Infectious Illness Symptoms Are Associated with Elevated Anxiety in a Sample of Sexual and Gender Minority Young Adults During the COVID-19 Pandemic.

BACKGROUND: To evaluate whether infectious illness symptoms (IIS) are associated with generalized anxiety symptoms during the COVID-19 pandemic in sexual/gender (SGM) minority young adults assigned male at birth (AMAB). METHOD: Four hundred eighteen participants (median age = 25; range, 20-40) were recruited through RADAR, an ongoing Chicago-based cohort study of SGM-AMAB between September 2020 and February 2021. Participants completed online surveys. A subset (n = 145) provided dried blood spot samples to assess SARS-CoV-2 serostatus. RESULTS: One hundred twenty participants (28.7%) had GAD-7 scores of 10 or greater, which indicates generalized anxiety symptoms that may be clinically significant. In a binomial logistic regression model adjusting age, gender identity, race/ethnicity, substance use, and HIV status, the authors found that having a higher IIS count since March 1, 2020, was associated with greater odds of having a GAD-7 score of 10 or greater (OR = 1.14; 95% CI, 1.04, 1.25; P = 0.007). This effect was more pronounced in a binomial logistic regression model adjusting for the same covariates but using current IIS count as the independent variable (OR = 1.39; 95% CI, 1.13, 1.74; P = 0.002). CONCLUSION: Among SGM-AMAB young adults, those who experienced ISS reported higher scores on the GAD-7, a widely used and validated screening measure for generalized anxiety symptoms. These findings highlight the importance of screening for anxiety disorders when patients present with IIS in clinical settings and psychobehavioral health follow-ups when indicated.

Conditional deletion of SMN in cell culture identifies functional SMN alleles.

Spinal muscular atrophy (SMA) is caused by mutation or deletion of survival motor neuron 1 (SMN1) and retention of SMN2 leading to SMN protein deficiency. We developed an immortalized mouse embryonic fibroblast (iMEF) line in which full-length wild-type Smn (flwt-Smn) can be conditionally deleted using Cre recombinase. iMEFs lacking flwt-Smn are not viable. We tested the SMA patient SMN1 missense mutation alleles A2G, D44V, A111G, E134K and T274I in these cells to determine which human SMN (huSMN) mutant alleles can function in the absence of flwt-Smn. All missense mutant alleles failed to rescue survival in the conditionally deleted iMEFs. Thus, the function lost by these mutations is essential to cell survival. However, co-expression of two different huSMN missense mutants can rescue iMEF survival and small nuclear ribonucleoprotein (snRNP) assembly, demonstrating intragenic complementation of SMN alleles. In addition, we show that a Smn protein lacking exon 2B can rescue iMEF survival and snRNP assembly in the absence of flwt-Smn, indicating exon 2B is not required for the essential function of Smn. For the first time, using this novel cell line, we can assay the function of SMN alleles in the complete absence of flwt-Smn.

Intragenic complementation of amino and carboxy terminal SMN missense mutations can rescue Smn null mice.

Spinal muscular atrophy is caused by reduced levels of SMN resulting from the loss of SMN1 and reliance on SMN2 for the production of SMN. Loss of SMN entirely is embryonic lethal in mammals. There are several SMN missense mutations found in humans. These alleles do not show partial function in the absence of wild-type SMN and cannot rescue a null Smn allele in mice. However, these human SMN missense allele transgenes can rescue a null Smn allele when SMN2 is present. We find that the N- and C-terminal regions constitute two independent domains of SMN that can be separated genetically and undergo intragenic complementation. These SMN protein heteromers restore snRNP assembly of Sm proteins onto snRNA and completely rescue both survival of Smn null mice and motor neuron electrophysiology demonstrating that the essential functional unit of SMN is the oligomer.

Mild SMN missense alleles are only functional in the presence of SMN2 in mammals.

Spinal muscular atrophy (SMA) is caused by reduced levels of full-length SMN (FL-SMN). In SMA patients with one or two copies of the Survival Motor Neuron 2 (SMN2) gene there are a number of SMN missense mutations that result in milder-than-predicted SMA phenotypes. These mild SMN missense mutation alleles are often assumed to have partial function. However, it is important to consider the contribution of FL-SMN as these missense alleles never occur in the absence of SMN2. We propose that these patients contain a partially functional oligomeric SMN complex consisting of FL-SMN from SMN2 and mutant SMN protein produced from the missense allele. Here we show that mild SMN missense mutations SMND44V, SMNT74I or SMNQ282A alone do not rescue mice lacking wild-type FL-SMN. Thus, missense mutations are not functional in the absence of FL-SMN. In contrast, when the same mild SMN missense mutations are expressed in a mouse containing two SMN2 copies, functional SMN complexes are formed with the small amount of wild-type FL-SMN produced by SMN2 and the SMA phenotype is completely rescued. This contrasts with SMN missense alleles when studied in C. elegans, Drosophila and zebrafish. Here we demonstrate that the heteromeric SMN complex formed with FL-SMN is functional and sufficient to rescue small nuclear ribonucleoprotein assembly, motor neuron function and rescue the SMA mice. We conclude that mild SMN missense alleles are not partially functional but rather they are completely non-functional in the absence of wild-type SMN in mammals.

Muscle contractility dysfunction precedes loss of motor unit connectivity in SOD1(G93A) mice.

INTRODUCTION: Electrophysiological measurements are used in longitudinal clinical studies to provide insight into the progression of amyotrophic lateral sclerosis (ALS) and the relationship between muscle weakness and motor unit (MU) degeneration. Here, we used a similar longitudinal approach in the Cu/Zn superoxide dismutase (SOD1[G93A]) mouse model of ALS. METHODS: In vivo muscle contractility and MU connectivity assays were assessed longitudinally in SOD1(G93A) and wild type mice from postnatal days 35 to 119. RESULTS: In SOD1(G93A) males, muscle contractility was reduced by day 35 and preceded MU loss. Muscle contractility and motor unit reduction were delayed in SOD1(G93A) females compared with males, but, just as with males, muscle contractility reduction preceded MU loss. DISCUSSION: The longitudinal contractility and connectivity paradigm employed here provides additional insight into the SOD1(G93A) mouse model and suggests that loss of muscle contractility is an early finding that may precede loss of MUs and motor neuron death. Muscle Nerve 59:254-262, 2019.

HuD and the Survival Motor Neuron Protein Interact in Motoneurons and Are Essential for Motoneuron Development, Function, and mRNA Regulation.

Motoneurons establish a critical link between the CNS and muscles. If motoneurons do not develop correctly, they cannot form the required connections, resulting in movement defects or paralysis. Compromised development can also lead to degeneration because the motoneuron is not set up to function properly. Little is known, however, regarding the mechanisms that control vertebrate motoneuron development, particularly the later stages of axon branch and dendrite formation. The motoneuron disease spinal muscular atrophy (SMA) is caused by low levels of the survival motor neuron (SMN) protein leading to defects in vertebrate motoneuron development and synapse formation. Here we show using zebrafish as a model system that SMN interacts with the RNA binding protein (RBP) HuD in motoneurons in vivo during formation of axonal branches and dendrites. To determine the function of HuD in motoneurons, we generated zebrafish HuD mutants and found that they exhibited decreased motor axon branches, dramatically fewer dendrites, and movement defects. These same phenotypes are present in animals expressing low levels of SMN, indicating that both proteins function in motoneuron development. HuD binds and transports mRNAs and one of its target mRNAs, Gap43, is involved in axonal outgrowth. We found that Gap43 was decreased in both HuD and SMN mutants. Importantly, transgenic expression of HuD in motoneurons of SMN mutants rescued the motoneuron defects, the movement defects, and Gap43 mRNA levels. These data support that the interaction between SMN and HuD is critical for motoneuron development and point to a role for RBPs in SMA.SIGNIFICANCE STATEMENT In zebrafish models of the motoneuron disease spinal muscular atrophy (SMA), motor axons fail to form the normal extent of axonal branches and dendrites leading to decreased motor function. SMA is caused by low levels of the survival motor neuron (SMN) protein. We show in motoneurons in vivo that SMN interacts with the RNA binding protein, HuD. Novel mutants reveal that HuD is also necessary for motor axonal branch and dendrite formation. Data also revealed that both SMN and HuD affect levels of an mRNA involved in axonal growth. Moreover, expressing HuD in SMN-deficient motoneurons can rescue the motoneuron development and motor defects caused by low levels of SMN. These data support that SMN:HuD complexes are essential for normal motoneuron development and indicate that mRNA handling is a critical component of SMA.

SMN expression is required in motor neurons to rescue electrophysiological deficits in the SMNΔ7 mouse model of SMA.

Proximal spinal muscular atrophy (SMA) is the most frequent cause of hereditary infant mortality. SMA is an autosomal recessive neuromuscular disorder that results from the loss of the Survival Motor Neuron 1 (SMN1) gene and retention of the SMN2 gene. The SMN2 gene produces an insufficient amount of full-length SMN protein that results in loss of motor neurons in the spinal cord and subsequent muscle paralysis. Previously we have shown that overexpression of human SMN in neurons in the SMA mouse ameliorates the SMA phenotype while overexpression of human SMN in skeletal muscle had no effect. Using Cre recombinase, here we show that either deletion or replacement of Smn in motor neurons (ChAT-Cre) significantly alters the functional output of the motor unit as measured with compound muscle action potential and motor unit number estimation. However ChAT-Cre alone did not alter the survival of SMA mice by replacement and did not appreciably affect survival when used to deplete SMN. However replacement of Smn in both neurons and glia in addition to the motor neuron (Nestin-Cre and ChAT-Cre) resulted in the greatest improvement in survival of the mouse and in some instances complete rescue was achieved. These findings demonstrate that high expression of SMN in the motor neuron is both necessary and sufficient for proper function of the motor unit. Furthermore, in the mouse high expression of SMN in neurons and glia, in addition to motor neurons, has a major impact on survival.

Low levels of Survival Motor Neuron protein are sufficient for normal muscle function in the SMNΔ7 mouse model of SMA.

Spinal Muscular Atrophy (SMA) is an autosomal recessive disorder characterized by loss of lower motor neurons. SMA is caused by deletion or mutation of the Survival Motor Neuron 1 (SMN1) gene and retention of the SMN2 gene. The loss of SMN1 results in reduced levels of the SMN protein. SMN levels appear to be particularly important in motor neurons; however SMN levels above that produced by two copies of SMN2 have been suggested to be important in muscle. Studying the spatial requirement of SMN is important in both understanding how SMN deficiency causes SMA and in the development of effective therapies. Using Myf5-Cre, a muscle-specific Cre driver, and the Cre-loxP recombination system, we deleted mouse Smn in the muscle of mice with SMN2 and SMNΔ7 transgenes in the background, thus providing low level of SMN in the muscle. As a reciprocal experiment, we restored normal levels of SMN in the muscle with low SMN levels in all other tissues. We observed that decreasing SMN in the muscle has no phenotypic effect. This was corroborated by muscle physiology studies with twitch force, tetanic and eccentric contraction all being normal. In addition, electrocardiogram and muscle fiber size distribution were also normal. Replacement of Smn in muscle did not rescue SMA mice. Thus the muscle does not appear to require high levels of SMN above what is produced by two copies of SMN2 (and SMNΔ7).

SMN deficiency disrupts gastrointestinal and enteric nervous system function in mice.

The 2007 Consensus Statement for Standard of Care in Spinal Muscular Atrophy (SMA) notes that patients suffer from gastroesophageal reflux, constipation and delayed gastric emptying. We used two mouse models of SMA to determine whether functional GI complications are a direct consequence of or are secondary to survival motor neuron (Smn) deficiency. Our results show that despite normal activity levels and food and water intake, Smn deficiency caused constipation, delayed gastric emptying, slow intestinal transit and reduced colonic motility without gross anatomical or histopathological abnormalities. These changes indicate alterations to the intrinsic neural control of gut functions mediated by the enteric nervous system (ENS). Indeed, Smn deficiency led to disrupted ENS signaling to the smooth muscle of the colon but did not cause enteric neuron loss. High-frequency electrical field stimulation (EFS) of distal colon segments produced up to a 10-fold greater contractile response in Smn deficient tissues. EFS responses were not corrected by the addition of a neuronal nitric oxide synthase inhibitor indicating that the increased contractility was due to hyperexcitability and not disinhibition of the circuitry. The GI symptoms observed in mice are similar to those reported in SMA patients. Together these data suggest that ENS cells are susceptible to Smn deficiency and may underlie the patient GI symptoms.

Obesity impairs cell-mediated immunity during the second trimester of pregnancy.

OBJECTIVE: Obese pregnancy is associated with significantly higher rates of infection, which can harm both mother and fetus. The objective of this study was to determine the impact of obesity on maternal blood immune function. STUDY DESIGN: This was a cross-sectional, case control study of 15 obese (Ob) and 15 lean (Lc) subjects. Immune cell subsets, intracellular and serum cytokine production, and lymphocyte proliferation were measured in maternal blood during the second trimester of pregnancy. RESULTS: Obese women had a significantly lower proportion of CD8+ and NKT cells and a higher proportion of B cells, impaired cytokine production when stimulated ex vivo, and impaired ability of lymphocytes to proliferate compared with their lean counterparts. CONCLUSION: Obese pregnancy is associated with impaired cell-mediated immunity. Because perinatal infections can have serious maternal and fetal consequences, it is imperative to better understand these mechanistic underpinnings to optimize prevention and devise targeted therapy.

ECC Status, CRAFT Categorization and OHRQoL Assessment in 3-6-year-old Children: A Cross-sectional Study.

Introduction: Early Childhood Caries (ECC) can affect the health and quality of life of the children. Assessing a patient's risk of developing caries is an important aspect of caries management; however, can assessing the caries risk predict the impact of ECC on the OHRQoL? Few Indian studies have reported association between caries status, risk, and the impact on OHRQoL. Aim: To assess the association between dental caries status, risk assessment, and OHRQoL in 3-6-year-old children. Methodology: A total of 50 healthy children were recruited in a cross-sectional study. Parents filled the ECOHIS questionnaire. Caries status, risk, and OHRQoL were measured as dmft-pufa, CRAFT (Caries Risk Assessment for Treatment- an indigenous tool) and ECOHIS scores, respectively. Results: Moderate correlation was seen between dmft and ECOHIS scores (r = 0.496, p < 0.01), and pufa and ECOHIS scores (r = 0.408, p < 0.05). More number of subjects with higher scores of ECOHIS were in the high-risk category of CRAFT (p < 0.05). Conclusion: Caries status, risk and OHRQoL were associated in 3-6-year-old children. Thus, caries risk assessment may predict poor OHRQoL. How to cite this article: Iyer CR, Jawdekar AM. ECC Status, CRAFT Categorization and OHRQoL Assessment in 3-6-year-old Children: A Cross-sectional Study. Int J Clin Pediatr Dent 2023;16(2):199-204.

Examining the impact of social distancing and methamphetamine use on sexual risk and intimate partner violence in sexual and gender minority young adults during the COVID-19 pandemic.

BACKGROUND: During the COVID-19 pandemic in 2020, concerns were raised about the potential impact of pandemic-related social distancing measures on existing health disparities among sexual and gender minority (SGM) young adults, including HIV transmission risk and intimate partner violence (IPV). Another concern was the potential for increased methamphetamine use during the pandemic, which is a known risk factor for HIV transmission and IPV. METHODS: The present analysis examines the impact of COVID-19 social distancing (social distancing and quarantining) and methamphetamine use on HIV risk and IPV in a combined dataset from 3 cohort studies of SGM young adults (two in Los Angeles and one in Chicago) from May 2020 to April 2021 (n = 1142). Bivariate analyses and multivariable logistic regressions were estimated. RESULTS: The median age was 26. All participants were assigned male at birth and most participants were men (93.8%). The largest racial groups were Hispanic/Latinx (44.6%) and Black (29.0%). In adjusted models methamphetamine use was consistently associated with having a new sex partner, higher numbers of sex partners, and experience of IPV, during the pandemic. Reporting no social distancing and reporting one social distancing behavior, were associated with experience of IPV relative to reporting 2 social distancing behaviors. Social distancing was not associated with sexual risk behavior or Pre-exposure Prophylaxis use. CONCLUSIONS: SGM young adults live at the intersection of multiple vulnerabilities during the COVID-19 pandemic. Addiction services, HIV prevention services, and violence support services should be prepared to support young adult SGM needs, particularly those who use methamphetamine.

Complete Molar Pregnancies with a Coexisting Fetus: Pregnancy Outcomes and Review of Literature.

Objective The objective of the study was to review the obstetric outcomes of complete hydatidiform molar pregnancies with a coexisting fetus (CHMCF), a rare clinical entity that is not well described. Materials and Methods We performed a retrospective case series with pathology-confirmed HMCF. The cases were collected via solicitation through a private maternal-fetal medicine physician group on social media. Each contributing institution from across the United States ( n = 9) obtained written informed consent from the patients directly, obtained institutional data transfer agreements as required, and transmitted the data using a Health Insurance Portability and Accountability Act of 1996 (HIPAA) compliant modality. Data collected included maternal, fetal/genetic, placental, and delivery characteristics. For descriptive analysis, continuous variables were reported as median with standard deviation and range. Results Nine institutions contributed to the 14 cases collected. Nine (64%) cases of CHMCF were a product of assisted reproductive technology and one case was trizygotic. The median gestational age at diagnosis was 12 weeks and 2 days (9 weeks-19 weeks and 4 days), and over half were diagnosed in the first trimester. The median human chorionic gonadotropin (hCG) at diagnosis was 355,494 mIU/mL (49,770-700,486 mIU/mL). Placental mass size universally enlarged over the surveillance period. When invasive testing was performed, insufficient sample or no growth was noted in 40% of the sampled cases. Antenatal complications occurred in all delivered patients, with postpartum hemorrhage (71%) and hypertensive disorders of pregnancy (29%) being the most frequent outcomes. Delivery outcomes were variable. Four patients developed gestational trophoblastic neoplasia. Conclusion This series is the largest report of obstetric outcomes for CHMCF to date and highlights the need to counsel patients about the severe maternal and fetal complications in continuing pregnancies, including progression to gestational trophoblastic neoplastic disease. Key Points CHMCF is a rare obstetric complication and may be associated with the use of assisted reproductive technology.Universally, patients with CHMCF who elected to manage expectantly developed antenatal complications.The risk of developing gestational trophoblastic neoplasia after CHMCF is high, and termination of the pregnancy did not decrease this risk.

The m6A methyltransferase METTL3 regulates muscle maintenance and growth in mice.

Skeletal muscle serves fundamental roles in organismal health. Gene expression fluctuations are critical for muscle homeostasis and the response to environmental insults. Yet, little is known about post-transcriptional mechanisms regulating such fluctuations while impacting muscle proteome. Here we report genome-wide analysis of mRNA methyladenosine (m6A) dynamics of skeletal muscle hypertrophic growth following overload-induced stress. We show that increases in METTL3 (the m6A enzyme), and concomitantly m6A, control skeletal muscle size during hypertrophy; exogenous delivery of METTL3 induces skeletal muscle growth, even without external triggers. We also show that METTL3 represses activin type 2 A receptors (ACVR2A) synthesis, blunting activation of anti-hypertrophic signaling. Notably, myofiber-specific conditional genetic deletion of METTL3 caused spontaneous muscle wasting over time and abrogated overload-induced hypertrophy; a phenotype reverted by co-administration of a myostatin inhibitor. These studies identify a previously unrecognized post-transcriptional mechanism promoting the hypertrophic response of skeletal muscle via control of myostatin signaling.

Voluntary wheel running with and without follistatin overexpression improves NMJ transmission but not motor unit loss in late life of C57BL/6J mice.

Sarcopenia, or pathological loss of muscle mass and strength during aging, is an important contributor to loss of physical function in older adults. Sarcopenia is a multifactorial syndrome associated with intrinsic muscle and upstream neurological dysfunction. Exercise is well-established as an effective intervention for sarcopenia, but less is known about the long-term neurobiological impact of exercise. The goals of this study were to investigate the effects of exercise, alone or in combination with follistatin (FST) overexpression (antagonist of myostatin), on neuromuscular junction transmission and motor unit numbers in mice between the age of 22 and 27 months, ages at which prior studies have demonstrated that some motor unit loss is already evident. C57BL/6J mice underwent baseline assessment and were randomized to housing with or without voluntary running wheels and injection with adeno-associated virus to overexpress FST or vehicle. Groups for comparison included sedentary and running with and without FST. Longitudinal assessments showed significantly increased muscle mass and contractility in the 'running plus FST' group, but running, with and without FST, showed no effect on motor unit degeneration. In contrast, running, with and without FST, demonstrated marked improvement of neuromuscular junction transmission stability.

Follistatin-induced muscle hypertrophy in aged mice improves neuromuscular junction innervation and function.

Sarcopenia, or age-related loss of muscle mass and strength, is an important contributor to loss of physical function in older adults. The pathogenesis of sarcopenia is likely multifactorial, but recently the role of neurological degeneration, such as motor unit loss, has received increased attention. Here, we investigated the longitudinal effects of muscle hypertrophy (via overexpression of human follistatin, a myostatin antagonist) on neuromuscular integrity in C57BL/6J mice between the ages of 24 and 27 months. Following follistatin overexpression (delivered via self-complementary adeno-associated virus subtype 9 injection), muscle weight and torque production were significantly improved. Follistatin treatment resulted in improvements of neuromuscular junction innervation and transmission but had no impact on age-related losses of motor units. These studies demonstrate that follistatin overexpression-induced muscle hypertrophy not only increased muscle weight and torque production but also countered age-related degeneration at the neuromuscular junction in mice.

Neuromuscular junction transmission failure is a late phenotype in aging mice.

Neurodegeneration has increasingly been considered an important factor in the pathogenesis of sarcopenia or age-related loss of muscle mass and strength. Experiments were designed to investigate the fidelity of neuromuscular junction (NMJ) transmission across the lifespan in hindlimb muscles of male and female C57BL/6J mice (at 12, 20, 24, 27, and 29 months of age). Single-fiber electromyography recordings demonstrated abrupt onset of NMJ transmission failure at 27 months of age. Failed NMJ transmission was a later onset phenotype as compared with other assessments of motor unit numbers, muscle contractility, and frailty which showed alterations at 20 months of age. Ex vivo NMJ recordings demonstrated no reduction of endplate current amplitude in support of reduced muscle fiber excitability as the cause of failed NMJ transmission in aged mice. Improved understanding of age-related neurodegeneration will likely have important implications in designing novel therapeutic interventions specific for different stages of sarcopenia. Our findings suggest reduced muscle excitability may be a potential therapeutic target for improvement of physical function in older adults.

Early-onset aging and mitochondrial defects associated with loss of histone acetyltransferase 1 (Hat1).

Histone acetyltransferase 1 (Hat1) is responsible for the acetylation of newly synthesized histone H4 on lysines 5 and 12 during the process of chromatin assembly. To understand the broader biological role of Hat1, we have generated a conditional mouse knockout model of this enzyme. We previously reported that Hat1 is required for viability and important for mammalian development and genome stability. In this study, we show that haploinsufficiency of Hat1 results in a significant decrease in lifespan. Defects observed in Hat1+/- mice are consistent with an early-onset aging phenotype. These include lordokyphosis (hunchback), muscle atrophy, minor growth retardation, reduced subcutaneous fat, cancer, and paralysis. In addition, the expression of Hat1 is linked to the normal aging process as Hat1 mRNA and protein becomes undetectable in many tissues in old mice. At the cellular level, fibroblasts from Hat1 haploinsufficient embryos undergo early senescence and accumulate high levels of p21. Hat1+/- mouse embryonic fibroblasts (MEFs) display modest increases in endogenous DNA damage but have significantly higher levels of reactive oxygen species (ROS). Consistently, further studies show that Hat1-/- MEFs exhibit mitochondrial defects suggesting a critical role for Hat1 in mitochondrial function. Taken together, these data show that loss of Hat1 induces multiple hallmarks of early-onset aging.

Muscle strength and size are associated with motor unit connectivity in aged mice.

In older adults, the loss of muscle strength (dynapenia) and the loss of muscle mass (sarcopenia) are important contributors to the loss of physical function. We sought to investigate dynapenia, sarcopenia, and the loss of motor unit function in aging mice. C57BL/6J mice were analyzed with cross-sectional (males: 3 vs. 27 months; males and females: 8 vs. 12 vs. 20 months) and longitudinal studies (males: 10-25 months) using in vivo electrophysiological measures of motor unit connectivity (triceps surae compound muscle action potential and motor unit number estimation), in vivo measures of plantar flexion torque, magnetic resonance imaging of hind limb muscle volume, and grip strength. Compound muscle action potential amplitude, motor unit number estimation, and plantar flexion torque were decreased at 20 months. In contrast, grip strength was reduced at 24 months. Motor unit number estimates correlated with muscle torque and hind limb muscle volume. Our results demonstrate that the loss of motor unit connectivity is an early finding in aging male and female mice and that muscle size and contractility are both associated with motor unit number.