

moderate injury severity), the uniform follow-up period(6 months) and the comprehensive markers of recovery

used, our data suggest that the APOE-«4 allele does not

adversely impact outcome in this group of TBI patients.

Keywords: APOE-e4 allele; cognitive testing; mood; psychosocial outcome; head injury

Abbreviations: GCS = Glasgow Coma Scale; GOS = Glasgow Outcome Scale; LOC = loss of consciousness; MANOVA =

multivariate analysis of variance; PTA = post-traumatic amnesia; SRT = Simple Reaction Time; TBI = traumatic brain injury.

Received April 27, 2004. Revised July 5, 2004. Accepted July 28, 2004. Advanced Access publication October 20, 2004

IntroductionIt has been suggested (Sorbi et al., 1995; Jordan et al., 1997;

Teasdale et al., 1997; Friedman et al., 1999; Kerr et al., 1999;

Crawford et al., 2002; Chiang et al., 2003) that outcome

following traumatic brain injury (TBI) is influenced by poly-

morphism of the apolipoprotein E (APOE) gene, located on

chromosome 19. Of the three common alleles (e2, e3, e4),

APOE-e4 allele has been the one associated with unfavour-

able cognitive (Friedman et al., 1999; Crawford et al., 2002)

and functional recovery (Teasdale et al., 1997; Lichtman et al.,

2000; Chiang et al., 2003), deposition of b-amyloid following

head injury (Roberts et al., 1994; Nicoll et al., 1995), pro-

longed posttraumatic coma (Sorbi et al., 1995; Friedman et al.,

1999), lower cerebral blood flow during the first 24 h after

injury (Kerr et al., 1999) and greater neurological deficits in

boxers with history of 12 or more professional bouts (Jordan

et al., 1997). It has also been shown to act synergistically

(Mayeux et al., 1995; Tang et al., 1996) and additively

(Katzman et al., 1996) with a previous TBI as risk factors

for Alzheimer’s disease, although recent studies have failed to

support these findings (O’Meara et al., 1997; Weiner et al.,

1999; Guo et al., 2000; Plassman et al., 2000; Jellinger et al.,

2001).

While informative, these studies have mostly focused on

subjects with severe head injuries (Roberts et al., 1994; Nicoll

et al., 1995; Sorbi et al., 1995; Friedman et al., 1999; Kerr et al.,

1999; Lichtman et al., 2000; Crawford et al., 2002). With

respect to mildly brain-injured individuals, who account for

almost 85% of all TBI cases, the role of the APOE-e4 allele

is less clear. In addition, outcome measures have often been

limited, relying on brief cognitive assessments (Jordan et al.,

1997; Crawford et al., 2002) or on disability scales (Teasdale

et al., 1997; Chiang et al., 2003) (such as the Glasgow

Brain Vol. 127 No. 12 # Guarantors of Brain 2004; all rights reserved

Outcome Scale) (Jennett and Bond, 1975) that lack the neces-

sary details in providing a thorough depiction of various

aspects of recovery following head injury. Although a recent

study (Liberman et al., 2002) with predominantly mild TBI

patients recorded no significant relationship between APOE-

e4 allele status and a limited number of cognitive tasks 6 weeks

following head injury, it did not assess psychosocial function-

ing. Our study investigated the influence of the APOE-e4

allele on multiple measures of neuropsychiatric recovery in

mild to moderate TBI at a follow-up period extended to

6 months after injury.

MethodsSubjects were recruited prospectively from a traumatic brain injury

clinic at a tertiary care hospital. All patients who have sustained a

TBI and seen in the hospital’s emergency room are routinely given a

follow-up clinic appointment within weeks of injury and thereafter

followed for a minimum of 6 months. A consecutive sample of

90 clinic attendees was enrolled in our study at the time of their

first clinic assessment. Subjects were between 18 and 60 years of age

and had sustained a non-penetrating mild (Esselman and Uomoto,

1995) [Glasgow Coma Scale (GCS) = 13–15; loss of consciousness

(LOC) <20 min; post-traumatic amnesia (PTA) <24 h] or moderate

TBI [GCS = 9–12; PTA >24 h but less than 1 week]. All participants

underwent a thorough neuropsychiatric evaluation, including

detailed cognitive testing 6 months after head injury, at which

time a buccal smear was collected to determine APOE genotype.

The study sample was split into those with (n = 19) and without

(n = 71) the APOE-e4 allele. These two groups were then compared

on the neuropsychiatric measures outlined below, which were per-

formed without prior knowledge of the patients’ APOE status.

Background informationThe demographic and TBI-related data collected included age, gen-

der, race, marital and pre-injury employment status, level of educa-

tion, type of occupation, history of alcohol and substance abuse, past

psychiatric history, prior head injury, family history of psychiatric

illnesses or dementia/Alzheimer’s disease, mechanism of injury,

head injury severity indices, such as GCS recorded at the emergency

room (Levin et al., 1987), LOC, PTA (Russell and Smith, 1961),

initial CT brain results. In addition, all subjects were assessed with

the Abbreviated Injury Severity Score (AISS) (Civil and Schwab,

1988), which provides a measure of trauma severity to various body

regions, including the head. The presence of physical pain and

medication use were also recorded.

APOE genotypingDNA was extracted from buccal epithelial cells using the Qiagen

Blood Mini Kit, and amplified by PCR with primers specific for the

APOE alleles e2, e3 and e4: 50-TCC AAG GAG CTG CAG GCG

GCG CA-30 and 50-ACA GAA TTC GCC CCG GCC TGG TAC

ACT GCC A-30. Cycling conditions were as follows: 94�C for 4 min,

35 cycles of 94�C for 30 s, 66�C for 30 s, and 70�C for 1:30 min, with

final extension at 70�C for 10 min. The amplimers were digested with

the HhaI restriction endonuclease for 2 h and then electrophoresed on

a 4% high-resolution agarose gel.

Neuropsychiatric evaluationGlasgow Outcome Scale (GOS) (Jennett and

Bond, 1975)

This widely used clinician-rated five-point scale assesses global

adjustment to activities of daily living and general outcome.

A score of 5 indicates a return to the premorbid level of functioning

whereas lower scores denote a poor global outcome.

Rivermead Head Injury Follow-up Questionnaire

(RHFUQ) (Crawford et al., 1996)

This is a five-point self-report scale with a total score ranging from

0 to 48. It addresses 10 aspects of a patient’s functioning (relation-

ships, domestic and vocational activities, ability to participate in a

conversation) following TBI, and hence provides a more detailed

description of psychosocial functioning than the GOS. High scores

on the RHFUQ are indicative of poor recovery.

Rivermead Post-Concussion Symptoms

Questionnaire (RPQ) (King et al., 1995)

This is a five-point self-report scale measuring the presence and the

severity of 17 somatic symptoms commonly experienced following

head injury. High scores on the RPQ indicate a greater level of

physical distress.

Twenty-eight-item General Health Questionnaire

(GHQ) (Goldberg and Hiller, 1979)

This questionnaire assesses self-reported symptoms of emotional

distress. It contains four subscales of seven questions each, pertain-

ing to somatic complaints, anxiety, social dysfunction and depres-

sion. For each question, the answer is chosen among four possible

responses that are scored in a binomial fashion (0–0–1–1). High

scores on the GHQ indicate a greater level of psychological distress.

Mood disorder section of the Structured Clinical

Interview for the DSM-IV (SCID for DSM-IV)

(First et al., 1994)

This was used to establish a diagnosis of major depression. The

clinic’s neuropsychiatrist who interviewed the study participants

was blind to the subjects’ cognitive data and APOE genotype.

Resumption of work or studies

Patients were asked if they had resumed work or studies. Those who

had not returned to work or studies because of injuries other than their

TBI (n = 36) were excluded from this part of the analysis.

Cognitive battery

Wechsler Adult Intelligence Scale—III: working memory (Wechsler,

1997a). This measure of attention and working memory is a com-

posite of the scores computed from the following subsets: Digit span,

Arithmetic and Letter sequencing.

Wechsler Memory Scale—III: logical memory I and II (Wechsler,

1997b). This assesses verbal memory by examining the patient’s

ability to recall two orally presented stories immediately (I) and

after a 30-min delay (II).

2622 L. Chamelian et al.

California Verbal Learning Test-II: total, long delay free recall and

recognition hits (Delis et al., 2000). This provides an assessment of

learning and memory of verbal material. The subject is presented

with a 16-item shopping list over five free recall trials. We recorded

the sum of recalled words from List A across the five trials and from

delayed free-recall as well as from recognition trials.

Brief Visuospatial Memory Test—Revised: immediate and delay total

recall (Benedict, 1997). With multiple trials, it is possible with this

test to study the patient’s visuospatial learning and memory. Testing

involves the reproduction and subsequent delayed recall of a series of

geometric designs.

Paced Auditory Serial Addition Task (Gronwall, 1977). This task

assesses information processing speed and sustained and divided

attention. The subject is required to add consecutive pairs of tape-

recorded digits so that each number is added to the one immediately

preceding it. Four series of digits are presented, each at an increas-

ingly quick rate of number presentation: 2.4, 2.0, 1.6 and 1.2 s. The

number of correct responses for each of the four series was recorded.

Controlled Oral Word Association Test (Spreen and Benton,

1969). This measures verbal association fluency, tapping into

higher-level executive functioning abilities. Subjects are asked to

generate as many words as possible beginning with a given letter

(F, A or S). Three trials are administered, each trial lasting 60 s.

Proper nouns, numbers and the same word with a different suffix are

excluded. The sum of admissible words generated during the three

trials was recorded.

Wisconsin Card Sorting Test (WCST): total and perseverative

responses (Heaton et al., 1993). This provides measures of mental

flexibility and problem solving. Subjects are required to sort cards

according to specific categories (colour, shape, number) based on

feedback from the examiner. The total number of categories achieved

and the number of perseverative responses were recorded.

Simple reaction time (SRT) (Feinstein et al., 1992). This gives an

index of basic psychomotor speed. The test comprised 60 trials for

each hand. The imperative stimulus to which the subject had to react

was the filling of a square either to the left (for the left hand) or the

right (for the right hand) of a central blank square on the computer

monitor. The subject reacted by pushing either the left or right button

on a button box. The right-hand responses were completed before

proceeding to the left-hand ones. Prior to the imperative stimulus, an

arrow appeared in the central square pointing in the direction of the

square to be filled. The arrow appeared 1.6, 0.8 or 0.2 s before the

imperative stimulus, each for 25% of the time. For the remaining

25% the arrow appeared simultaneously with the imperative stimu-

lus. The order of the interval was assigned randomly, to prevent the

subject anticipating the exact occurrence of the stimulus. The interval

between the end of one trial and the appearance of the arrow for the

next trial was also assigned randomly between 1 and 4 s.

Choice reaction time (CRT) (Feinstein et al., 1992). The test

comprised 80 trials. As in the SRT, the imperative stimulus to

which the subjects had to react was a filling of a square either to

the left or right of the central blank square. A mixture of warned and

cued CRT trials was used. In the warned trials, a cross appeared in the

central square prior to the imperative stimulus. This indicated that the

stimulus was about to appear, but not which side. In the cued trials,

the arrow appeared in the central square pointing in the direction of

the square to be filled. The 80 trials were equally and randomly

divided between warned and cued responses. Within each 40, half

the responses were right and half were left. The timing for the cross or

arrow to appear prior to the imperative stimulus was the same as for

the SRT and was also assigned randomly to prevent anticipation.

Vocabulary subscale of the Wechsler Abbreviated Intelligence Scale

(Wechsler, 1999). This was used to provide an estimate of premor-

bid intelligence quotient.

Statistical analysisPatient groups with and without the APOE-e4 allele were compared

using t tests for continuous demographic/injury, psychosocial and

cognitive variables and x2 analyses for categorical variables. Fisher’s

exact test was reported when appropriate. A 1% level of significance

was chosen to adjust for multiple comparisons. In addition, two

separate multivariate analyses of variance (MANOVAs) were per-

formed on the 6-month neuropsychiatric and cognitive outcome

measures. For each of the MANOVAs, the maximum P value was

set at 0.05 (two-tailed test), as is recommended when conducting

multiple comparisons (Keppel, 1982).

EthicsWritten consent was provided from all subjects. The study was

approved by the Sunnybrook and WCH Research Ethics Board.

ResultsThe mean age for the total study sample (N = 90) was 33 years

(SD 12.6). Subjects were predominantly male (60%),

Caucasian (76.7%) and had sustained a mild head injury

(56.7%). The frequencies for the APOE-e2, e3 and e4 alleles

were 14, 71 and 15%, respectively, with the following geno-

types: APOE 2/3 = 14 (15.5%); APOE 2/4 = 3 (3.3%); APOE

3/3 = 57 (63.3%); APOE 3/4 = 16 (17.8%). There were no

homozygotes for APOE-e2 and APOE-e4 alleles.

Comparisons between those with and without the APOE-e4

allele revealed no significant differences on demographic and

injury-related variables (Table 1). In terms of global, physical

and psychosocial functioning, both groups had similar out-

comes, including returning to work or school 6 months after

injury (Table 2). Cognitive function did not differ between the

groups on all measures tested (Tables 3). In the two separate

MANOVAs, no significant differences were apparent for

neuropsychiatric [F(7,61) = 0.4; P = 0.9] and cognitive

[F(20,56) = 0.6; P = 0.9] outcomes.

DiscussionWe did not find an association between the presence of the

APOE-e4 allele and poor outcome across multiple beha-

vioural domains 6 months following mild to moderate TBI.

This finding is supported by the close group matching of

patients with and without the APOE-e4 allele with respect

to demographic and injury-related variables that may influ-

ence recovery from mild to moderate TBI (Williams et al.,

1990; van der Naalt, 2001). To date, our study is the first to

APOE-e4 allele and mild to moderate TBI 2623

Table 1 Demographic and injury-related characteristics compared between those with and without the APOE-e4 allele

Demographics APOE-e4 positive (n = 19) APOE-e4 negative (n = 71) t test/x2 P valuesMean (SD*) Mean (SD)

Age (years) 31.2 (13.3) 34.1 (12.3) t(df,88) = 0.9 0.4Gender (male) 52.6% 62.0% x2(df,1) = 0.5 0.5Race Fisher’s exact test 0.8

Caucasian 73.7% 77.5%Other 26.3% 22.5%

Marital status (single or divorced) 57.9% 63.4% x2(df,1) = 0.2 0.7Education (beyond high school) 52.6% 40.8% x2(df,1) = 0.8 0.4Employment (employed) 52.6% 78.6% x2(df,1) = 5.1 0.1Occupation (professional/semiprofessional)

18.8% 14.5% Fisher’s exact test 0.7

Past alcohol abuse 47.4% 38.0% x2(df,1) = 0.5 0.5Past substance abuse 31.6% 11.3% Fisher’s exact test 0.1Prior TBI 31.6% 22.9% Fisher’s exact test 0.5Past psychiatric history 22.2% 17.1% Fisher’s exact test 0.7Family psychiatric history x2(df,2) = 3.9 0.1

None 57.9% 66.7%Yes 36.8% 33.3%Dementia/AD 5.3% 0%Injury-related characteristics

Mechanism of injury(MVA-related)

73.7% 63.4% x2(df,1) = 0.7 0.4

Loss of consciousness Fisher’s exact test 0.2Dazed or LOC <20 min 83.3% 93.8%LOC >20 min 16.7% 6.2%

Post-traumatic amnesia x2(df,1) = 0.8 0.4<24 h 47.4% 59.2%>24 h and <1 week or sedated 52.6% 40.8%

Glasgow Coma Score at theemergency room

Fisher’s exact test 0.7

13–15 88.2% 91.0%9–12 11.8% 9.0%

CT scan abnormalities 61.1%a 36.2%b x2(df,1) = 3.5 0.1AISS 12.6 (9.5) 13.5 (10.3) t(df,72) = 0.3 0.8Pain symptoms 56.3% 65.5% x2(df,1) = 0.5 0.5Medication intake 56.3% 45.8% x2(df,1) = 0.5 0.5

an = 18; bn = 58. AD = Alzheimer’s disease; MVA = motor vehicle accident; LOC = loss of consciousness; AISS = Abbreviated InjurySeverity Score.

Table 2 Neuropsychiatric 6-month outcomes compared between those with and without the APOE-e4 allele

APOE-e4-positive (n = 19) APOE-e4-negative (n = 71) t test/x2 P valuesMean (SD*) Mean (SD)

GOS 4.3 (0.5) 4.3 (0.6) t(df,71) = –0.3 0.7RHFUQ 17.9 (14.0) 18.7 (13.7) t(df,75) = 0.2 0.8RPQ 19.6 (18.2) 24.6 (18.1) t(df,72) = 1.0 0.3GHQ

Somatic 1.9 (2.8) 2.5 (2.6) t(df,76) = 0.8 0.4Anxiety 2.2 (2.6) 3.0 (2.7) t(df,76) = 1.1 0.2Social dysfunction 2.1 (2.6) 3.2 (2.8) t(df,74) = 1.4 0.2Depression 0.7 (1.5) 1.0 (1.9) t(df,74) = 0.5 0.6Total 7.0 (9.0) 9.6 (8.6) t(df,74) = 1.1 0.3

SCID depressed 18.2%a 11.8%b Fisher’s exact test 0.6Return to work/studies x2(df,1) = 0.9 0.3

No 53.8%c 39.0%d

Yes 46.2%c 61.0%d

an = 11; bn = 51; cn = 13; dn = 41. GOS = Glasgow Outcome Scale; RHFUQ = Rivermead Head Injury Follow-up Questionnaire; RPQ =Rivermead Post-Concussion Symptoms Questionnaire; GHQ = General Health Questionnaire; SCID = Structured Clinical Interviewfor DSM-IV.

2624 L. Chamelian et al.

address outcome in a homogeneous sample of TBI patients

(mild to moderate injury severity) at a uniform follow-up

period (6 months) with an extensive array of tests that

incorporated validated and reliable indices of mood, beha-

viour and cognitive disturbance. With regard to the latter, a

detailed neuropsychological battery covering different

cognitive domains was employed.

Our data support and extend the results of a recent study

(Liberman et al., 2002) that examined cognitive dysfunction

6 weeks following mild to moderate TBI. No relationship

between cognitive performance and the APOE-e4 allele

was found. In this report, TBI severity was based on a single

variable, namely the Glasgow Coma Scale, the cognitive bat-

tery was limited in scope, and no measures of mood and

behaviour were included. Despite these limitations, the

data provided some evidence that recovery from mild to mod-

erate TBI in the subacute phase was not dependent on genetic

markers, a conclusion that our data now extend to the 6-month

watermark, with the added caveat that neither mood, psycho-

logical distress nor additional aspects of cognition appear to

be linked to the presence of the APOE-e4 allele. Our delinea-

tion of TBI severity based on a confluence of three variables,

namely GCS, PTA and duration of LOC, adds weight to our

findings. In addition, our sample provided a fair representation

of patients with head injury, since, unlike the previous

report, we included subjects with premorbid psychiatric

history or with alcohol/drug use problems, making our results

generalizable. In this regard, our APOE-e4-positive group had

a lower employment rate despite a higher education level and

greater incidence of prior TBIs, past psychiatric illness, alco-

hol and substance abuse, major depression and brain CT scan

abnormalities. Although none of these findings approached

statistical significance, there may be theoretically a relation-

ship between the possession of the APOE-e4 allele and neuro-

cognitive dysfunction, which in turn leaves patients at

increased risk of injury. However, our method did not

allow us to answer this question. To do so, it would have

required us to include a third subject group composed of

patients who were APOE-e4-positive but who had never

sustained a traumatic brain injury.

Indirect support for our findings comes from another

source. In the MIRAGE study (Bachman et al., 2003), in

which various possible aetiological factors for Alzheimer’s

disease were examined in 443 African Americans and

2336 Caucasian Americans, no significant interaction was

found between the APOE-e4 allele and a number of risk

factors of poor outcome, of which TBI was one. The racial

breakdown of the sample was necessary, given the higher

prevalence rate of the APOE-e4 allele in patients of African

descent (Zekraoui et al., 1997; Corbo and Scacchi, 1999). In

this regard, it is germane to note that the 15% occurrence rate

for the APOE-e4 allele in our sample was consistent with the

Table 3 Cognitive performances compared between those with and without the APOE-e4 allele

APOE-e4 positive (n = 19) APOE-e4 negative (n = 71) t test P valuesMean (SD*) Mean (SD)

Time between injury and cognitivetesting (days)

208.8 (68.6) 200.7 (53.3) t(df,88) = �0.5 0.6

WASI vocabulary (premorbid IQ) 55.4 (10.2) 53.5 (12.0) t(df,84) = �0.6 0.5WAIS-III working memory 29.3 (7.0) 28.31 (8.1) t(df,84) = �0.5 0.6WMS logical memory story I 45.8 (15.8) 43.7 (11.6) t(df,86) = �0.6 0.5WMS logical memory story II 30.5 (9.0) 27.3 (8.8) t(df,85) = �1.4 0.2CVLT-II total 56.6 (10.3) 53.9 (11.4) t(df,88) = �0.9 0.3CVLT-II long delay free recall 12.2 (3.5) 11.3 (3.5) t(df,87) = �1.0 0.3CVLT-II recognition hits 14.4 (2.7) 14.8 (1.7) t(df,22) = 0.7 0.5BVMT-R total 25.8 (6.5) 22.9 (8.5) t(df,85) = �1.4 0.2BVMT-R delay 9.8 (2.4) 9.2 (2.6) t(df,84) = �0.9 0.4PASAT 2.4 s 42.5 (10.0) 38.3 (11.5) t(df,83) = �1.4 0.1PASAT 2.0 s 37.8 (8.9) 34.6 (10.6) t(df,81) = �1.2 0.2PASAT 1.6 s 30.8 (7.5) 27.2 (9.2) t(df,81) = �1.5 0.1PASAT 1.2 s 23.2 (6.6) 21.1 (6.6) t(df,80) = �1.2 0.2COWAT 36.7 (13.2) 35.2 (10.7) t(df,86) = �0.5 0.6WCST total 5.4 (1.4) 4.9 (1.7) t(df,85) = �1.1 0.3WCST perseverative responses 13.7 (12.4) 21.2 (20.9) t(df,85) = 1.5 0.1SRT, mean, both hands (s) 359.3 (145.1) 1037.2 (5316.0) t(df,81) = 0.5 0.6CRT, mean warned trials, bothhands (s)

444.4 (116.0) 464.0 (181.5) t(df,80) = 0.4 0.8

CRT mean cued trials, both hands (s) 382.2 (104.5) 407.8 (176.1) t(df,80) = 0.6 0.6CRT grand mean of cued and warnedtrials (s)

413.3 (107.5) 437.5 (180.4) t(df,80) = 0.5 0.6

WASI = Wechsler Abbreviated Intelligence Scale; WAIS = Wechsler Adult Intelligence Scale; IQ = intelligence quotient; WMS =Wechsler Memory Scale; CVLT = California Verbal Learning Test; BVMT = Brief Visuospatial Memory Test; PASAT = PacedAuditory Serial Addition Task; COWAT = Controlled Oral Word Association Test; WCST = Wisconsin Card Sorting Test; SRT = SimpleReaction Time; CRT = Choice Reaction Time.

APOE-e4 allele and mild to moderate TBI 2625

predominantly Caucasian population that attends our hospital

and from which our study sample was derived. A unique study

(Nathoo et al., 2003) that focused exclusively on the Zulu

tribe in South Africa once again found that, despite the high

prevalence of the APOE-e4 allele in 110 subjects, outcome

following mostly mild to moderate TBI was not linked to

APOE polymorphism. Language barriers may have precluded

a detailed cognitive assessment in determining recovery,

which was based exclusively on the GOS.

Our data refute the findings from three other studies (Jordan

et al., 1997; Teasdale et al., 1997; Chiang et al., 2003) that

reported an association between the presence of the APOE-e4

allele and poor outcome following predominantly mild to

moderate TBI. In two of these (Teasdale et al., 1997; Chiang

et al., 2003), outcome was based on a single measure, the

GOS, a five-point Likert scale that provides a coarse measure

of functioning after a head trauma. Neither of these studies

looked at mood or cognition, two indices that provide the most

sensitive measure of recovery following brain injuries that are

deemed either mild or moderate. In the third study (Jordan

et al., 1997), the ill effects of repetitive mild TBI were invest-

igated in 30 retired and active boxers. To assess outcome, the

authors devised a 10-point Chronic Brain Injury Scale that

incorporated three dimensions, namely motor, cognitive and

behavioural. Boxers who were considered to have received

‘high exposure’, (i.e. those with more that 11 professional

bouts) and found to be APOE-e4-positive were the most

impaired. However, the assessment of cognition was based

on the Mini-Mental State Examination (MMSE) (Folstein

et al., 1975), which lacks sensitivity in patients at the less

severe end of the TBI spectrum. In addition, deficits on the

Chronic Brain Injury Scale appear to be quantified based on

clinical observations, for which standardized testing instru-

ments were not used (except for the MMSE). Furthermore, the

small sample size adds to the difficulty when it comes to data

interpretation.

The best evidence linking the APOE-e4 allele with poor

outcome comes from patients who have sustained predomin-

antly severe TBI, but once again some of the methodological

limitations inherent in the mild to moderate group apply,

particularly the absence of valid measures of mentation

(Sorbi et al., 1995; Friedman et al., 1999; Kerr et al.,

1999; Lichtman et al., 2000; Crawford et al., 2002). In two

studies, both with small sample sizes, the emphasis was on

psychological and neurosurgical indices of outcome, and here

the data showed an association between the APOE-e4 allele

and prolonged duration of coma (Sorbi et al., 1995) and a

reduction in cerebral blood flow during the first 24 h following

trauma (Kerr et al., 1999). In the latter, the combination of an

APOE-e4 allele and reduced blood flow was linked to worse

3-month outcome, as assessed by the GOS and the Disability

Rating scale. Of note, however, was that poor outcome was

defined as ‘dead’ or ‘vegetative’ as per the GOS ratings, yet

the category ‘severe disability’, which applied to most of

the non-APOE-e4 allele bearers, was not included in the

negative outcome group. Consequently, this methodology

may have led the authors to overestimate the impact of the

APOE-e4 allele on poor recovery.

In other studies with larger sample sizes and more com-

prehensive markers of outcome, it was unclear whether valid-

ated assessment procedures were used. An investigation

(Friedman et al., 1999) of 69 patients with predominantly

severe TBI found that patients with the APOE-e4 allele

were almost six times more likely to remain comatose for

more than 7 days and were 14 times less likely to have a

good overall functional outcome 6–8 months after TBI.

This global outcome index was derived from a composite

set of examinations: mobility, seizures, speech, mood and

cognition. However, no mention was made in the protocol

of how the latter two indices were assessed. In addition, the

overall outcome was designated as excellent versus subopti-

mal based on an arbitrary cut-off point. The limitations of this

study were voided by Lichtman et al. (2000), who used the

Functional Independence Measures (FIM) to study the effect

of the APOE-e4 allele on recovery in a group of patients who

had completed a course of acute in-patient rehabilitation. The

FIM assesses a patient’s functioning across six areas: self-

care, sphincter control, mobility, locomotion, communication

and social cognition. Although the APOE-e4 allele was linked

to lower scores on the motor subscale, no association was

found with cognition. When more sensitive psychometric

tests are used, the yield is better, with 6-month correlations

reported between the APOE-e4 allele and memory deficits, as

per the California Verbal Learning Test (Crawford et al.,

2002). However, this relationship did not extend to measures

of executive functioning, and once again mood was not part of

the assessment. This investigation, which also included sub-

jects with mild to moderate head injury, neglected to control

for depression when evaluating cognitive performances

despite accumulating evidence in the literature suggesting

a strong association between major depression and poor

performance on cognitive testing following mild to moderate

TBI (Barth et al., 1983; Bornstein et al., 1989; Levin et al.,

2001; Fann et al., 2001).

In summary, our study, which made use of a well-matched

control group and widely used, validated measures of mood,

behaviour and cognition, failed to elucidate any genetic pre-

disposition to adverse outcome 6 months after trauma. This

finding is of clinical relevance. The emotional (Mooney and

Speed, 2001), physical and economic costs (Feinstein and

Rapoport, 2000; Yasuda et al., 2001) of mild head injury

are considerable. Attempts at providing routine treatment

to all patients have been disappointing in terms of reducing

the morbidity (King et al., 1997; Wade et al., 1997, 1998;

Paniak et al., 1998, 2000). Finding a predictable marker of

poor outcome would offer many advantages, allowing

resources to be focused in the immediate aftermath of injury

on those patients deemed vulnerable. The APOE-e4 allele

offered one possible marker in this regard, but the data

thus far suggest, at least in those with mild to moderate

TBI, that outcome may be more closely linked to other

factors. Future research involving catecholaminergic

2626 L. Chamelian et al.

(McAllister et al., 2004) and 5-HT receptor subtypes (Lopez-

Figueroa et al., 2004; Roth et al., 2004) might offer additional

clues with respect to the genetic influence on outcome follow-

ing mild to moderate TBI. However, before this question can

be answered with greater certainty, the results of a 25-year

follow-up study of patients with severe head injury (Millar

et al., 2003) that failed to find an association between poor

outcome and the APOE genotype need replicating, but this

time in subjects whose brain injuries are milder. Since 15% of

mild TBI patients remain persistently symptomatic 1 year

after injury (Alexander, 1995), a further extension to the

follow-up period may unmask deficits that are in part

genetically modulated.

AcknowledgementsA. F. is supported by funding from the Canadian Institutes of

Health Research, Grant 36535. We would also like to thank

Marilyn Slater, MLT, for molecular genetics testing.

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