A genome-wide analysis of putative functional and exonic variation associated with extremely high intelligence.

Although individual differences in intelligence (general cognitive ability) are highly heritable, molecular genetic analyses to date have had limited success in identifying specific loci responsible for its heritability. This study is the first to investigate exome variation in individuals of extremely high intelligence. Under the quantitative genetic model, sampling from the high extreme of the distribution should provide increased power to detect associations. We therefore performed a case-control association analysis with 1409 individuals drawn from the top 0.0003 (IQ >170) of the population distribution of intelligence and 3253 unselected population-based controls. Our analysis focused on putative functional exonic variants assayed on the Illumina HumanExome BeadChip. We did not observe any individual protein-altering variants that are reproducibly associated with extremely high intelligence and within the entire distribution of intelligence. Moreover, no significant associations were found for multiple rare alleles within individual genes. However, analyses using genome-wide similarity between unrelated individuals (genome-wide complex trait analysis) indicate that the genotyped functional protein-altering variation yields a heritability estimate of 17.4% (s.e. 1.7%) based on a liability model. In addition, investigation of nominally significant associations revealed fewer rare alleles associated with extremely high intelligence than would be expected under the null hypothesis. This observation is consistent with the hypothesis that rare functional alleles are more frequently detrimental than beneficial to intelligence.

Disease severity and genetic pathways in attenuated familial adenomatous polyposis vary greatly but depend on the site of the germline mutation.

BACKGROUND: Attenuated familial adenomatous polyposis (AFAP) is associated with germline mutations in the 5', 3', and exon 9 of the adenomatous polyposis coli (APC) gene. These mutations probably encode a limited amount of functional APC protein. METHODS AND RESULTS: We found that colonic polyp number varied greatly among AFAP patients but members of the same family tended to have more similar disease severity. 5' Mutants generally had more polyps than other patients. We analysed somatic APC mutations/loss of heterozygosity (LOH) in 235 tumours from 35 patients (16 families) with a variety of AFAP associated germline mutations. In common with two previous studies of individual kindreds, we found biallelic changes ("third hits") in some polyps. We found that the "third hit" probably initiated tumorigenesis. Somatic mutation spectra were similar in 5' and 3' mutant patients, often resembling classical FAP. In exon 9 mutants, in contrast, "third hits" were more common. Most "third hits" left three 20 amino acid repeats (20AARs) on the germline mutant APC allele, with LOH (or proximal somatic mutation) of the wild-type allele; but some polyps had loss of the germline mutant with mutation leaving one 20AAR on the wild-type allele. CONCLUSIONS: We propose that mutations, such as nt4661insA, that leave three 20AARs are preferentially selected in cis with some AFAP mutations because the residual protein function is near optimal for tumorigenesis. Not all AFAP polyps appear to need "three hits" however. AFAP is phenotypically and genetically heterogeneous. In addition to effects of different germline mutations, modifier genes may be acting on the AFAP phenotype, perhaps influencing the quantity of functional protein produced by the germline mutant allele.

Posturography and balance problems in older people.

OBJECTIVE: To determine which measurements and test conditions on posturography are most useful for identifying balance problems in older people. SUBJECTS: Two samples of 70 community-dwelling older subjects (> 75 years). One group (controls) considered their balance normal for their age, and the other (patients) complained of imbalance. MEASUREMENTS: Velocity of sway on static (with and without foam) and dynamic posturography, Tinetti gait and balance score, self-reported fear of falling, and number and circumstances of falls. RESULTS: Mean sway velocity was significantly increased in patients compared with controls. The greatest difference between patients and controls occurred with measures of anterior-posterior sway velocity during angular tilt of the platform. Sway velocity was not significantly increased in patients or controls who reported falls compared with those who did not report falls. Even when comparing those who fell as a result of loss of balance with those who fell because of trips or slips, there was no significant difference in sway velocity. By contrast, those who reported fear of falling (patients and controls) had significantly increased sway velocity compared with those who did not report fear of falling. CONCLUSION: On average, velocity of sway (particularly in the anterior-posterior direction) is higher in older subjects who complain of imbalance compared with age-matched controls, and the difference is greater with dynamic posturography than with static posturography. However, the posturography data provided little information about the cause of the imbalance and did not correlate with the frequency of reported falls.

Extracellular-free Ca++ accounts for the sex difference in the aggregation of human platelets in citrated platelet-rich plasma.

It has been shown in Poiseuille flow, that the ADP-induced aggregation of human platelets in citrated plasma from female donors is significantly greater than from male donors over a range of mean tube shear rate, G, from 41.9 s-1 to 1920 s-1 and mean transit time, t, from 0.2 to 86 s. The present work verifies the sex difference at G = 335 s-1 and t = 43 s and deals with the effect of free Ca2+ on it. An inverse correlation between the extent of single platelet aggregation and donor hematocrit, and between hematocrit and the plasma ionized calcium concentration, [Ca2+], as well as a positive correlation between the extent of single platelet aggregation and [Ca2+] was found. This indicated that the sex difference is due to hematocrit-dependent differences in the [Ca2+] that result when a fixed volume of the chelating agent citrate is used to anticoagulate blood. When the initial citrate concentration was adjusted to compensate for the variable volume dilution of citrate in plasma among donors and the [Ca2+] of males raised above that of females, the sex difference was reversed. Again, aggregation correlated with [Ca2+]. At the physiological [Ca2+] in both heparinized PRP and hirudinized PRP, the rate of aggregation and aggregate size were much greater than in citrated plasma but no sex difference was detected.

The effect of red blood cells on the ADP-induced aggregation of human platelets in flow through tubes.

The effect of red blood cells, rbc, and shear rate on the ADP-induced aggregation of platelets in whole blood, WB, flowing through polyethylene tubing was studied using a previously described technique (1). Effluent WB was collected into 0.5% glutaraldehyde and the red blood cells removed by centrifugation through Percoll. At 23 degrees C the rate of single platelet aggregation was upt to 9 x greater in WB than previously found in platelet-rich plasma (2) at mean tube shear rates G = 41.9, 335, and 1,920 s-1, and at both 0.2 and 1.0 microM ADP. At 0.2 microM ADP, the rate of aggregation was greatest at G = 41.9 s-1 over the first 1.7 s mean transit time through the flow tube, t, but decreased steadily with time. At G greater than or equal to 335 s-1 the rate of aggregation increased between t = 1.7 and 8.6 s; however, aggregate size decreased with increasing shear rate. At 1.0 microM ADP, the initial rate of single platelet aggregation was still highest at G = 41.9 s-1 where large aggregates up to several millimeters in diameter containing rbc formed by t = 43 s. At this ADP concentration, aggregate size was still limited at G greater than or equal to 335 s-1 but the rate of single platelet aggregation was markedly greater than at 0.2 microM ADP. By t = 43 s, no single platelets remained and rbc were not incorporated into aggregates. Although aggregate size increased slowly, large aggregates eventually formed. White blood cells were not significantly incorporated into aggregates at any shear rate or ADP concentration. Since the present technique did not induce platelet thromboxane A2 formation or cause cell lysis, these experiments provide evidence for a purely mechanical effect of rbc in augmenting platelet aggregation in WB.

Adenosine diphosphate-induced aggregation of human platelets in flow through tubes. I. Measurement of concentration and size of single platelets and aggregates.

A double infusion flow system and particle sizing technique were developed to study the effect of time and shear rate on adenosine diphosphate-induced platelet aggregation in Poiseuille flow. Citrated platelet-rich plasma, PRP, and 2 microM ADP were simultaneously infused into a 40-microliters cylindrical mixing chamber at a fixed flow ratio, PRP/ADP = 9:1. After rapid mixing by a rotating magnetic stirbar, the platelet suspension flowed through 1.19 or 0.76 mm i.d. polyethylene tubing for mean transit times, t, from 0.1 to 86 s, over a range of mean tube shear rate, G, from 41.9 to 1,000 s-1. Known volumes of suspension were collected into 0.5% buffered glutaraldehyde, and all particles in the volume range 1-10(5) microns 3 were counted and sized using a model ZM particle counter (Coulter Electronics Inc., Hialeah, FL) and a logarithmic amplifier. The decrease in the single platelet concentration served as an overall index of aggregation. The decrease in the total particle concentration was used to calculate the collision capture efficiency during the early stages of aggregation, and aggregate growth was followed by changes in the volume fraction of particles of successively increasing size. Preliminary results demonstrate that both collision efficiency and particle volume fraction reveal important aspects of the aggregation process not indicated by changes in the single platelet concentration alone.

Adenosine diphosphate-induced aggregation of human platelets in flow through tubes. II. Effect of shear rate, donor sex, and ADP concentration.

The effect of shear rate on the adenosine diphosphate-induced aggregation of human platelets in Poiseuille flow was studied using the method described in part I (Bell, D.N., S. Spain, and H.L. Goldsmith. 1989. Biophys. J. 56:817-828). The rate and extent of aggregation in citrated platelet-rich plasma were measured over a range of mean transit time from 0.2 to 8.6 s and mean tube shear rate, G, from 41.9 to 1,920 s-1. At 0.2 microM ADP, changes in the single platelet concentration with time suggest that more than one type of platelet-platelet bond mediates platelet aggregation at physiological shear rates. At low G, a high initial rate of aggregation reflects the formation of a weak bond of high affinity, the strength of which diminishes with time. Here, the fraction of collisions yielding stable doublets, the collision efficiency, reached a maximum of 26%. The collision efficiency decreased with increasing G and was accompanied by a progressive delay in the onset of aggregation. However, the gradual expression of a more shear rate-resistant bond at high shear rates and long mean transit times produced a subsequent increase in collision efficiency and a corresponding increase in the rate of aggregation. Although the collision efficiencies here were less than 1%, the high collision frequencies were able to sustain a high rate of aggregation. At 0.2 microM ADP, aggregate size generally decreased with increasing G. At 1.0 microM ADP, aggregate size was still limited at high shear rates even though the rate of single platelet aggregation was much higher than at 0.2 microM ADP. Platelet aggregation was greater for female than for male donors, an effect related to differences in the hematocrit of donors before preparing platelet-rich plasma.

Margination of leukocytes in blood flow through small tubes.

Leukocyte margination in the vessels of the microcirculation has been attributed to a flow-dependent interaction with red cells. To determine the extent of this effect, experiments with human blood were done in 100- to 180-micron tubes to detect changes in cell distribution as a function of hematocrit and flow rate. Using a flow visualization technique, the leukocyte concentration distribution was determined in 45% ghost cell suspensions. Migration of cells toward the wall was observed at centerline velocities greater than 1 mm sec-1 and increased with increasing flow rate. The effect was probably due to a more rapid inward migration of ghosts than leukocytes because of fluid inertia and cell density differences. Experiments were therefore carried out in whole blood at hematocrits from 20 to 60%, measuring the number concentration of leukocytes and erythrocytes within the tube, nt, and comparing it to that in the infusing reservoir, no, (Fahraeus effect). At mean tube shear rates G less than 100 sec-1, nt/no less than 1 for both leukocytes and erythrocytes showing net migration of cells away from the wall, although at nearly all hematocrits there was an enrichment of leukocytes relative to erythrocytes in the tubes. At G less than 50 sec-1, nt/no remained less than 1 for erythrocytes but increased to greater than 1 for leukocytes showing migration toward the wall, the increase being greatest at 20% hematocrit in the 100-micron tubes. The nature of the effect was revealed by cine films which showed that, as the flow rate decreased, erythrocytes formed rouleaux which migrated inward creating a core and displacing leukocytes to the periphery. In control experiments using washed blood cells in phosphate buffer-albumin, nt/no less than 1 for both leukocytes and erythrocytes at all G and hematocrits, and leukocytes were now distributed. Cine films of washed blood confirmed that, in the absence of rouleaux, no significant inward migration of erythrocytes occurred.