Indirect H2O2 synthesis without H2

Industrial hydrogen peroxide (H2O2) is synthesized using carbon-intensive H2 gas production and purification, anthraquinone hydrogenation, and anthrahydroquinone oxidation. Electrochemical hydrogenation (ECH) of anthraquinones offers a carbon-neutral alternative for generating H2O2 using renewable electricity and water instead of H2 gas. However, the H2O2 formation rates associated with ECH are too low for commercialization. We report here that a membrane reactor enabled us to electrochemically hydrogenate anthraquinone (0.25 molar) with a current efficiency of 70% at current densities of 100 milliamperes per square centimeter. We also demonstrate continuous H2O2 synthesis from the hydrogenated anthraquinones over the course of 48 h. This study presents a fast rate of electrochemically-driven anthraquinone hydrogenation (1.32 ± 0.14 millimoles per hour normalized per centimeter squared of geometric surface of electrode), and provides a pathway toward carbon-neutral H2O2 synthesis.

From beer to breadboards: yeast as a force for biological innovation

The history of yeast Saccharomyces cerevisiae, aka brewer's or baker's yeast, is intertwined with our own. Initially domesticated 8,000 years ago to provide sustenance to our ancestors, for the past 150 years, yeast has served as a model research subject and a platform for technology. In this review, we highlight many ways in which yeast has served to catalyze the fields of functional genomics, genome editing, gene-environment interaction investigation, proteomics, and bioinformatics-emphasizing how yeast has served as a catalyst for innovation. Several possible futures for this model organism in synthetic biology, drug personalization, and multi-omics research are also presented.

Organic electrochromic molecules: synthesis, properties, applications and impact

Organic electronics are at the forefront of modern research, with goals of creating more efficient and environmentally benign devices. Organic molecules can achieve this as they typically result in materials that are solution-processable and less toxic than their transition-metal counterparts. Electrochromic molecules have unique color changing properties upon passing an electrical current making them highly sought after for colored displays, dimming mirrors, and smart windows. Part of my PhD work was devoted to developing a new class of electrochromic molecules, the phosphoryl-bridged viologens, with more favorable redox properties and new color changing modes. In order to understand the necessity and potential of new electrochromes, it is important to assess the history of the field and its future. In addition to designing new molecules for electrochromic devices, it is equally important to design a multifunctional species with a bright, competitive future across various organic electronic applications.

A Highly Stable Organic Radical Cation

Functionalization of a methylviologen with four methyl ester substituents significantly facilitates the first two reduction steps. The easily generated radical cation shows markedly improved air stability compared to the parent methylviologen, making this derivative of interest in organic electronic applications.

Functional conjugated pyridines via main-group element tuning

The functional properties arising from a combination of main-group elements with pyridine-based organic conjugated scaffolds are highlighted.

A Convenient N-Arylation Route for Electron-Deficient Pyridines: The Case of π-Extended Electrochromic Phosphaviologens

A simple and representative procedure for the synthesis of N,N'-diarylated phosphaviologens directly from both electron-rich and electron-poor diaryliodonium salts and 2,7-diazadibenzophosphole oxide is reported. The latter are electron-deficient congeners of the widely utilized N,N'-disubstituted 4,4'-bipyridinium cations, also known as viologens, that proved to be inaccessible by the classical two-step route. The single-step preparation method for phosphaviologens described herein could be extended to genuine viologens but reached its limit when sterically demanding diaryliodonium salts were used. The studied phosphaviologens feature a significantly lowered reduction threshold as compared to all other (phospha)viologens known to date due to the combination of an extended π-system with an electron deficient phosphole core. In addition, a considerably smaller HOMO-LUMO gap was observed due to efficient π-delocalization across the phosphaviologen core, as well as the N-aryl substituents, which was corroborated by quantum chemical calculations. Detailed characterizations of the singly reduced radical species by EPR spectroscopy and DFT calculations verified delocalization of the radical over the extended π-system. Finally, to gain deeper insight into the suitability of the new compounds as electroactive and electrochromic materials, multicolored proof-of-concept electrochomic devices were manufactured.

Organic n-type materials for charge transport and charge storage applications

Conjugated materials have attracted much attention toward applications in organic electronics in recent years. These organic species offer many advantages as potential replacement for conventional materials (i.e., silicon and metals) in terms of cheap fabrication and environmentally benign devices. While p-type (electron-donating or hole-conducting) materials have been extensively reviewed and researched, their counterpart n-type (electron-accepting or electron-conducting) materials have seen much less popularity despite the greater need for improvement. In addition to developing efficient charge transport materials, it is equally important to provide a means of charge storage, where energy can be used on an on-demand basis. This perspective is focused on discussing a selection of representative n-type materials and the efforts toward improving their charge-transport efficiencies. Additionally, this perspective will also highlight recent organic materials for battery components and the efforts that have been made to improve their environmental appeal.

Substance use and behaviour disorders in Puerto Rican youth: a migrant family study

BACKGROUND

Hispanics in the USA have higher rates of substance use disorders than similar ethnic groups residing in Latin American nations, and recent evidence suggests an increase in substance use among US Hispanic youth. This investigation examines the familial and societal correlates of this increase by comparing Puerto Rican families residing in the mainland USA and Puerto Rico.

METHODS

Using migrant and controlled family study methods, 279 probands in San Juan and 236 probands in New Haven were recruited from treatment clinics and the general community to compose four diagnostic groups: drug abuse/dependence; alcohol abuse/dependence; psychiatric controls; unaffected controls. 806 biological offspring aged 12-17 were then directly interviewed.

RESULTS

Total rates for alcohol use were greater among San Juan youth than their migrant counterparts. By contrast, US migrant adolescents were more likely to use cannabis. A strong association was observed between parental and child substance use at both sites, particularly for boys, and offspring of probands with drug use disorders were at greatest risk for substance use and related disorders. Familial aggregation patterns did not vary substantially by site.

CONCLUSIONS

Despite societal influences on the magnitude and patterns of substance use in migrant youth, the consistent influence of parental disorders across sites reveals that the cross-generational transmission of substance use disorders in prior studies extends to Hispanic families and is an important factor to consider in the development of prevention strategies.

Impact of clozapine prescription on inpatient resource utilization

Although clozapine has been demonstrated to be clinically superior to typical neuroleptics in refractory schizophrenia, it is also more expensive. It had been hoped that the increased costs associated with its use would be offset by decreases in the utilization of other expensive resources, especially inpatient care. All patients who had clozapine initiated during an inpatient hospitalization within the VA for schizophrenia over a 4-year period (N = 1415) were matched with a comparison group (N = 2,830) on key service utilization variables and other possible confounding demographic and clinical variables using propensity scoring-an accepted statistical method, although still relatively little used in psychiatry. By using centralized VA databases, subsequent inpatient resource utilization for the 3 years after index discharge was examined. Veterans exposed to clozapine while inpatients recorded 33 (36%) more inpatient days in the subsequent 3 years after discharge than the comparison group (124 +/- 190 days vs. 91 +/- 181 days, p = .0002). When all patients exposed to clozapine were divided according to whether they had received 1 year of clozapine treatment after discharge, those that received less than 1 year's treatment recorded significantly more inpatient days than either those maintained on clozapine or controls. These results suggest that in actual practice clozapine treatment may cost substantially more than treatment with conventional neuroleptics.

Association between psychiatric disorders and the progression of tobacco use behaviors

OBJECTIVE

To examine the progression of tobacco use and the patterns of comorbidity of tobacco use and psychiatric disorders.

METHOD

The authors conducted analyses of prospective and retrospective reports, collected from 1988 to 1998, of a sample of high- and low-risk youths identified on the basis of the presence or absence of a parental history of substance abuse or dependence.

RESULTS

A parental history of substance use disorders was associated with regular tobacco use and nicotine dependence, but not with experimentation for all youths. Individual and composite psychiatric diagnoses were strongly associated with nicotine dependence, but not with regular use or experimentation. While the presence of an affective disorder and drug abuse/dependence generally increased the risk for co-occurring nicotine dependence, analyses based on the temporal onset of disorders showed that it was the initiation of alcohol or drug use that predicted the progression to nicotine dependence. For low-risk youths, oppositional defiant disorder was the single psychiatric risk factor that predicted the transition to nicotine dependence.

CONCLUSIONS

This study adds to the accumulating evidence that has implicated comorbid psychiatric disorders in the etiology and subsequent course of nicotine dependence. In addition, family history may represent an important indicator of an increased risk for nicotine dependence.

Service delivery and community: social capital, service systems integration, and outcomes among homeless persons with severe mental illness

OBJECTIVES

This study evaluated the influence of features of community social environment and service system integration on service use, housing, and clinical outcomes among homeless people with serious mental illness.

STUDY SETTING

A one-year observational outcome study was conducted of homeless people with serious mental illness at 18 sites.

DATA SOURCES

Measures of community social environment (e.g., social capital) were based on local surveys and voting records. Housing affordability was assessed with housing survey data. Service system integration was assessed through interviews with key informants at each site to document interorganizational transactions. Standardized clinical measures were used to assess clinical and housing outcomes in face-to-face interviews.

RESEARCH DESIGN

Structural equation modeling was used to determine the relationship between (1) characteristics of the social environment (social capital, housing affordability); (2) the level of integration of the service system for persons who are homeless in each community; (3) access to and use of services by individual clients; and (4) successful exit from homelessness or clinical improvement.

PRINCIPAL FINDINGS

Social capital was associated with greater service systems integration, which was associated in turn with greater access to assistance from a public housing agency and to a greater probability of exiting from homelessness at 12 months. Housing affordability also predicted exit from homelessness. Neither environmental factors nor systems integration predicted outcomes for psychiatric problems, substance abuse, employment, physical health, or income support.

CONCLUSION

Community social capital and service system integration are related through a series of direct and indirect pathways with better housing outcomes but not with superior clinical outcomes for homeless people with mental illness. Implications for designing improved service systems are discussed.

Comorbidity of depression in children and adolescents: models and evidence from a prospective high-risk family study

Despite abundant research demonstrating the magnitude of comorbidity and its importance in understanding childhood psychopathology, there has been limited empirical research designed to examine the nature and causes of comorbidity among youth. This article reviews the current literature on the magnitude and mechanisms of depressive comorbidity and presents data to exemplify the application of high-risk and longitudinal study designs to investigate patterns and explanations for comorbidity. A prospective family study of offspring at high and low risk for the development of anxiety was used to examine the specificity of familial comorbidity of depression and anxiety and the longitudinal stability of "pure" and comorbid disorders over an 8-year period. Findings suggest some specificity of familial expression, as well as longitudinal specificity, of depression and anxiety. The onset of depression follows the onset of most anxiety subtypes, suggesting the sequential nature of depressive comorbidity. Evaluation of mechanisms for comorbidity is important for the identification of homogeneous syndrome categories that will inform research designed to gain understanding of the pathogenesis of mood or anxiety disorders.

Impact of clozapine on completed suicide

OBJECTIVE

Clozapine has been found to be superior to typical neuroleptics in ameliorating the symptoms of refractory schizophrenia. This study evaluated clozapine's effect on the rate of death due to suicide.

METHOD

All patients over a 4-year period who initiated treatment with clozapine while hospitalized within the Department of Veterans Affairs (VA) system (N=1,415) were matched with a schizophrenic control group (N=2,830) by propensity scoring-a widely accepted statistical method that has been used relatively little in psychiatric research. Centralized VA databases and a national death registry were used to identify all deaths within the two groups, along with listed causes, for the 3 years after discharge.

RESULTS

Veterans exposed to clozapine while inpatients were significantly less likely to die during the follow-up period than those in the control group, but this was entirely attributable to the much lower rate of death due to respiratory disorders in the clozapine group. There were no significant differences in rates of suicide or accidental death.

CONCLUSIONS

These results fail to support the hypothesis that clozapine treatment is associated with significantly fewer deaths due to suicide.

Consistency of atypical antipsychotic superiority to placebo in recent clinical trials

BACKGROUND

The use of control placebos in clinical trials of new antipsychotic medications is increasingly under examination. The active controlled equivalence study could offer a potential alternative design. First, however, it must be clear that any proposed standard control agent has been consistently superior to placebo in previous studies.

METHODS

Through a Freedom of Information Act request, we identified nine placebo-controlled trials of risperidone, olanzapine, or quetiapine.

RESULTS

Meta-analysis indicated that the pooled estimate of the true population effect size +/- SE was 0.46 +/- 0.06 for categorical response rates and >0.53 +/- 0.07 for the continuous Brief Psychiatric Rating Scale change score outcome measure. If the desired detectable effect size is set very conservatively at a 95% confidence lower bound for the estimate of true effect size, statistical power for random samples of 80 per group drawn from a population of subjects similar to that of the nine meta-analyzed studies is.67 for categorical response rates and >.82 for the continuous measure, based on one-sided alpha =.05.

CONCLUSIONS

These data suggest substantial confidence that a therapeutic dose of an atypical antipsychotic will be statistically superior to placebo in an adequately sized randomized trial, when reporting a continuous measure as the principal outcome.

Outcomes monitoring and the testing of new psychiatric treatments: work therapy in the treatment of chronic post-traumatic stress disorder

OBJECTIVE

To evaluate the effectiveness of a work therapy intervention, the Department of Veterans Affairs (VA) Compensated Work Therapy program (CWT), in the treatment of patients suffering from chronic war-related post-traumatic stress disorder (PTSD); and to demonstrate methods for using outcomes monitoring data to screen previously untested treatments.

DATA SOURCES/STUDY SETTING

Baseline and four-month follow-up questionnaires administered to 3,076 veterans treated in 52 specialized VA inpatient programs for treatment of PTSD at facilities that also had CWT programs. Altogether 78 (2.5 percent) of these patients participated in CWT during the four months after discharge.

STUDY DESIGN

The study used a pre-post nonequivalent control group design.

DATA COLLECTION/EXTRACTION METHODS

Questionnaires documented PTSD symptoms, violent behavior, alcohol and drug use, employment status, and medical status at the time of program entry and four months after discharge from the hospital to the community. Administrative databases were used to identify participants in the CWT program. Propensity scores were used to match CWT participants and other patients, and hierarchical linear modeling was used to evaluate differences in outcomes between treatment groups on seven outcomes.

PRINCIPAL FINDINGS

The propensity scaling method created groups that were not significantly different on any measure. No greater improvement was observed among CWT participants than among other patients on any of seven outcome measures.

CONCLUSIONS

Substantively this study suggests that work therapy, as currently practiced in VA, is not an effective intervention, at least in the short term, for chronic, war-related PTSD. Methodologically it illustrates the use of outcomes monitoring data to screen previously untested treatments and the use of propensity scoring and hierarchical linear modeling to adjust for selection biases in observational studies.

Effect of declining mental health service use on employees of a large corporation

This study examines concurrent changes in use of mental and general health services and in annual sick days among 20,814 employees of a large corporation. From 1993 to 1995 mental health service use and costs declined by more than one-third, more than three times as much as the decline in non-mental health service use. However, employees who used mental health services showed a 37 percent increase in use of non-mental health services and significantly increased sick days, whereas other employees showed no such increases. Savings in mental health services were fully offset by increased use of other services and lost workdays.

Patient satisfaction and administrative measures as indicators of the quality of mental health care

OBJECTIVE

Although measures of consumer satisfaction are increasingly used to supplement administrative measures in assessing quality of care, little is known about the association between these two types of indicators. This study examined the association between these measures at both an individual and a hospital level.

METHODS

A satisfaction questionnaire was mailed to veterans discharged during a three-month period from 121 Veterans Administration inpatient psychiatric units; 5,542 responded, for a 37 percent response rate. These data were merged with data from administrative utilization files. Random regression analysis was used to determine the association between satisfaction and administrative measures of quality for subsequent outpatient follow-up.

RESULTS

At the patient level, satisfaction with several aspects of service delivery was associated with fewer readmissions and fewer days readmitted. Better alliance with inpatient staff was associated with higher administrative measures of rates of follow-up, promptness of follow-up, and continuity of outpatient care, as well as with longer stay for the initial hospitalization. At the hospital level, only one association between satisfaction and administrative measures was statistically significant. Hospitals where patients expressed greater satisfaction with their alliance with outpatient staff had higher scores on administrative measures of promptness and continuity of follow-up.

CONCLUSIONS

The associations between patient satisfaction and administrative measures of quality at the individual level support the idea that these measures address a common underlying construct. The attenuation of the associations at the hospital level suggests that neither type can stand alone as a measure of quality across institutions.

Assessing quality of care: administrative indicators and clinical outcomes in posttraumatic stress disorder

BACKGROUND

Although the use of quality of care indicators based on data collected for administrative purposes has become widespread, the relationship between those measures and clinical outcomes has yet to be evaluated.

RESEARCH DESIGN

This study used hierarchical linear modeling to examine the relationship between 12 performance indicators derived from administrative data sets and 6 clinical outcome measures addressing symptoms, substance abuse, and social functions.

SUBJECTS

Patient interviews were conducted with 4,165 veterans 4 months after their discharge from 62 specialized VA inpatient programs for treatment of Posttraumatic Stress disorder.

RESULTS

Five of twelve administrative measures were significantly associated with at least one of the clinical outcome measures, which was all in the expected directions. The number of hospital readmissions during the 6 months after the index discharge was significantly related to poor outcomes on all 5 of 6 measures. Measures of readmission and post-discharge hospital use were more strongly and consistently related to outcome than to measures of access, intensity, or continuity of outpatient care.

CONCLUSION

Administrative data, especially measures of hospital readmission, are significantly related to clinical outcomes. Correlations, however, are small to modest in magnitude indicating that these 2 types of performance measures assess different aspects of quality and can not be substituted for one another.

Familial transmission of substance use disorders

BACKGROUND

There is increasing evidence that substance use disorders are familial and that genetic factors explain a substantial degree of their familial aggregation. To perform a controlled family study of probands with several different predominant drugs of abuse, including opioids, cocaine, cannabis, and/or alcohol.

METHODS

The subjects for the present study included 231 probands with dependence on opioids, cocaine, cannabis, and/or alcohol and 61 control probands, and their 1267 adult first-degree relatives. Diagnostic estimates were based on semistructured diagnostic interviews and/or structured family history interviews regarding each proband, spouse, and adult first-degree relative. The interview data were reviewed blindly and independently by clinicians with extensive experience in the evaluation and treatment of substance use disorders.

RESULTS

There was an 8-fold increased risk of drug disorders among the relatives of probands with drug disorders across a wide range of specific substances, including opioids, cocaine, cannabis, and alcohol, which is largely independent from the familial aggregation of both alcoholism and antisocial personality disorder. There was also evidence of specificity of familial aggregation of the predominant drug of abuse.

CONCLUSIONS

Elevation in risk of this magnitude places a family history of drug disorder as one of the most potent risk factors for the development of drug disorders. These results suggest that there may be risk factors that are specific to particular classes of drugs as well as risk factors that underlie substance disorders in general.

Predictors of differential response to clozapine and haloperidol. Veterans Affairs Cooperative Study Group on Clozapine in Refractory Schizophrenia

BACKGROUND

We sought to identify baseline predictors of response to clozapine.

METHODS

Data were from a 15-site randomized clinical trial comparing clozapine and haloperidol in hospitalized patients with refractory schizophrenia (n = 423). Three-month outcomes were analyzed with the full sample (n = 368 due to attrition). Because of crossovers, analyses of 12-month outcomes were conducted with crossovers excluded (n = 291). Clinical predictors included age, race, diagnosis (current substance abuse, paranoid subtype of schizophrenia, or depressive syndrome), severity of symptoms, quality of life, age at onset of schizophrenia, extrapyramidal symptoms, and VA compensation payment. Multiple regression analysis was used to examine the interaction of treatment condition and each of these variables in predicting outcomes for symptoms, quality of life, side effects, and days hospitalized.

RESULTS

Patients with higher quality of life at baseline (p = .04) and higher symptoms (p = .02) had relatively smaller declines in hospital days at 6 months. In the 12-month sample patients with higher levels of symptoms had greater symptom reductions at 12 months (p = .03) and greater improvement in quality of life (p = .004).

CONCLUSIONS

Although high levels of symptoms were associated with greater improvement on clozapine, these findings are not robust enough to suggest that any specific, clinically defined subgroup of refractory patients should be preferentially targeted for clozapine treatment.

Co-morbidity and familial aggregation of alcoholism and anxiety disorders

BACKGROUND

This study examined the patterns of familial aggregation and co-morbidity of alcoholism and anxiety disorders in the relatives of 165 probands selected for alcoholism and/or anxiety disorders compared to those of 61 unaffected controls.

METHODS

Probands were either selected from treatment settings or at random from the community. DSM-III-R diagnoses were obtained for all probands and their 1053 first-degree relatives, based on direct interview or family history information.

RESULTS

The findings indicate that: (1) alcoholism was associated with anxiety disorders in the relatives, particularly among females; (2) both alcoholism and anxiety disorders were highly familial; (3) the familial aggregation of alcoholism was attributable to alcohol dependence rather than to alcohol abuse, particularly among male relatives; and (4) the the pattern of co-aggregation of alcohol dependence and anxiety disorders in families differed according to the subtype of anxiety disorder; there was evidence of a partly shared diathesis underlying panic and alcoholism, whereas social phobia and alcoholism tended to aggregate independently.

CONCLUSIONS

The finding that the onset of social phobia tended to precede that of alcoholism, when taken together with the independence of familial aggregation of social phobia and alcoholism support a self-medication hypothesis as the explanation for the co-occurrence of social phobia and alcoholism. In contrast, the lack of a systematic pattern in the order of onset of panic and alcoholism among subjects with both disorders as well as evidence for shared underlying familial risk factors suggests that co-morbidity between panic disorder and alcoholism is not a consequence of self-medication of panic symptoms. The results of this study emphasize the importance of examining co-morbid disorders and subtypes thereof in identifying sources of heterogeneity in the pathogenesis of alcoholism.

Access to public mental health services: determinants of population coverage

OBJECTIVES

This study examined factors that affect access to Veterans Administration mental health services.

METHODS

Data from national Veterans Affairs databases and the 1990 Decennial Census were used to estimate rates of Veterans Affairs mental health service use in each US county (n = 3,156) among all US veterans and in three subpopulations defined by eligibility and clinical status. Independent variables examined in standard multivariate analyses and using hierarchical linear modeling techniques included county-level sociodemographic characteristics (age, race, and income); "unmanaged" service system characteristics (those not directly controlled by Veterans Affairs program managers, eg, distance from residence to Veterans Affairs and to non-Veterans Affairs services, local supply of non-Veterans Affairs services); and "managed" service system factors (those directly controlled by Veterans Affairs program managers, eg, per capita Veterans Affairs funding level and the efficiency of Veterans Affairs service delivery).

RESULTS

Altogether, 2.0% of US veterans used Veterans Affairs mental health services. More than one third (36%) of the variance in utilization was explained by sociodemographic factors; 8% was explained by unmanaged service system factors and 7% was explained by managed service system factors, with variations among subgroups. Substitution effects were demonstrated between Veterans Affairs and non-Veterans Affairs systems and appeared to be diagnosis-specific.

CONCLUSIONS

Both per capita funding levels and efficient service delivery were significantly associated with increased access to mental health services. Implications for health system performance assessment and management are discussed.

Management of hepatitis C: a national survey of gastroenterologists and hepatologists

A survey on the management of hepatitis C virus (HCV) infection was conducted by the American Digestive Health Foundation among United States physicians who are most familiar with the disease. The two-page survey was completed by 57% of a random sample of 2,500 members of the American Gastroenterological Association and the American Association for the Study of Liver Diseases. Analysis was limited to the 1,249 responses from physicians who spent at least 1 day per week in patient care. These physicians frequently managed patients with HCV, and nearly three quarters treated patients with interferon. To prevent transmission, the large majority of physicians recommended measures to avoid blood exposures, were uncertain or disagreed about the importance of sexual contact, and did not caution patients about casual contact. More than 70% of physicians told their patients to stop or minimize alcohol consumption. In the management of a patient with antibody to HCV but normal serum aminotransferase activities, 87% of physicians would have ordered a supplemental test, and if HCV were confirmed, 46% would have obtained a liver biopsy, but only 15% would have treated the patient with interferon. For a patient with chronic HCV infection and elevated serum aminotransferase activities, more than 90% of physicians would have obtained a liver biopsy and approximately 60% would have treated with interferon. Physicians who are most familiar with the management of patients with HCV generally agreed with the recommendations of the Consensus Development Conference Panel regarding prevention of transmission, minimizing alcohol consumption, and managing patients with typical presentations. Controversies remain regarding some issues of general management, the value of molecular testing, and the need to treat certain patients with interferon.

Heterogeneity of circulating growth hormone

Human growth hormone (GH) represents a family of related proteins arising from two genes, alternative mRNA splicing, and several post-translational modifications. In addition, post-secretory events occur when GH enters the circulation. The full scale of GH heterogeneity is only beginning to be appreciated, and new GH forms or related proteins may be discovered in the future. GH measurements are affected by GH heterogeneity. Immunoassays are influenced by the mixture of GH variants, but are not sensitive to GH binding proteins (GHBPs). In contrast, radioreceptor assays are sensitive to both GH variant mixtures and to the high affinity GHBP. It is hoped that in the future, these problems can be minimized by rigorous characterization of existing antibodies with respect to epitope recognition on various GH forms, and ultimately, by production of GH variant-specific antibodies that permit direct and individual assessment of the circulating members of the GH family.