Grandmaternal pre-pregnancy body mass index and infant birthweight: a mediation analysis of maternal pre-pregnancy body mass index.

The objectives of this study were to examine the total effect of grandmaternal [G0] pre-pregnancy body mass index (BMI) on infant [G2] birthweight z-score and to quantify the mediation role of maternal [G1] pre-pregnancy BMI. Data were extracted from the Nova Scotia 3G Multigenerational Cohort. The association between G0 pre-pregnancy BMI and G2 birthweight z-score and the mediated effect by G1 pre-pregnancy BMI were estimated using g-computation with adjustment for confounders identified using a directed acyclic graph and accounting for intermediate confounding. 20822 G1-G2 dyads from 18450 G0 were included. Relative to G0 normal weight, G0 underweight decreased mean G2 birthweight z-score (-0.11, 95% confidence interval (CI) -0.20, -0.030), while G0 overweight and obesity increased mean G2 birthweight z-score (0.091 [95% CI 0.034, 0.15] and 0.22 [95% CI 0.11, 0.33]). G1 pre-pregnancy BMI partly mediated the association, with the largest effect size observed for G0 obesity (0.11, 95% CI 0.080, 0.14). Estimates of the direct effect were close to the null. In conclusion, grandmaternal pre-pregnancy BMI was associated with infant birthweight z-score. Maternal pre-pregnancy BMI partly mediated the association, suggesting that factors related to BMI may play an important role in the transmission of weight across the maternal line.

Prolonged HPA axis dysregulation in postpartum depression associated with adverse early life experiences: A cross-species translational study.

Childhood and adolescent stress increase the risk of postpartum depression (PPD), often providing an increased probability of treatment refractoriness. Nevertheless, the mechanisms linking childhood/adolescent stress to PPD remain unclear. Our study investigated the longitudinal effects of adolescent stress on the hypothalamic-pituitary-adrenal (HPA) axis and postpartum behaviors in mice and humans. Adolescent social isolation prolonged glucocorticoid elevation, leading to long-lasting postpartum behavioral changes in female mice. These changes were unresponsive to current PPD treatments but improved with post-delivery glucocorticoid receptor antagonist treatment. Childhood/adolescent stress significantly impacted HPA axis dysregulation and PPD in human females. Repurposing glucocorticoid receptor antagonists for some cases of treatment-resistant PPD may be considered.

Efficacy of the Flo App in Improving Health Literacy, Menstrual and General Health, and Well-Being in Women: Pilot Randomized Controlled Trial.

BACKGROUND: Reproductive health literacy and menstrual health awareness play a crucial role in ensuring the health and well-being of women and people who menstruate. Further, awareness of one's own menstrual cycle patterns and associated symptoms can help individuals identify and manage conditions of the menstrual cycle such as premenstrual syndrome (PMS) and premenstrual dysphoric disorder (PMDD). Digital health products, and specifically menstrual health apps, have the potential to effect positive change due to their scalability and ease of access. OBJECTIVE: The primary aim of this study was to measure the efficacy of a menstrual and reproductive health app, Flo, in improving health literacy and health and well-being outcomes in menstruating individuals with and without PMS and PMDD. Further, we explored the possibility that the use of the Flo app could positively influence feelings around reproductive health management and communication about health, menstrual cycle stigma, unplanned pregnancies, quality of life, work productivity, absenteeism, and body image. METHODS: We conducted 2 pilot, 3-month, unblinded, 2-armed, remote randomized controlled trials on the effects of using the Flo app in a sample of US-based (1) individuals who track their cycles (n=321) or (2) individuals who track their cycles and are affected by PMS or PMDD (n=117). RESULTS: The findings revealed significant improvements at the end of the study period compared to baseline for our primary outcomes of health literacy (cycle tracking: D̄=1.11; t311=5.73, P<.001; PMS or PMDD: D̄=1.20; t115=3.76, P<.001) and menstrual health awareness (D̄=3.97; t311=7.71, P<.001), health and well-being (D̄=3.44; t311=5.94, P<.001), and PMS or PMDD symptoms burden (D̄=-7.08; t115=-5.44, P<.001). Improvements were also observed for our secondary outcomes of feelings of control and management over health (D̄=1.01; t311=5.08, P<.001), communication about health (D̄=0.93; t311=2.41, P=.002), menstrual cycle stigma (D̄=-0.61; t311=-2.73, P=.007), and fear of unplanned pregnancies (D̄=-0.22; t311=-2.11, P=.04) for those who track their cycles, as well as absenteeism from work and education due to PMS or PMDD (D̄=-1.67; t144=-2.49, P=.01). CONCLUSIONS: These pilot randomized controlled trials demonstrate that the use of the Flo app improves menstrual health literacy and awareness, general health and well-being, and PMS or PMDD symptom burden. Considering the widespread use and affordability of the Flo app, these findings show promise for filling important gaps in current health care provisioning such as improving menstrual knowledge and health. TRIAL REGISTRATION: OSF Registries osf.io/pcgw7; https://osf.io/pcgw7 ; OSF Registries osf.io/ry8vq; https://osf.io/ry8vq.

Correction: Synthetic ramoplanin analogues are accessible by effective incorporation of arylglycines in solid-phase peptide synthesis.

[This corrects the article DOI: 10.1039/D3SC01944F.].

Blood extracellular vesicles carrying brain-specific mRNAs are potential biomarkers for detecting gene expression changes in the female brain.

The absence of non-invasive tests that can monitor the status of the brain is a major obstacle for psychiatric care. In order to address this need, we assessed the feasibility of using tissue-specific gene expression to determine the origin of extracellular vesicle (EV) mRNAs in peripheral blood. Using the placenta as a model, we discovered that 26 messenger RNAs that are specifically expressed in the placenta are present in EVs circulating in maternal blood. Twenty-three of these transcripts were either exclusively or highly expressed in maternal blood during pregnancy only and not in the postpartum period, verifying the feasibility of using tissue-specific gene expression to infer the tissue of origin for EV mRNAs. Using the same bioinformatic approach, which provides better specificity than isolating L1 cell-adhesion molecule containing EVs, we discovered that 181 mRNAs that are specifically expressed in the female brain are also present in EVs circulating in maternal blood. Gene set enrichment analysis revealed that these transcripts, which are involved in synaptic functions and myelination, are enriched for genes implicated in mood disorders, schizophrenia, and substance use disorders. The EV mRNA levels of 13 of these female brain-specific transcripts are associated with postpartum depression (adjusted p-vals = 3 × 10-5 to 0.08), raising the possibility that they can be used to infer the state of the brain. In order to determine the extent to which EV mRNAs reflect transcription in the brain, we compared mRNAs isolated from cells and EVs in an iPSC-derived brain microphysiological system differentiated for 3 and 9 weeks. We discovered that, although cellular and extracellular mRNA levels are not identical, they do correlate, and it is possible to extrapolate cellular RNA expression changes in the brain via EV mRNA levels. Our findings bring EV mRNAs to the forefront of peripheral biomarker development efforts in psychiatric diseases by demonstrating the feasibility of inferring transcriptional changes in the brain via blood EV mRNA levels.

GABAergic neuroactive steroid response to sertraline in premenstrual dysphoric disorder.

RATIONALE: Premenstrual dysphoric disorder (PMDD) affects approximately 5% of menstruating individuals, with significant negative mood symptoms in the luteal phase of the menstrual cycle. PMDD's pathophysiology and treatment mechanisms are poorly characterized, but may involve altered neuroactive steroid function in the brain. Selective serotonin reuptake inhibitors (SSRIs), a first-line PMDD treatment, reportedly alter gamma-aminobutyric acid (GABA)ergic neuroactive steroid levels in PMDD. AIMS: The aims of this study were to determine whether the SSRI sertraline increased serum levels of neuroactive steroids that modulate the effect of GABA at GABA-A receptors (GABAAR) and if so, whether an increase was associated with improvement in PMDD symptoms. METHODS: Participants included controls and individuals with PMDD. Serum levels of 9 neuroactive steroids were measured (3α,5α-THP; 3α5ß-THP; pregnenolone; 3α,5α-androsterone; 3α,5ß-androsterone; 3α,5α-A-diol; 3α5ß-A-diol; 3α,5α-THDOC; 3α5ß-THDOC) in the follicular and luteal phases. In the subsequent luteal phase, neuroactive steroids were measured during sertraline treatment (50 mg sertraline from approximate ovulation to menses onset) in the PMDD group. Mixed models assessed associations among diagnostic group, menstrual cycle phase, and sertraline treatment. RESULTS: Participants included 38 controls and 32 women with PMDD. There were no significant differences in neuroactive steroid levels between controls and participants with PMDD in the luteal phase (p > 0.05). Within the PMDD group, sertraline treatment significantly increased serum pregnanolone levels and the pregnanolone:progesterone ratio, and decreased 3α,5α-androsterone. CONCLUSIONS: This was the first study to assess the impact of SSRI treatment on peripheral levels of GABAergic neuroactive steroids in PMDD. Within the PMDD group, sertraline treatment was associated with a significant increase in luteal phase serum pregnanolone levels and a significantly increased pregnanolone:progesterone ratio, a novel finding. Future research should examine alterations in the metabolic pathways among GABAergic neuroactive steroids in individuals with PMDD, in a placebo-controlled design.

Gender Diversity in the Psychiatric Workforce: It's Still a (White) Man's World in Psychiatry.

Academic psychiatry has slightly higher rates of women in the upper ranks and leadership positions than academic medicine as a whole but women continue to be seriously underrepresented. Psychiatry departments should take specific steps to address barriers for women in psychiatry including harassment and discrimination, Imposter Syndrome, lack of mentorship and sponsorship, work-life integration issues, and overinvolvement in nonpromotion generating activities. Addressing these barriers within academic psychiatry will improve the environment for all minorities.

Synthetic ramoplanin analogues are accessible by effective incorporation of arylglycines in solid-phase peptide synthesis.

The threat of antimicrobial resistance to antibiotics requires a continual effort to develop alternative treatments. Arylglycines (or phenylglycines) are one of the signature amino acids found in many natural peptide antibiotics, but their propensity for epimerization in solid-phase peptide synthesis (SPPS) has prevented their use in long peptide sequences. We have now identified an optimized protocol that allows the synthesis of challenging non-ribosomal peptides including precursors of the glycopeptide antibiotics and an analogue of feglymycin (1 analogue, 20%). We have exploited this protocol to synthesize analogues of the peptide antibiotic ramoplanin using native chemical ligation/desulfurization (1 analogue, 6.5%) and head-to-tail macrocyclization in excellent yield (6 analogues, 3-9%), with these compounds extensively characterized by NMR (U-shaped structure) and antimicrobial activity assays (two clinical isolates). This method significantly reduces synthesis time (6-9 days) when compared with total syntheses (2-3 months) and enables drug discovery programs to include arylglycines in structure-activity relationship studies and drug development.

Metabolites of progesterone in pregnancy: Associations with perinatal anxiety.

BACKGROUND: Anxiety disorders are the most common psychiatric disorder during the perinatal period and one of the major risk factors for postpartum depression, yet we know little about biological factors in the etiology of perinatal anxiety. A growing literature points to neuroactive steroid (NAS) dysregulation in perinatal mental illness, but directionality has not been clearly demonstrated, results are not consistent, and no studies have investigated NAS in a population with pure anxiety without comorbid depression. We aimed to add to the limited literature by examining the association between anxiety without comorbid depression and metabolic pathways of NAS longitudinally across the peripartum. METHODS: We measured anxiety symptoms by psychological scales and NAS levels using Gas Chromatography-Mass Spectrometry (GC-MS) at the second and third trimester (T2 and T3) and week 6 postpartum (W6) in n = 36 women with anxiety and n = 38 healthy controls. The anxiety group was determined by a data-driven approach, and cross-sectional and longitudinal statistical methods were used to examine the relationship between the study population and NAS. RESULTS: We found that anxiety had a significant moderating effect on the relationship between progesterone and allopregnanolone, with no such effect for the relationships between progesterone and the intermediate (5α-DHP) or isomeric (isoallopregnanolone) compounds in this pathway, and no effects on the corresponding pathway converting progesterone to pregnanolone and epipregnanolone. We also found a less precipitous decline in the ratio of allopregnanolone to progesterone between T3 and W6 in the anxiety group compared to the non-anxiety group. A genotype analysis of a single-nucleotide polymorphism in the AKR1C2 gene demonstrated that the relationship of allopregnanolone to the intermediate metabolite, 5α-DHP, differed by genotype. CONCLUSION: Our exploratory findings indicate that, for pregnant people with anxiety, metabolism is shunted more aggressively toward the endpoint of the progesterone to allopregnanolone metabolic pathway than it is for those without anxiety.

Perinatal Depression: A Review and an Update.

Perinatal depression is a common psychiatric condition that has negative effects on pregnancy and infant outcomes. Screening for the condition is relatively easy and should be done routinely in all medical care of the pregnant and postpartum woman and her infant. The risk-benefit analysis favors the use of antidepressant medications during pregnancy and lactation compared with the risk of untreated maternal depression. Other, nonpharmacological treatments will be discussed as well as new treatments, including a new class of medications that act on the inhibitory GABAergic neurotransmitter system.

Transgenerational Inheritance and Systemic Racism in America.

Objective: It is well established that personal experiences of trauma, adversity, and discrimination can "get under the skin" and increase risk for a whole host of negative mental and physical health outcomes. The aim of this article is to review emerging research on transgenerational epigenetic inheritance which suggests that negative exposures in one generation, can also be passed down to affect the health and well-being of future generations. Method: This paper reviews key concepts in transgenerational epigenetic inheritance research, select animal and human studies examining the role of epigenetic mechanisms in transmitting the impact of ancestral stress and trauma, poor nutrition, and toxicant exposure across generations, and factors that can mitigate the effects of these experiences. Results: The animal studies provide compelling evidence for a role for these mechanisms in the transmission of the negative effects associated with ancestral adversities. Animal and clinical studies also suggest that the negative impact of personal and ancestral traumas can be prevented, with a role for in humans for evidence-based trauma treatments, culturally adapted prevention and intervention programs, and enrichment opportunities strongly indicated. Conclusions: Although comparable definitive data is lacking in multigenerational human cohorts, preliminary data supports a potential role for transgenerational epigenetic mechanisms in explaining persistent health disparities in the absence of personal exposures, and further elucidation of these mechanisms may guide the design of novel interventions. In addressing ancestral traumas, however, true change and healing will require acknowledgement of the harms that were done, and broader systemic policy level changes.

The end of Roe v. Wade: implications for Women's mental health and care.

The Supreme Court decision in Dobbs v. Jackson in June 2022 reversed precedent which had previously protected abortion prior to fetal viability as a universal right within the United States. This decision almost immediately led to abortion restrictions across 25 states. The resulting lack of access to abortion care for millions of pregnant people will have profound physical and mental health consequences, the full effects of which will not be realized for years to come. Approximately 1 in 5 women access abortions in the U.S. each year. These women are diverse and represent all American groups. The Supreme court decision, however, will affect populations that have and continue to be marginalized the most. Forcing pregnant individuals to carry unwanted pregnancies worsens health outcomes and mortality risk for both the perinatal individual and the offspring. The US has one of the highest maternal mortality rates and this rate is projected to increase with abortion bans. Abortion policies also interfere with appropriate medical care of pregnant people leading to less safe pregnancies for all. Beyond the physical morbidity, the psychological sequelae of carrying a forced pregnancy to term will lead to an even greater burden of maternal mental illness, exacerbating the already existing maternal mental health crisis. This perspective piece reviews the current evidence of abortion denial on women's mental health and care. Based on the current evidence, we discuss the clinical, educational, societal, research, and policy implications of the Dobbs v. Jackson Supreme Court decision.

Towards understanding the biology of premenstrual dysphoric disorder: From genes to GABA.

Premenstrual dysphoric disorder (PMDD) is a severe mood disorder, with affective symptoms that rise and fall in concert with the hormonal fluctuations of the menstrual cycle. PMDD's pathophysiology is poorly understood. This review describes recent research on potential biological contributors to PMDD, with a focus on neuroactive steroids, genetics, neuroimaging and cellular studies. Studies suggest that a key contributor is abnormal central nervous system (CNS) response to fluctuations in neuroactive steroid hormones. Imaging studies are limited but support alterations in serotonergic and GABA transmission. Genetic studies suggest heritability, yet specific genetic contributors have not been characterized. Finally, recent cutting-edge cellular studies indicate an underlying vulnerability to the effect of sex hormones at a cellular level. Overall the findings across studies do not yet fit together into a complete description of the underlying biology of PMDD. It is possible that PMDD consists of biological subtypes, and future research may benefit from a subtyping approach.

Menstrual cycle-associated symptoms and workplace productivity in US employees: A cross-sectional survey of users of the Flo mobile phone app.

Objective: Mood and physical symptoms related to the menstrual cycle affect women's productivity at work, often leading to absenteeism. However, employer-led initiatives to tackle these issues are lacking. Digital health interventions focused on women's health (such as the Flo app) could help fill this gap. Methods: 1867 users of the Flo app participated in a survey exploring the impact of their menstrual cycle on their workplace productivity and the role of Flo in mitigating some of the identified issues. Results: The majority reported a moderate to severe impact of their cycle on workplace productivity, with 45.2% reporting absenteeism (5.8 days on average in the previous 12 months). 48.4% reported not receiving any support from their manager and 94.6% said they were not provided with any specific benefit for issues related to their menstrual cycle, with 75.6% declaring wanting them. Users stated that the Flo app helped them with the management of menstrual cycle symptoms (68.7%), preparedness and bodily awareness (88.7%), openness with others (52.5%), and feeling supported (77.6%). Users who reported the most positive impact of the Flo app were 18-25% less likely to report an impact of their menstrual cycle on their productivity and 12-18% less likely to take days off work for issues related to their cycle. Conclusions: Apps such as Flo could equip individuals with tools to better cope with issues related to their menstrual cycle and facilitate discussions around menstrual health in the workplace.

Altered extracellular mRNA communication in postpartum depression is associated with decreased autophagy.

We investigated whether extracellular RNA communication, which is a recently discovered mode of intercellular communication that is involved in a variety of important biological processes including pregnancy, is associated with postpartum depression (PPD). Extracellular RNA communication is increased during pregnancy and is involved in embryo implantation, uterine spiral artery remodeling, parturition, preterm birth, immunity, and the inflammatory response. Since immune anomalies are associated with PPD, we characterized the mRNA content of extracellular vesicles (EV) in a cohort of prospectively collected blood plasma samples at six time-points throughout pregnancy and the postpartum (2nd trimester, 3rd trimester, 2 weeks postpartum, 6 weeks postpartum, 3 months postpartum, and 6 months postpartum) in an academic medical setting from women who went on to develop PPD (N = 7, defined as euthymic in pregnancy with postpartum-onset depressive symptoms assessed by Edinburgh Postnatal Depression Scale ≥13 at any postpartum time point) and matched unaffected controls (N = 7, defined as euthymic throughout pregnancy and postpartum). Blood samples were available for all participants at the T2 and W6 timepoints, with fewer samples available at other time points. This analysis revealed that EV mRNA levels during pregnancy and the postpartum period were extensively altered in women who went on to develop PPD. Gene set enrichment analysis revealed that mRNAs associated with autophagy were decreased in PPD cases. In contrast, EV mRNAs from ribosomes and mitochondria, two organelles that are selectively targeted by autophagy, were elevated in PPD cases. Cellular deconvolution analysis discovered that EV mRNAs associated with PPD originated from monocytes and macrophages. Quantitative PCR analysis for four relevant genes in another cohort replicated these findings and confirmed that extracellular RNA levels are altered in PPD. We demonstrate that EV mRNA communication is robustly altered during pregnancy and the postpartum period in women who go on to develop PPD. Our work also establishes a direct link between reduced autophagy and PPD in patient samples. These data warrant investigating the feasibility of developing EV mRNA based biomarkers and therapeutic agents for PPD.

Premenstrual symptoms across the lifespan in an international sample: data from a mobile application.

Premenstrual symptoms, including physical and mood symptoms, affect a large proportion of women worldwide. Data on premenstrual symptoms across nations and age groups is limited. In the present study, we leveraged a large international dataset to explore patterns in premenstrual symptom frequency with age. A survey was administered to users of the Flo mobile application (app), aged 18 to 55. The survey queried app users about a range of premenstrual symptoms. Respondents were asked whether they experienced each symptom every menstrual cycle, some cycles, or never. Age was also captured and categorized as 18-27, 28-37, 38-47, 48-55. Data was summarized and Pearson's chi square test for count data assessed differences in symptom frequency by age group. A sample of 238,114 app users from 140 countries responded to the survey. The most common symptoms reported were food cravings (85.28%), mood swings or anxiety (64.18%), and fatigue (57.3%). Absentmindedness, low libido, sleep changes, gastrointestinal symptoms, weight gain, headaches, sweating or hot flashes, fatigue, hair changes, rashes, and swelling were significantly more frequent with increasing age (p's < 0.001). Mood swings and anxiety did not vary by age group. Of the respondents, 28.61% reported that premenstrual symptoms interfered with their everyday life each menstrual cycle. In a large international sample, the majority of women reported premenstrual food cravings, mood changes, and fatigue every menstrual cycle. Mood symptoms did not vary by age group, suggesting that premenstrual mood changes are a persistent issue among women of reproductive age.

Nutritional Considerations for the Power Athlete.

ABSTRACT: Nutrition is a significant factor in a power athlete's ability to achieve hypertrophy, strength, lean body mass, and overall performance goals. Optimizing an athlete's macronutrient balance, timing of intake, and hydration is essential for advancing performance and should be fluid as the athlete transitions between cycles of training, matching nutrient requirements to intensity of training throughout periodization. Supplement use can help athletes meet their performance and nutrition goals when used as an adjunct to a well-chosen diet, both by direct ergogenic effect and by reducing risk of illness or injury. Educating athletes and coaches on an optimal nutrition plan to support training, performance, and health is critical to prevent the negative effects that may come from poor diet, dangerous weight cutting practices, and relative energy deficiency in sport.

Gender Diversity in the Psychiatric Workforce: It's Still a (White) Man's World in Psychiatry.

Academic psychiatry has slightly higher rates of women in the upper ranks and leadership positions than academic medicine as a whole but women continue to be seriously underrepresented. Psychiatry departments should take specific steps to address barriers for women in psychiatry including harassment and discrimination, Imposter Syndrome, lack of mentorship and sponsorship, work-life integration issues, and overinvolvement in nonpromotion generating activities. Addressing these barriers within academic psychiatry will improve the environment for all minorities.

Expression of the GFP-mammalian pleckstrin homology (PH) domain of the phospholipase C δ1 in Saccharomyces cerevisiae BY4741.

BACKGROUND: Pleckstrin homology (PH) domains are common modules of ∼120 amino acids found in proteins involved in signalling, cytoskeletal organization, membrane transport, and modification of phospholipids. Previous live cell studies have involved the use of the green-fluorescent protein (GFP) labelling of PH-domain of phospholipase C δ1 (PLC δ1) to study the interactions of molecules at the membrane interface. METHODS AND RESULTS: For this study, the aim was to construct and express the GFP-PH domain of PLC δ1 in the Saccharomyces cerevisiae BY4741. The transformants expressing GFP-PH domain of PLC δ1 displayed localised fluorescence to the cell periphery (plasma membrane) while the negative control expressed GFP within the cytoplasm only. No GFP was observed in the non-transformed yeast cells. CONCLUSIONS: Thus, this technique could be useful in future molecular interactions studies targeted specifically at the yeast cell membrane interface in live yeast cells.

Rates of self-reported postpartum depressive symptoms in the United States before and after the start of the COVID-19 pandemic.

BACKGROUND: This study aimed to determine the relationship between the start of the COVID-19 pandemic and changes in postpartum depressive symptoms (PDS) in individuals in the United States. Further analyses explored how these changes related to state-level measures of pandemic severity, economic hardship, and social isolation. METHODS: Data were collected from users of the Flo mobile health application who completed a survey about their mood within 90 days of giving birth. Analyses assessed changes in national and state-level self-reported PDS from a pre-pandemic period (N = 159,478) to a pandemic period (N = 118,622). Linear regression determined which state-level pandemic severity or economic factors were associated with changes in PDS. RESULTS: National rates of PDS increased from 6.5% (pre-pandemic) to 6.9% (pandemic). There was a significant increase in PDS over the course of the pandemic timeframe. Linear regressions revealed a negative association between percent change in PDS across states and COVID-19 deaths per 100 K residents as well as 2020 women's unemployment rate. There was no association between change in PDS and COVID-19 cases per 100 K residents, percent job loss, percent change in women's unemployment rate, or percentage of population staying at home. CONCLUSIONS: There was a national increase in PDS that worsened over the course of a year following the start of the COVID-19 pandemic. States with a greater increase in PDS tended to show overall fewer deaths from COVID-19 and lower women's unemployment rates. Further work is needed to identify what individual-level factors may be driving these differences.