Understanding how the Corpus Callosum works part2(Neuroscience)
1.Agenesis of the corpus callosum: lessons from humans and mice(PubMed)
Author : Deepak Kamnasaran
Abstract : Background and purpose: The corpus callosum serves as a bridge to associate fibres between the two cerebral hemispheres. In placental mammals, this commissure provides for higher order neurological advantages. The molecular pathways involved in the development and pathogenesis of accallosal defects are sparse. The article reviews the current progress of studies undertaken to discern the embryological and genetic basis of the development of the corpus callosum.
Sources of data: The literature, including from sources such as MEDLINE and OMIM, were subjected to searches for articles reporting findings on corpus callosum development in humans and mice.
Principal findings: At least forty-six malformation syndromes and metabolic disorders have been reported in patients with complete agenesis or hypoplasia (dysgenesis) of the corpus callosum. Thirteen of these syndromes have an unknown mode of genetic inheritance, and the remaining syndromes and metabolic disorders exhibit either autosomal or X-linked inheritance among affected families. The use of patients with accallosal defects have identified mutations in at least thirty genes of the human genome, and therefore with roles implicated in the development of the corpus callosum. Patients with chromosome aberrations have been useful in defining regions on chromosomes that contain candidate genes for the development of the corpus callosum. At least eighteen different human chromosomes with numerical and/or structural aberrations have been reported in patients with acallosal defects. The mouse is an excellent model to study the structural and genetic factors that influence the development of the corpus callosum, with many similarities evident in humans. Spontaneous development of acallosal defects has been reported in at least seventeen mouse strains. Furthermore, with the use of Genetically Engineered Mice, a minimum of 15 candidate callosal agenesis genes were modeled in order to provide insightful knowledge of the molecular-structural parameters required for development of the corpus callosum. Of these mice, six had complete true agenesis of the corpus callosum, five had either true agenesis or hypoplasia of the corpus callosum, and four had hypoplasia of the corpus callosum.
Conclusions: The molecular mechanisms implicated in the pathogenesis of agenesis or hypoplasia of the corpus callosum are at the verge of discovery, and are challenged by the complexity of many genes involved. Despite these barriers, findings from a complementary human-mouse model system have been helpful in understanding the genetic (molecular) causes of accallosal defects, a fascinating phenotype for over a century.
2.Corpus callosum shape and morphology in youth across the psychosis Spectrum (PubMed)
Author : D M Prendergast , K H Karlsgodt , C L Fales , B A Ardekani , P R Szeszko
Abstract : The corpus callosum is the largest white matter tract in the human brain connecting and coordinating homologous regions of the right and left hemispheres and has been strongly implicated in the pathogenesis of psychosis. We investigated corpus callosum morphology in a large community cohort of 917 individuals (aged 8–21), including 267 endorsing subsyndromal or threshold psychotic symptoms (207 on the psychosis spectrum and 60 with limited psychosis based on previously published criteria) and 650 non-psychotic volunteers. We used a highly reliable and previously published algorithm to automatically identify the midsagittal plane and to align the corpus callosum along the anterior and posterior commissures for segmentation, thereby eliminating these sources of error variance in dependent measures, which included perimeter, length, mean thickness and shape (circularity). The parcellation scheme divided the corpus callosum into 7 subregions that consisted of the rostrum, genu, rostral body, anterior midbody, posterior midbody, isthmus, and splenium. Both individuals endorsing psychotic symptoms and those with limited psychosis had significantly (p<.05) smaller area and lower thickness measures compared to healthy volunteers, but did not differ significantly from each other. Findings were relatively widespread indicating a relatively global effect not circumscribed to any particular corpus callosum subregion. These data are consistent with the hypothesis that corpus callosum abnormalities may be evident early in the course of illness and predate the onset of frank psychosis. Given that these measures can be easily obtained and are highly reliable they may assist in the identification of individuals at future risk for psychosis.
3. The Value of Corpus Callosum Measurement in the Diagnosis of Cerebral Atrophy(PubMed)
Author : Zhao Ji-Ping , Cui Chun-Xiao , Duan Chong-Feng , Niu Lei , Liu Xue-Jun
Abstract : Objective: The study aimed to investigate the relationship between the corpus callosum area (CCa) and the degree of cerebral atrophy in patients with cerebral atrophy.
Methods: 119 patients with brain atrophy were grouped according to the degree of brain atrophy. Median sagittal CCa and intracranial area (ICa) were measured, and the ratio of corpus callosum to the intracranial area (CCa-ICa ratio) was calculated. The data were analyzed using ANOVA.
Results: CCa significantly reduced in patients with cerebral atrophy, and the degree of cerebral atrophy was found to be positively correlated with the degree of reduction in the CCa.
Conclusion: The reduction in the CCa and the CCa-ICa ratio in the median sagittal can be used as a reference indicator for the diagnosis and grading of brain atrophy in clinical practice.
