Study characteristics including the country where the study was conducted, mean age of participants, genotype, study quality number, adaptations, and primary findings of each study
| Study . | Country . | SCD, n/control, n . | Mean age (range), y . | Genotype . | Study quality . | Measures . | Language and test adaptation . | Primary findings . |
|---|---|---|---|---|---|---|---|---|
| Ampomah et al50 | Ghana | 63/60 (age- and education-matched controls) | 29.4 (18-50) | HbSS, HbSC | 4 | WRAT-4 RQCST, Trails A + B, MCST, DSST, grooved pegboard, recognition memory test, ROCF, cognitive features questionnaire | None reported | Individuals with SCD scored lower than the non-SCD comparison group in all cognitive domains Individuals with SCD showed declines in visuospatial ability, executive functioning, and processing speed at 7-year follow-up |
| Castro and Viana43 | Brazil | 64/64 (age- and sex-matched controls) | SCD: 10.8 (7-13), no SCD: 10.9 (7-13) | HbSS, HbSB0 | 3 | WISC-III | None reported | Individuals with SCD had lower scores across all domains assessed (significantly lower processing speed, distraction resistance, and perceptual organization) than individuals without SCD |
| Dias et al51 | Brazil | 60/74 (community controls) | (6-11) | Not reported | 3 | Raskin's optotype letter "E"; Ishihara test; Raven's colored progressive matrices test, special scale; testing trails, parts A and B; 5-digit test; WISC-IV scale digits subtest; Tower of London | Standardized for Brazilian population | Individuals with SCD aged 6-7 years displayed worsened attention interference on 5-digit test Individuals with SCD aged 8-9 years displayed slower execution time in the counting stage Individuals with SCD aged 10-11 years performed worse on working memory than non-SCD individuals |
| Elalfy et al52 | Egypt | 32/11 (community controls) | SCD: 15.25 (3.69), control: 17.73 (4.84) | Not reported | 3 | WAIS-IV, Benton visual retention test | None reported | Nearly 2/3 individuals with SCD had an IQ of <90 |
| Erdem et al53 | Turkey | 100/82 (age-, sex-, and education-matched controls) | Only median reported, SCD: 30 | HbSS | 4 | MoCA | Turkish adaptation of the MoCA54 | Individuals with SCD had significantly lower MoCA scores than individuals without SCD Individuals with SCD had poorer performance in visuospatial skills, executive function, attention, language, abstraction, delayed recall, and orientation History of chronic/frequent headache episodes associated with significantly lower MoCA scores |
| Ezenwosu et al55 | Nigeria | 90/90 (age- and sex-matched classmate controls) | 8.88 (5-11) | HbSS/HbSB0 | 6 | DAPT | Nigerian adaptation56 | Individuals with SCD had significantly lower performance in English language Nonsignificant difference between individuals with and without SCD on DAPT |
| Fernandes et al57 | Brazil | 65/65 (sex- and age-matched) | 9.5 (8-12) | HbSS, HbSC | 4 | Academic performance test, WISC-III | None reported | Individuals with SCD had lower IQ scores than individuals without SCD |
| Green et al58 | Uganda | 265/— | 5.5 (1-12) | HbSS/HbSB0 | 6 | KABC-II, Mullen scales of early learning | Translated into/validated in Luganda59-63 | 3% of children with SCD aged 1-4 years had abnormal scores (−2 or less z scores below age-specific norms) 16.7% of children with SCD aged 5-12 years had abnormal subscale scores with neurocognition related to previous stroke |
| Jacob et al64 | Tanzania | 73/71 (healthy sibling controls) | SCD: 11.9 (6-16), control: 11.1 (6-16) | HbSS/HbSB0 | 4 | WISC-IV (only PSI, PRI, WMI), Raven's standard progressive matrices | Tests administered in Swahili | Individuals with SCD performed worse than siblings on PSI, PRI, and WMI Rates of score improvement were slower for individuals with SCD on coding/cancellation |
| Knight et al65 | West Indies | 60/60 (sex- and age-matched controls) | (15-18) | HbSS | 3 | WISC-R, WAIS-R | test item/direction wording modified for local conditions, vocabulary/picture arrangement subtests eliminated | Individuals with SCD had lower IQ scores than individuals without SCD across domains IQ was not correlated with age and did not differ by sex |
| Matondo et al66 | Tanzania | 233/80 (healthy sibling controls) | (9-15) | HbSS/HbSB0 | 5 | ROCF, KOH’s block design | Validated in an in-house study at Muhimbili University of Health and Allied Sciences | Individuals with SCD displayed greater impairment on an IQ measure than siblings Negative association between age and neurocognitive performance |
| Montanaro et al67 | Nigeria | 68/15 (age-matched sibling controls) | SCD: 8.95 | HbSS, HbSB+, HbSC | 4 | WISC-III, WPPSI | Assessments were adapted to Italian standardization and all tests were administered in Italian | Bilingual immigrant individuals with SCD had a more noticeable and earlier onset of language difficulties compared with monolingual peers with SCD |
| Nunes et al42 | Brazil | 15/— | SCD: 10 (6-15) | HbSS/HbSB0 | 3 | NEPSY-II, WISC-III | Brazilian adaptation of WISC-III | 66.6% of participants performed within normal range, 26.6% scored below average range, and 6.6% scored above average on a measure of IQ Below average performance on at least 1 NEPSY-II subtest for 60% of individuals Individuals with a stroke history had lower performance on overall intellectual ability and across cognitive domains |
| Olatunya et al68 | Southwest Nigeria | 101/101 (sociodemographic-matched classmate controls) | SCD: 9.13, No SCD: 9.20 (4-12) | HbSS/HbSB0 | 5 | DAPT | Validated for Nigerian children55 | No difference between groups in school performance, but school absenteeism was associated with poorer performance across groups School absenteeism independently predicted poor school performance in all participants |
| Oluwole et al69 | Nigeria | 56/44 (healthy siblings and community controls) | SCD: 9.2, No SCD: 9.41 | HbSS | 4 | WISC-IV | English is teaching language of the population thus adaptations did not take place. | Individuals with SCD had poorer neurocognitive performance (IQ and processing speed) than controls Cognitive functioning was correlated with sociodemographic factors |
| Prussien et al70 | Nigeria | 83/— | SCD: 9.10 | HbSS, HbSB0 | 3 | Raven’s standard progressive matrices, Tower of London, WISC-IV | Instructions were translated to Hausa for testing | Children’s average score on Raven’s matrices below normative mean (corresponding IQ = 85) Nigerian children did not differ from US children with SCD on working memory (WISC) Significant association between higher transcranial Doppler velocity and lower executive planning efficiency |
| Rajendran et al71 | India | 22/22 (age-, sex-, and community matched controls) | Both SCD and no SCD: 9.9 (6-15) | HbSS, HbSB0 | 5 | MISIC, CPMS, PGI memory scale | The MISIC is the Indian adaptation of the WISC. Translations to local language of the other measures took place.72 | Individuals with SCD presented with lower IQ scores and tended to have more psychological problems compared with individuals without SCD |
| Rodgers et al73 | Haiti | 22/— | SCD: 24.50 (10-58) | Not reported | 3 | Conners continuous auditory test of attention | None reported | Individuals with SCD had no associations between disordered sleep, attention/emotion regulation, and attention in an impoverished community |
| Salama et al74 | Egypt | 55/55 (age- and sex-matched healthy controls) | SCD:10.7, no SCD: 12.5 | HbSS, HbSB+ | 2 | Stanford Binet intelligence scale | None reported | Over half of individuals with SCD had abnormal IQ scores, whereas individuals without SCD had higher IQ scores |
| Martínez Triana et al75 | Cuba | 119/42 (healthy controls) | SCD: (6-18) | HbSS, HbSC HbBS0, HbSB+ | 3 | WISC, WAIS | Spanish adaptation | Individuals with SCD showed a decrease in IQ compared with individuals without SCD More severe (HbSS and HbSB0) genotypes were associated with a decrease in neurocognition |
| Youssry et al76 | Egypt | 40/— | SCD: (6-20) | HbSS, HbSB0 | 3 | Stanford Binet intelligence test | Adaptation to the Arab Stanford Binet intelligence test | Half of individuals with SCD had a below-average IQ No association between SES and IQ |
| Study . | Country . | SCD, n/control, n . | Mean age (range), y . | Genotype . | Study quality . | Measures . | Language and test adaptation . | Primary findings . |
|---|---|---|---|---|---|---|---|---|
| Ampomah et al50 | Ghana | 63/60 (age- and education-matched controls) | 29.4 (18-50) | HbSS, HbSC | 4 | WRAT-4 RQCST, Trails A + B, MCST, DSST, grooved pegboard, recognition memory test, ROCF, cognitive features questionnaire | None reported | Individuals with SCD scored lower than the non-SCD comparison group in all cognitive domains Individuals with SCD showed declines in visuospatial ability, executive functioning, and processing speed at 7-year follow-up |
| Castro and Viana43 | Brazil | 64/64 (age- and sex-matched controls) | SCD: 10.8 (7-13), no SCD: 10.9 (7-13) | HbSS, HbSB0 | 3 | WISC-III | None reported | Individuals with SCD had lower scores across all domains assessed (significantly lower processing speed, distraction resistance, and perceptual organization) than individuals without SCD |
| Dias et al51 | Brazil | 60/74 (community controls) | (6-11) | Not reported | 3 | Raskin's optotype letter "E"; Ishihara test; Raven's colored progressive matrices test, special scale; testing trails, parts A and B; 5-digit test; WISC-IV scale digits subtest; Tower of London | Standardized for Brazilian population | Individuals with SCD aged 6-7 years displayed worsened attention interference on 5-digit test Individuals with SCD aged 8-9 years displayed slower execution time in the counting stage Individuals with SCD aged 10-11 years performed worse on working memory than non-SCD individuals |
| Elalfy et al52 | Egypt | 32/11 (community controls) | SCD: 15.25 (3.69), control: 17.73 (4.84) | Not reported | 3 | WAIS-IV, Benton visual retention test | None reported | Nearly 2/3 individuals with SCD had an IQ of <90 |
| Erdem et al53 | Turkey | 100/82 (age-, sex-, and education-matched controls) | Only median reported, SCD: 30 | HbSS | 4 | MoCA | Turkish adaptation of the MoCA54 | Individuals with SCD had significantly lower MoCA scores than individuals without SCD Individuals with SCD had poorer performance in visuospatial skills, executive function, attention, language, abstraction, delayed recall, and orientation History of chronic/frequent headache episodes associated with significantly lower MoCA scores |
| Ezenwosu et al55 | Nigeria | 90/90 (age- and sex-matched classmate controls) | 8.88 (5-11) | HbSS/HbSB0 | 6 | DAPT | Nigerian adaptation56 | Individuals with SCD had significantly lower performance in English language Nonsignificant difference between individuals with and without SCD on DAPT |
| Fernandes et al57 | Brazil | 65/65 (sex- and age-matched) | 9.5 (8-12) | HbSS, HbSC | 4 | Academic performance test, WISC-III | None reported | Individuals with SCD had lower IQ scores than individuals without SCD |
| Green et al58 | Uganda | 265/— | 5.5 (1-12) | HbSS/HbSB0 | 6 | KABC-II, Mullen scales of early learning | Translated into/validated in Luganda59-63 | 3% of children with SCD aged 1-4 years had abnormal scores (−2 or less z scores below age-specific norms) 16.7% of children with SCD aged 5-12 years had abnormal subscale scores with neurocognition related to previous stroke |
| Jacob et al64 | Tanzania | 73/71 (healthy sibling controls) | SCD: 11.9 (6-16), control: 11.1 (6-16) | HbSS/HbSB0 | 4 | WISC-IV (only PSI, PRI, WMI), Raven's standard progressive matrices | Tests administered in Swahili | Individuals with SCD performed worse than siblings on PSI, PRI, and WMI Rates of score improvement were slower for individuals with SCD on coding/cancellation |
| Knight et al65 | West Indies | 60/60 (sex- and age-matched controls) | (15-18) | HbSS | 3 | WISC-R, WAIS-R | test item/direction wording modified for local conditions, vocabulary/picture arrangement subtests eliminated | Individuals with SCD had lower IQ scores than individuals without SCD across domains IQ was not correlated with age and did not differ by sex |
| Matondo et al66 | Tanzania | 233/80 (healthy sibling controls) | (9-15) | HbSS/HbSB0 | 5 | ROCF, KOH’s block design | Validated in an in-house study at Muhimbili University of Health and Allied Sciences | Individuals with SCD displayed greater impairment on an IQ measure than siblings Negative association between age and neurocognitive performance |
| Montanaro et al67 | Nigeria | 68/15 (age-matched sibling controls) | SCD: 8.95 | HbSS, HbSB+, HbSC | 4 | WISC-III, WPPSI | Assessments were adapted to Italian standardization and all tests were administered in Italian | Bilingual immigrant individuals with SCD had a more noticeable and earlier onset of language difficulties compared with monolingual peers with SCD |
| Nunes et al42 | Brazil | 15/— | SCD: 10 (6-15) | HbSS/HbSB0 | 3 | NEPSY-II, WISC-III | Brazilian adaptation of WISC-III | 66.6% of participants performed within normal range, 26.6% scored below average range, and 6.6% scored above average on a measure of IQ Below average performance on at least 1 NEPSY-II subtest for 60% of individuals Individuals with a stroke history had lower performance on overall intellectual ability and across cognitive domains |
| Olatunya et al68 | Southwest Nigeria | 101/101 (sociodemographic-matched classmate controls) | SCD: 9.13, No SCD: 9.20 (4-12) | HbSS/HbSB0 | 5 | DAPT | Validated for Nigerian children55 | No difference between groups in school performance, but school absenteeism was associated with poorer performance across groups School absenteeism independently predicted poor school performance in all participants |
| Oluwole et al69 | Nigeria | 56/44 (healthy siblings and community controls) | SCD: 9.2, No SCD: 9.41 | HbSS | 4 | WISC-IV | English is teaching language of the population thus adaptations did not take place. | Individuals with SCD had poorer neurocognitive performance (IQ and processing speed) than controls Cognitive functioning was correlated with sociodemographic factors |
| Prussien et al70 | Nigeria | 83/— | SCD: 9.10 | HbSS, HbSB0 | 3 | Raven’s standard progressive matrices, Tower of London, WISC-IV | Instructions were translated to Hausa for testing | Children’s average score on Raven’s matrices below normative mean (corresponding IQ = 85) Nigerian children did not differ from US children with SCD on working memory (WISC) Significant association between higher transcranial Doppler velocity and lower executive planning efficiency |
| Rajendran et al71 | India | 22/22 (age-, sex-, and community matched controls) | Both SCD and no SCD: 9.9 (6-15) | HbSS, HbSB0 | 5 | MISIC, CPMS, PGI memory scale | The MISIC is the Indian adaptation of the WISC. Translations to local language of the other measures took place.72 | Individuals with SCD presented with lower IQ scores and tended to have more psychological problems compared with individuals without SCD |
| Rodgers et al73 | Haiti | 22/— | SCD: 24.50 (10-58) | Not reported | 3 | Conners continuous auditory test of attention | None reported | Individuals with SCD had no associations between disordered sleep, attention/emotion regulation, and attention in an impoverished community |
| Salama et al74 | Egypt | 55/55 (age- and sex-matched healthy controls) | SCD:10.7, no SCD: 12.5 | HbSS, HbSB+ | 2 | Stanford Binet intelligence scale | None reported | Over half of individuals with SCD had abnormal IQ scores, whereas individuals without SCD had higher IQ scores |
| Martínez Triana et al75 | Cuba | 119/42 (healthy controls) | SCD: (6-18) | HbSS, HbSC HbBS0, HbSB+ | 3 | WISC, WAIS | Spanish adaptation | Individuals with SCD showed a decrease in IQ compared with individuals without SCD More severe (HbSS and HbSB0) genotypes were associated with a decrease in neurocognition |
| Youssry et al76 | Egypt | 40/— | SCD: (6-20) | HbSS, HbSB0 | 3 | Stanford Binet intelligence test | Adaptation to the Arab Stanford Binet intelligence test | Half of individuals with SCD had a below-average IQ No association between SES and IQ |
CPMS, childhood psychopathology measurement schedule; DSST, digit symbol substitution test; Hb, hemoglobin; KABC-II, Kaufman assessment battery for children, second edition; MCST, modified card-sorting test; NEPSY-II, a developmental neuropsychological assessment; PRI, perceptual reasoning index; PSI, processing speed index; ROCF, Rey-Osterrieth complex figure test; RQCST, revised quick cognitive screening test; SES, socioeconomic status; WAIS-IV, WAIS fourth edition; WAIS-R, WAIS revised; WISC-III, WISC third edition; WISC-IV, WISC fourth edition; WISC-R, WISC revised; WMI, working memory index; WRAT-4, wide range achievement test fourth edition.