The effects of conditioning on probands to correct for multiple ascertainment

Cannings and Thompson suggested conditioning on the phenotypes of the probands to correct for ascertainment in the analysis of pedigree data. The method assumes single ascertainment and can be expected to yield asymptotically biased parameter estimates except in this specific case. However, because the method is easy to apply, we investigated the degree of bias in the more typical situation of multiple ascertainment, in the hope that the bias might be small and that the method could be applied more generally. To explore the utility of conditioning on probands to correct for multiple ascertainment, we calculated the asymptotic value of the segregation ratio for two versions of the simple Mendelian segregation model on sibship data. For both versions, we found that this asymptotic value decreased approximately linearly as the ascertainment probability increased. When ascertainment was complete, the segregation-ratio estimates were zero, not just asymptotically but for finite sample size as well. In some cases, conditioning on probands actually resulted in greater parameter bias than no ascertainment correction at all. These results hold for a variety of sibship-size distributions, several modes of inheritance, and a wide range of population prevalences of affected individuals.

Calcium entry activators: distinct sites of dihydropyridine and aminopyridine action

The dihydropyridine compound BAY K 8644, a putative calcium entry activator, inhibits binding of the dihydropyridine calcium entry blocker, [3H]nitrendipine, to rat skeletal muscle membranes. In contrast, aminopyridine compounds also believed to stimulate calcium flux do not interact with [3H]nitrendipine binding sites in skeletal muscle or brain. These findings suggest that calcium entry activators, like calcium entry blockers, affect voltage-dependent calcium channels by diverse mechanisms.

Calcium channel 'agonist' BAY K 8644 inhibits calcium antagonist binding to brain and PC12 cell membranes

BAY K 8644, a drug that elicits calcium-dependent muscle contraction, inhibits binding of the voltage-dependent calcium channel antagonist [3H]nitrendipine to brain and PC12 pheochromocytoma cell membranes. This effect is due to high-affinity (Ki = 4.5 nM) competitive inhibition at the binding site for dihydropyridine calcium antagonists. Allosteric sites that mediate calcium channel blockade by non-dihydropyridine calcium antagonists are not similarly affected. Our findings indicate that BAY K 8644 is active at central, as well as peripheral, calcium channels and are compatible with a multi-state model of the voltage-dependent calcium channel in which antagonist drugs promote a closed state of the channel, while BAY K 8644 promotes an open state.

Ethanol and the gamma-aminobutyric acid-benzodiazepine receptor complex

Ethanol appears to enhance gamma-aminobutyric acid (GABA)-mediated synaptic transmission. Using radioligand binding techniques, we investigated the possibility that the GABA-benzodiazepine receptor complex is the site responsible for this effect. Ethanol at concentrations up to 100 mM failed to alter binding of [3H]flunitrazepam (FNZ), [3H]Ro 15-1788, or [3H]methyl-beta-carboline-3-carboxylate (MBCC) to benzodiazepine receptors, or of [3H]muscimol to GABA receptors in rat brain membranes. Scatchard analyses of the binding of these radioligands at 4 degrees C and 37 degrees C revealed no significant effects of 100 mM ethanol on receptor affinity or number. A variety of drugs as well as chloride ion increased binding of [3H]FNZ and/or [3H]muscimol, but these influences were not modified by ethanol. These findings indicate that ethanol probably potentiates GABAergic neurotransmission at a signal transduction site beyond the GABA-benzodiazepine receptor complex.

Simulation studies of segregation analysis: application to two-locus models

We tested the power of a segregation analysis method (first proposed by Elandt-Johnson) to distinguish between single-locus and two-locus models, with and without environmentally caused reduced penetrance. We also looked at the effect of ascertainment probability on the analysis and at the proband-conditioned ascertainment correction proposed by Cannings and Thompson. We found that: (1) the segregation analysis has sufficient power to distinguish between the fully-penetrant double-recessive (RR) model and the fully-penetrant single-locus dominant and recessive models; (2) the method can also distinguish fairly well between the dominant-recessive (DR) and RR models, even when one does not take into account the population prevalence; (3) the method has much less power to distinguish between the fully-penetrant RR model and the single-locus models with reduced penetrance; (4) when environmental penetrance is taken account of in the analysis, the power of the method to distinguish between the one- and two-locus models improved substantially; (5) the estimates of ascertainment probability, pi, were robust, regardless of the model under which the data were generated; and (6) the Cannings-Thompson approach to ascertainment correction worked well only when the pi used to generate the data was less than .1.

The search for heterogeneity in insulin-dependent diabetes mellitus: evidence for familial and nonfamilial forms

Using five different published sets of data, we looked at the distribution of HLA-DR genotypes among diabetic probands. It was possible to reject dominant inheritance at the HLA-associated locus, but some of the data were compatible with recessive inheritance while some were not. An attempt to reconcile the conflicting data by proposing a three-allele model apparently failed. It proved possible to resolve some of the conflicting data by proposing that simplex families represent primarily a recessive form of insulin dependent diabetes mellitus (IDDM) while multiplex families represent primarily two other subforms: one showing three-allele inheritance and one not. We also propose that the HLA locus involved in IDDM mediates the effect of an environmental agent on a second disease locus.

Periodic EEG complexes in infectious mononucleosis encephalitis

The presence of periodic EEG complexes in patients with an acute viral encephalitis is generally held to suggest that infection is due to herpes simplex. We now report a patient with clinical and laboratory findings of infectious mononucleosis, and neurologic involvement manifested by lymphocyte meningitis, coma, seizures, aphasia, hemiparesis and hemianopsia. Serial EEGs showed periodic, predominantly left-sided slow wave complexes occurring every 4 to 5 seconds, which disappeared with clinical resolution of the illness. In view of our findings and the similar findings reported previously by others in another case of infectious mononucleosis encephalitis, an EEG showing periodic complexes in the clinical setting of acute viral encephalitis should not be considered pathognomonic of herpes encephalitis, and infectious mononucleosis should be included in the differential diagnosis.

Estimation of the frequency of hexosaminidase a variant alleles in the American Jewish population

There appear to be several alleles of the hexosaminidase A (HEX A) gene that lead to different clinical syndromes. In addition to the infantile-onset Tay-Sachs disease (TSD), there is a juvenile-onset and an adult-onset form, which are also characterized by low HEX A levels. There are also apparently healthy adults with low HEX A activity. Based primarily on data from population screening for TSD carrier status, we estimate the allele frequency of the combined variant alleles for which data are available to be about 4.5 x 10(-4) and the frequency of adults showing zero HEX A levels (when tested using artificial substrate) to be about 1:67,000. The implications for population screening and prenatal diagnosis are discussed.

Flexor and extensor postures in sedative drug-induced coma

Flexor and extensor postural reflexes are most commonly seen in coma after structural brain lesions, but may also occur in metabolic coma. We report 10 patients who exhibited flexor or extensor posturing as an early and transient feature of coma resulting from sedative drug ingestion. In comatose patients with normal pupillary reactivity but no ocular movements, these postural responses suggest sedative drug overdose.

Evidence for recessive and against dominant inheritance at the HLA-"linked" locus in coeliac disease

It has been proposed that gluten sensitive enteropathy (GSE) results from the interaction of two loci: one locus linked to HLA and associated with dominant inheritance, and the other, a non-HLA-linked GSE-associated B-cell alloantigen, exhibiting recessive inheritance. We have shown in previous analyses that a two-locus, dominant-recessive model is less compatible with the existing population prevalence and observed familial segregation data than is a recessive-recessive two-locus model. Here we present additional analyses of reported population and familial HLA data that support the recessive mode of inheritance for the HLA-linked disease locus. Reported data from HLA typing of affected sib pairs, the association of GSE with DR3 and DR7 in different populations, and the proportions of different HLA phenotypes and genotypes were compared with expected data derived by three different methods. The HLA data analyses consistently reject a dominant mode of inheritance for the presumed HLA-linked disease allele but do not reject a recessive model. The affected sib-pair data also support a recessive model. These analyses are consistent with our previous prediction that the HLA-"linked" disease allele in GSE is recessive inherited.

The senescent cataract patient: a management philosophy

Senescent cataracts are a frequently encountered anomaly in optometric practice. Optometric management of these patients is an ongoing process only beginning with the physical diagnosis and encompassing necessary patient education, counseling, and advocacy.

A simple method for testing two-locus models of inheritance

A graphic method for testing simple two-locus models of inheritance is developed. The model assumes two alleles at each locus where both loci exhibit dominant, both exhibit recessive, or one locus exhibits dominant and one locus exhibits recessive inheritance. Examples of applying the graphs using published data on three diseases are given.

Two locus models for gluten sensitive enteropathy: population genetic considerations

Familial occurrence of coeliac disease (gluten-sensitive enteropathy, GSE) is well known, but the mode of inheritance remains unclear. Pena et al proposed that the genetic basis for GSE was due to disease-predisposing alleles at two loci: DRw3 at the HLA-D locus and a GSE-associated B-cell alloantigen at another, unlinked locus. They concluded that clinical disease required one DRw3 (dominant inheritance) and two B-cell alloantigen alleles (recessive inheritance), but the observed gene frequencies were not consistent with the observed disease prevalence. Here we examine the gene frequencies allowed, assuming a 2-locus model, under the constraints of known disease prevalence limits and the segregation ratio calculated from 42 published families. The gene frequencies found by Pena et al predict the segregation ratio observed in the published pedigrees and the best estimates of disease prevalence of GSE, provided 1) a 2-locus model is assumed and 2) both loci exhibit recessive inheritance. The segregation ratio appears incompatible with a 2-locus dominant-recessive model without assuming reduced penetrance.

Second-order approximations of ascertainment probabilities

A second-order correction is derived for the usual first-order order approximation to the probability of ascertaining a pedigree. Both the first- and second-order approximations are compared to the exact ascertainment probability for selected examples of monogenic and polygenic traits. The second-order approximation is shown to be accurate within 10% when the individual ascertainment probability is less than 0.2, for most cases examined. In all cases, the first- and second-order approximations provide upper and lower bounds, respectively, for the exact ascertainment probability.

Hollenhorst plaques--II

Detection of Hollenhorst plaques in the retinal circulation of the asymptomatic patient should be considered to be indicative of atherosclerotic disease. Such patients should be referred for medical evaluation and amelioration of risk factors.

Hollenhorst plaques

Detection of Hollenhorst plaques in the retinal circulation of the asymptomatic patient should be considered to be indicative of atherosclerotic disease. Such patients should be referred for medical evaluation and amelioration of risk factors.