Genetics
John R. Nofsinger, Corey A. Shank in The Biology of Investing, 2020
Scholars have examined the degree to which genetics, childhood experiences, and adult experiences influence financial choices. One method for exploring this topic is the use of data from twin studies. Twins share a portion of their genetic code (nature), a similar upbringing (nurture), and different adult environments (unique experiences). The social sciences have been studying twin behavior for many decades to examine similarities in health, social activities, values, and religious activities, etc. These studies exploit the fact that identical twins (monozygotic twins) come from one egg and one sperm. The Swedish government has kept track of all twins born in Sweden since 1886. The data identifies tens of thousands of identical and fraternal twins. These twins have been asked to complete telephone surveys, mail surveys, and internet surveys to discover demographic and lifestyle information about them.
ANSWERS TO PAPER TWO
Dr Andy Pickersgill, Dr Apollo Meskhi, Dr Sudipta Paul in Key Questions in Obstetrics and Gynaecology, 1999
The creatinine clearance would be expected to be low (normal: 90-120 ml/ min) and the FDP level would be higher. Reference Unintended visceral damage occurs more often with vaginal surgery. Monozygotic multiple pregnancy 25, 26 (Multiple pregnancy) Only 3% of monozygotic twins are monoamniotic. The incidence is not influenced by geographical area, ovulation induction, maternal age, family etc. (which do influence polyzygotic pregnancies). Triplets are usually polyzygotic.
Causation and mechanisms of GAD
Spilios Argyropolous, Sam Forshall, David Nutt in Generalized Anxiety Disorder: Pocketbook, 1999
A twin study56 found no evidence for genetic transmission of GAD. A high frequency of non-anxiety psychiatric disorders in co-twins was observed. This indicates that GAD is probably aetiologically heterogenous. A second twin study57 was also negative, showing that genes contributed to the predisposition of personality traits, but not to specific diagnoses of GAD or panic. However, a third twin study58 produced a concordance for GAD among monozygotic twins versus dizygotic twins of 4.3:1, thus suggesting a genetic influence. Further, another study59 reported an increased rate of GAD (but not other anxiety disorders) in the first degree relatives of patients. Therefore, there may be a degree of familial transmission of the condition and differentiation from other anxiety disorders, such as panic,60 while GAD and depression appear to share, to a degree, the same genes.61
The sex ratio of monoamniotic twin pairs
Published in Annals of Human Biology, 1977
Summary Data on more than 300 monoamniotic twin pairs have been reviewed. The sex ratios (proportions of males) of normal and of malformed monoamniotic twins seem to be lower than that of all monozygotic twins as a whole. The sex ratio of acardiac monsters (which are all members of monochorionic monozygotic twins) seems to be lower than that of monozygotic twins as a whole. Taken in conjunction, these two pieces of evidence suggest that monochorionic monozygotic twins have a lower sex ratio than dichorionic monozygotic twins. It is argued that this is evidence for the hypothesis that the sex of a zygote is associated with the time within the menstrual cycle that it is formed.
Factors Precipitating and Predisposing to R. A. as Illustrated by Studies on Monozygotic Twins
Published in Acta Rheumatologica Scandinavica, 1959
Summary An attempt was made to elucidate the relative importance of heredity and exogenous factors in the etiology of rheumatoid arthritis by a study of the concordance rate in monozygotic twins. Four sets of such monozygotic twins are reported and discussed. Three of them were discordant and one concordant, but with an atypical syndrome. When added to previously published cases in monozygotic twins, these cases bring the number up to 50 sets of monozygotic twins with rheumatoid arthritis 32 or 64 % of whom have shown discordance. It is concluded that an exogenous factor must be operative.
A comparison of neuropsychological function between monozygotic twins with neurofibromatosis, type 1: A case report
Published in The Clinical Neuropsychologist, 2020
Cody Pendergrass, Jennifer Peraza
Objective: Neurofibromatosis type 1 (NF-1) is an autosomal dominant genetic disorder that commonly presents with cognitive impairment and greater rates of learning disorders and academic difficulty compared to the general population. Investigations of neurological and physiological expression of NF-1 in monozygotic twins identified intrapair similarities and differences. Monozygotic twins with NF-1 have been found to have similar IQ scores as well as concordant diagnoses of attention-deficit/hyperactivity disorder and learning disabilities. There have been no previous reports on similarities and differences in neuropsychological profiles between monozygotic twins with NF-1. The purpose of this article is to examine the results of comprehensive neuropsychological evaluations for a pair of monozygotic twins with NF-1. Method: A pair of 19-year-old female, African-American monozygotic twins with NF-1 underwent neuropsychological evaluations in an outpatient clinic. Findings are reported following the CAse REport (CARE) guidelines. Results: The twins demonstrated similar impairment in processing speed, working memory, and attention span; however, differences also were found. Conclusions: Intrapair similarities and differences on neuropsychological assessment were found between monozygotic twins with NF-1. Primary deficits were suggestive of a frontal-subcortical pattern and could be consistent with remote neuroimaging. When differences did occur, performance was typically better for Twin A, who had also showed greater improvement on neuroimaging. Implications and directions for future research are discussed. Specifically, this case demonstrates the need for inclusion of neuropsychological assessment in studies of larger cohorts of monozygotic twins with NF-1 and correlation of neuropsychological findings with neuroimaging and postzygotic mutations.