Association of exposure to secondhand smoke at home with early age at menarche in South Korea

OBJECTIVES

The secular trend in age at menarche (AAM) has declined both worldwide and in Korea. Early AAM is associated with the risk of several diseases, reproductive capacity, and psychological problems. We aimed to investigate the relationship between secondhand smoke (SHS) exposure at home and early puberty onset using AAM in Korean adolescents.

STUDY DESIGN

This is a retrospective cross-sectional study.

METHODS

This study used data from the Korea Youth Risk Behavior Web-based Survey 2014-2015. We used the mean AAM (12.2 years) as a determinant of early AAM. After the exclusion of girls without menarche or who did not respond, the total population comprised 63,618 participants. We categorized AAM as 'early' and 'average or late.' Adolescents with SHS exposure were assigned to the 'never exposed,' 'light exposure,' and 'heavy exposure' groups. Multiple logistic regression analyses were performed.

RESULTS

We observed a positive association, approximately 1.12 times, between early AAM and high SHS exposure (odds ratio [OR], 1.12; 95% confidence interval [CI], 1.05-1.19). Girls who started smoking before the age of 12 years (OR, 1.68; 95% CI, 1.41-1.99) showed a stronger association with early AAM than non-smokers. Active smoking showed a stronger association with early AAM. Never smokers with high SHS exposure at home were 1.13 times likelier to have an early AAM (OR, 1.13; 95% CI, 1.05-1.22) than those without SHS exposure.

CONCLUSIONS

In addition to active smoking, SHS may also be a risk factor for early AAM. Education aimed at active and secondhand smoking prevention is needed to protect children against early AAM.

Effect of Sedentary Time on the Risk of Orthopaedic Problems in People Aged 50 Years and Older

OBJECTIVE

Many people experience orthopaedic problems (OPPs), such as knee joint pain, hip joint pain, low back pain, and knee stiffness in their lifetimes. OPPs can impair lower extremity function, cause depression, and worsen quality of life. The aim of this study was to investigate the association between sedentary time (SDT) and OPPs.

DESIGN

Retrospective cross-sectional study.

SETTING

This study used data from the 2014-2015 Korea National Health and Nutrition Examination Survey. Survey participants with previous or current osteoarthritis or rheumatoid arthritis, as diagnosed by a doctor, were excluded. OPPs were defined as knee joint pain, hip joint pain, low back pain, and knee stiffness. The cut-off value for SDT was 7.5 hours/day. The study population comprised 3,671 people (1,856 men and 1,815 women), all of whom were ≥50 years-old. Multiple logistic regression analyses were performed.

RESULTS

A total of 328 men (17.7%) and 519 women (28.6%) had OPPs. Men with SDTs ≥7.5 hours had a greater risk of OPPs than did men with SDTs <7.5 hours (odds ratio [OR], 1.45; 95% confidence interval [CI], 1.08-1.93). A pink-collar job, physical inactivity during leisure time, and passive (e.g. riding in a car or train) versus active (e.g. walking or riding a bicycle) transportation predicted OPPs in men with SDTs ≥7.5 hours. SDT was a risk factor for knee joint pain in men (OR, 1.80; 95% CI, 1.11-2.92) and hip joint pain in women (OR, 2.05; 95% CI, 1.35-3.11).

CONCLUSIONS

In men, prolonged SDT is a risk factor for OPPs. More physical activity programmes should be launched at the community level for people ≥50 years-old to reduce the occurrence of OPPs.

Do severe maternal morbidity and adequate prenatal care affect the delivery cost? A nationwide cohort study for 11 years with follow up

OBJECTIVE

To explore whether severe maternal morbidity (SMM) and adequate prenatal care (PNC) affect delivery cost.

DESIGN

Population-based retrospective cohort study.

SETTING

National Health Insurance Service National Sample Cohort in Korea.

POPULATION

A total of 90 035 deliveries in 2003 and 2013.

METHODS

Severe maternal morbidity was determined using the Centers for Disease Control and Prevention's algorithm. Delivery medical costs were calculated by estimating claimed total medical costs using year-specific inflation adjustment factors. Adequate PNC was estimated by the Kessner Adequacy of Prenatal Care Index. To estimate adjusted mean delivery medical costs related to SMM, we applied a generalised estimating equation model with log link and γ distribution, by adjusting for all covariates.

MAIN OUTCOME MEASURES

Delivery cost was calculated by estimating claimed total medical cost during delivery hospitalisation using year-specific inflation.

RESULTS

Of the 90 035 deliveries, 2041 (2.27%) involved SMM. Women with SMM had a greater adjusted mean cost of delivery (US$ 1,263, 95% CI US$ 1,196-1,334) than those without (US$ 740, 95% CI US$ 729-750). Interestingly, women who had inadequate PNC had higher delivery medical costs than those with adequate PNC, adjusted for all covariates.

CONCLUSION

Delivery involving SMM was associated with nearly doubled medical costs. Additionally, inadequate PNC increased the medical costs of delivery. The current study confirmed the burden of SMM and found that adequate PNC might be a useful preventive factor in reducing medical costs.

TWEETABLE ABSTRACT

We found that women with severe maternal morbidity and inadequate prenatal care had increased medical costs during delivery hospitalisation.

Do family meals affect childhood overweight or obesity?: nationwide survey 2008-2012

BACKGROUND

The prevalence of childhood obesity is increasing worldwide and this trend is no exception for South Korea. A multidisciplinary approach is needed for the prevention and management of childhood obesity. To do so, among many other strategies, managing the family unit can be a very effective strategy.

OBJECTIVES

The purpose of this study was to identify the relationship between frequency of family meals and overweight/obesity in elementary students and to suggest the management and prevention strategies of childhood obesity.

METHODS

Data from a total of 2904 elementary students were analyzed from the 2008-2012 Korea National Health and Nutrition Examination Survey. Multiple logistic regression analysis was used to examine the association between overweight/obesity and family meals.

RESULTS

Of the total 2904 elementary students, 573 (19.4%) were overweight or obese. The odds ratio of overweight or obese students who had family dinner only was 1.21 (95% CI: 0.89-1.64), that of those who had family breakfast only was 3.20 (95% CI: 1.70-6.02), and that of those who had neither family breakfast nor family dinner was 4.17 (95% CI: 1.98-8.78) compared with those who had both family breakfast and family dinner.

CONCLUSIONS

The frequency of family meals was strongly an inverse association with childhood overweight or obesity. Therefore, we suggest that the intervention of childhood obesity should include family meals.

Chronic obstructive lung disease-related health care utilisation in Korean adults with obstructive lung disease

OBJECTIVES

The numbers of nationwide epidemiological surveys about chronic obstructive pulmonary disease (COPD) prevalence and prospective cohort studies for health care utilisation are limited. We investigated COPD-related health care utilisation in adults with obstructive lung disease in the second Korean National Health and Nutritional Survey (KNHANES II) in 2001 using Korean national medical insurance claim data.

METHODS

Among people aged >40 years, obstructive lung disease (OLD) is defined according to Global Initiative for Chronic Obstructive Lung Disease criteria. Data from a total of 1942 subjects were linked with Korean national medical insurance claims data, and we investigated their COPD-related out-patient visits from 2002 to 2005.

RESULTS

Among the 1942 subjects, 256 (13.2%) had airflow obstruction. COPD-related out-patient visits were reported for 8.2% of patients without airway obstruction, 18.1% of those with mild airway obstruction, and 33.9% of those with moderate to very severe airway obstruction. Multivariate analysis revealed that previous COPD diagnosis by a physician (OR 2.54; P = 0.02) and lower socio-economic status (OR 0.45; P = 0.02) were independent predictors of COPD-related out-patient visits in subjects with OLD.

CONCLUSIONS

Of the subjects with airway obstruction, those with poor financial status utilised COPD-related health care services less frequently, and those previously diagnosed as having COPD by a physician utilised the services more frequently.

Smoking, alcohol and gastric cancer risk in Korean men: the National Health Insurance Corporation Study

We investigated the risk of gastric cancer by subsite in relation to cigarette smoking and alcohol in a large population-based cohort of 669 570 Korean men in an insurance plan followed for an average 6.5 years, yielding 3452 new cases of gastric cancer, of which 127 were cardia and upper-third gastric cancer, 2409 were distal gastric cancer and 1007 were unclassified. A moderate association was found between smoking, cardia and upper-third (adjusted relative risk (aRR) 2.2; 95% confidence interval (CI) 1.4-3.5) and distal cancers (aRR=1.4; 95% CI=1.3-1.6). We also found a positive association between alcohol consumption and distal (aRR=1.3; 95% CI=1.2-1.5) and total (aRR=1.2; 95% CI=1.1-1.4) gastric cancer. Combined exposure to high levels of tobacco and alcohol increased the risk estimates further; cardia and upper-third gastric cancers were more strongly related to smoking status than distal gastric cancer.British Journal of Cancer (2007) 97, 700-704. doi:10.1038/sj.bjc.6603893 www.bjcancer.com Published online 17 July 2007.

EFFECTS OF LOCAL ANESTHETICS ON THE CONTRACTILITY OF RAT BLADDERS

PURPOSE

We investigated the effect of local anesthetic agents on the detrusor muscle in rats.

MATERIALS AND METHODS

In vitro isometric contraction of rat detrusor strips was measured. We investigated the effects of tetracaine, bupivacaine and lidocaine on baseline spontaneous contractions and contractions induced by various stimuli, including 60 mM. KCl, carbachol and electricalal field stimulation with a pulse duration of 0.8 or 100 milliseconds.

RESULTS

Local anesthetic agents have complex effects on baseline spontaneous contractility that depend on the type of agent used and its concentration. These agents inhibited nerve mediated contraction resulting from electricalal field stimulation with a pulse duration of 0.8 milliseconds in a concentration dependent manner and also inhibited nonnerve mediated detrusor contractions induced by KCl, carbachol or electricalal field stimulation with a pulse duration of 100 milliseconds Higher concentrations of local anesthetic agents were needed to inhibit nonnerve than nerve mediated contractions. In rat detrusor muscle carbachol induced a sustained tonic contraction even after the depletion of internal and external Ca2+ sources, which was also inhibited by local anesthetic agents.

CONCLUSIONS

These results show that local anesthetic agents have a wide spectrum of inhibitory effects on the contraction of bladder smooth muscle induced by various stimulants at different concentrations, which may be potentially useful for treating overactive bladder.

NT-4/5 exacerbates free radical-induced neuronal necrosis in vitro and in vivo

Neurotrophins render neurons highly vulnerable to certain injuries. We examined the possibility that NT-4/5 would enhance free radical neurotoxicity in vivo as well as in vitro. Striatal neurons exposed to 10 microM Fe(2+) or 1 mM l-buthionine-[S, R]-sulfoximine (BSO) underwent mild degeneration within 24 h. With concurrent addition of 10-100 ng/ml NT-4/5, neuronal death following exposure to Fe(2+) or BSO was significantly increased and suppressed by addition of 100 microM trolox, an antioxidant. In the adult brain, the intrastriatal injections of 20 nmol Fe(2+) revealed features of neuronal necrosis such as swelling cell body and mitochondria, fenestration of plasma membrane prior to nuclear membrane, and scattering condensation of nuclear chromatin. Cotreatment with 1.8 microg NT-4/5 augmented the striatal damage 24 h following the injections of Fe(2+). This study implies that free radicals produce necrotic degeneration in vivo as well as in vitro that becomes more sensitive in the presence of neurotrophins.

Nuclear factor kappa B-mediated kainate neurotoxicity in the rat and hamster hippocampus

Administration of the excitotoxin kainate produces seizure activity and selective neuronal death in various brain areas. We examined the degeneration pattern of hippocampal neurons following systemic injections of kainate in the hamster and the rat. As reported, treatment with kainate resulted in severe neuronal loss in the hilus and CA3 in the rat. While the hilar neurons were also highly vulnerable to kainate in the hamster, neurons in the CA1 area, but not CA3, were highly sensitive to kainate. In both animals, immunoreactivity to anti-p50 nuclear factor kappa B antibody was increased in nuclei of the hilar neurons within 4 h following administration of kainate. Kainate treatment also increased the nuclear factor kappa B immunoreactivity in hamster CA1 neurons and rat CA3 neurons 24 h later. Neurons showing intense nuclear factor kappa B signal were stained with acid fuchsin. Kainate also increased DNA binding activity of p50 and p65 nuclear factor kappa B in the nuclear extract of the hippocampal formation as analysed by electrophoretic mobility shift assay in the hamster, suggesting that activation of nuclear factor kappa B may contribute to kainate-induced hippocampal degeneration. Administration of 100 nmol dizocilpine maleate 3 h prior to kainate attenuated kainate-induced activation of nuclear factor kappa B and neuronal death in CA1 in the hamster. The present study provides evidence that the differential vulnerability of neurons in the rat and the hamster hippocampus to kainate is partly mediated by mechanisms involving N-methyl-D-aspartate-dependent activation of nuclear factor kappa B.

Quality of life in Korean patients with inflammatory bowel diseases: ulcerative colitis, Crohn's disease and intestinal Behçet's disease

Health-related quality of life (HRQOL) is an important outcome factor in chronic diseases such as inflammatory bowel disease (IBD). This study used the Korean translation of the disease-specific, self-administered Inflammatory Bowel Disease Questionnaire (IBDQ) to compare HRQOL in ulcerative colitis (UC; n = 98), Crohn's disease (CD; n = 49), and intestinal Behçet's disease (BD; n = 34). In addition to the current status, patients were asked retrospectively to recall their symptoms at the beginning and during the worst period of their disease. Disease activity was measured by St. Mark's Activity Index, Crohn's disease Activity Index (CDAI), and the Harvey-Bradshaw Index (HBI). In all IBD patients, including those with BD, the IBDQ total score during the worst period was significantly lower than that at present and that at the beginning of the disease. However, there were no significant differences between groups regarding the total IBDQ score or its various dimensions. In UC a strong correlation between IBDQ scores and St. Mark's Activity Index was observed (r = -0.708, P < 0.001). IBDQ scores were also highly correlated with CDAI and HBI in both CD (r = -0.506, P < 0.001 for CDAI; r = -0.600, P < 0.001 for HBI) and BD (r = -0.687, P < 0.001 for CDAI; r = -0.531, P < 0.001 for HBI). However, the current IBDQ score was not related to demographic parameters such as gender, age, educational status, economic status, and marital status as well as disease factors such as duration of disease, history of operation or hospital admission, extent of disease in UC, involved region in CD, and clinical type in BD. We conclude that the Korean IBDQ is a responsive and promising instrument for measuring HRQOL of IBD patients in clinical trials. In addition, the IBDQ can be helpful in developing a disease-specific activity index in BD.

Tumor induction of VEGF promoter activity in stromal cells

We have established a line of transgenic mice expressing the A. victoria green fluorescent protein (GFP) under the control of the promoter for vascular endothelial growth factor (VEGF). Mice bearing the transgene show green cellular fluorescence around the healing margins and throughout the granulation tissue of superficial ulcerative wounds. Implantation of solid tumors in the transgenic mice leads to an accumulation of green fluorescence resulting from tumor induction of host VEGF promoter activity. With time, the fluorescent cells invade the tumor and can be seen throughout the tumor mass. Spontaneous mammary tumors induced by oncogene expression in the VEGF-GFP mouse show strong stromal, but not tumor, expression of GFP. In both wound and tumor models the predominant GFP-positive cells are fibroblasts. The finding that the VEGF promoter of nontransformed cells is strongly activated by the tumor microenvironment points to a need to analyze and understand stromal cell collaboration in tumor angiogenesis.

Nerve growth factor potentiates the oxidative necrosis of striatal cholinergic neurons

We examined the effects of nerve growth factor (NGF) on free radical neurotoxicity in striatal cell cultures. Following exposure to 30 microM Fe2+ or 1 mM L-buthionine-[S,R]-sulfoximine (BSO), an inhibitor of gamma-glutamylcysteine synthetase, striatal neurons underwent cell body swelling and then widespread death over the next 24 h. The degeneration was prevented by addition of 100 microM trolox, an antioxidant. Addition of 100 ng/ml BDNF beginning 12 h before Fe2+ or BSO potentiated necrosis of most striatal neurons after exposure to 10 microM Fe2+ or 1 mM BSO. In contrast, treatment with 100 ng/ml NGF selectively potentiated the oxidative degeneration of striatal cholinergic neurons. The present findings provide additional evidence that NGF, like other neurotrophins, can potentiate oxidative neuronal cell necrosis.

Codon usage limitation in the expression of HIV-1 envelope glycoprotein

BACKGROUND

The expression of both the env and gag gene products of human immunodeficiency virus type 1 (HIV-1) is known to be limited by cis elements in the viral RNA that impede egress from the nucleus and reduce the efficiency of translation. Identifying these elements has proven difficult, as they appear to be disseminated throughout the viral genome.

RESULTS

Here, we report that selective codon usage appears to account for a substantial fraction of the inefficiency of viral protein synthesis, independent of any effect on improved nuclear export. The codon usage effect is not specific to transcripts of HIV-1 origin. Re-engineering the coding sequence of a model protein (Thy-1) with the most prevalent HIV-1 codons significantly impairs Thy-1 expression, whereas altering the coding sequence of the jellyfish green fluorescent protein gene to conform to the favored codons of highly expressed human proteins results in a substantial increase in expression efficiency.

CONCLUSIONS

Codon-usage effects are a major impediment to the efficient expression of HIV-1 genes. Although mammalian genes do not show as profound a bias as do Escherichia coli genes, other proteins that are poorly expressed in mammalian cells can benefit from codon re-engineering.

Cross-specialty linkage and extrapolation of resource-based relative value scales

This article describes methods used to produce a RBRVS (resource-based relative value scales), a common scale from two specialties (internal medicine and general surgery) and explains the newly developed extrapolation process within each specialty. To produce a common scale, we selected six 'same' services as linking services common to both specialties. Then we used the bi-weighted least squares method to locate all the same services on a single, common scale. By using the same method, we tried to extrapolate all the services within each specialty, not by the method of Kelly et al, dividing all the services within the specialty into families (small homogeneous groups of services) to apply charge-based ratios. To compare both methods, we extrapolated all the services of general surgery according to each method. With the correlation analysis to compare both results to American RVUs, we found that general surgery's RVUs from our own extrapolation method turned out to be more highly correlated with American RVUs than from Kelly's extrapolation method. Consequently, extrapolation with bi-weighted least squares method gave reasonable results.

An epidemiological study of metagonimiasis along the upper reaches of the Namhan River

An epidemiological study of Metagonimus infection was undertaken along the upper reaches of the Namhan River, with special consideration on the species (type) of the worms collected from humans. Eggs of Metagonimus spp. were detected from 15 (9.7%) of 154 people examined in Umsong-gun, and from each infected person (5 cases) 6,015-24,060 worms (mean 13,233) were recovered after treatment with praziquantel (10 mg/kg). Eggs were also detected from 37 (48.1%) of 77 people in Yongwol-gun, from whom (27 cases) 1-4,965 worms (means 1,215) were collected. The worm from Umsong-gun consisted of both Metagonimus Miyata type and Metagonimus takahashii, whereas those from Yongwol-gun consisted of only Metagonimus Miyata type. When the uterine eggs of the two kinds and M. yokogawai (obtained from people in Tamjin River basin) were morphologically compared, it was suggested that the egg size should be a good indicator for discrimination of the species or type. The source of human infection was proved to be fresh water fishes; 49 of 52 Zacco platypus examined, 6 of 8 Hemibarbus longirostris, 13 of 15 Pseudogobio esocinus, 4 of 6 Odontobutis obscura interrupta, and 17 of 18 Carassius carassius were found infected with Metagonimus metacercariae. From the results, it is concluded that the upper reaches of the Namhan River are endemic foci of Metagonimus Miyata type and M. takahashii.

ARD1 and NAT1 proteins form a complex that has N-terminal acetyltransferase activity

Two yeast genes, ARD1 and NAT1, are required for the expression of an N-terminal protein acetyltransferase. This activity is required for full repression of the silent mating type locus HML, for sporulation, and for entry into G0. While the NAT1 gene product is thought to be the catalytic subunit of the enzyme, the role of the ARD1 protein has remained unclear. We have used epitope tagged derivatives of ARD1 and NAT1 to provide biochemical evidence for the formation of an ARD1-NAT1 complex, and to show that both proteins are required for the N-terminal acetyltransferase activity. We also present evidence for the formation of ARD1-ARD1 homodimers. Deletion analysis suggests that the C-terminal region of ARD1 may be involved in the formation of both ARD1-ARD1 and ARD1-NAT1 complexes.

A strategy for the generation of conditional mutations by protein destabilization

Conditional mutations such as temperature-sensitive (ts) mutations are important for the analysis of protein function but are often difficult, or impossible, to obtain. Here we present a simple method for generating conditional mutations based on the use of a protein-destabilizing genetic element in combination with systems allowing the induction and repression of gene expression. This genetic cassette can be fused to other protein-coding sequences, and once transcription is turned off and synthesis of the gene product ceases, the preexisting protein is rapidly degraded. We have applied this method to the analysis of the yeast ARD1 gene product, a subunit of an N-terminal acetyltransferase, and show that a complete loss of ARD1 product can be achieved in less than one generation. Despite the rapid loss of ARD1 protein, there is a prolonged delay in the expression of the ard1 mutant phenotype, suggesting that the acetylated substrates of ARD1 are metabolically stable and/or exert a long-lasting effect on processes such as the repression of the silent mating type cassettes.

Point mutations in the yeast histone H4 gene prevent silencing of the silent mating type locus HML

The N-terminal serine and four conserved lysine residues near the N-terminus of yeast histone H4 are acetylated. We found that a mutation that changed the fourth lysine to alanine resulted in specific derepression of the silent mating type locus HML, while mutations that altered the N-terminal serine or the first three lysines had only minor phenotypic effects. Our results support an active role for histone H4 in the silencing of gene expression at this locus.

The Caenorhabditis elegans rol-6 gene, which interacts with the sqt-1 collagen gene to determine organismal morphology, encodes a collagen

The rol-6 gene is one of the more than 40 loci in Caenorhabditis elegans that primarily affect organismal morphology. Certain mutations in the rol-6 gene produce animals that have the right roller phenotype, i.e., they are twisted into a right-handed helix. The rol-6 gene interacts with another gene that affects morphology, sqt-1; a left roller allele of sqt-1 acts as a dominant suppressor of a right roller allele of rol-6. The sqt-1 gene has previously been shown to encode a collagen. We isolated and sequenced the rol-6 gene and found that it also encodes a collagen. The rol-6 gene was identified by physical mapping of overlapping chromosomal deficiencies that cover the gene and by identification of an allele-specific restriction site alteration. The amino acid sequence of the collagen encoded by rol-6 is more similar to that of the sqt-1 collagen than to any of the other ten C. elegans cuticle collagen sequences compared. The locations of cysteine residues flanking the Gly-X-Y repeat regions of rol-6 and sqt-1 are identical, but differ from those in the other collagens. The sequence similarities between rol-6 and sqt-1 indicate that they represent a new collagen subfamily in C. elegans. These findings suggest that these two collagens physically interact, possibly explaining the genetic interaction seen between the rol-6 and sqt-1 genes.

Acute appendicitis mimicking pelvic neoplasm

Acute appendicitis can be difficult to diagnose when it presents in an atypical manner. We report a case of perforated appendicitis mimicking a pelvic neoplasm.

Modification of the Kock pouch urinary diversion in a child

We constructed a continent ileal urinary reservoir (Kock pouch) in a 9-year-old boy. The length of bowel required to achieve a satisfactory outcome was scaled down for this young, small child.

Mutations with dominant effects on the behavior and morphology of the nematode Caenorhabditis elegans

We have analyzed 31 mutations that have dominant effects on the behavior or morphology of the nematode Caenorhabditis elegans. These mutations appear to define 15 genes. We have studied ten of these genes in some detail and have been led to two notable conclusions. First, loss of gene function for four of these ten genes results in a wild-type phenotype; if these genes represent a random sample from the genome, then we would estimate that null mutations in about half of the genes in C. elegans would result in a nonmutant phenotype. Second, the dominant effects of mutations in nine of these ten genes are caused by novel gene functions, and in all nine cases the novel function is antagonized by the wild-type function.

C. elegans unc-105 mutations affect muscle and are suppressed by other mutations that affect muscle

Certain mutations in the unc-105 II gene of the nematode Caenorhabditis elegans have dominant effects on morphology and behavior: animals become small, severely hypercontracted and paralyzed. These unc-105 mutants revert both spontaneously and with mutagens at high frequencies to a wild-type phenotype. Most of the reversion events are intragenic, apparently because the null (loss-of-function) phenotype of unc-105 is wild type. One revertant defined an extragenic suppressor locus, sup-20 X. Such suppressor alleles of sup-20 are rare, and the apparent null phenotype of sup-20 is embryonic lethality. By constructing animals genetically mosaic for sup-20, we have shown that the primary effect of sup-20 is in muscle cells. In addition to mutations in sup-20, other mutations causing muscle defects, such as unc-54 and unc-22 mutations, suppress the hypercontracted phenotype of unc-105. The ease of identifying nonhypercontracted revertants of unc-105 mutants greatly facilitates the isolation of new mutants defective in muscle structure and function.