Article Commentary: Considering Sex as a Biological Variable in Biomedical Research

The Appropriateness of Medical Devices Is Strongly Influenced by Sex and Gender

Until now, research has been performed mainly in men, with a low recruitment of women; consequentially, biological, physiological, and physio-pathological mechanisms are less understood in women. Obviously, without data obtained on women, it is impossible to apply the results of research appropriately to women. This issue also applies to medical devices (MDs), and numerous problems linked to scarce pre-market research and clinical trials on MDs were evidenced after their introduction to the market. Globally, some MDs are less efficient in women than in men and sometimes MDs are less safe for women than men, although recently there has been a small but significant decrease in the sex and gender gap. As an example, cardiac resynchronization defibrillators seem to produce more beneficial effects in women than in men. It is also important to remember that MDs can impact the health of healthcare providers and this could occur in a sex- and gender-dependent manner. Recently, MDs' complexity is rising, and to ensure their appropriate use they must have a sex-gender-sensitive approach. Unfortunately, the majority of physicians, healthcare providers, and developers of MDs still believe that the human population is only constituted by men. Therefore, to overcome the gender gap, a real collaboration between the inventors of MDs, health researchers, and health providers should be established to test MDs in female and male tissues, animals, and women.

Biological sex-related differences in whole-body coordination during standing turns in healthy young adults

Biological sexes (male and female) have been reported to influence postural control and balance due to differences in musculoskeletal structures, hormonal factors, and neuromuscular control. These factors can contribute to the turning performance, potentially leading to an increased incidence of falls, particularly during turning. Therefore, this study aimed to explore the whole-body coordination and stepping characteristics and during standing turns in healthy adults to determine the effects of biological sex and turn speed. Fifty participants (25 males and 25 females) completed 180° standing turns on level ground. Inertial Measurement Units (XSENS) were used to measure whole-body movement turning kinematics and stepping characteristics. Moreover, clinical outcome of dynamic balance was measured by the Timed Up and Go (TUG). Participants were randomly tasked to turn at three speeds; fast, moderate, or slow to the left and right sides. Mann-Whitney U tests were used to compare the independent variables between male and females, and Friedman tests with Dunn's tests for pairwise comparisons were used to compare between the three turning speeds within the two groups. The results demonstrated that significant differences were seen between males and females during fast turning for the leading foot onset (p = 0.048) and in the slow speed for the total step (p = 0.033), showing that these were greater in female with an increase in turn speed. In addition, significant differences were seen only in the males when comparing different speeds in the trailing foot onset latency (p = 0.035), step size (p = 0.009), and total number of steps (p = 0.002), while in the females a significant difference was found in peak head yaw velocity between fast and slow turn speeds, and moderate and slow turn speeds. Finally, there was no significant difference in TUG between groups. Therefore, these findings show differences between biological sexes in the response to whole-body coordination and step characteristics, indicating that females tend to have more changes in stepping characteristics compared to males due to differences in turning speed. This can affect their balance and stability. However, the differences in biological sex did not impact the dynamic balance and fall risk due to the lack of a significant difference shown by TUG between males and females.

Why and How to Account for Sex and Gender in Brain and Behavioral Research

Long overlooked in neuroscience research, sex and gender are increasingly included as key variables potentially impacting all levels of neurobehavioral analysis. Still, many neuroscientists do not understand the difference between the terms "sex" and "gender," the complexity and nuance of each, or how to best include them as variables in research designs. This TechSights article outlines rationales for considering the influence of sex and gender across taxa, and provides technical guidance for strengthening the rigor and reproducibility of such analyses. This guidance includes the use of appropriate statistical methods for comparing groups as well as controls for key covariates of sex (e.g., total intracranial volume) and gender (e.g., income, caregiver stress, bias). We also recommend approaches for interpreting and communicating sex- and gender-related findings about the brain, which have often been misconstrued by neuroscientists and the lay public alike.

Why do we need sex-balanced studies of autism?

Males are diagnosed with autism much more frequently than females, and most research study samples reflect this male predominance. The result is that autistic females are understudied. There is a critical need to increase our understanding of autistic females, both biologically and clinically. The only way to do this is to recruit sex-balanced cohorts in studies so that similarities and differences between males and females can be evaluated in all autism research studies. The purpose of this commentary is to (1) provide historical context about how females came to be under-represented in all research, not just in the field of autism and (2) learn from other areas of health and medicine about the potentially dire consequences of not studying both sexes, and (3) draw attention to the need to recruit sex-balanced cohorts in autism research, particularly in neuroimaging studies.

Sex and Gender Multidimensionality in Epidemiologic Research

Along with age and race, sex has historically been a core stratification and control variable in epidemiologic research. While in recent decades research guidelines and institutionalized requirements have incorporated an approach differentiating biological sex from social gender, neither sex nor gender is itself a unidimensional construct. The conflation of dimensions within and between sex and gender presents a validity issue wherein proxy measures are used for dimensions of interest, often without explicit acknowledgement or evaluation. Here, individual-level dimensions of sex and gender are outlined as a guide for epidemiologists, and 2 case studies are presented. The first case study demonstrates how unacknowledged use of a sex/gender proxy for a sexed dimension of interest (uterine status) resulted in decades of cancer research misestimating risks, racial disparities, and age trends. The second illustrates how a multidimensional sex and gender framework may be applied to strengthen research on coronavirus disease 2019 incidence, diagnosis, morbidity, and mortality. Considerations are outlined, including: 1) addressing the match between measures and theory, and explicitly acknowledging and evaluating proxy use; 2) improving measurement across dimensions and social ecological levels; 3) incorporating multidimensionality into research objectives; and 4) interpreting sex, gender, and their effects as biopsychosocial.

Gender Differences in Visual Functioning Questionnaire Scores among Patients with Age-Related Macular Degeneration

PURPOSE

To examine gender differences in visual functioning using the National Eye Institute Visual Functioning Questionnaire-25 (VFQ-25) in a Colorado cohort of patients with age-related macular degeneration (AMD).

METHODS

A retrospective cohort study was conducted using a registry of AMD patients who attended the Sue Anschutz-Rodgers Eye Center (2014 to 2019). Demographic, clinical, and image data were collected, and AMD was categorized as Early/Intermediate AMD, or unilateral/bilateral neovascular (NV) AMD, geographic atrophy (GA), or Both Advanced using the Beckman Classification. Each patient completed the VFQ-25, which evaluates visual functioning, generating a composite score and subscale scores for vision-specific activities. Univariate and multivariable general linear models were used to estimate the associations between gender and VFQ-25 scores with parameter estimates (PE) and standard errors (SE).

RESULTS

Among 739 patients with AMD, 294 (39.8%), 115 (15.6%), 168 (22.7%), and 162 (21.9%) were diagnosed with Early/Intermediate AMD, GA, NV AMD, and Both Advanced, respectively. Adjusted for AMD classification, age and habitual visual acuity in the better-seeing and worse-seeing eyes, female gender was not significantly associated with lower composite VFQ-25 scores (PE (SE): -1.2 (0.9), p = .193), and was significantly associated with reportedly worse ocular pain and driving subscale scores (PE (SE): -4.6 (1.0), p < .0001 and -9.1 (2.1), p < .0001, respectively).

CONCLUSION

Gender plays a role in reported driving activities and ocular pain among patients with AMD. This may need to be accounted for in future research related to the use of VFQ-25 for AMD.

Sex and gender considerations in reporting guidelines for health research: a systematic review

Background

Despite growing recognition of the importance of sex and gender considerations in health research, they are rarely integrated into research design and reporting. We sought to assess the integration of sex, as a biological attribute, and gender, as a socially constructed identity, in published reporting guidelines.

Methods

We conducted a systematic review of published reporting guidelines listed on the EQUATOR website (www.equator-nework.org) from inception until December 2018. We selected all reporting guidelines (original and extensions) listed in the EQUATOR library. We used EndNote Citation Software to build a database of the statements of each guideline identified as a "full bibliographic reference" and retrieved the full texts. Reviewers independently extracted the data on use of sex and gender terms from the checklist/abstract/main text of guidelines. Data were analyzed using descriptive statistics and narrative synthesis.

Results

A total of 407 reporting guidelines were included; they were published between 1995 and 2018. Of the 407 guidelines, 235 (57.7%) mentioned at least one of the sex- and gender-related words. In the checklist of the reporting guidelines (n = 363), “sex” and “gender” were mentioned in 50 (13.8%) and 40 (11%), respectively. Only one reporting guideline met our criteria (nonbinary, appropriate categorization, and non-interchangeability) for correct use of sex and gender concepts. Trends in the use of "sex" and "gender" in the checklists showed that the use of “sex” only started in 2003, while “gender” has been in use since 1996.

Conclusions

We assessed the integration of sex and gender in reporting guidelines based on the use of sex- and gender-related words. Our findings showed a low use and integration of sex and gender concepts and their incorrect use. Authors of reporting guidelines should reduce this gap for a better use of research knowledge.

Trial registration PROSPERO no. CRD42019136491.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13293-021-00404-0.

Omission of sex and gender considerations is a recurring deficiency in research design and reporting

Integration of sex and gender considerations in health research reporting guidelines is very low

Three criteria were used to assess correct use of sex and gender concepts

Only one reporting guideline met the three criteria

A call to action is made to address these deficiencies

Co-production, multiplied: Enactments of sex as a biological variable in US biomedicine

In 2016 the US National Institutes of Health introduced a policy mandating consideration of Sex as a Biological Variable (SABV) in preclinical research. In this article, I ask what, precisely, is meant by the designation of sex as a 'biological variable', and how has its inclusion come to take the form of a policy mandate? Given the well documented complexity of 'sex' and the degree to which it is politically and scientifically contested, its enactment via policy as a biological variable is not a given. I explore how sex is multiply enacted in efforts to legitimate and realize the SABV policy and consider how the analytical lens of co-production sheds light on how and why this occurs. I show that the policy works to reassert scientific and political order by addressing two institutional concerns: the so-called reproducibility crisis in preclinical research, and pervasive gender inequality across the institution of biomedicine. From here, the entity that underpins this effort - sex as a biological variable - becomes more than one thing, with enactments ranging from an assigned category, to an outcome, to a causal biological force in its own right. Sex emerges as simultaneously entangled with yet distinct from gender, and binary (female/male) yet complex in its variation. I suggest that it is in the very attempt to delineate natural from social order, and in the process create the conditions to privilege a particular kind of science and account of embodied difference, that ontological multiplicity becomes readily visible. That this multiplicity goes unrecognized points to the unifying role of an overarching ideological commitment to sex as a presumed binary and biological scientific object, the institutional dominance of which is never guaranteed.

Diet-induced obesity in genetically diverse collaborative cross mouse founder strains reveals diverse phenotype response and amelioration by quercetin treatment in 129S1/SvImJ, PWK/EiJ, CAST/PhJ, and WSB/EiJ mice

Significant evidence suggests protective effects of flavonoids against obesity in animal models, but these often do not translate to humans. One explanation for this disconnect is use of a few mouse strains (notably C57BL/6 J) in obesity studies. Obesity is a multifactorial disease. The underlying causes are not fully replicated by the high-fat C57BL/6 J model, despite phenotypic similarities. Furthermore, the impact of genetic factors on the activities of flavonoids is unknown. This study was designed to explore how diverse mouse strains respond to diet-induced obesity when fed a representative flavonoid. A subset of Collaborative Cross founder strains (males and females) were placed on dietary treatments (low-fat, high-fat, high-fat with quercetin, high-fat with quercetin and antibiotics) longitudinally. Diverse responses were observed across strains and sexes. Quercetin appeared to moderately blunt weight gain in male C57 and both sexes of 129S1/SvImJ mice, and slightly increased weight gain in female C57 mice. Surprisingly, quercetin dramatically blunted weight gain in male, but not female, PWK/PhJ mice. For female mice, quercetin blunted weight gain (relative to the high-fat phase) in CAST/PhJ, PWK/EiJ and WSB/EiJ mice compared to C57. Antibiotics did not generally result in loss of protective effects of quercetin. This highlights complex interactions between genetic factors, sex, obesity stimuli, and flavonoid intake, and the need to move away from single inbred mouse models to enhance translatability to diverse humans. These data justify use of genetically diverse Collaborative Cross and Diversity Outbred models which are emerging as invaluable tools in the field of personalized nutrition.

Randomized placebo-controlled clinical trial investigating the effect of antioxidants and a vasodilator on overall safety and residual hearing preservation in cochlear implant patients

BACKGROUND

The standard therapy for patients suffering from sensorineural hearing loss is cochlear implantation. The insertion of the electrode array into the cochlea, with potential mechanical trauma and the presence of this foreign body inside the cochlea, may lead to free radical formation and reduced blood perfusion of the cochlea which can result in a loss of residual hearing. Studies have suggested that a particular combination of the antioxidants vitamins A, C and E as well as the vasodilator magnesium (together: ACEMg) may protect the residual hearing.

METHODS

The potential protective effect of ACEMg on residual hearing preservation in cochlear implant (CI) patients was investigated in a single-centre, randomized, placebo-controlled, double-blind phase II clinical trial. CI candidates with some residual hearing in low frequencies receiving MED-EL implants of different FLEX electrode array lengths were treated with ACEMg tablets or placebo respectively 2 days preoperatively and up to 3 months postoperatively. The study objective was to demonstrate that ACEMg is more efficacious than placebo in preserving residual hearing during cochlear implantation by comparing the hearing loss (change in hearing thresholds at 500 Hz from baseline) 3 months after the first fitting between the two treatment groups and to investigate the treatments' safety.

RESULTS

Fifty-one patients were included in the study, which had to be terminated before the recruitment goal was reached because of IMP-resupply mismanagement of one partner. In the intention-to-treat population, 25 patients were treated with ACEMg and 24 patients with placebo. The mean hearing loss at 500 Hz was (± 15.84) 30.21 dB (placebo) or (± 17.56) 26.00 dB (ACEMg) 3 months after the initial fitting. Adjusting the postoperative hearing loss for the baseline residual hearing, planned electrode length and surgeon results in 8.01 dB reduced hearing loss in ACEMg-treated patients compared to placebo-treated ones. The safety analysis revealed that ACEMg was generally well-tolerated with adverse event frequencies below the placebo level.

CONCLUSION

This is the first clinical trial investigating a drug effect on residual hearing in CI patients. These first-in-man data may suggest that a perioperative oral administration of ACEMg is safe and may provide protection of residual hearing in CI patients.

TRIAL REGISTRATION

EU Clinical Trial Register No. 2012-005002-22 . Registered on 6 December 2013.

FUNDING

European Commission FP7-HEALTH-2012-INNOVATION-2.

Sex/gender differences in brain function and structure in alcohol use: A narrative review of neuroimaging findings over the last 10 years

Over the last 10 years, rates of alcohol use disorder (AUD) have increased in women by 84% relative to a 35% increase in men. Rates of alcohol use and high-risk drinking have also increased in women by 16% and 58% relative to a 7% and 16% increase in men, respectively, over the last decade. This robust increase in drinking among women highlights the critical need to identify the underlying neural mechanisms that may contribute to problematic alcohol consumption across sex/gender (SG), especially given that many neuroimaging studies are underpowered to detect main or interactive effects of SG on imaging outcomes. This narrative review aims to explore the recent neuroimaging literature on SG differences in brain function and structure as it pertains to alcohol across positron emission tomography, magnetic resonance imaging, and functional magnetic resonance imaging modalities in humans. Additional work using magnetic resonance spectroscopy, diffusion tensor imaging, and event-related potentials to examine SG differences in AUD will be covered. Overall, current research on the neuroimaging of AUD, alcohol consumption, or risk of AUD is limited, and findings are mixed regarding the effect of SG on neurochemical, structural, and functional mechanisms associated with AUD. We address SG disparities in the neuroimaging of AUD and propose a call to action to include women in brain imaging research. Future studies are crucial to our understanding of the neurobiological underpinnings of AUD across neural systems and the vulnerability for AUD among women and men.

Thymus Regeneration and Future Challenges

Thymus regenerative therapy implementation is severely obstructed by the limited number and expansion capacity in vitro of tissue-specific thymic epithelial stem cells (TESC). Current solutions are mostly based on growth factors that can drive differentiation of pluripotent stem cells toward tissue-specific TESC. Target-specific small chemical compounds represent an alternative solution that could induce and support the clonal expansion of TESC and reversibly block their differentiation into mature cells. These compounds could be used both in the composition of culture media designed for TESC expansion in vitro, and in drugs development for thymic regeneration in vivo. It should allow reaching the ultimate objective - autologous thymic tissue regeneration in paediatric patients who had their thymus removed in the course of cardiac surgery.

Sex still matters: has the prevalence of male-only studies of drug effects on rodent behaviour changed during the past decade?

During the past 10 years, for a number of biomedical disciplines, including behavioural pharmacology, there have been appeals to include both sexes in animal studies of processes that are not sex specific. In 2007, a survey of experimental studies of drug or other chemical effects on rodent behaviour, published in five prominent journals over 20 months (February 2005 to September 2006, inclusive), revealed that 85% of these conducted with rats and 78% of these conducted with mice involved males only. This was in spite of the evidence of sex differences in responsiveness to an increasing number of compounds. To see if the situation has improved, the survey was repeated with the same journals for a comparable period namely, February 2016 to September 2017 (inclusive). Even though there have been repeated appeals for biomedical research that is not sex specific to involve both sexes, it was apparent that little has changed since 2005-2006, as 82% of rat and 75% of mouse studies were again conducted with males only. However, there was an increase in studies with mice, which may be owing to a greater interest in genetic factors. The male-only situation could be rectified by appropriate funding agencies and journals that publish behavioural pharmacological research insisting that both sexes must be included in research that is not sex specific along with valid scientific justification for single-sex studies, as now typifies some other disciplines.

Bolus Airway Invasion Observed During Videofluoroscopy in Healthy, Non-dysphagic Community-Dwelling Adults

OBJECTIVES

Typical aging may result in subclinical swallowing alterations (presbyphagia), which can place an individual at risk for dysphagia-related conditions, such as aspiration pneumonia, secondary to loss of functional reserve and rising incidence of age-related diseases associated with dysphagia. The purpose of this study was to investigate occurrence of airway invasion among healthy, nondysphagic community-dwelling adults. Further, we tested for differences of airway invasion across age categories and between sexes.

METHODS

Each eligible participant underwent a videofluoroscopic swallow study using a standardized approach of various volumes and viscosities. Ten swallows observed in the lateral viewing plane was assessed for observation of bolus airway invasion using the Penetration-Aspiration Scale (PAS) scoring system. Eligible participants (N = 195) were categorized according to 1 of 3 age categories (21-39 years, 40-59 years, 60 years and older) and sex (male, female) for analyses.

RESULTS

Out of 1936 swallows analyzed, we observed penetration in 113 swallows (5.8%) and aspiration in 6 swallows (0.3%). Majority (98%) of bolus airway invasion events occurred during the swallow. Mean or worst PAS scores did not significantly differ across age categories or between sexes. The odds ratios of PAS impairment between age categories did not reveal any significant differences. Males were more likely to have impaired PAS scores relative to females (odds ratio [OR] = 3.5; P = .01).

CONCLUSIONS

Entrance of ingested material into the airway observed during videofluoroscopy is uncommon in healthy adults, which helps support the notion that aging may not directly correlate with increased risk of aspiration. Rather, the increased risk of aspiration observed in the aging population may result from the increased incidence of neurological and other diseases with dysphagia as common sequelae with advancing age. Future investigations should compare age-matched healthy controls with a diseased population (eg, cerebral vascular accident) to further explore the relationship between aspiration risk as a function of age compared to consequence of disease/injury.

The importance of selection and reporting of the sex of experimental animals

Biased use of males and females in animal studies or omitting specific details of the sex of animals used in publications limits reproducibility, hampers the pace and likelihood of new discoveries and invites adverse events in ensuing clinical research. Hence unbiased use of males and females in animal studies and specific reporting of animal details are increasingly required by funding bodies and scientific journals worldwide. An analysis to determine how males and females are used in animal studies involving the Commonwealth Scientific and Industrial Research Organisation (CSIRO) was undertaken as part of a process to review and further support best practice. In the study 178 publications that contain animal studies and include CSIRO researchers published between January 2014 and December 2016 were analysed for the sex of animals used. The overall sex distribution was males only 26.4% (47/178), females only 15.7% (28/178), males and females 18.0% (32/178) and sex of animals unspecified 39.9% (71/178). Reasons for this distribution include species biology, farming practices and commercial relevance. Although including sex as an experimental variable provides the most information, using both sexes in an animal study requires careful consideration and planning. Furthermore, there are valid biological and experimental reasons why sex distribution in a study may not be balanced. Biological reasons include cases where the severity of disease in a given model differs between males and females, superior husbandry or production traits in one sex and hermaphroditic species that change sex with age. Examples where experiments can only be undertaken in one sex of animal include animal models of female breast cancer, female reproductive traits, male fertility studies and post-castration welfare outcomes. Where there is no biological or experimental reason for using a single sex of animal, future studies should obtain an estimate of sex effect either from the literature or with a pilot study, and experiments should be planned and reported accordingly.

Working Together to Address Women's Health in Research and Drug Development: Summary of the 2017 Women's Health Congress Preconference Symposium

Historically, women have been underrepresented in clinical research, requiring physicians to extrapolate medical recommendations for women from clinical research done in cohorts consisting predominantly of male participants. While government-funded clinical research has achieved gender parity in phase-3 clinical trials across many biomedical disciplines, improvements are still needed in several facets of women's health research, such as the inclusion of women in early-phase clinical trials, the inclusion of pregnant women and women with physical and intellectual disabilities, the consideration of sex as a biological variable in preclinical research, and the analysis and reporting of sex and gender differences across the full biomedical research continuum. The National Institutes of Health (NIH) Office of Research on Women's Health and the Office of Women's Health of the U.S. Food and Drug Administration (FDA) cosponsored a preconference symposium at the 25th Annual Women's Health Congress, held in Arlington, VA in April, 2017, to highlight gains made and remaining needs regarding the representation of women in clinical research, to introduce innovative procedures and technologies, and to outline revised policy for future studies. Six speakers presented information on a range of subjects related to the representation of women in clinical research and federal initiatives to advance precision medicine. Topics included the following: the return on investment from the NIH-funded Women's Health Initiative; progress in including women in clinical trials for FDA-approved drugs and products; the importance of clinical trials in pregnant women; FDA initiatives to report drug safety during pregnancy; the NIH-funded All of Us Research Program; and efforts to enhance FDA transparency and communications, including the introduction of Drug Trials Snapshots. This article summarizes the major points of the presentations and the discussions that followed.

Reversing the Trends toward Shorter Lives and Poorer Health for U.S. Women: A Call for Innovative Interdisciplinary Research

The United States (U.S.) is a leader and innovator in biomedicine, yet trails behind for many key health indicators, especially for women. This paper highlights key evidence indicating that not only is the state of women's health in the U.S. lagging, but it is at risk for falling off the curve. Women's health care remains fragmented; research in the field can be disconnected and difficult to integrate across disciplines-silos prevail. Structural obstacles contribute to this lack of cohesion, and innovative, interdisciplinary research approaches which integrate the multidimensional aspects of sex and gender, and race and ethnicity, with a life course perspective are sorely needed. Such synergistic, scientific strategies have the potential to reverse the trend towards shorter life expectancy and poorer health for women in the U.S. The National Institute for Health (NIH) seeks to raise the bar for the health of all women by tackling these issues through enhancing the relevance of biomedical research to the health of women and driving the sustained advancement of women in biomedical careers.

Sex and Gender Differences Research Design for Basic, Clinical, and Population Studies: Essentials for Investigators

A sex- and gender-informed perspective increases rigor, promotes discovery, and expands the relevance of biomedical research. In the current era of accountability to present data for males and females, thoughtful and deliberate methodology can improve study design and inference in sex and gender differences research. We address issues of motivation, subject selection, sample size, data collection, analysis, and interpretation, considering implications for basic, clinical, and population research. In particular, we focus on methods to test sex/gender differences as effect modification or interaction, and discuss why some inferences from sex-stratified data should be viewed with caution. Without careful methodology, the pursuit of sex difference research, despite a mandate from funding agencies, will result in a literature of contradiction. However, given the historic lack of attention to sex differences, the absence of evidence for sex differences is not necessarily evidence of the absence of sex differences. Thoughtfully conceived and conducted sex and gender differences research is needed to drive scientific and therapeutic discovery for all sexes and genders.