Rhodopsin and the retinal G-protein distinguish among G-protein beta gamma subunit forms

The beta gamma subunits of G-proteins are composed of closely related beta 35 and beta 36 subunits tightly associated with diverse 6-10 kDa gamma subunits. We have developed a reconstitution assay using rhodopsin-catalyzed guanosine 5'-3-O-(thio)triphosphate (GTP gamma S) binding to resolved alpha subunit of the retinal G-protein transducin (Gt alpha) to quantitate the activity of beta gamma proteins. Rhodopsin facilitates the exchange of GTP gamma S for GDP bound to Gt alpha beta gamma with a 60-fold higher apparent affinity than for Gt alpha alone. At limiting rhodopsin, G-protein-derived beta gamma subunits catalytically enhance the rate of GTP gamma S binding to resolved Gt alpha. The isolated beta gamma subunit of retinal G-protein (beta 1, gamma 1 genes) facilitates rhodopsin-catalyzed GTP gamma S exchange on Gt alpha in a concentration-dependent manner (K0.5 = 254 +/- 21 nM). Purified human placental beta 35 gamma, composed of beta 2 gene product and gamma-placenta protein (Evans, T., Fawzi, A., Fraser, E.D., Brown, L.M., and Northup, J.K. (1987) J. Biol. Chem. 262, 176-181), substitutes for Gt beta gamma reconstitution of rhodopsin with Gt alpha. However, human placental beta 35 gamma facilitates rhodopsin-catalyzed GTP gamma S exchange on Gt alpha with a higher apparent affinity than Gt beta gamma (K0.5 = 76 +/- 54 nM). As an alternative assay for these interactions, we have examined pertussis toxin-catalyzed ADP-ribosylation of the Gt alpha subunit which is markedly enhanced in rate by beta gamma subunits. Quantitative analyses of rates of pertussis modification reveal no differences in apparent affinity between Gt beta gamma and human placental beta 35 gamma (K0.5 values of 49 +/- 29 and 70 +/- 24 nM, respectively). Thus, the Gt alpha subunit alone does not distinguish among the beta gamma subunit forms. These results clearly show a high degree of functional homology among the beta 35 and beta 36 subunits of G-proteins for interaction with Gt alpha and rhodopsin, and establish a simple functional assay for the beta gamma subunits of G-proteins. Our data also suggest a specificity of recognition of beta gamma subunit forms which is dependent both on Gt alpha and rhodopsin. These results may indicate that the recently uncovered diversity in the expression of beta gamma subunit forms may complement the diversity of G alpha subunits in providing for specific receptor recognition of G-proteins.

Angular homeostasis VII: non-monotonic correction systems

We extend our model of angular homeostasis to correction functions that have a single maximum at a discrepant angle less than pi radians. We find that there are stable, and asymptotically stable, solutions that in general consist of self-intersecting curves. We investigate conditions for these curves to be periodic, and describe their symmetries. One typical pattern of such a closed curve involves a finite number of loops, each having a reflection axis of symmetry, with the complete curve having a cyclic rotation group. These bear a close resemblance to patterns found in lobulated biological structures (such as the petals of a flower or the primitive fetal hand). We further discuss implications for morphogenesis.

Rheumatoid arthritis: workload and outcome over 10 years

Rheumatoid arthritis remains a chronic disabling disorder in which medical and surgical intervention may provide amelioration but not cure. In this study a cohort of 123 rheumatoid patients were followed for a period of 10 years from the time of prescription of their initial second-line agent. The workload involved in managing articular, extra-articular and intercurrent disease in these patients has been documented and outcome in relation to continued use of 'disease modifying' therapy evaluated. At 10 years 24 patients (20 per cent) had died and 7 (5 per cent) were not traced; of the 92 (75 per cent) who were assessed, three had become wheelchairbound, two for reasons other than rheumatoid arthritis. Seventy-one per cent of patients required joint surgery, 36 per cent management of peptic ulcer and 45 per cent experienced major episodes of sepsis. Analysis of the results in the 92 patients who were evaluated at 10 years showed significant improvement in Ritchie articular index, pain score, morning stiffness, haemoglobin, platelets, ESR, total globulins, IgG and IgM. Grip strength and Lee functional index showed a trend towards deterioration which did not reach significance. Sixty-seven (73 per cent) of the 92 patients remained on a second- or third-line agent at 10 years (median duration of treatment 107 months); 25 (27 per cent) were not receiving such therapy (median duration of second- and third-line therapy 13 months). The group remaining on treatment showed significant improvement similar to that of the total study group. Those not on treatment improved only for articular index; Lee functional index deteriorated significantly. There was a correlation between area under the curve for ESR over 10 years and radiological progression of disease in hands (r = 0.29, p = 0.026) and in knees and hips (r = 0.3748, p = 0.012) over the 10 year period. Radiographic score correlated well with Lee functional index at the outset and at 10 years and also with the change in the radiographic score over the 10-year period. Unlike the results of previous studies, there was no morbidity from vertebral collapse; this may be related to the low dose of corticosteroids in this cohort (seven patients received systemic corticosteroids). Thus while the aim of treating patients for prolonged periods with second- or third-line therapy was achieved in the majority with no overt evidence of cumulative toxicity, sustained medical and surgical intervention was and will be needed in order to minimize disability in these and other patients with rheumatoid arthritis.

Case-control studies of environmental influences in diseases with genetic determinants, with an application to Alzheimer's disease

Many diseases have both genetic and environmental determinants. Some require both, and the disease phenotype then appears only when a vulnerable genotype is expressed after interaction with environmental factors. The detection of such environmental factors has received little prior consideration in diseases with genetic causes. In particular, case-control studies of such diseases may compare exposures among cases, who have the susceptible genotype, and controls who mostly lack it. The authors explored the likely results of such studies, using the example of Alzheimer's disease as an illness where environmental factors may interact with a necessary susceptible genotype to accelerate disease expression. They found that case-control studies of environmental factors in complex genetic diseases will usually produce an odds ratio that differs little from the relative risk among susceptible individuals. In rare situations, however, the discrepancy may be gross. The statistical power of such studies also agrees well with familiar published estimates, suggesting that little power is lost even though the controls are mostly not susceptible. Power may be increased, however, in studies of common illnesses with genetic determinants when the case-control method is applied among discordant monozygotic twins.

Twin studies of Alzheimer's disease: an approach to etiology and prevention

Epidemiologic studies of environmental factors associated with risk of Alzheimer's disease (AD) have produced inconsistent and disappointing results. By contrast, family/genetic studies and case control investigations suggest that genetic causes of AD are important. The investigation of such genetic causes remains an important aim in all forms of AD including typical, late-onset disease where linkage work is impractical. But the public health burden of AD creates an especially urgent need to identify environment risk factors, if these exist, since they will more likely be susceptible to intervention. Such environmental factors may interact with genetic susceptibility to accelerate or retard disease expression, and environmental interventions that delay onset may constitute an important strategy for prevention. All these issues may be addressed by twin studies of AD, but the few such studies to date have been limited by small samples and other methodologic difficulties. This paper reviews the rationale for twin studies of AD, and describes briefly the work in this area to date. It also discusses a number of suggestions for methodologic improvements. We conclude that the time is ripe for twin studies of AD, and that such work holds considerable potential for the investigation of etiology and, possibly, for the identification of strategies for prevention.

A truncation mutation in the avian beta-adrenergic receptor causes agonist-induced internalization and GTP-sensitive agonist binding characteristic of mammalian receptors

Recombinant turkey erythrocyte beta-adrenergic receptors expressed in murine L cells exhibited characteristic avian subtype selectivity for agonists and antagonists. In 10 of the 11 clones studied, no agonist-induced internalization of receptor was observed, although agonist-induced uncoupling of receptor and adenylyl cyclase occurred rapidly. GTP caused little or no decrease in affinity for beta-adrenergic agonists. Such behavior is commonly observed in avian erythrocytes. In contrast, one clone was susceptible to agonist-induced receptor internalization and down-regulation even though it exhibited characteristic avian beta-adrenergic ligand-binding properties. The affinity of this variant receptor for agonists was also notably reduced by GTP. Electrophoresis of affinity-labeled receptor from this clone indicated an apparent size of about 33 kDa, about 12 kDa less than that of the native or recombinant turkey beta-adrenergic receptor. Genomic DNA from this cell line that encodes the receptor was cloned and partially sequenced. The coding region of the original receptor cDNA was interrupted after codon 412 (out of 483) and was followed by 36 base pairs of novel sequence prior to the first in-frame stop codon. These results suggest that the lack of both hormone-induced internalization and GTP-sensitive, high affinity binding of agonists that is characteristic of the beta-adrenergic receptor in avian erythrocytes is due to intrinsic properties of the receptor. The restoration of these phenomena in a C-terminally truncated mutant receptor suggests the importance of the C-terminal domain in determining these processes.

Angular homeostasis: VI. Threshold processes with bivariate liabilities

The general structure of the threshold model of multifactorial determination is discussed. It is supposed that in place of a single liability (in Falconer's sense) there are two separate liabilities; and whether or not the pathological trait is present depends on a non-additive interaction between the liabilities, so that the region has curved boundaries. The genetics of ontogeny of a process involving spatial orientation (e.g., cardiac ontogeny) is used as a substantive illustration. Genetic analysis of the trait (as contrasted with the liabilities) yields results that on the one hand may seem quite counterintuitive, yet on the other hand they correspond to the kind of bizarre patterns encountered in quasi-empirical genetic counseling for cleft palate or neural tube defect. The impact of refinement of phenotype made possible by non-invasive methods is sketched. This model can be generalized to any number of liabilities, independent or not.

Dynamics of quantitative homeostasis: VIII. Processes that oscillate finitely many times

There is no well-established method of dealing with medical processes that oscillate only a finite number of times. A lagged homeostatic model of higher power in certain circumstances follows such a pattern and critical values are here explored by numerical integration. Abrupt ending of the oscillation occurs with processes of higher powers. The model is illustrated by clonus, chosen because reflexes are naturally lagged responses and because clonus may be unsustained. In applying the model to clonus, there are some incongruities (notably inertia) that call for caution; however, published data suggest that they may not be important. These imperfections notwithstanding, the correspondence is remarkably good. The model dealt with here, being simple and economical, is a useful first step to genetics; and some empirically testable deductions from the model are listed.

Angular homeostasis: III. The formalism of discrete orbits in ontogeny

The formal properties of orbits in a plane are explored by elementary topology. The notions developed from first principles include: convex and polygonal orbits; convexity; orientation, winding number and interior; convex and star-shaped regions. It is shown that an orbit that is convex with respect to each of its interior points bounds a convex region. Also, an orbit that is convex with respect to a fixed point bounds a star-shaped region. Biological considerations that directed interest to these patterns are indicated, and the implications of the prospect of higher orders of star-shapedness mentioned.

Angular homeostasis: IV. Polygonal orbits

Some properties are discussed of regular polygons that may result from angular homeostatic processes in stable orbit. To characterize these "homeostatic polygons" we need to discuss the winding number, the sidedness (integer, fractional and irrational), multiplicity, envelopes, and density. A regular (i.e., equilateral, equiangular) polygon may be closed in one revolution about its unique center, in multiple revolutions, or not at all. A homeostatic polygon can be generated only if all vertices are included in a single polygon, which occurs if and only if the number of vertices and the number of revolutions required to complete the polygon are relatively prime. For the homeostatic polygon to have a finite number of sides (without repeating itself) the angle subtended by any two successive vertices at the center must be a rational multiple of 2 pi. Biological implications of these properties are illustrated.

Genetics and congenital heart disease: perspectives and prospects

Elucidating the role of genes in the ontogenesis of the cardiovascular system is a task that involves many fields of inquiry. Recent dramatic advances in the molecular biology of transcription and its variations and the prospects for sequencing the entire human genome must not induce complacency; the major task of determining how a one-dimensional code specifies a three-dimensional structure demands an understanding of biologic systems considerably beyond the current level. The study of pathologic cardiovascular ontogeny is equally in need of new insight and fresh approaches. Although all clinicians might agree that genes are important contributors to both the etiology and the pathogenesis of congenital heart defects, with the exception of a few Mendelian conditions, this knowledge cannot be put to practice beyond crude statements of empirically determined probabilities. In this review, we selectively examine studies that are addressing what we perceive as provocative issues and suggest some areas, such as chaos theory, in which new ideas might be found.

Public and private hypotheses

The uses of hypothesis in scientific medicine and in clinical medicine are broadly similar; but they differ in subtle but important logical details. The key distinction is that scientific medicine deals with broad ("public") hypotheses about entire populations; and the predominant problem of inference is statistics in the face of epistemological uncertainty. In contrast, clinical medicine deals with individual, tailor-made ("private") hypotheses; the uncertainty (e.g. the diagnosis or recurrence risk in relatives) is ontological, and the main feature of the analysis is probability. The same logical rules are at times mistakenly applied to both. Disregard of these subtleties may lead to paradoxes, contradictions, and at times diastrously false conclusion. The basic principles and distinctions are laid out with illustrations that are most readily provided from medical genetics, but apply to all branches of medicine.

Angular homeostasis. V: Some issues in genetics, ontogeny, and evolution

We discuss a provisional model that deals with aspects of normal control of the direction in which cells grow; hence, the organization of structure. The interacting issues of genetics, ontogeny, and phylogeny in relationship to normal development and its defects are addressed. Our main goal is to define a model with a small and sufficient set of conditions that would make it possible to undertake statistically efficient genetic studies of certain congenital defects. But to do so in plausible and heuristic terms, one must address two classical questions: 1) How is the genome translated (or sometimes mistranslated) into a phenotype that is clinically conspicuous and that can be the object of genetic selection, and hence of evolution? 2) Granted that evolution of species occurs in small, rare steps, what is the path that calls for the smallest number of mutations through which ontogenesis could have developed, the intermediate stages being conserved because of actual phenotypic advantage?

Angular homeostasis II: Pursuit of a moving target in a plane and some implications for cardiac teratology

A model of cardiac ontogenesis is analyzed. It is cast in terms of the geometry of the pursuit of a linearly moving target by the growth of a chain of cells in the same plane, the pursuer, which at each step adjusts its direction of growth towards the current position of the target. The endpoint is the fusion between them, which can occur in 2 modes: either by the leading cell of the pursuer catching up with the target (pursuer-mediated fusion, or PMF) or by the target running into the preformed side of the pursuer (target-mediated fusion, or TMF). The causal specifications are the step size, the speed of the pursuer, the speed of the target, the restoration constant, and the initial direction of the pursuer; the outcome variables are the number of steps to fusion and the mode of fusion. The pattern of behavior is complicated, being more-or-less regular over large tracts of values, interspersed with abrupt, threshold-like changes that may generate a dichotomous pattern of inheritance despite a continuous gradation of genetic or other causes. The temporary abolition of the correction process (a change introduced to simulate the pattern of the effect of a teratogen) may delay fusion and suggest how a septum may fail to fuse, the ductus arteriosus to close, or an endocardial cushion to form. But the model also predicts that under certain plausible conditions, the "teratogen" would speed up fusion and hence perhaps offset a genetic predisposition to a congenital defect.

Age-dependent expression of familial risk in Alzheimer's disease

There is growing evidence for genetic causes of Alzheimer's disease; therefore, consideration of its age at onset among genetically predisposed individuals is timely. The authors studied the onset of Alzheimer-like dementia in families of 79 probands ascertained clinically for the Bronx Veterans Administration/Mt. Sinai School of Medicine longitudinal studies of Alzheimer's disease. Analyses among their 379 first-degree relatives, living and decreased, suggested that 1) early onsets form a distribution that is distinct from that of later onsets, and thus, different causes or mechanisms may operate in early- and late-appearing disease; 2) age at onset varies as a familial characteristic; 3) with present population survival, only one third of the theoretical predisposition to Alzheimer's disease will become manifest during the lifetime of relatives at risk; and 4) a stable annual incidence of 1.5 per cent in the early ninth decade, reported by others, can be explained by the operation of a dominant gene with a population allele frequency of 0.13. The authors conclude that different (possibly genetic) causes of Alzheimer's disease may operate in different families or individuals, although much of its predisposition remains latent during the lifetime of those at risk.

Spirometry and chest wall dimensions in achondroplasia

Standard values for pulmonary function in short-limbed dwarfism are not available. Therefore, chest diameters and expiratory spirograms were measured in 58 female and 44 male subjects between 7 and 60 years of age with achondroplasia, the most common form of dwarfism. Standing height in adults was 49.6 +/- 3.2 (SD) inches with a sitting/standing height ratio of 0.66 (normal 0.52-0.53). Despite extremely short stature, only AP chest diameters in males were smaller than control subjects of similar age. The following equations were derived for forced vital capacity (FVC): males (under 25 years), FVC(L) = -3.56 + 0.162 X sitting height (in) + 0.067 X age (yrs); males (over 25 years), FVC(L) = -0.73 + 0.162 X sitting height (in) -0.047 X age (yrs); females (under 20 years), FVC(L) = -3.56 + 0.150 X sitting height (in) + 0.067 X age (yrs); females (over 20 years), FVC(L) = -1.92 + 0.150 X sitting height (in) -0.016 X age (years). Similar prediction equations were derived for FEV1 and FEF25-75%: FEV1/FVC % was 84.2 (+/- 6.5) for females and 88.0 (+/- 6.5) for males. We also compared the observed FVC measurements to values calculated using standing heights derived from the subject's sitting height, assuming a normal body proportion. The observed vital capacity in achondroplasia was only 67.6 (+/- 19.2) percent of that predicted for normally proportioned females and 72.4 (+/- 13.6) percent for males, suggesting reduced vital capacity in achondroplasia, due to reduced chest wall compliance or abnormal lung growth.

The bingo model. IV. The statistics of survivorship in the bingo-gamma model

The survivorship (time to death or failure) of a bingo-gamma (BG) model is defined as the minimum among the waiting times for completion among k independent gamma processes. The ith process is of order ni, with a mean rate for the occurrence of hits of ai. In this paper we address the case where, for all competing processes, the order and the rate at which hits occur are the same but both they and k are unknown. We denote by k the multiplicity, by n the order or the number of hits to failure, and by a the transition parameter. The joint maximum likelihood estimator (MLE) of the three parameters of this BG process is developed. An algorithm for calculating it has been devised and a computer program in BASIC has been written. The properties of the MLE have been explored systematically, mainly by Monte Carlo simulation. The distributions, means, variances, covariances, and correlation coefficients of the three parameters are explored for samples of size 25 and samples of size 100. Also, the simple average of the observed survival times (which gives a method of moments estimator of the mean survival) is compared with the MLE of the mean survival; the two estimators seem to be unbiased and about equally efficient.

A geneticist's approach to psychiatric disease

The pattern of the genetics of psychiatric disease is various, in detail and in kind; one cannot always expect to find simple, trustworthy explanations of what are complex relationships. There will be some diseases, mostly of the disruptive type, that will prove to be Mendelian defects; but it would be idle to expect that of most. Many disorders will be elucidated only when the nub of the problem is better defined. Mindless application of standard genetic techniques devised for quite different purposes is no substitute for articulate speculation built on sound fact and cogent testing. In this respect genetic evidence is no different from that of physiology, pathology and pharmacology, which are perhaps less unfamiliar to readers than genetics. Finally, no answer has been found unless it deals in those terms in which the question first arose. If the topic of the genetic analysis is some psychosis, the final predicate must be a statement about the psychosis, not about some arbitrary abstraction from it.