Role of the repeat expansion size in predicting age of onset and severity in RFC1 disease

RFC1 disease, caused by biallelic repeat expansion in RFC1, is clinically heterogeneous in terms of age of onset, disease progression and phenotype. We investigated the role of the repeat size in influencing clinical variables in RFC1 disease. We also assessed the presence and role of meiotic and somatic instability of the repeat. In this study, we identified 553 patients carrying biallelic RFC1 expansions and measured the repeat expansion size in 392 cases. Pearson's coefficient was calculated to assess the correlation between the repeat size and age at disease onset. A Cox model with robust cluster standard errors was adopted to describe the effect of repeat size on age at disease onset, on age at onset of each individual symptoms, and on disease progression. A quasi-Poisson regression model was used to analyse the relationship between phenotype and repeat size. We performed multivariate linear regression to assess the association of the repeat size with the degree of cerebellar atrophy. Meiotic stability was assessed by Southern blotting on first-degree relatives of 27 probands. Finally, somatic instability was investigated by optical genome mapping on cerebellar and frontal cortex and unaffected peripheral tissue from four post-mortem cases. A larger repeat size of both smaller and larger allele was associated with an earlier age at neurological onset [smaller allele hazard ratio (HR) = 2.06, P < 0.001; larger allele HR = 1.53, P < 0.001] and with a higher hazard of developing disabling symptoms, such as dysarthria or dysphagia (smaller allele HR = 3.40, P < 0.001; larger allele HR = 1.71, P = 0.002) or loss of independent walking (smaller allele HR = 2.78, P < 0.001; larger allele HR = 1.60; P < 0.001) earlier in disease course. Patients with more complex phenotypes carried larger expansions [smaller allele: complex neuropathy rate ratio (RR) = 1.30, P = 0.003; cerebellar ataxia, neuropathy and vestibular areflexia syndrome (CANVAS) RR = 1.34, P < 0.001; larger allele: complex neuropathy RR = 1.33, P = 0.008; CANVAS RR = 1.31, P = 0.009]. Furthermore, larger repeat expansions in the smaller allele were associated with more pronounced cerebellar vermis atrophy (lobules I-V β = -1.06, P < 0.001; lobules VI-VII β = -0.34, P = 0.005). The repeat did not show significant instability during vertical transmission and across different tissues and brain regions. RFC1 repeat size, particularly of the smaller allele, is one of the determinants of variability in RFC1 disease and represents a key prognostic factor to predict disease onset, phenotype and severity. Assessing the repeat size is warranted as part of the diagnostic test for RFC1 expansion.

In-depth molecular profiling of an intronic GNAO1 mutant as the basis for personalized high-throughput drug screening

BACKGROUND

The GNAO1 gene, encoding the major neuronal G protein Gαo, is mutated in a subset of pediatric encephalopathies. Most such mutations consist of missense variants.

METHODS

In this study, we present a precision medicine workflow combining next-generation sequencing (NGS) diagnostics, molecular etiology analysis, and personalized drug discovery.

FINDINGS

We describe a patient carrying a de novo intronic mutation (NM_020988.3:c.724-8G>A), leading to epilepsy-negative encephalopathy with motor dysfunction from the second decade. Our data show that this mutation creates a novel splice acceptor site that in turn causes an in-frame insertion of two amino acid residues, Pro-Gln, within the regulatory switch III region of Gαo. This insertion misconfigures the switch III loop and creates novel interactions with the catalytic switch II region, resulting in increased GTP uptake, defective GTP hydrolysis, and aberrant interactions with effector proteins. In contrast, intracellular localization, Gβγ interactions, and G protein-coupled receptor (GPCR) coupling of the Gαo[insPQ] mutant protein remain unchanged.

CONCLUSIONS

This in-depth analysis characterizes the heterozygous c.724-8G>A mutation as partially dominant negative, providing clues to the molecular etiology of this specific pathology. Further, this analysis allows us to establish and validate a high-throughput screening platform aiming at identifying molecules that could correct the aberrant biochemical functions of the mutant Gαo.

FUNDING

This work was supported by the Joint Seed Money Funding scheme between the University of Geneva and the Hebrew University of Jerusalem.

[Short telomere syndrome in adults: a rare entity that should be evoked]

Short telomere syndrome (STS) is a group of rare, often underrecognized, diseases caused by defects in telomere-maintenance genes, leading to abnormal telomere shortening and associated with diverse multi-organ manifestations. In pediatric patients, STS typically presents with mucocutaneous or gastrointestinal lesions, bone marrow failure and neoplasia. In adulthood, aplastic bone marrow disease, liver disease and pulmonary fibrosis are classic clinical manifestations. At present, medical treatment options for STS remain limited. Danazol, a synthetic androgenic hormone, can slow down telomere shortening and thus limit the progression of the disease. Finally, hematopoietic, hepatic and pulmonary transplantation, sometimes combined, may be discussed in a multidisciplinary setting in certain situations.

De novo DHDDS variants cause a neurodevelopmental and neurodegenerative disorder with myoclonus

Subcellular membrane systems are highly enriched in dolichol, whose role in organelle homeostasis and endosomal-lysosomal pathway remains largely unclear besides being involved in protein glycosylation. DHDDS encodes for the catalytic subunit (DHDDS) of the enzyme cis-prenyltransferase (cis-PTase), involved in dolichol biosynthesis and dolichol-dependent protein glycosylation in the endoplasmic reticulum. An autosomal recessive form of retinitis pigmentosa (retinitis pigmentosa 59) has been associated with a recurrent DHDDS variant. Moreover, two recurring de novo substitutions were detected in a few cases presenting with neurodevelopmental disorder, epilepsy and movement disorder. We evaluated a large cohort of patients (n = 25) with de novo pathogenic variants in DHDDS and provided the first systematic description of the clinical features and long-term outcome of this new neurodevelopmental and neurodegenerative disorder. The functional impact of the identified variants was explored by yeast complementation system and enzymatic assay. Patients presented during infancy or childhood with a variable association of neurodevelopmental disorder, generalized epilepsy, action myoclonus/cortical tremor and ataxia. Later in the disease course, they experienced a slow neurological decline with the emergence of hyperkinetic and/or hypokinetic movement disorder, cognitive deterioration and psychiatric disturbances. Storage of lipidic material and altered lysosomes were detected in myelinated fibres and fibroblasts, suggesting a dysfunction of the lysosomal enzymatic scavenger machinery. Serum glycoprotein hypoglycosylation was not detected and, in contrast to retinitis pigmentosa and other congenital disorders of glycosylation involving dolichol metabolism, the urinary dolichol D18/D19 ratio was normal. Mapping the disease-causing variants into the protein structure revealed that most of them clustered around the active site of the DHDDS subunit. Functional studies using yeast complementation assay and in vitro activity measurements confirmed that these changes affected the catalytic activity of the cis-PTase and showed growth defect in yeast complementation system as compared with the wild-type enzyme and retinitis pigmentosa-associated protein. In conclusion, we characterized a distinctive neurodegenerative disorder due to de novo DHDDS variants, which clinically belongs to the spectrum of genetic progressive encephalopathies with myoclonus. Clinical and biochemical data from this cohort depicted a condition at the intersection of congenital disorders of glycosylation and inherited storage diseases with several features akin to of progressive myoclonus epilepsy such as neuronal ceroid lipofuscinosis and other lysosomal disorders.

Phenotypic expansion of CACNA1C-associated disorders to include isolated neurological manifestations

PURPOSE

CACNA1C encodes the alpha-1-subunit of a voltage-dependent L-type calcium channel expressed in human heart and brain. Heterozygous variants in CACNA1C have previously been reported in association with Timothy syndrome and long QT syndrome. Several case reports have suggested that CACNA1C variation may also be associated with a primarily neurological phenotype.

METHODS

We describe 25 individuals from 22 families with heterozygous variants in CACNA1C, who present with predominantly neurological manifestations.

RESULTS

Fourteen individuals have de novo, nontruncating variants and present variably with developmental delays, intellectual disability, autism, hypotonia, ataxia, and epilepsy. Functional studies of a subgroup of missense variants via patch clamp experiments demonstrated differential effects on channel function in vitro, including loss of function (p.Leu1408Val), neutral effect (p.Leu614Arg), and gain of function (p.Leu657Phe, p.Leu614Pro). The remaining 11 individuals from eight families have truncating variants in CACNA1C. The majority of these individuals have expressive language deficits, and half have autism.

CONCLUSION

We expand the phenotype associated with CACNA1C variants to include neurodevelopmental abnormalities and epilepsy, in the absence of classic features of Timothy syndrome or long QT syndrome.

NGS-Based Diagnosis of Treatable Neurogenetic Disorders in Adults: Opportunities and Challenges

The identification of neurological disorders by next-generation sequencing (NGS)-based gene panels has helped clinicians understand the underlying physiopathology, resulting in personalized treatment for some rare diseases. While the phenotype of distinct neurogenetic disorders is generally well-known in childhood, in adulthood, the phenotype can be unspecific and make the standard diagnostic approach more complex. Here we present three unrelated adults with various neurological manifestations who were successfully diagnosed using NGS, allowing for the initiation of potentially life-changing treatments. A 63-year-old woman with progressive cognitive decline, pyramidal signs, and bilateral cataract was treated by chenodeoxycholic acid following the diagnosis of cerebrotendinous xanthomatosis due to a homozygous variant in CYP27A1. A 32-year-old man with adult-onset spastic paraplegia, in whom a variant in ABCD1 confirmed an X-linked adrenoleukodystrophy, was treated with corticoids for adrenal insufficiency. The third patient, a 28-year-old woman with early-onset developmental delay, epilepsy, and movement disorders was treated with a ketogenic diet following the identification of a variant in SLC2A1, confirming a glucose transporter type 1 deficiency syndrome. This case study illustrates the challenges in the timely diagnosis of medically actionable neurogenetic conditions, but also the considerable potential for improving patient health through modern sequencing technologies.

Syndromic disorders caused by gain-of-function variants in KCNH1, KCNK4, and KCNN3-a subgroup of K+ channelopathies

Decreased or increased activity of potassium channels caused by loss-of-function and gain-of-function (GOF) variants in the corresponding genes, respectively, underlies a broad spectrum of human disorders affecting the central nervous system, heart, kidney, and other organs. While the association of epilepsy and intellectual disability (ID) with variants affecting function in genes encoding potassium channels is well known, GOF missense variants in K⁺ channel encoding genes in individuals with syndromic developmental disorders have only recently been recognized. These syndromic phenotypes include Zimmermann–Laband and Temple–Baraitser syndromes, caused by dominant variants in KCNH1, FHEIG syndrome due to dominant variants in KCNK4, and the clinical picture associated with dominant variants in KCNN3. Here we review the presentation of these individuals, including five newly reported with variants in KCNH1 and three additional individuals with KCNN3 variants, all variants likely affecting function. There is notable overlap in the phenotypic findings of these syndromes associated with dominant KCNN3, KCNH1, and KCNK4 variants, sharing developmental delay and/or ID, coarse facial features, gingival enlargement, distal digital hypoplasia, and hypertrichosis. We suggest to combine the phenotypes and define a new subgroup of potassium channelopathies caused by increased K⁺ conductance, referred to as syndromic neurodevelopmental K⁺ channelopathies due to dominant variants in KCNH1, KCNK4, or KCNN3.

Birt-Hogg-Dubé syndrome

Birt–Hogg–Dubé syndrome (BHD) is a rare inherited autosomal dominant disorder caused by germline mutations in the tumour suppressor gene FLCN, encoding the protein folliculin. Its clinical expression typically includes multiple pulmonary cysts, recurrent spontaneous pneumothoraces, cutaneous fibrofolliculomas and renal tumours of various histological types. BHD has no sex predilection and tends to manifest in the third or fourth decade of life. Multiple bilateral pulmonary cysts are found on chest computed tomography in >80% of patients and more than half experience one or more episodes of pneumothorax. A family history of pneumothorax is an important clue, which suggests the diagnosis of BHD. Unlike other cystic lung diseases such as lymphangioleiomyomatosis and pulmonary Langerhans cell histiocytosis, BHD does not lead to progressive loss of lung function and chronic respiratory insufficiency. Renal tumours affect about 30% of patients during their lifetime, and can be multiple and recurrent. The diagnosis of BHD is based on a combination of genetic, clinical and/or skin histopathological criteria. Management mainly consists of early pleurodesis in the case of pneumothorax, periodic renal imaging for tumour detection, and diagnostic work-up in search of BHD in relatives of the index patient.

Birt–Hogg–Dubé syndrome is a rare genetic disorder characterised by multiple lung cysts, recurrent pneumothoraces, skin lesions and kidney tumours. As the presenting symptoms may be respiratory, chest physicians should be able to identify this disease.https://bit.ly/2xsOTuk

A New Variant in the MYH11 Gene in a Familial Case of Thoracic Aortic Aneurysm

MYH11 (myosin heavy chain 11) gene is involved in vascular contractility and several autosomal dominant mutations have been linked to thoracic aortic aneurysms. Three male members of the same family were found to carry a heterozygous missense variant in the MYH11 gene and all 3 individuals presented a thoracic aortic aneurysm/dilation. We identified a rare missense variant in the MYH11 gene predicted to be damaging and affecting a conserved amino acid in the myosin tail of the protein. This variant appears to be responsible for our familial case of thoracic aortic aneurysms, as the clinical expression reunited all features of genetic aneurysms.

Cascading speciation among mutualists and antagonists in a tree-beetle-fungi interaction

Cascading speciation is predicted to occur when multiple interacting species diverge in parallel as a result of divergence in one species promoting adaptive differentiation in other species. However, there are few examples where ecological interactions among taxa have been shown to result in speciation that cascades across multiple trophic levels. Here, we test for cascading speciation occurring among the western pine beetle (Dendroctonus brevicomis), its primary host tree (Pinus ponderosa), and the beetle's fungal mutualists (Ceratocystiopsis brevicomi and Entomocorticium sp. B). We assembled genomes for the beetle and a fungal symbiont and then generated reduced representation genomic data (RADseq) from range-wide samples of these three interacting species. Combined with published data for the host tree, we present clear evidence that the tree, the beetle, and the fungal symbionts are all genetically structured into at least two distinct groups that have strongly codiverged with geographical isolation. We then combine our genomic results with diverse population and laboratory-based data to show evidence for reproductive isolation at each level of the cascade and for coevolution of both antagonistic and mutualistic species interactions within this complex network.

Genetic and phenotypic influences on copulatory plug survival in mice

Across a diversity of animals, male seminal fluid coagulates upon ejaculation to form a hardened structure known as a copulatory plug. Previous studies suggest that copulatory plugs evolved as a mechanism for males to impede remating by females, but detailed investigations into the time course over which plugs survive in the female's reproductive tract are lacking. Here, we cross males from eight inbred strains to females from two inbred strains of house mice (Mus musculus domesticus). Plug survival was significantly affected by male genotype. Against intuition, plug survival time was negatively correlated with plug size: long-lasting plugs were small and relatively more susceptible to proteolysis. Plug size was associated with divergence in major protein composition of seminal vesicle fluid, suggesting that changes in gene expression may play an important role in plug dynamics. In contrast, we found no correlation to genetic variation in the protein-coding regions of five genes thought to be important in copulatory plug formation (Tgm4, Svs1, Svs2, Svs4 and Svs5). Our study demonstrates a complex relationship between copulatory plug characteristics and survival. We discuss several models to explain unexpected variation in plug phenotypes.

Divergence with gene flow within the recent chipmunk radiation (Tamias)

Increasing data have supported the importance of divergence with gene flow (DGF) in the generation of biological diversity. In such cases, lineage divergence occurs on a shorter timescale than does the completion of reproductive isolation. Although it is critical to explore the mechanisms driving divergence and preventing homogenization by hybridization, it is equally important to document cases of DGF in nature. Here we synthesize data that have accumulated over the last dozen or so years on DGF in the chipmunk (Tamias) radiation with new data that quantify very high rates of mitochondrial DNA (mtDNA) introgression among para- and sympatric species in the T. quadrivittatus group in the central and southern Rocky Mountains. These new data (188 cytochrome b sequences) bring the total number of sequences up to 1871; roughly 16% (298) of the chipmunks we have sequenced exhibit introgressed mtDNA. This includes ongoing introgression between subspecies and between both closely related and distantly related taxa. In addition, we have identified several taxa that are apparently fixed for ancient introgressions and in which there is no evidence of ongoing introgression. A recurrent observation is that these introgressions occur between ecologically and morphologically diverged, sometimes non-sister taxa that engage in well-documented niche partitioning. Thus, the chipmunk radiation in western North America represents an excellent mammalian example of speciation in the face of recurrent gene flow among lineages and where biogeography, habitat differentiation and mating systems suggest important roles for both ecological and sexual selection.

A novel mutation in SCN4A causes severe myotonia and school-age-onset paralytic episodes

Mutations in the pore-forming subunit of the skeletal muscle sodium channel (SCN4A) are responsible for hyperkalemic periodic paralysis, paramyotonia congenita and sodium channel myotonia. These disorders are classified based on their cardinal symptoms, myotonia and/or paralysis. We report the case of a Japanese boy with a novel mutation of SCN4A, p.I693L, who exhibited severe episodic myotonia from infancy and later onset mild paralytic attack. He started to have apneic episodes with generalized hypertonia at age of 11 months, then developed severe episodic myotonia since 2 years of age. He presented characteristic generalized features which resembled Schwarz-Jampel syndrome. After 7 years old, paralytic episodes occurred several times a year. The compound muscle action potential did not change during short and long exercise tests. Functional analysis of the mutant channel expressed in cultured cell revealed enhancement of the activation and disruption of the slow inactivation, which were consistent with myotonia and paralytic attack. The severe clinical features in his infancy may correspond to myotonia permanence, however, he subsequently experienced paralytic attacks. This case provides an example of the complexity and overlap of the clinical features of sodium channel myotonic disorders.

Targeted resequencing of a genomic region influencing tameness and aggression reveals multiple signals of positive selection

The identification of the causative genetic variants in quantitative trait loci (QTL) influencing phenotypic traits is challenging, especially in crosses between outbred strains. We have previously identified several QTL influencing tameness and aggression in a cross between two lines of wild-derived, outbred rats (Rattus norvegicus) selected for their behavior towards humans. Here, we use targeted sequence capture and massively parallel sequencing of all genes in the strongest QTL in the founder animals of the cross. We identify many novel sequence variants, several of which are potentially functionally relevant. The QTL contains several regions where either the tame or the aggressive founders contain no sequence variation, and two regions where alternative haplotypes are fixed between the founders. A re-analysis of the QTL signal showed that the causative site is likely to be fixed among the tame founder animals, but that several causative alleles may segregate among the aggressive founder animals. Using a formal test for the detection of positive selection, we find 10 putative positively selected regions, some of which are close to genes known to influence behavior. Together, these results show that the QTL is probably not caused by a single selected site, but may instead represent the joint effects of several sites that were targets of polygenic selection.

Phylogeography of the red-tailed chipmunk (Tamias ruficaudus), a northern Rocky Mountain endemic

The northern Rocky Mountains have experienced a complex history of geological events and environmental fluctuation, including Pleistocene glaciation. To provide an initial assessment of the genetic impact of this history on the regional biota we estimated phylogenetic relationships within Tamias ruficaudus, a regional endemic, from cytochrome b sequence variation using parsimony, maximum likelihood, and nested clade analysis. Analyses of sequence variation in 187 individuals from 43 localities across the distribution of T. ruficaudus indicate a history of vicariance events and range fluctuation consistent with successive periods of extensive Pleistocene glaciation in the northern Rocky Mountains. Intraspecific divergence levels (c. 4.7% uncorrected) and phylogenetic structure are consistent with a genealogical vicariance initiated prior to the Late Pleistocene, whereas nested clade analyses indicate more recent population history structured by both fragmentation and range expansion. A comparison of sequence variation with bacular morphology indicates that the two genetically and morphologically differentiated entities exhibit a zone of differential character introgression. Sequence data support a multiple refugia hypothesis and provide a phylogeographical case study for the ongoing synthesis of regional biogeography for northern Rocky Mountain endemics.

Disciplining social psychology: a case study of boundary relations in the history of the human sciences

This paper explores the disciplinary status of social psychology through an analysis of the history of the boundary relations of psychology, sociology, and social psychology. After outlining some research on the nature of scientific disciplines, on the role of rhetoric in the constitution of disciplines, and on "boundary work," I consider the singular importance of social psychology as a discipline for the analysis of boundary relations, examining its units of analysis and its "disciplining." The boundaries of the disciplines of social psychology were seen as fluid, contingent, local, and contestable, reflecting the thematic preoccupations, disciplinary origins, and meta-theoretical commitments of social psychologists, of the parent disciplines, and of those who represent disciplinary practices.

Renal response to candoxatrilat in patients with heart failure

OBJECTIVES

Our primary objective was to compare the effects of three different doses of candoxatrilat with the effects of placebo on urinary volume in patients with moderately severe heart failure. The effects of candoxatrilat on urinary composition, neuroendocrine indexes and renal hemodynamic function were also studied.

BACKGROUND

Candoxatrilat, a neutral endopeptidase inhibitor, reduces degradation of atrial natriuretic peptide and provokes diuresis in patients with mild heart failure, but the renal effects have not been studied in patients with moderately severe heart failure in a placebo-controlled study.

METHODS

In a double-blind crossover trial, the effects of intravenous boluses of saline vehicle (placebo) and 50, 100 and 200 mg of candoxatrilat were compared on separate days in 12 patients with heart failure. Urinary output and composition were measured for 8 h. Renal blood flow and glomerular filtration rate were determined by radionuclide techniques. Blood was withdrawn for the measurement of hormones before and 3 h after dosing.

RESULTS

All doses of candoxatrilat increased urinary volume (e.g., [mean +/- SEM] 263 +/- 53 to 490 +/- 82 ml for saline solution and the 200-mg dose, respectively, p < 0.01) and sodium content (14 +/- 4 to 37 +/- 11 mmol, p < 0.001) in the 1st 4 h after dosing. Plasma atrial natriuretic peptide increased (140 +/- 26 to 279 +/- 37 pg/ml, p < 0.01), whereas aldosterone decreased (178 +/- 41 to 125 +/- 35 pg/ml, p < 0.01), and renin activity was unchanged (10 +/- 2 to 12 +/- 3 ng/ml per h).

CONCLUSIONS

Candoxatrilat given acutely causes diuresis, even in patients with moderately severe heart failure.

Pyometra after endometrial resection and ablation

BACKGROUND

Hysteroscopic endometrial ablation is increasingly accepted as a safe means of controlling excessive uterine bleeding.

CASE

A 47-year-old woman underwent endometrial resection and ablation for menorrhagia and subsequently developed pyometra and bacteremia. Placement of an intrauterine drain and intravenous antibiotic therapy led to full recovery.

CONCLUSION

Postoperative pyometra occurred after endometrial resection and ablation, a procedure reported to have few complications. To our knowledge, this has not been reported before.

Elevated plasma endothelin concentrations in heart failure; an effect of angiotensin II?

Endothelin is a powerful vasoconstrictor that may be partly responsible for the increases in venous and arterial tone characteristic of heart failure. The release of endothelin from endothelial cells in culture is stimulated by angiotensin II. We investigated the relationship between plasma concentrations of immuno reactive endothelin-1 and angiotensin II in 25 patients with heart failure and eight with ischaemic heart disease but normal left ventricular function. Plasma concentrations of endothelin and angiotensin II were correlated (Spearman rank correlation coefficient of 0.72; P < 0.0001) in patients with heart disease. Plasma concentrations of angiotensin II and endothelin were higher in those patients with heart failure. Angiotensin II was infused over a 3 h period in eight healthy volunteers. Infusion of angiotensin II increased plasma concentrations of angiotensin II to levels greater than those usually found in patients with severe heart failure but induced only a modest rise in plasma concentrations of immunoreactive endothelin-1 (0.77 +/- 0.16 to 1.03 +/- 0.03 pmol.l-1, P < 0.02). Increased plasma concentrations of angiotensin II and endothelin-1 both appear to reflect the presence and severity of heart failure. Although a significant correlation exists between plasma concentrations of angiotensin II and endothelin in patients with heart failure, the relationship may not be causal.

Effect of intense angiotensin II suppression on the diuretic response to furosemide during chronic ACE inhibition

BACKGROUND

Contrary to expectation, most studies have demonstrated that initiation of an angiotensin-converting enzyme (ACE) inhibitor in conventional doses in patients with heart failure reduces the diuretic efficacy of furosemide. Recently, it has been suggested that single low doses (1 mg) but not high doses (25 mg) of captopril enhance furosemide-induced diuresis. It is not known whether the interaction between diuretics and ACE inhibitors are altered during long-term dosing.

METHODS AND RESULTS

Eight patients with heart failure treated with diuretics and ACE inhibitors for at least 3 months were studied. All patients were established on captopril 12.5 mg three times daily for 2 weeks before the study. Sodium intake was fixed before the study, and usual medication was withheld on study days. Intravenous furosemide was given on each of 2 study days to maintain a moderate, constant diuresis. Renal plasma flow and glomerular filtration rate (GFR) were determined using clearance techniques, and urine was collected hourly over 4 hours. Captopril 12.5 mg or placebo was given in a randomized, single-blind fashion at the end of the first hour. Compared with placebo, captopril reduced plasma concentrations of angiotensin II (23 +/- 18 versus 4 +/- 3 pg/ml 1 hour after dosing, P < .02) and systolic (131 +/- 31 versus 122 +/- 29 mm Hg, P < .01) and diastolic (74 +/- 15 versus 67 +/- 13 mm Hg, P < .05) blood pressures. GFR fell (55 +/- 24 versus 51 +/- 22 mL/min, P < .02) and effective renal plasma flow rose during the first (198 +/- 76 versus 231 +/- 49 mL/min) and second hours after dosing (185 +/- 69 versus 247 +/- 74 mL/min, P < .02). Similarly, urine volumes, in response to furosemide, increased after captopril (238 +/- 90 versus 283 +/- 111 mL, P < .05, and 245 +/- 78 versus 311 +/- 92 mL, P < .01, 1 and 2 hours after dosing). Urinary electrolyte concentrations fell, but total urinary sodium (22 +/- 7 versus 28 +/- 12 mmol/hr, P < .01) and chloride (20 +/- 6 versus 25 +/- 11 mmol/hr, P < .05) excretion increased in the 2 hours after dosing, as did fractional excretion of sodium (urinary sodium/urinary creatinine) (61 +/- 27 versus 75 +/- 36 mmol/mumol, P < .01).

CONCLUSIONS

Intense although transient ACE inhibition with captopril enhances the diuretic effects of furosemide during long-term ACE inhibition.

Population dynamics of plant nematodes in cultivated soil: effects of combinations of cropping systems and nematicides

The population density of Meloidogyne incognita was significantly reduced in land that was fallowed or cropped to crotalaria, marigold, bermudagrass, or bahiagrass. The rate of population decline caused by different cropping systems was influenced by initial population densities. Crotalaria, marigold, and bare fallow were about equally effective in reducing the density of M. incognita below dctectable lcvels, usually requiring 1-3 yr. Bahiagrass and bcrmudagrass required 4-5 yr or longer to reduce M. incognita below a detectable level. A high population density of Trichodorus christiei developed in land cropped 5 yr to bermudagrass, bahiagrass, okra, and marigold. Population densities of Pratylenchus brachyurus and Xiphinema americanum increased in land cropped to crotalaria or bermudagrass. Belonolabnus Iongicaudatus was detected only in land cropped to bermudagrass, The effectiveness of nematicides in reducing M. incognita infection was rclatcd to nematode population density resulting from 5 yr of different cropping systems. Treatment with aldicarb reduced M. incognita below detectable levels following all cropping systems; treatment with ethoprop following all cropping systems except okra, treatment wflh ethylene dibromide following bahiagrass or fallow; and treatment with DBCP only after 5 yr of fallow. Tomato transplant growth was affected .by both cropping systems and nematicide treatment. Transplants grown after crotalaria and bahiagrass were significantly larger than those grown after other crops. Also, treatment with aldicarb and ethoprop significantly increased transplant size.

Population dynamics of plant nematodes in cultivated soil: length of rotation in newly cleared and old agricultural land

During a 6-year study of 1-, 2-, and 3-year crop rotations, population densities of Pratylenchus brachyurus, Trichodorus christiei, and Meloidogyne incognita were significantly affected by the choice of crops but not by length of crop rotation. The density of P. brachyurus and T. christiei increased rapidly on milo (Sorghum vulgate). In addition, populations of P. brachyurus increased significantly in cropping systems that involved crotalaria (C. rnucronata), millet (Setaria italica), and sudangrass (Sorghum sudanense). Lowest numbers of P. brachyurus occurred where okra (Hibiscus esculentus) was grown or where land was fallow. The largest increase in populations of T. christiei occurred in cropping systems that involved millet, sudangrass, and okra whereas the smallest increase occurred in cropping systems that involved crotalaria or fallow. A winter cover of rye (Secale cereale) had no distinguishable effect on population densities of P. brachyurus or T. christiei. Meloidogyne incognita was detected during the fourth year in both newly cleared and old agricultural land when okra was included in the cropping system. Detectable populations of M. incognita did not develop in any of the other cropping systems. Yields of tomato transplants were higher on the newly cleared land than on the old land. Highest yields were obtained when crotalaria was included in the cropping system. Lowest yields were obtained when milo, or fallow were included in the cropping system. Length of rotation had no distinguishable effect on yields of tomato transplants.

Relative Efficacy of Selected Volatile and Nonvolatile Nematicides for Control of Meloidogyne incognita on Tobacco

Root-knot nematode control and tobacco yields in plots infested with Meloidogyne incognita and treated with the nonvolatile nematicides, aldicarb, Mocap (R), or Nemacur (R) were greater than those on similar plots treated with volatile nematicides such as DD, DD + MENCS, SD14647 or tetrachlorothiophene. Root-knot control and tobacco yields in plots treated with carbofuran or Dasanit (R) were eqtual to that obtained with DD + MENCS, but less than that obtained with the other volatile soil nematicides. The most efficient dosage was 3.4 kg/hectare active ingredient for aldicarb and Mocap (R) and 10.0 kg/hectare for Dasanit (R). Carbofuran and Nemacur (R) were equally as effective at 4.2 kg/hectare as they were at higher dosages. The most efficient dosage of DD and SD14647 was 84 liters/hectare. Aldicarb and Dasanit (R) resulted in better nematode control and tobacco yields when incorporated into the top 15-20 cm of soil than when incorporated into the top 5-10 cm of soil. Nemacur (R) and Mocap (R) performed better when incorporated into the top 5-10 cm of soil, and carbofuran performed better when applied in the seed furrow (placed 15-20 cm deep in a 5-cm band and bedded).

Population dynamics of plant nematodes in cultivated soil: effect of summer cover crops in newly cleared land

Five nematode species were studied for ability to develop on seven summer cover crops in rotation with tomato transplants grown every third year. Increase of Tylenchorhynchus claytoni, Trichodorus christiei, Pratylenchus brachyurus, Helicotylenchus dihystera, and Xiphinema americanum in newly cleared soil varied with different cover crops. No substantial nematode population increases occurred until the third summer of crop growth. All species except X. americanum and H. dihystera developed best on sudangrass and millet. Crotalaria caused substantial increase of H. dihystera and P. brachyurus but suppressed the other species. Marigold suppressed all species except X. americanum which increased substantially on marigold during the 5th year. Cotton favored rapid increase of T. christiei, and moderate increases of all species except T. claytoni which was suppressed. Beggarweed favored moderate increases of T. christiei and H. dihystera but suppressed the other species. Hairy indigo favored rapid increase of H. dihystera, moderate increases of T. christiei and X. americanum, and suppressed the other species. Number of marketable transplants was reduced after 2 years of sudangrass and cotton; these crops favored increases of T. christiei and T. claytoni. The better cover crops prevented increases of most plant parasitic nematodes in land cropped to tomato, a suitable host.

Population Dynamics of Plant Nematodes in Cultivated Soil: Effect of Sod-based Rotations in Tifton Sandy Loam

In an 8-year sod-based rotation study, nematode population densities varied with different row-crop sequences and grass sods. In continuous row-crop rotations (cotton-corn-peanut), cotton and corn favored rapid increase of Belonolaimus longicaudatus and Trichodorus christiei. Numbers of Pratylenchus brachyurus were quite variable on all crops. Peanuts favored an increase of Criconemoides ornatum but suppressed the other three species. 'Coastal' bermudagrass supported more than twice the number of B. longicaudatus than did 'Pensacola' bahiagrass. Numbers of T. christiei and P. brachyurus also were larger on bermudagrass than on bahiagrass. Numbers of C. ornatum were largest in row-crop sequence culture. Average numbers of B. longicaudatus, T. christiei, and P. brachyurus in a sod-based, 3-years of row-crop sequence were smallest when cotton and corn did not follow each other. These nematodes were further suppressed when the sequence corn-peanut-cotton followed bahiagrass. Numbers of C. ornatum were smallest when corn and cotton followed each other, except after 3 years of bahiagrass. Nematode populations were less influenced by row-crop sequence following bermudagrass than they were following bahiagrass.

Population dynamics of plant nematodes in cultivated soil: effect of summer cover crops in old agricultural land

In a 6-year cover crop sequence study, nematode population densities varied with different cover crops. Millet favored rapid increase of Belonolaimus longicaudatus and supported relatively large numbers of Pratylenchus brachyurus. Beggarweed and 'Coastal' bermudagrass favored rapid increase of B. Iongicaudatus and to a lesser extent P. brachyurus and Trichodorus christiei. Hairy indigo and Crotalaria supported relatively large numbers of P. brachyurus but suppressed B. longicaudatus. Hairy indigo also supported increases of T. christiei and Xiphinema americanum. Marigold did not favor development of any parasitic nematode species present. Tomato transplant yield was inversely related to nematode population, particularly to B. Iongicaudatus. Largest yields were obtained from plots with smallest numbers of B. longicaudatus and smallest yields were from plots with largest numbers of B. longicaudatus.

Population Dynamics of Plant Nematodes in Cultivated Soil: Effect of Sod-based Rotations in Cecil Sandy Loam

In a 6-year study of four nematode species in sod-based corn (Zea mays) rotations, population densities varied with different cropping systems. Continuous corn, with or without a winter rye (Secale cereale) or vetch (Vicia villosa) cover, favored an increase of Pratylenchus zeae and suppressed Trichodorus christiei, Helicotylenchus dihystera, and Xiphinema americanum. A four-year sod-based rotation (3 years sod, 1 year corn) of 'Coastal' bermudagrass (Cynodon dactylon) and fescue (Festuca arundinacea) was less favorable for P. zeae than was monocultured corn but was more favorable for T. christiei. Alfalfa (Medicago sativum) and rescue favored an increase of T. christiei but suppressed the other three species. 'Coastal' bermudagrass and 'Pensacola' bahiagrass (Paspalum notaturn) were not favorable for extensive development of any nematode species present. In longer term studies, of which these are a part, all four species survived for 10 years in relatively low numbers in bermudagrass and bahiagrass sods.