Observation of Gravitational Waves from a Binary Black Hole Merger

On September 14, 2015 at 09:50:45 UTC the two detectors of the Laser Interferometer Gravitational-Wave Observatory simultaneously observed a transient gravitational-wave signal. The signal sweeps upwards in frequency from 35 to 250 Hz with a peak gravitational-wave strain of 1.0×10(-21). It matches the waveform predicted by general relativity for the inspiral and merger of a pair of black holes and the ringdown of the resulting single black hole. The signal was observed with a matched-filter signal-to-noise ratio of 24 and a false alarm rate estimated to be less than 1 event per 203,000 years, equivalent to a significance greater than 5.1σ. The source lies at a luminosity distance of 410(-180)(+160)  Mpc corresponding to a redshift z=0.09(-0.04)(+0.03). In the source frame, the initial black hole masses are 36(-4)(+5)M⊙ and 29(-4)(+4)M⊙, and the final black hole mass is 62(-4)(+4)M⊙, with 3.0(-0.5)(+0.5)M⊙c(2) radiated in gravitational waves. All uncertainties define 90% credible intervals. These observations demonstrate the existence of binary stellar-mass black hole systems. This is the first direct detection of gravitational waves and the first observation of a binary black hole merger.

The Ensembl genome database project

The Ensembl (http://www.ensembl.org/) database project provides a bioinformatics framework to organise biology around the sequences of large genomes. It is a comprehensive source of stable automatic annotation of the human genome sequence, with confirmed gene predictions that have been integrated with external data sources, and is available as either an interactive web site or as flat files. It is also an open source software engineering project to develop a portable system able to handle very large genomes and associated requirements from sequence analysis to data storage and visualisation. The Ensembl site is one of the leading sources of human genome sequence annotation and provided much of the analysis for publication by the international human genome project of the draft genome. The Ensembl system is being installed around the world in both companies and academic sites on machines ranging from supercomputers to laptops.

GW170817: Observation of Gravitational Waves from a Binary Neutron Star Inspiral

On August 17, 2017 at 12∶41:04 UTC the Advanced LIGO and Advanced Virgo gravitational-wave detectors made their first observation of a binary neutron star inspiral. The signal, GW170817, was detected with a combined signal-to-noise ratio of 32.4 and a false-alarm-rate estimate of less than one per 8.0×10^{4}  years. We infer the component masses of the binary to be between 0.86 and 2.26  M_{⊙}, in agreement with masses of known neutron stars. Restricting the component spins to the range inferred in binary neutron stars, we find the component masses to be in the range 1.17-1.60  M_{⊙}, with the total mass of the system 2.74_{-0.01}^{+0.04}M_{⊙}. The source was localized within a sky region of 28  deg^{2} (90% probability) and had a luminosity distance of 40_{-14}^{+8}  Mpc, the closest and most precisely localized gravitational-wave signal yet. The association with the γ-ray burst GRB 170817A, detected by Fermi-GBM 1.7 s after the coalescence, corroborates the hypothesis of a neutron star merger and provides the first direct evidence of a link between these mergers and short γ-ray bursts. Subsequent identification of transient counterparts across the electromagnetic spectrum in the same location further supports the interpretation of this event as a neutron star merger. This unprecedented joint gravitational and electromagnetic observation provides insight into astrophysics, dense matter, gravitation, and cosmology.

Gene for von Recklinghausen neurofibromatosis is in the pericentromeric region of chromosome 17

Linkage analysis of 15 Utah kindreds demonstrated that a gene responsible for von Recklinghausen neurofibromatosis (NF) is located near the centromere on chromosome 17. The families also gave no evidence for heterogeneity, indicating that a significant proportion of NF cases are due to mutations at a single locus. Further genetic analysis can now refine this localization and may lead to the eventual identification and cloning of the defective gene responsible for this disorder.

The fetal and childhood growth of persons who develop type 2 diabetes

BACKGROUND

Type 2 diabetes is associated with low birthweight followed by obesity in adulthood. Persons who develop the disease may therefore have a particular pattern of growth from birth through childhood.

OBJECTIVE

To examine the relation of type 2 diabetes to size at birth and childhood growth.

DESIGN

Cohort study.

SETTING

Helsinki, Finland.

PARTICIPANTS

Men (n = 3,639) and women (n = 3,447) who were bom at the Helsinki University Central Hospital between 1924 and 1933, who went to school in Helsinki, and who still lived in Finland in 1971. Detailed birth and school health records were available for all 7,086 participants. We identified 471 men and women who developed type 2 diabetes by using the national Social Insurance Institution's register of all persons in Finland who are receiving long-term therapy with medication.

MEASUREMENTS

Incidence of diabetes ascertained from a national register. The main explanatory measurements were size at birth and childhood growth in terms of height, weight, and body mass index.

RESULTS

The cumulative incidence of type 2 diabetes was 7.9% (n = 286) in men and 5.4% (n = 185) in women. The incidence increased with decreasing birthweight, birth length, ponderal index (birthweight/length(3)), and placental weight The odds ratio for type 2 diabetes was 1.38 (95% CI, 1.15 to 1.66; P < 0.001) for each 1-kg decrease in birthweight. The mean weights and heights of the children at 7 years of age who later developed type 2 diabetes were about average. Thereafter, their growth in weight and height was accelerated until 15 years of age. The odds ratio for development of type 2 diabetes was 1.39 (CI, 1.21 to 1.61; P < 0.001) for each standard deviation increase in weight between 7 and 15 years of age. The odds ratio became 1.83 (CI, 1.37 to 2.45; P< 0.001) in an analysis restricted to persons whose birthweights were below 3,000 g. Children of both sexes whose mothers had a high body mass index in pregnancy had more rapid growth during childhood and an increased incidence of type 2 diabetes.

CONCLUSIONS

These findings are consistent with the hypothesis that type 2 diabetes is programmed in utero in association with low rates of fetal growth. The increased risk for type 2 diabetes associated with small size at birth is further increased by high growth rates after 7 years of age.

Restriction sites containing CpG show a higher frequency of polymorphism in human DNA

Unique loci in the human genome were examined with restriction enzymes in order to detect restriction fragment length polymorphisms (RFLPs). Of 31 arbitrary loci, nine were detectably polymorphic, reflecting ten polymorphic restriction sites. Nine of the ten polymorphic sites were revealed with two restriction enzymes, Msp I and Taq I, whose recognition sequences have in common the dimer sequence CpG. The cytosines in the CpG sequence are known to be frequently methylated in mammals, and the occurrence of significant variation in Msp I and Taq I sites supports the view that methylated cytosine residues are hotspots for mutation in mammalian DNA.

GW151226: Observation of Gravitational Waves from a 22-Solar-Mass Binary Black Hole Coalescence

We report the observation of a gravitational-wave signal produced by the coalescence of two stellar-mass black holes. The signal, GW151226, was observed by the twin detectors of the Laser Interferometer Gravitational-Wave Observatory (LIGO) on December 26, 2015 at 03:38:53 UTC. The signal was initially identified within 70 s by an online matched-filter search targeting binary coalescences. Subsequent off-line analyses recovered GW151226 with a network signal-to-noise ratio of 13 and a significance greater than 5σ. The signal persisted in the LIGO frequency band for approximately 1 s, increasing in frequency and amplitude over about 55 cycles from 35 to 450 Hz, and reached a peak gravitational strain of 3.4_{-0.9}^{+0.7}×10^{-22}. The inferred source-frame initial black hole masses are 14.2_{-3.7}^{+8.3}M_{⊙} and 7.5_{-2.3}^{+2.3}M_{⊙}, and the final black hole mass is 20.8_{-1.7}^{+6.1}M_{⊙}. We find that at least one of the component black holes has spin greater than 0.2. This source is located at a luminosity distance of 440_{-190}^{+180}  Mpc corresponding to a redshift of 0.09_{-0.04}^{+0.03}. All uncertainties define a 90% credible interval. This second gravitational-wave observation provides improved constraints on stellar populations and on deviations from general relativity.

GW170104: Observation of a 50-Solar-Mass Binary Black Hole Coalescence at Redshift 0.2

We describe the observation of GW170104, a gravitational-wave signal produced by the coalescence of a pair of stellar-mass black holes. The signal was measured on January 4, 2017 at 10∶11:58.6 UTC by the twin advanced detectors of the Laser Interferometer Gravitational-Wave Observatory during their second observing run, with a network signal-to-noise ratio of 13 and a false alarm rate less than 1 in 70 000 years. The inferred component black hole masses are 31.2_{-6.0}^{+8.4}M_{⊙} and 19.4_{-5.9}^{+5.3}M_{⊙} (at the 90% credible level). The black hole spins are best constrained through measurement of the effective inspiral spin parameter, a mass-weighted combination of the spin components perpendicular to the orbital plane, χ_{eff}=-0.12_{-0.30}^{+0.21}. This result implies that spin configurations with both component spins positively aligned with the orbital angular momentum are disfavored. The source luminosity distance is 880_{-390}^{+450}  Mpc corresponding to a redshift of z=0.18_{-0.07}^{+0.08}. We constrain the magnitude of modifications to the gravitational-wave dispersion relation and perform null tests of general relativity. Assuming that gravitons are dispersed in vacuum like massive particles, we bound the graviton mass to m_{g}≤7.7×10^{-23}  eV/c^{2}. In all cases, we find that GW170104 is consistent with general relativity.

Fetal and childhood growth and hypertension in adult life

The association between low birth weight and raised blood pressure has been extensively replicated. Little is known about the way childhood growth modifies the effects of low birth weight. We report on the fetal and childhood growth of 1958 men and women who received treatment for hypertension and belong to a cohort of 7086 people born in Helsinki, Finland, during 1924-1933. As expected, the men and women who developed hypertension had low birth weight (P=0.002). They were also shorter in body length at birth (P=0.02). After birth they experienced accelerated growth, so that by 7 years their heights and weights were approximately average. In a simultaneous regression, both birth length and tall height had statistically significant although opposing effects on hypertension (P=0.003 for birth length and 0.009 for height at 7 years). Accelerated postnatal growth was associated with better childhood living conditions. Children who later developed both hypertension and type 2 diabetes, rather than hypertension alone, had small placental size as well as small body size at birth, and their accelerated postnatal growth continued beyond 7 years. We suggest that hypertension may originate through retarded growth in utero followed by accelerated postnatal growth as a result of good living conditions. Retarded fetal growth leads to permanently reduced cell numbers in the kidney and other tissues, and subsequent accelerated growth may lead to excessive metabolic demand on this limited cell mass.

Cystic fibrosis locus defined by a genetically linked polymorphic DNA marker

A polymorphic DNA marker has been found genetically linked, in a set of 39 human families, to an autosomal recessive gene that causes cystic fibrosis (CF), a disease affecting one in 2000 Caucasian children. The DNA marker (called D0CRI-917) is also linked to the PON locus, which by independent evidence is linked to the CF locus. The best estimates of the genetic distances are 5 centimorgans between the DNA marker and PON and 15 centimorgans between the DNA marker and the CF locus, meaning that the location of the disease gene has been narrowed to about 1 percent of the human genome (about 30 million base pairs). Although the data are consistent with the interpretation that a single locus causes cystic fibrosis, the possibility of genetic heterogeneity remains. The discovery of a linked DNA polymorphism is the first step in molecular analysis of the CF gene and its causative role in the disease.

Construction of linkage maps with DNA markers for human chromosomes

DNA markers and sampling of three-generation families can be used to construct complete linkage maps of human chromosomes. This is important in mapping disease loci and in determining the genetic or environmental component of a disease.

GW170814: A Three-Detector Observation of Gravitational Waves from a Binary Black Hole Coalescence

On August 14, 2017 at 10∶30:43 UTC, the Advanced Virgo detector and the two Advanced LIGO detectors coherently observed a transient gravitational-wave signal produced by the coalescence of two stellar mass black holes, with a false-alarm rate of ≲1 in 27 000 years. The signal was observed with a three-detector network matched-filter signal-to-noise ratio of 18. The inferred masses of the initial black holes are 30.5_{-3.0}^{+5.7}M_{⊙} and 25.3_{-4.2}^{+2.8}M_{⊙} (at the 90% credible level). The luminosity distance of the source is 540_{-210}^{+130}  Mpc, corresponding to a redshift of z=0.11_{-0.04}^{+0.03}. A network of three detectors improves the sky localization of the source, reducing the area of the 90% credible region from 1160   deg^{2} using only the two LIGO detectors to 60  deg^{2} using all three detectors. For the first time, we can test the nature of gravitational-wave polarizations from the antenna response of the LIGO-Virgo network, thus enabling a new class of phenomenological tests of gravity.

Childhood growth, physical activity, and peak bone mass in women

Peak bone mass is an important determinant of the risk of osteoporotic fracture, and preventive strategies against osteoporosis require a clear understanding of the factors influencing bone gain in early life. We report a longitudinal study aiming to identify the relationships between childhood growth, lifestyle, and peak bone mass in women. One hundred and fifty-three women born in a British city during 1968-1969 were traced and studied in 1990. Data on their growth in childhood was obtained from linked birth and school health records; current bone mineral measurements were made by dual X-ray absorptiometry. There were statistically significant associations between weight at 1 year and BMC (but not BMD) at the lumbar spine (r = 0.32, p < 0.01) and femoral neck (r = 0.26, p < 0.01). These remained significant after adjusting for current weight. There were also strong relationships between childhood height measurements and adult BMC at the two skeletal sites. Physical activity was the major lifestyle determinant of BMD after allowing for body build. We conclude that infant growth and physical activity in childhood are important determinants of peak bone mass in women. Growth primarily determines the size of the skeletal envelope, and its trajectory is established by age 1 year. Activity, in contrast, modulates the mineral density within the skeletal envelope and may contribute to the consolidation of bone following the end of linear growth.

Size at birth, childhood growth and obesity in adult life

BACKGROUND

Several studies have shown tracking of obesity from childhood to adult life. People who develop obesity in adult life may therefore have had a particular path of growth from birth through childhood.

OBJECTIVE

To examine the relationship of obesity to size at birth and childhood growth.

DESIGN

Birth cohort study.

PARTICIPANTS

A total of 5210 individuals alive and living in Finland in 1997, who were born at the Helsinki University Central Hospital between 1924 and 1933 and who went to school in Helsinki were sent a questionnaire in order to get information about adult weight and height. Detailed birth and school health records were available for all subjects. In all, 3847 responded and 3659 (1552 men and 2107 women) with adequate data are included in the present study.

MEASUREMENTS

Incidence of obesity based upon lifetime maximum body mass index (BMI) ascertained from a postal questionnaire and defined as a BMI>30 kg/m(2). The main explanatory measurements were size at birth and childhood growth in height, weight and BMI.

RESULTS

The cumulative incidence of obesity was 34.2% in men and 33.9% in women. The incidence rose with increasing birth weight and ponderal index (birthweight/length(3); P=0.01 and P=0.04, respectively). These associations were statistically significant only among males. By the age of 7 y the mean weights, heights and BMI of people who later became obese exceeded the average and remained above average at all ages from 7 to 15 y. In both men and women there was a 3-fold increase in obesity associated with a BMI>16 kg/m(2) at age 7 compared with a BMI<14.5 kg/m(2) (P<0.0001). Boys and girls whose mothers had a high BMI in pregnancy had more rapid childhood growth and an increased risk of becoming obese. This effect was stronger among boys (P=0.008).

CONCLUSIONS

Obesity is initiated early in life. These results emphasise the importance of early preventive measures for its treatment.

Growth in infancy and bone mass in later life

OBJECTIVE

To examine the association between weight in infancy and bone mass during the seventh decade of life in a population based cohort for which detailed birth and childhood records were preserved.

METHODS

189 women and 224 men who were aged 63-73 years and were born in East Hertfordshire underwent bone densitometry by dual energy x ray absorptiometry. Measurements were also made of serum osteocalcin and urinary excretion of type 1 collagen cross linked N-telopeptide.

RESULTS

There were statistically significant associations between weight at 1 year and bone mineral content (but not bone mineral density) at the spine (P < 0.02) and femoral neck (P < 0.01) among women, and spine (P < 0.03) among men. Although serum osteocalcin was negatively correlated with bone mineral density at both sites among men and women, infant weight was not significantly associated with either biochemical marker of bone turnover.

CONCLUSIONS

These data confirm our previous observations that growth in infancy is associated with skeletal size in adulthood, and suggest that skeletal growth may be programmed during intrauterine or early postnatal life.

GW170817: Measurements of Neutron Star Radii and Equation of State

On 17 August 2017, the LIGO and Virgo observatories made the first direct detection of gravitational waves from the coalescence of a neutron star binary system. The detection of this gravitational-wave signal, GW170817, offers a novel opportunity to directly probe the properties of matter at the extreme conditions found in the interior of these stars. The initial, minimal-assumption analysis of the LIGO and Virgo data placed constraints on the tidal effects of the coalescing bodies, which were then translated to constraints on neutron star radii. Here, we expand upon previous analyses by working under the hypothesis that both bodies were neutron stars that are described by the same equation of state and have spins within the range observed in Galactic binary neutron stars. Our analysis employs two methods: the use of equation-of-state-insensitive relations between various macroscopic properties of the neutron stars and the use of an efficient parametrization of the defining function p(ρ) of the equation of state itself. From the LIGO and Virgo data alone and the first method, we measure the two neutron star radii as R_{1}=10.8_{-1.7}^{+2.0}  km for the heavier star and R_{2}=10.7_{-1.5}^{+2.1}  km for the lighter star at the 90% credible level. If we additionally require that the equation of state supports neutron stars with masses larger than 1.97  M_{⊙} as required from electromagnetic observations and employ the equation-of-state parametrization, we further constrain R_{1}=11.9_{-1.4}^{+1.4}  km and R_{2}=11.9_{-1.4}^{+1.4}  km at the 90% credible level. Finally, we obtain constraints on p(ρ) at supranuclear densities, with pressure at twice nuclear saturation density measured at 3.5_{-1.7}^{+2.7}×10^{34}  dyn cm^{-2} at the 90% level.

Tests of General Relativity with GW150914

The LIGO detection of GW150914 provides an unprecedented opportunity to study the two-body motion of a compact-object binary in the large-velocity, highly nonlinear regime, and to witness the final merger of the binary and the excitation of uniquely relativistic modes of the gravitational field. We carry out several investigations to determine whether GW150914 is consistent with a binary black-hole merger in general relativity. We find that the final remnant's mass and spin, as determined from the low-frequency (inspiral) and high-frequency (postinspiral) phases of the signal, are mutually consistent with the binary black-hole solution in general relativity. Furthermore, the data following the peak of GW150914 are consistent with the least-damped quasinormal mode inferred from the mass and spin of the remnant black hole. By using waveform models that allow for parametrized general-relativity violations during the inspiral and merger phases, we perform quantitative tests on the gravitational-wave phase in the dynamical regime and we determine the first empirical bounds on several high-order post-Newtonian coefficients. We constrain the graviton Compton wavelength, assuming that gravitons are dispersed in vacuum in the same way as particles with mass, obtaining a 90%-confidence lower bound of 10^{13}  km. In conclusion, within our statistical uncertainties, we find no evidence for violations of general relativity in the genuinely strong-field regime of gravity.

A polymorphic DNA marker linked to cystic fibrosis is located on chromosome 7

Although cystic fibrosis (CF) is among the most common inherited diseases in Caucasian populations, the basic biochemical defect is not yet known. CF is inherited as an autosomal recessive trait apparently due to mutations in a single gene, whence the efforts made to identify the genetic locus responsible by linkage studies. Two markers have recently been identified that are genetically linked to CF: one is a genetic variation in serum level of activity of the enzyme paraoxonase, and the other is a restriction fragment length polymorphism (RFLP) identified with a randomly isolated DNA probe. We report here that the genetic locus DOCRI-917 defined by the cloned DNA probe is located on chromosome 7.

Effects of infant birthweight and maternal body mass index in pregnancy on components of the insulin resistance syndrome in China

BACKGROUND

Reduced birthweight is associated with increased risk for the insulin resistance syndrome. Part of this risk is hypothesized to originate from undernutrition in utero. The prevalence of the insulin resistance syndrome increases in countries that undergo the transition from chronic malnutrition to adequate nutrition, when postnatal nutrition improves more rapidly than prenatal nutrition.

OBJECTIVE

To determine whether the components of the insulin resistance syndrome are associated with reduced fetal growth and maternal undernutrition.

DESIGN

A nonconcurrent, prospective study of men and women whose mothers' heights and weights were recorded during pregnancy.

SETTING

Beijing, China.

PARTICIPANTS

627 men and women (mean age, 45 years) whose mothers' obstetric records were preserved.

MEASUREMENTS

Adult offspring's blood pressure, plasma glucose levels, insulin levels, and lipid concentrations during an oral glucose tolerance test. The main explanatory measurements were mothers' body mass index during pregnancy and offspring's birthweight and adult size.

RESULTS

After adjustment for sex and current body mass index, low birthweight was associated with elevated plasma glucose levels, insulin levels, triglyceride concentrations, and blood pressure. For every 1-kg increase in birthweight, systolic blood pressure decreased by 2.9 mm Hg (95% CI, 0.3 to 5.4 mm Hg) and the 2-hour plasma glucose level decreased by 5.1% (CI, 0.7% to 9.3%). Low maternal body mass index in early and late pregnancy was associated with elevated levels of plasma glucose, insulin, and triglycerides in adult offspring but was not associated with elevated blood pressure.

CONCLUSIONS

Risk for the insulin resistance syndrome may be partially established through low maternal body mass before pregnancy and consequent fetal undernutrition. This risk is independent of that associated with adult obesity. In developing countries such as China, improved nutrition in girls and young women may offer long-term benefits to offspring.

Ensembl 2002: accommodating comparative genomics

The Ensembl (http://www.ensembl.org/) database project provides a bioinformatics framework to organise biology around the sequences of large genomes. It is a comprehensive source of stable automatic annotation of human, mouse and other genome sequences, available as either an interactive web site or as flat files. Ensembl also integrates manually annotated gene structures from external sources where available. As well as being one of the leading sources of genome annotation, Ensembl is an open source software engineering project to develop a portable system able to handle very large genomes and associated requirements. These range from sequence analysis to data storage and visualisation and installations exist around the world in both companies and at academic sites. With both human and mouse genome sequences available and more vertebrate sequences to follow, many of the recent developments in Ensembl have focusing on developing automatic comparative genome analysis and visualisation.

Obesity from cradle to grave

BACKGROUND

Obesity is known to track from early life into adult life.

OBJECTIVE

To examine the relation of obesity in adult life to growth and living conditions during childhood.

DESIGN

Birth cohort study.

PARTICIPANTS

A total of 4515 people (2135 men and 2380 women) who were born at Helsinki University Central Hospital between 1934 and 1944, who attended child welfare clinics and were still resident in Finland in the year 2000.

MEASUREMENTS

Incidence of obesity based upon lifetime maximum body mass index (BMI) ascertained from a postal questionnaire and defined as a BMI>or=30 kg/m(2). The main explanatory measurements were size at birth, childhood growth, and socioeconomic status in childhood and in adult life.

RESULTS

The cumulative incidence of obesity was 33.8% in men and 32.4% in women. The incidence rose with increasing body size at birth. From birth the mean weight and BMI of people who later became obese exceeded the average and remained above average at a statistically significant level at all ages from 6 months to 12 y. Childhood BMI was a stronger predictor of adult obesity than body size at birth. A higher maternal BMI in pregnancy was associated with a more rapid childhood growth and an increased risk of becoming obese in adult life. Higher socioeconomic status and better educational attainment were associated with a lower prevalence of obesity. There was no association between the duration of breastfeeding and later obesity.

CONCLUSIONS

These results emphasize the importance of early life factors in the pathogenesis of adult obesity.

Childhood growth and age at menarche

OBJECTIVE

To study the influence of birthweight, and weight and height at age seven years, on menarcheal age in a national sample of 1471 girls in England, Scotland and Wales.

METHODS

We studied 1471 girls included in the MRC National Survey of Health and Development. During medical examinations carried out by school doctors in this cohort, born in the first week of March 1946, the mothers of girls were asked whether their daughters had started to menstruate, and if so, the month and year when this happened. Anthropometric measurements at birth and at age seven years were also obtained.

RESULTS

Girls who were heavier at age seven years had menarche at an earlier age. The average age at menarche of those in the highest fifth of the distribution of weight at seven years was 7.3 months less than that of those in the lowest fifth of the distribution. In contrast, girls who were heavier at birth had menarche at a later age. The average age at menarche of those in the highest fifth of the birthweight distribution was 2.2 months more than those in the lowest fifth. These opposing trends of birthweight and weight at seven years on age at menarche were observed across the distribution of each variable, and exerted statistically significant (P < 0.001) independent effects in a multivariate model.

CONCLUSIONS

These observations are consistent with the hypothesis that menarcheal age is linked to programmed patterns of gonadotrophin release established in utero, when the fetal hypothalamus is imprinted, and is subsequently modified by weight gain in childhood.

Types of intra- and extrafusal muscle fibre innervated by dynamic skeleto-fusimotor axons in cat peroneus brevis and tenuissimus muscles, as determined by the glycogen-depletion method

1. The types of intra- and extrafusal muscle fibre innervated by dynamic skeleto-fusimotor (beta) axons were determined by using a modification of the glycogen-depletion method of Edström & Kugelberg (1968) combined with histochemical tests for various enzyme reactions. A single beta axon was prepared in each of the experiments, which were carried out on six peroneus brevis and two tenuissimus muscles. 2. The intrafusal distribution of dynamic beta axons is almost exclusively restricted to bag1 fibres. The bags fibre was depleted in each of twenty-four beta-innervated spindle poles; the only fibres of a different type depleted intrafusally were a bag2 fibre in one pole and a long chain in another. 3. Depletion in the bag1 fibres was usually restricted to one zone in one pole, generally in a mid-polar location. 4. The extrafusal muscle fibres depleted by dynamic beta axons belong to the slow oxidative type as defined by Ariano, Armstrong & Edgerton (1973). The number of such fibres in each motor unit could not be accurately determined, but is almost certainly small. 5. The slow oxidative muscle fibres innervated by dynamic beta axons were not depleted over their entire length. Since there is no reason to assume that they are not twitch fibres, it would seem that the localized depletions result from the conditions required to obtain glycogen depletion, i.e. long periods of motor stimulation applied during the occlusion of the muscle's blood supply. Under similar experimental conditions depletion of glycogen was also restricted to portions of fibres in fast oxidative-glycolytic motor units, but extended over most of the length of the fibres in fast glycolytic units.

The epidemiology of Paget's disease in Britain: is the prevalence decreasing?

To estimate changes in the age- and gender-specific prevalence of Paget's disease in Britain, we performed a radiographic survey of the disorder in 10 British centers, using sampling and radiographic methods identical to a study performed in 1974. In each center, a sample of abdominal radiographs of people aged 55 years and over was taken from stored films within the radiology department of the principal general hospital. The radiographs were identified by screening radiographic records over the period 1993-1995. Any abdominal radiograph in a subject aged 55 years and over which included the entire pelvis, sacrum, femoral heads, and all lumbar vertebrae was studied. The radiographs were evaluated by a trained observer and the consultant radiologist who participated in the original 1974 survey. Nine thousand eight hundred and twenty-eight radiographs (4625 men, 5203 women) were assessed in the 10 towns. The overall age/gender standardized prevalence rate was 2%, with a male/female ratio of 1.6. Prevalence increased steeply with age among men and women, rising to 6.9% of men and 5.8% of women aged 85 years and over. The prevalence of Paget's disease in the 10 towns in 1994 was only 40% of that observed during the 1974 study. The decline in prevalence was apparent in all 10 centers, but was most marked in those with high rates in the original study. This survey of Paget's disease in 10 British towns suggests a prevalence of 2.5% among men and 1.6% among women aged 55 years and over. Age-adjusted prevalence rates declined steeply between 1974 and 1994. These declines suggest an environmental contribution to the etiology of this disorder that requires further investigation.