Megan Hansen - Academia.edu (original) (raw)

Papers by Megan Hansen

PLOS ONE

Background Cystic fibrosis (CF) leads to pancreatic endocrine dysfunction with progressive glycem... more Background Cystic fibrosis (CF) leads to pancreatic endocrine dysfunction with progressive glycemic disturbance. Approximately 30%–50% of people with CF eventually develop CF–related diabetes (CFRD). Pre-CFRD states progress from indeterminant glycemia (INDET) to impaired fasting glucose (IFG) or impaired glucose tolerance (IGT). Screening guidelines recommend inconvenient annual 2-hour oral glucose tolerance tests (OGTTs), beginning at age 10 years. More efficient methods, such as hemoglobin A1C (HbA1c), have been evaluated, but only limited, relatively small studies have evaluated the association between HbA1c and pre-CFRD dysglycemic states. Objective To determine whether HbA1c is an appropriate screening tool for identifying patients with pre-CFRD dysglycemia to minimize the burden of annual OGTTs. Methods This retrospective review evaluated medical records data of all University of Massachusetts Memorial Health System CF patients with an HbA1c result within 90 days of an OGTT b...

International Journal of Radiation Oncology*Biology*Physics

PURPOSE Healthcare practices across the U.S. have been consolidating in response to various marke... more PURPOSE Healthcare practices across the U.S. have been consolidating in response to various market forces. The degree of practice consolidation varies widely across specialties but has not been well studied within radiation oncology. This study used Medicare data to characterize the extent of practice consolidation among radiation oncologists and to investigate associated market factors. METHODS We utilized Medicare Provider Enrollment, Chain, and Ownership System (PECOS) data to assess the practice size and billing patterns of U.S. radiation oncologists in 2013 and again in 2017. Individual practices were categorized by the number of radiation oncologists practicing together: solo practices had 1 radiation oncologist, small practices 2 to 10, and large practices 11 or more. Market consolidation within each hospital referral region (HRR) across the country was quantified using the Herfindahl-Hirschman Index (HHI). Hospital and market level data were obtained for each HRR, and factors associated with the growth of radiation oncology practices over time were calculated via multivariable linear regression. RESULTS Across the U.S., radiation oncology practices appear to be highly consolidated. The mean HHI was 0.4711 in 2013--indicating high levels of consolidation at baseline--and increased further to 0.4865 by 2017. Between 2013 and 2017, the number of practices with radiation oncologists in the U.S. decreased 3.8%, from 1,679 to 1,615, while the number of practicing radiation oncologists increased 9.4%, from 4,948 to 5,415. Over the study period, the number of solo practices fell 11% (from 708 in 2013 to 627 in 2017), while the number of large practices (those with 11 or more radiation oncologists) increased 50% (from 60 to 90). Large practices likewise grew to employ a greater share of all radiation oncologists (23.9% to 32.4%) and accounted for a larger proportion of total Medicare billing (21% to 26%). Two market factors were predictive for increases in the mean radiation oncology practice size. HRRs with greater hospital market consolidation, and those with lower levels of baseline radiation oncology consolidation were more likely to experience higher levels of growth over the study period. CONCLUSIONS Radiation oncologists are increasingly working in larger practices. By 2017, nearly one-third of all practicing radiation oncologists in the U.S. were employed by just the 90 largest practices. Radiation oncology, as a field, is highly concentrated, and represents one of the most consolidated specialties across the country. The implications of practice consolidation among radiation oncologists warrants further investigation.

Evolution

The rate of divergence for Z or X chromosomes is usually observed to be greater than autosomes, b... more The rate of divergence for Z or X chromosomes is usually observed to be greater than autosomes, but the proposed evolutionary causes for this pattern vary, as do empirical results from diverse taxa. Even among moths and butterflies (Lepidoptera), which generally share a single-origin Z chromosome, the handful of available studies give mixed support for faster or more adaptive evolution of the Z chromosome, depending on the species assayed. Here, we examine the molecular evolution of Z chromosomes in two additional lepidopteran species: the Carolina sphinx moth and the monarch butterfly, the latter of which possesses a recent chromosomal fusion yielding a segment of newly Z-linked DNA. We find evidence for both faster and more adaptive Z chromosome evolution in both species, though this effect is strongest in the neo-Z portion of the monarch sex chromosome. The neo-Z is less male-biased than expected of a Z chromosome, and unbiased and female-biased genes drive the signal for adaptive evolution here. Together these results suggest that male-biased gene accumulation and haploid selection have opposing effects on long-term rates of adaptation and may help explain the discrepancies in previous findings as well as the repeated evolution of neo-sex chromosomes in Lepidoptera. This article is protected by copyright. All rights reserved.

The rate of divergence for Z or X chromosomes is theoretically predicted to be greater than autos... more The rate of divergence for Z or X chromosomes is theoretically predicted to be greater than autosomes, but the possible explanations for this pattern vary, as do empirical results from diverse taxa. Even among moths and butterflies (Lepidoptera), which generally share a single-origin Z chromosome, the handful of available studies give mixed support for faster or more adaptive evolution of the Z chromosome, depending on the species assayed. Here, we examine the molecular evolution of Z chromosomes in two additional lepidopteran species: the Carolina sphinx moth and the monarch butterfly, the latter of which possesses a recent chromosomal fusion yielding a segment of newly Z-linked DNA. We find evidence for both faster and more adaptive Z chromosome evolution in both species, though this effect is strongest in the neo-Z portion of the monarch sex chromosome. The neo-Z is less male-biased than expected of a Z chromosome, and unbiased and female-biased genes drive the signal for adaptiv...

Sperm are among the most variable cells in nature. Some of this variation results from non-adapti... more Sperm are among the most variable cells in nature. Some of this variation results from non-adaptive errors in spermatogenesis, but many species consistently produce multiple sperm morphs, the adaptive significance of which remains unknown. Here, we investigate the evolution of dimorphic sperm in Lepidoptera, the butterflies and moths. Males of this order produce both fertilizing sperm and a secondary, non-fertilizing type that lacks DNA. Previous organismal studies suggested a role for non-fertilizing sperm in sperm competition, but this hypothesis has never been evaluated from a molecular framework. We combined published datasets with new sequencing in two species, the monandrous Carolina sphinx moth and the highly polyandrous monarch butterfly. Based on population genetic analyses, we see evidence for increased adaptive evolution in fertilizing sperm, but only in the polyandrous species. This signal comes primarily from a decrease in non-synonymous polymorphism in sperm proteins c...

PLOS ONE

Background Cystic fibrosis (CF) leads to pancreatic endocrine dysfunction with progressive glycem... more Background Cystic fibrosis (CF) leads to pancreatic endocrine dysfunction with progressive glycemic disturbance. Approximately 30%–50% of people with CF eventually develop CF–related diabetes (CFRD). Pre-CFRD states progress from indeterminant glycemia (INDET) to impaired fasting glucose (IFG) or impaired glucose tolerance (IGT). Screening guidelines recommend inconvenient annual 2-hour oral glucose tolerance tests (OGTTs), beginning at age 10 years. More efficient methods, such as hemoglobin A1C (HbA1c), have been evaluated, but only limited, relatively small studies have evaluated the association between HbA1c and pre-CFRD dysglycemic states. Objective To determine whether HbA1c is an appropriate screening tool for identifying patients with pre-CFRD dysglycemia to minimize the burden of annual OGTTs. Methods This retrospective review evaluated medical records data of all University of Massachusetts Memorial Health System CF patients with an HbA1c result within 90 days of an OGTT b...

International Journal of Radiation Oncology*Biology*Physics

PURPOSE Healthcare practices across the U.S. have been consolidating in response to various marke... more PURPOSE Healthcare practices across the U.S. have been consolidating in response to various market forces. The degree of practice consolidation varies widely across specialties but has not been well studied within radiation oncology. This study used Medicare data to characterize the extent of practice consolidation among radiation oncologists and to investigate associated market factors. METHODS We utilized Medicare Provider Enrollment, Chain, and Ownership System (PECOS) data to assess the practice size and billing patterns of U.S. radiation oncologists in 2013 and again in 2017. Individual practices were categorized by the number of radiation oncologists practicing together: solo practices had 1 radiation oncologist, small practices 2 to 10, and large practices 11 or more. Market consolidation within each hospital referral region (HRR) across the country was quantified using the Herfindahl-Hirschman Index (HHI). Hospital and market level data were obtained for each HRR, and factors associated with the growth of radiation oncology practices over time were calculated via multivariable linear regression. RESULTS Across the U.S., radiation oncology practices appear to be highly consolidated. The mean HHI was 0.4711 in 2013--indicating high levels of consolidation at baseline--and increased further to 0.4865 by 2017. Between 2013 and 2017, the number of practices with radiation oncologists in the U.S. decreased 3.8%, from 1,679 to 1,615, while the number of practicing radiation oncologists increased 9.4%, from 4,948 to 5,415. Over the study period, the number of solo practices fell 11% (from 708 in 2013 to 627 in 2017), while the number of large practices (those with 11 or more radiation oncologists) increased 50% (from 60 to 90). Large practices likewise grew to employ a greater share of all radiation oncologists (23.9% to 32.4%) and accounted for a larger proportion of total Medicare billing (21% to 26%). Two market factors were predictive for increases in the mean radiation oncology practice size. HRRs with greater hospital market consolidation, and those with lower levels of baseline radiation oncology consolidation were more likely to experience higher levels of growth over the study period. CONCLUSIONS Radiation oncologists are increasingly working in larger practices. By 2017, nearly one-third of all practicing radiation oncologists in the U.S. were employed by just the 90 largest practices. Radiation oncology, as a field, is highly concentrated, and represents one of the most consolidated specialties across the country. The implications of practice consolidation among radiation oncologists warrants further investigation.

Evolution

The rate of divergence for Z or X chromosomes is usually observed to be greater than autosomes, b... more The rate of divergence for Z or X chromosomes is usually observed to be greater than autosomes, but the proposed evolutionary causes for this pattern vary, as do empirical results from diverse taxa. Even among moths and butterflies (Lepidoptera), which generally share a single-origin Z chromosome, the handful of available studies give mixed support for faster or more adaptive evolution of the Z chromosome, depending on the species assayed. Here, we examine the molecular evolution of Z chromosomes in two additional lepidopteran species: the Carolina sphinx moth and the monarch butterfly, the latter of which possesses a recent chromosomal fusion yielding a segment of newly Z-linked DNA. We find evidence for both faster and more adaptive Z chromosome evolution in both species, though this effect is strongest in the neo-Z portion of the monarch sex chromosome. The neo-Z is less male-biased than expected of a Z chromosome, and unbiased and female-biased genes drive the signal for adaptive evolution here. Together these results suggest that male-biased gene accumulation and haploid selection have opposing effects on long-term rates of adaptation and may help explain the discrepancies in previous findings as well as the repeated evolution of neo-sex chromosomes in Lepidoptera. This article is protected by copyright. All rights reserved.

The rate of divergence for Z or X chromosomes is theoretically predicted to be greater than autos... more The rate of divergence for Z or X chromosomes is theoretically predicted to be greater than autosomes, but the possible explanations for this pattern vary, as do empirical results from diverse taxa. Even among moths and butterflies (Lepidoptera), which generally share a single-origin Z chromosome, the handful of available studies give mixed support for faster or more adaptive evolution of the Z chromosome, depending on the species assayed. Here, we examine the molecular evolution of Z chromosomes in two additional lepidopteran species: the Carolina sphinx moth and the monarch butterfly, the latter of which possesses a recent chromosomal fusion yielding a segment of newly Z-linked DNA. We find evidence for both faster and more adaptive Z chromosome evolution in both species, though this effect is strongest in the neo-Z portion of the monarch sex chromosome. The neo-Z is less male-biased than expected of a Z chromosome, and unbiased and female-biased genes drive the signal for adaptiv...

Sperm are among the most variable cells in nature. Some of this variation results from non-adapti... more Sperm are among the most variable cells in nature. Some of this variation results from non-adaptive errors in spermatogenesis, but many species consistently produce multiple sperm morphs, the adaptive significance of which remains unknown. Here, we investigate the evolution of dimorphic sperm in Lepidoptera, the butterflies and moths. Males of this order produce both fertilizing sperm and a secondary, non-fertilizing type that lacks DNA. Previous organismal studies suggested a role for non-fertilizing sperm in sperm competition, but this hypothesis has never been evaluated from a molecular framework. We combined published datasets with new sequencing in two species, the monandrous Carolina sphinx moth and the highly polyandrous monarch butterfly. Based on population genetic analyses, we see evidence for increased adaptive evolution in fertilizing sperm, but only in the polyandrous species. This signal comes primarily from a decrease in non-synonymous polymorphism in sperm proteins c...