Optical networks for local loop applications

Some of the options for optical technology within the local loop environment are examined. In particular, passive shared access networks have been considered in some detail. These networks show great promise for delivering existing telephone services to small to medium business customers (4-30 lines) economically by the early 1990s. Extending fiber to the home will also be possible by virtue of a similar passive network infrastructure for customers requiring new broadband services beyond the single telephone line. For one-line plain old telephone service (POTS) customers, an intermediate approach of terminating the fiber network at the final network distribution point, with copper retained for the final leg, may be used prior to the provision of broadband services. A key feature of the passive optical network architecture is the use of wavelength-division multiplexing (WDM) as an upgrade strategy, allowing graceful upgrading from telephone services to multichannel high-definition television (HDTV) on gigabit/second bearers and full two-way switched broadband services employing wavelength routing across the network     

The validity of new memory complaints in the elderly

OBJECTIVE: To determine the validity of new subjective memory complaints (MCs) from individuals who previously, when without dementia, denied having MCs. DESIGN: Prospective cohort. SETTING: Longitudinal, community-based study of aging and dementia. PATIENTS: One hundred thirty-three community-dwelling elderly individuals who were part of a registry for the study of conditions related to aging in North Manhattan, NY. Patients were selected if they were initially without dementia and had completed at least 2 successive annual clinical and neuropsychological evaluations and provided their own medical history. MAIN OUTCOME MEASURES: Performance on memory tests--the Buschke Selective Reminding Test and a visual memory task--and global performance on a neuropsychological test battery and clinical evaluation, by which questionable dementia or dementia was diagnosed according to a well-defined paradigm. RESULTS: Fifty-three subjects with MCs at the initial evaluation performed no worse on the memory test than the 80 subjects who denied MCs initially. There was a weak association between MCs and the diagnosis of questionable dementia at baseline (P = .04), but this was nonsignificant after adjusting for age and education. At 1-year follow-up, 21 of the 80 without baseline MCs now reported MCs. At the follow-up evaluation, these 21 subjects performed significantly worse on the memory tests, were 5 times more likely to have significant cognitive impairment, and had shown significantly greater decline over the preceding year on several of the cognitive measures than the 59 who continued to deny MCs. CONCLUSION: New MCs from individuals, who when without dementia recently denied MCs, may suggest the presence of significant impairment of memory or cognition.     

Estimation of the interindividual variability in the one-compartment pharmacokinetic model for methylmercury: implications for the derivation of a reference dose

A critical step in the U.S. EPA's derivation of an Reference Dose (RfD) for methylmercury is conversion of the maternal hair Hg concentration of 11 ppm to average daily intake using the one-compartment pharmacokinetic model. A default uncertainty factor (UF) adjustment of 3 for interindividual variability was then applied to this conversion. A probabilistic (Monte Carlo) analysis is presented estimating the interindividual variability inherent in this dose conversion for women 18-40 years old based on data in the scientific literature. The dose of 1.1 micrograms/kg/day, calculated by the U.S. EPA to correspond to 11 ppm Hg in hair, is estimated in this analysis to be larger than 94-99% of corresponding doses. The application of a UF of 3 to this U.S. EPA value gives a dose which is estimated to be larger than 28-73% of corresponding doses. This analysis suggests that if the dose conversion in the RfD is intended to be inclusive of 95-99% of women 18-40, the daily intake should be set at 0.1-0.3 microgram/kg/day. The RfD of 0.03-0.1 microgram/kg/day, derived from this dose by the U.S. EPA's application of an additional UF of 3 for additional toxicologic concerns, is somewhat smaller than the current RfD of 0.1 microgram/kg/day.     

Partial cricotracheal resection with primary anastomosis in the pediatric age group

The traditional approach to severe subglottic stenosis (SGS) in the pediatric age group is laryngotracheal reconstruction (LTR). This approach may be complex and multistaged, with variable and unpredictable success rates in the individual patient. Excellent results have been reported in adults who had severe SGS and underwent partial resection of the cricoid and primary thyrotracheal anastomosis. This procedure has not been widely reported in infants and children. We report our experience with this procedure in 16 pediatric patients with grade III or IV SGS. Eleven patients had multiple previous LTR operations. The preoperative evaluation, surgical techniques, postoperative care, complications, and final results are described and discussed. Fourteen patients were decannulated after the procedure, 1 patient needed a second open procedure prior to decannulation, and 1 patient with concomitant bronchopulmonary dysplasia remains cannulated, for an overall 94% decannulation rate. Fourteen patients have no limitation of respiration, and 1 patient has moderate exercise intolerance. The results of this series suggest that partial cricotracheal resection with primary anastomosis is a relatively safe and effective procedure for pediatric patients with severe SGS.     

Activating mutations of the Gs alpha-gene in nonfunctioning pituitary tumors

The majority of pituitary tumors are of monoclonal origin; however, the molecular basis for their formation is poorly understood. Somatic mutations in the alpha-subunit of the GTP-binding protein, Gs alpha (gsp oncogene) have been found in about one third of GH-secreting tumors. Mutations in another alpha-subunit of a GTP-binding protein, Gi2 alpha (gip mutations) have been described in other endocrine tumors. In this study, we examined 21 nonfunctioning pituitary tumors and 4 macroprolactinomas for gsp mutations and 27 nonfunctioning tumors and 4 macroprolactinomas for gip mutations. Using the polymerase chain reaction and denaturing gradient gel electrophoresis, 2 nonfunctioning pituitary tumors displayed migration abnormalities when the Gs alpha-gene was analyzed. Sequence analysis of these abnormally migrating polymerase chain reaction products revealed two previously known gsp mutations: arginine at codon 201 altered to cysteine, and glutamine at codon 227 changed to leucine. No gip mutations could be demonstrated. These findings emphasize the monoclonal origin of nonfunctioning pituitary tumors and suggest that cAMP may play a role in tumorigenesis of nonfunctioning pituitary tumors.     

Regulation of V(D)J recombination activator protein RAG-2 by phosphorylation

Antigen receptor genes are assembled by site-specific DNA rearrangement. The recombination activator genes RAG-1 and RAG-2 are essential for this process, termed V(D)J rearrangement. The activity and stability of the RAG-2 protein have now been shown to be regulated by phosphorylation. In fibroblasts RAG-2 was phosphorylated predominantly at two serine residues, one of which affected RAG-2 activity in vivo. The threonine at residue 490 was phosphorylated by p34cdc2 kinase in vitro; phosphorylation at this site in vivo was associated with rapid degradation of RAG-2. Instability was transferred to chimeric proteins by a 90-residue portion of RAG-2. Mutation of the p34cdc2 phosphorylation site of the tumor suppressor protein p53 conferred a similar phenotype, suggesting that this association between phosphorylation and degradation is a general mechanism.     

The lack of long-term detrimental effects on liver allografts caused by donor-specific anti-HLA antibodies

Recent reports indicate a higher incidence of both acute and chronic liver allograft rejection when, at the time of transplantation, the recipients serum contains donor-specific anti-HLA antibodies. From 9/89 to 5/91, 133 liver allografts were performed at our institution. Thirteen liver recipients had donor-specific IgG anti-HLA antibodies (complement-fixing) at the time of transplantation. In eleven patients, antibodies reacted to donor class I antigens while in 1 patient the donor-specific antibody had class II reactivity. Twelve patients have been followed for a minimum of 12 months (median 18 months, range 28-12 months). No hyperacute rejection was seen in any of the cases and four patients had acute rejections. Thus far only one of the twelve patients has biopsy evidence suggestive of chronic liver injury. The remaining have normal liver enzymes and bilirubin. Three of these twelve patients died (one from a myocardial infarction and the others from sepsis) accounting for a one-year graft survival of 75%. There was no significant statistical difference in the one-year graft survival in those recipients without donor-specific antibodies (i.e., 80.5%). In eight of the twelve patients, pretransplant preformed antibody level (PRA) was > 50%. In six of the thirteen patients donor-specific antibody was present at dilutions greater than 1:64. As previously reported, the donor-specific antibody disappeared from the serum posttransplant within hours and did not reappear. In vitro studies demonstrated no factor in portal or hepatic artery blood that could inhibit rabbit complement mediated lysis of anti-HLA antibodies. We conclude that it is not a contraindication to do liver transplants in the presence of donor-specific anti-HLA antibodies.     

Determinants of genital human papillomavirus infection among cytologically normal women attending the University of New Mexico student health center

OBJECTIVES: To confirm the risk factors for genital human papillomavirus (HPV) infection. GOAL OF THIS STUDY: To investigate risk factors for HPV detection apart from the correlated risk factors for cervical neoplasia. STUDY DESIGN: Cervical human papillomavirus (HPV) DNA was assessed in 357 cytologically normal women attending the University of New Mexico student health center. Cervical swab samples were obtained for HPV DNA detection and typing using a PCR-based DNA amplification system. Possible determinants of cervical HPV were examined including age, ethnicity, history of sexually transmitted disease, oral contraceptive use, smoking, age at first intercourse, lifetime number of sex partners, marital status, and history of pregnancy. RESULTS: A 44.3% overall prevalence of cervical HPV was observed. On univariate analysis, factors associated with increasing HPV prevalence included higher lifetime number of sex partners and single marital status. After adjustment for potential confounding variables, we found that HPV prevalence increased with higher lifetime number of sexual partners. CONCLUSION: These findings, along with those from the companion reports in this issue of the journal, support the sexual route of transmission of the virus.     

Writer's cramp--a focal dystonia: etiology, diagnosis, and treatment

The complaint of hand cramps is common among patients who consult the neurologist or the hand surgeon. Classic writer's cramp is best characterized as a focal dystonia, and electromyographic studies reveal a characteristic pattern of cocontraction of the agonist and antagonist muscles of the forearm and hand. Although the outcome of treatment in the past has been unsatisfying, recent experience with new pharmacologic therapy, such as injections of botulinum toxin, has produced promising results. Further experience and improvement in this area will likely increase the therapeutic success in the treatment of writer's cramp and other focal dystonias.