Exploring semantic verbal fluency patterns and their relationship to age and Alzheimer's disease in adults with Down syndrome

INTRODUCTION

Adults with Down syndrome (DS) are at ultra-high risk of developing Alzheimer's disease (AD), characterized by poor episodic memory and semantic fluency in the preclinical phase in the general population. We explored semantic fluency performance in DS and its relationship to age, AD, and blood biomarkers.

METHODS

A total of 302 adults with DS at baseline and 87 at follow-up from the London Down Syndrome Consortium cohort completed neuropsychological assessments. Blood biomarkers were measured with the single molecule array technique in a subset of 94 participants.

RESULTS

Poorer verbal fluency performance was observed as age increases. Number of correct words declined in those with AD compared to those without over 2 years and was negatively correlated with neurofilament light (r = -0.37, P = .001) and glial fibrillary acidic protein (r = -0.31, P = .012).

DISCUSSION

Semantic fluency may be useful as an early indicator of cognitive decline and provide additional information on AD-related change, showing associations with biomarkers in DS.

Comparison of resting-state EEG between adults with Down syndrome and typically developing controls

Background

Down syndrome (DS) is the most common genetic cause of intellectual disability (ID) worldwide. Understanding electrophysiological characteristics associated with DS provides potential mechanistic insights into ID, helping inform biomarkers and targets for intervention. Currently, electrophysiological characteristics associated with DS remain unclear due to methodological differences between studies and inadequate controls for cognitive decline as a potential cofounder.

Methods

Eyes-closed resting-state EEG measures (specifically delta, theta, alpha, and beta absolute and relative powers, and alpha peak amplitude, frequency and frequency variance) in occipital and frontal regions were compared between adults with DS (with no diagnosis of dementia or evidence of cognitive decline) and typically developing (TD) matched controls (n = 25 per group).

Results

We report an overall ‘slower’ EEG spectrum, characterised by higher delta and theta power, and lower alpha and beta power, for both regions in people with DS. Alpha activity in particular showed strong group differences, including lower power, lower peak amplitude and greater peak frequency variance in people with DS.

Conclusions

Such EEG ‘slowing’ has previously been associated with cognitive decline in both DS and TD populations. These findings indicate the potential existence of a universal EEG signature of cognitive impairment, regardless of origin (neurodevelopmental or neurodegenerative), warranting further exploration.

Supplementary Information

The online version contains supplementary material available at 10.1186/s11689-021-09392-z.

Optimal age and outcome measures for Alzheimer's disease prevention trials in people with Down syndrome

INTRODUCTION

People with Down syndrome (DS) typically develop Alzheimer's disease (AD) neuropathology before age 40, but a lack of outcome measures and longitudinal data have impeded their inclusion in randomized controlled trials (RCTs).

METHODS

Cohort study. Event-based and dose-response Emax models were fitted to longitudinal cognitive data, to stage AD and determine the earliest ages of decline. Results informed sample size estimations for hypothetical RCTs of disease-modifying treatments that reduced decline by 35% or 75%.

RESULTS

Seventy-five percent of participants progressed or remained stable in the AD staging model; effect sizes varied by age group and tests. Varied treatment effects could be detected with 50-200 people per arm when using sensitive cognitive outcome measures and targeting recruitment to ages 36 to 45 years.

DISCUSSION

Efficient RCTs of AD preventative treatments can be conducted in the DS population using sensitive outcome measures to monitor early decline. Dose-response models could help tailor future RCTs.

Differential Associations of Apolipoprotein E ε4 Genotype With Attentional Abilities Across the Life Span of Individuals With Down Syndrome

IMPORTANCE

Risk of Alzheimer disease (AD) is particularly high for individuals with Down syndrome (DS). The ε4 allele of the apolipoprotein E gene (APOE ε4) is associated with an additional risk for AD. In typical development, there is evidence that the APOE ε4 genotype is associated with an early cognitive advantage. Here we investigate associations of APOE ε4 with attention across the life span of individuals with DS.

OBJECTIVE

To investigate associations between APOE ε4 and attentional abilities in young children and in adults with DS.

DESIGN, SETTINGS, AND PARTICIPANTS

In this cross-sectional study, data were collected from 80 young children with DS (8-62 months of age) and 240 adults with DS (16-71 years of age) during the period from 2013 to 2018 at a research center to examine the association between APOE status (ε4 carrier vs ε4 noncarrier) and attentional abilities.

EXPOSURE

APOE status (ε4 carrier vs ε4 noncarrier).

MAIN OUTCOMES AND MEASURES

For the children, attentional ability was assessed using an eye-tracking paradigm, the gap-overlap task; the size of the gap effect was the primary outcome. For the adults, attentional ability was assessed using the CANTAB simple reaction time task; the standard deviation of response time latencies was the primary outcome. Cross-sectional developmental trajectories were constructed linking attentional ability with age in ε4 carriers and ε4 noncarriers for children and adults separately.

RESULTS

The child sample comprised 23 ε4 carriers and 57 ε4 noncarriers. The adult sample comprised 61 ε4 carriers and 179 ε4 noncarriers. For the children, a significant difference between trajectory intercepts (ηp2 = 0.14) indicated that ε4 carriers (B = 100.24 [95% CI, 18.52-181.96]) exhibited an attentional advantage over ε4 noncarriers (B = 314.78 [95% CI, 252.17-377.39]). There was an interaction between APOE status and age (ηp2 = 0.10); while the gap effect decreased with age for ε4 noncarriers (B = -4.58 [95% CI, -6.67 to -2.48]), reflecting the development of the attention system, there was no change across age in ε4 carriers (B = 0.77 [95% CI, -1.57 to 3.12]). For the adults, there was no main effect of ε4 carrier status, but there was an interaction between APOE status and age (B = 0.02 [95% CI, 0.004-0.07]), so that ε4 carriers had poorer attentional ability than ε4 noncarriers at older ages.

CONCLUSIONS AND RELEVANCE

APOE ε4 is associated with an attentional advantage early in development and a disadvantage later in life for individuals with DS, similar to the pattern reported in typical development. Understanding the differential role of APOE across the life span is an important step toward future interventions.

Health comorbidities and cognitive abilities across the lifespan in Down syndrome

BACKGROUND

Down syndrome (DS) is associated with variable intellectual disability and multiple health and psychiatric comorbidities. The impact of such comorbidities on cognitive outcomes is unknown. We aimed to describe patterns of physical health and psychiatric comorbidity prevalence, and receptive language ability, in DS across the lifespan, and determine relationships with cognitive outcomes.

METHODS

Detailed medical histories were collected and cognitive abilities measured using standardised tests for 602 individuals with DS from England and Wales (age range 3 months to 73 years). Differences in prevalence rates between age groups and between males and females were determined using chi-squared or Fisher's exact tests. In adults, rates for psychiatric comorbidities were compared to expected population rates using standardised morbidity ratios (SMRs). Adapted ANCOVA functions were constructed to explore age and sex associations with receptive language ability across the lifespan, and regression analyses were performed to determine whether the presence of health comorbidities or physical phenotypes predicted cognitive abilities.

RESULTS

Multiple comorbidities showed prevalence differences across the lifespan, though there were few sex differences. In adults, SMRs were increased in males and decreased in females with DS for schizophrenia, bipolar disorder, and anxiety. Further, SMRs were increased in both males and females with DS for dementia, autism, ADHD, and depression, with differences more pronounced in females for dementia and autism, and in males for depression. Across the lifespan, receptive language abilities increasingly deviated from age-typical levels, and males scored poorer than females. Only autism and epilepsy were associated with poorer cognitive ability in those aged 16-35 years, with no relationships for physical health comorbidities, including congenital heart defects.

CONCLUSIONS

Our results indicate the prevalence of multiple comorbidities varies across the lifespan in DS, and in adults, rates for psychiatric comorbidities show different patterns for males and females relative to expected population rates. Further, most health comorbidities are not associated with poorer cognitive outcomes in DS, apart from autism and epilepsy. It is essential for clinicians to consider such differences to provide appropriate care and treatment for those with DS and to provide prognostic information relating to cognitive outcomes in those with comorbidities.

Plasma biomarkers for amyloid, tau, and cytokines in Down syndrome and sporadic Alzheimer's disease

BACKGROUND

Down syndrome (DS), caused by chromosome 21 trisomy, is associated with an ultra-high risk of dementia due to Alzheimer's disease (AD), driven by amyloid precursor protein (APP) gene triplication. Understanding relevant molecular differences between those with DS, those with sporadic AD (sAD) without DS, and controls will aid in understanding AD development in DS. We explored group differences in plasma concentrations of amyloid-β peptides and tau (as their accumulation is a characteristic feature of AD) and cytokines (as the inflammatory response has been implicated in AD development, and immune dysfunction is common in DS).

METHODS

We used ultrasensitive assays to compare plasma concentrations of the amyloid-β peptides Aβ40 and Aβ42, total tau (t-tau), and the cytokines IL1β, IL10, IL6, and TNFα between adults with DS (n = 31), adults with sAD (n = 27), and controls age-matched to the group with DS (n = 27), and explored relationships between molecular concentrations and with age within each group. In the group with DS, we also explored relationships with neurofilament light (NfL) concentration, due to its potential use as a biomarker for AD in DS.

RESULTS

Aβ40, Aβ42, and IL1β concentrations were higher in DS, with a higher Aβ42/Aβ40 ratio in controls. The group with DS showed moderate positive associations between concentrations of t-tau and both Aβ42 and IL1β. Only NfL concentration in the group with DS showed a significant positive association with age.

CONCLUSIONS

Concentrations of Aβ40 and Aβ42 were much higher in adults with DS than in other groups, reflecting APP gene triplication, while no difference in the Aβ42/Aβ40 ratio between those with DS and sAD may indicate similar processing and deposition of Aβ40 and Aβ42 in these groups. Higher concentrations of IL1β in DS may reflect an increased vulnerability to infections and/or an increased prevalence of autoimmune disorders, while the positive association between IL1β and t-tau in DS may indicate IL1β is associated with neurodegeneration. Finally, NfL concentration may be the most suitable biomarker for dementia progression in DS. The identification of such a biomarker is important to improve the detection of dementia and monitor its progression, and for designing clinical intervention studies.

Cognitive markers of preclinical and prodromal Alzheimer's disease in Down syndrome

INTRODUCTION

Down syndrome (DS) is associated with an almost universal development of Alzheimer's disease. Individuals with DS are therefore an important population for randomized controlled trials to prevent or delay cognitive decline, though it is essential to understand the time course of early cognitive changes.

METHODS

We conducted the largest cognitive study to date with 312 adults with DS to assess age-related and Alzheimer's disease-related cognitive changes during progression from preclinical to prodromal dementia, and prodromal to clinical dementia.

RESULTS

Changes in memory and attention measures were most sensitive to early decline. Resulting sample size calculations for randomized controlled trials to detect significant treatment effects to delay decline were modest.

DISCUSSION

Our findings address uncertainties around the development of randomized controlled trials to delay cognitive decline in DS. Such trials are essential to reduce the high burden of dementia in people with DS and could serve as proof-of-principle trials for some drug targets.

Association of Dementia With Mortality Among Adults With Down Syndrome Older Than 35 Years

Importance

This work quantifies the fatal burden of dementia associated with Alzheimer disease in individuals with Down syndrome (DS).

Objective

To explore the association of dementia associated with Alzheimer disease with mortality and examine factors associated with dementia in adults with DS.

Design, Settings and Participants

Prospective longitudinal study in a community setting in England. Data collection began March 29, 2012. Cases were censored on December 13, 2017. The potential sample consisted of all adults 36 years and older from the London Down Syndrome Consortium cohort with 2 data times and dementia status recorded (N = 300); 6 withdrew from study, 28 were lost to follow-up, and 55 had a single data collection point at time of analysis. The final sample consisted of 211 participants, with 503.92 person-years' follow-up.

Exposures

Dementia status, age, sex, APOE genotype, level of intellectual disability, health variables, and living situation.

Main Outcomes and Measures

Crude mortality rates, time to death, and time to dementia diagnosis with proportional hazards of predictors.

Results

Of the 211 participants, 96 were women (45.5%) and 66 (31.3%) had a clinical dementia diagnosis. Twenty-seven participants (11 female; mean age at death, 56.74 years) died during the study period. Seventy percent had dementia. Crude mortality rates for individuals with dementia (1191.85 deaths per 10 000 person-years; 95% CI, 1168.49-1215.21) were 5 times higher than for those without (232.22 deaths per 10 000 person-years; 95% CI, 227.67-236.77). For those with dementia, APOE ε4 carriers had a 7-fold increased risk of death (hazard ratio [HR], 6.91; 95% CI, 1.756-27.195). For those without dementia, epilepsy with onset after age 36 years was associated with mortality (HR, 9.66; 95% CI, 1.59-58.56). APOE ε4 carriers (HR, 4.91; 95% CI, 2.53-9.56), adults with early-onset epilepsy (HR, 3.61; 95% CI, 1.12-11.60), multiple health comorbidities (HR, 1.956; 95% CI, 1.087-3.519), and those living with family (HR, 2.14; 95% CI, 1.08-4.20) received significantly earlier dementia diagnoses.

Conclusions and Relevance

Dementia was associated with mortality in 70% of older adults with DS. APOE ε4 carriers and/or people with multiple comorbid health conditions were at increased risk of dementia and death, highlighting the need for good health care. For those who died without a dementia diagnosis, late-onset epilepsy was the only significant factor associated with death, raising questions about potentially undiagnosed dementia cases in this group.

Comparison of Receptive Verbal Abilities Assessed Using the KBIT-2 and BPVS3 in Adults With Down Syndrome

Down syndrome (DS) is the most common genetic cause of intellectual disability. There is, however, considerable variation in cognitive abilities between those with DS, with some individuals scoring at floor on some tests, particularly for age-standardised outcomes. This variation and these floor effects can pose a problem for comparing and combining study populations when different standardised measures have been used to assess individuals' cognitive abilities, for example combining results across studies to investigate genetic or other factors associated with cognitive abilities. To facilitate this comparison and combination of study populations assessed using different tests of verbal abilities, we administered two commonly used standardised tests of receptive language, the Kaufmann Brief Intelligence Test 2 (KBIT-2) verbal scale and the British Picture Vocabulary Scale 3 (BPVS3) to 34 adults with DS (age range 19-59) to investigate relationships between outcomes for these two tests. We found a very strong correlation between raw scores for the KBIT-2 verbal scale and the BPVS3, and determined equations to convert between scores for the two tests. Intraclass correlations between the two scales for age-equivalents and calculated z scores relative to population norms were also strong, though scores for both outcomes were significantly higher for the KBIT-2 verbal scale compared to the BPVS3. This deviation in scores between the two tests was greater as z scores decreased for both tests (i.e., for lower scoring individuals), with no such relationship observed for age-equivalents. These results indicate the conversion of raw scores between the KBIT-2 verbal scale and the BPVS3 may be a more valid method for the comparison or combination of study samples with DS compared to the use of standardised scores. Such comparisons or combinations will aid our understanding of cognitive variations and factors associated with these variations within the population with DS.

Validating the Cognitive Scale for Down Syndrome (CS-DS) to Detect Longitudinal Cognitive Decline in Adults With Down Syndrome

Down syndrome (DS) is associated with intellectual disability and an ultra-high risk of developing dementia. Informant ratings are invaluable to assess abilities and related changes in adults with DS, particularly for those with more severe intellectual disabilities and/or cognitive decline. We previously developed the informant rated Cognitive Scale for Down Syndrome (CS-DS) to measure everyday cognitive abilities across memory, executive function, and language domains in adults with DS, finding CS-DS scores are a valid measure of general abilities, and are significantly lower for those with noticeable cognitive decline compared to those without decline. To further test the validity of the CS-DS in detecting changes associated with cognitive decline we collected longitudinal data across two time points, approximately 1.5-2 years apart, for 48 adults with DS aged 36 years and over. CS-DS total scores (78.83 ± 23.85 vs. 73.83 ± 25.35, p = 0.042) and executive function scores (46.40 ± 13.59 vs. 43.54 ± 13.60, p = 0.048) significantly decreased between the two time points, with scores in the memory domain trending towards a significant decrease (22.19 ± 8.03 vs. 20.81 ± 8.63, p = 0.064). Adults with noticeable cognitive decline at follow-up showed a trend to significantly greater change in total scores (7.81 ± 16.41 vs. 3.59 ± 16.79, p = 0.067) and significantly greater change in executive function scores (5.13 ± 9.22 vs. 1.72 ± 9.97, p = 0.028) compared to those without decline. Change in total scores showed significant correlations with change in scores from other informant measures of everyday adaptive abilities and symptoms associated with dementia, and participant assessment of general cognitive abilities (all p < 0.005), while change in memory scores (R ² = 0.28, p = 0.001) better predicted change in participant cognitive assessment scores than change in executive function (R ² = 0.15, p = 0.016) or language (R ² = 0.15, p = 0.018) scores. These results suggest informants may better detect changes in the executive function domain, while change in informant rated memory scores best predicts change in assessed cognitive ability. Alternatively, memory domain scores may be sensitive to changes across both early and late cognitive decline, whereas executive function domain scores are more sensitive to changes associated with later noticeable cognitive decline. Our results provide further support for the validity of the CS-DS to assess everyday cognitive abilities and to detect associated longitudinal changes in individuals with DS.

Aging related cognitive changes associated with Alzheimer's disease in Down syndrome

OBJECTIVE

Individuals with Down syndrome (DS) have an extremely high genetic risk for Alzheimer's disease (AD), however, the course of cognitive decline associated with progression to dementia is ill-defined. Data-driven methods can estimate long-term trends from cross-sectional data while adjusting for variability in baseline ability, which complicates dementia assessment in those with DS.

METHODS

We applied an event-based model to cognitive test data and informant-rated questionnaire data from 283 adults with DS (the largest study of cognitive functioning in DS to date) to estimate the sequence of cognitive decline and individuals' disease stage.

RESULTS

Decline in tests of memory, sustained attention/motor coordination, and verbal fluency occurred early, demonstrating that AD in DS follows a similar pattern of change to other forms of AD. Later decline was found for informant measures. Using the resulting staging model, we showed that adults with a clinical diagnosis of dementia and those with APOE 3:4 or 4:4 genotype were significantly more likely to be staged later, suggesting that the model is valid.

INTERPRETATION

Our results identify tests of memory and sustained attention may be particularly useful measures to track decline in the preclinical/prodromal stages of AD in DS whereas informant-measures may be useful in later stages (i.e. during conversion into dementia, or postdiagnosis). These results have implications for the selection of outcome measures of treatment trials to delay or prevent cognitive decline due to AD in DS. As clinical diagnoses are generally made late into AD progression, early assessment is essential.

Neurofilament light as a blood biomarker for neurodegeneration in Down syndrome

Background

Down syndrome (DS) may be considered a genetic form of Alzheimer’s disease (AD) due to universal development of AD neuropathology, but diagnosis and treatment trials are hampered by a lack of reliable blood biomarkers. A potential biomarker is neurofilament light (NF-L), due to its association with axonal damage in neurodegenerative conditions.

Methods

We measured blood NF-L concentrations in 100 adults with DS using Simoa NF-light® assays, and we examined relationships with age as well as cross-sectional and longitudinal dementia diagnosis.

Results

NF-L concentrations increased with age (Spearman’s rho = 0.789, p < 0.001), with a steep increase after age 40, and they were predictive of dementia status (p = 0.022 adjusting for age, sex, and APOE4), but they showed no relationship with long-standing epilepsy or premorbid ability. Baseline NF-L concentrations were associated with longitudinal dementia status.

Conclusions

NF-L is a biomarker for neurodegeneration in DS with potential for use in future clinical trials to prevent or delay dementia.

The relationship between sound-shape matching and cognitive ability in adults with Down syndrome

Down syndrome (DS), the most common genetic cause of intellectual disability, is characterised by a pattern of cognitive deficits hypothesised as relating to later developing neural systems. Multisensory integration (MSI) has been shown to benefit cognitive performance on numerous tasks in the typically developing population and is implicated in the early development of various cognitive processes. Given these developmental links of both MSI and DS it is important to determine the relationship between MSI and DS. This study aimed to characterise sound-shape matching performance in young adults with DS as an indicator of MSI (correct response rate around 90% in typically developing individuals). We further investigated the relationship between task performance and estimated cognitive ability (verbal and non-verbal) in addition to everyday adaptive behavior skills. Those answering correctly (72.5%) scored significantly higher across cognitive and adaptive behavior measures compared to those answering incorrectly. Furthermore, 57.1% of individuals with estimated cognitive ability scores below the median value answered correctly compared to 89.5% of individuals scoring above the median, with similar values found for adaptive behavior skills (57.9% vs 94.4%). This preliminary finding suggests sound-shape matching deficits are relatively common in DS but may be restricted to individuals of lower ability as opposed to being a general characteristic of DS. Further studies investigating aspects of MSI across a range of modalities are necessary to fully characterise the nature of MSI in DS and to explore underlying neural correlates and mechanisms.

The LonDownS adult cognitive assessment to study cognitive abilities and decline in Down syndrome

Background: Down syndrome (DS), the most common genetic cause of intellectual disability, is associated with an ultra-high risk of developing Alzheimer’s disease. However, there is individual variability in the onset of clinical dementia and in baseline cognitive abilities prior to decline, particularly in memory, executive functioning, and motor coordination. The LonDownS Consortium aims to determine risk and protective factors for the development of dementia and factors relating to cognitive abilities in people with DS. Here we describe our cognitive test battery and related informant measures along with reporting data from our baseline cognitive and informant assessments.

Methods: We developed a cognitive test battery to assess general abilities, memory, executive function, and motor coordination abilities in adults with DS, with informant ratings of similar domains also collected, designed to allow for data on a broad range of participants. Participants (n=305) had a range of ages and abilities, and included adults with and without a clinical diagnosis of dementia.

Results: Results suggest the battery is suitable for the majority of adults with DS, although approximately half the adults with dementia were unable to undertake any cognitive task. Many test outcomes showed a range of scores with low floor and ceiling effects. Non-verbal age-adjusted IQ scores had lower floor effects than verbal IQ scores. Before the onset of any cognitive decline, females aged 16-35 showed better verbal abilities compared to males. We also identified clusters of cognitive test scores within our battery related to visuospatial memory, motor coordination, language abilities, and processing speed / sustained attention.

Conclusions: Our further studies will use baseline and longitudinal assessments to explore factors influencing cognitive abilities and cognitive decline related to ageing and onset of dementia in adults with DS.

Developing an Informant Questionnaire for Cognitive Abilities in Down Syndrome: The Cognitive Scale for Down Syndrome (CS-DS)

Down syndrome (DS) is the most common genetic cause of intellectual disability (ID). Abilities relating to executive function, memory and language are particularly affected in DS, although there is a large variability across individuals. People with DS also show an increased risk of developing dementia. While assessment batteries have been developed for adults with DS to assess cognitive abilities, these batteries may not be suitable for those with more severe IDs, dementia, or visual / hearing difficulties. Here we report the development of an informant rated questionnaire, the Cognitive Scale for Down Syndrome (CS-DS), which focuses on everyday abilities relating to executive function, memory and language, and is suitable for assessing these abilities in all adults with DS regardless of cognitive ability. Complete questionnaires were collected about 128 individuals with DS. After final question selection we found high internal consistency scores across the total questionnaire and within the executive function, memory and language domains. CS-DS scores showed a wide range, with minimal floor and ceiling effects. We found high interrater (n = 55) and test retest (n = 36) intraclass correlations. CS-DS scores were significantly lower in those aged 41+ with significant cognitive decline compared to those without decline. Across all adults without cognitive decline, CS-DS scores correlated significantly to measures of general abilities. Exploratory factor analysis suggested five factors within the scale, relating to memory, self-regulation / inhibition, self-direction / initiation, communication, and focussing attention. The CS-DS therefore shows good interrater and test retest reliability, and appears to be a valid and suitable informant rating tool for assessing everyday cognitive abilities in a wide range of individuals with DS. Such a questionnaire may be a useful outcome measure for intervention studies to assess improvements to cognition, in addition to detecting dementia-related cognitive decline. The CS-DS may also be a useful tool for other populations with ID.

Variation in the X-linked EFHC2 gene is associated with social cognitive abilities in males

Females outperform males on many social cognitive tasks. X-linked genes may contribute to this sex difference. Males possess one X chromosome, while females possess two X chromosomes. Functional variations in X-linked genes are therefore likely to impact more on males than females. Previous studies of X-monosomic women with Turner syndrome suggest a genetic association with facial fear recognition abilities at Xp11.3, specifically at a single nucleotide polymorphism (SNP rs7055196) within the EFHC2 gene. Based on a strong hypothesis, we investigated an association between variation at SNP rs7055196 and facial fear recognition and theory of mind abilities in males. As predicted, males possessing the G allele had significantly poorer facial fear detection accuracy and theory of mind abilities than males possessing the A allele (with SNP variant accounting for up to 4.6% of variance). Variation in the X-linked EFHC2 gene at SNP rs7055196 is therefore associated with social cognitive abilities in males.