ABSTRACT It used to be widely accepted that neural tube closure in the human initiates at the level of the future neck and proceeds both cranially and caudally like zip fastener closing. This continuous closure model was recently challenged, and observation of human embryos at the neurulation stage revealed that the closure of the human neural tube initiates at multiple sites. Multi-site closure of the neural tube has been observed in many other animal species, but the initiation sites and the process of neural tube closure are variable among species. Therefore we should be careful when extrapolating the data of normal and abnormal neurulation in laboratory animals to the human. Recent studies in mouse genetics and developmental biology have shown that neural tube defects are quite heterogeneous both etiologically and pathogenetically. Gene mutations responsible for human neural tube defects are largely unknown, but molecular studies of human cases of neural tube defects and their comparison with the mouse genome data should provide a molecular basis for human neural tube defects.
ABSTRACT This review summarizes recent studies in the morphological and functional abnormalities of cerebella in three ataxic mutant mice, i.e. tottering mouse, leaner mouse, and rolling mouse Nagoya (RMN). These mutants carry mutations in the Ca2+ channel α1A subunit gene, and become useful models for human neurological diseases such as episodic ataxia type-2, familial hemiplegic migraine, and spinocerebellar ataxia type-6. All three mutants exhibited altered morphology of the Purkinje cells, ectopic synaptic contacts between granule cell axons (parallel fibers) and Purkinje cell dendritic spines and abnormal expression of tyrosine hydroxylase in Purkinje cells. In leaner mice, Purkinje cell loss was observed in alternating sagittal compartments of the cerebellar cortex corresponding to the Zebrin II-negative zones. The mutated Ca2+ channel α1A subunit was highly expressed in granule and Purkinje cells, and the P-type Ca2+ currents in Purkinje cells were selectively reduced in the mutant mice. Therefore, we concluded that altered Ca2+ currents through the mutated Ca2+ channel α1A subunit might be involved in the functional and morphological abnormalities in granule and Purkinje cells, and might result in expressions of behavioral phenotypes including ataxia. Increased levels of corticotropin-releasing factor and cholecystokinin in some climbing and mossy fibers were observed in RMN. These neuropeptides modulated the excitability of granule and Purkinje cells, indicating the possible expression of ataxic symptoms.
ABSTRACT Embryos are more susceptible to ionizing radiation than adults. Heterotopic gray matter was found in the brain of victims prenatally exposed to the atomic bomb. We reproduced this malformation in mice. Many cells in the ventricular zone, except for radial glial fibers, were destroyed by radiation. Following the proliferation of surviving cells, postmitotic neurons migrated to the cortical plate. Some neurons in areas missing radial fibers could not migrate and remained as heterotopic gray matter. On the other hand, there is no evidence of human congenital abnormalities caused by nonionizing radiation. Teratogenicity of microwaves in experimental animals is regarded as their thermal effect. However, some studies have reported effects of radio frequency and extremely low-frequency electromagnetic fields on cell proliferation and differentiation.
ABSTRACT Our impression that the incidence of congenital heart disease in patients with Down syndrome was increasing in our outpatient clinic was investigated. The change in the incidence of congenital heart disease was investigated during the period from January 1981 to December 1998 in 196 patients with Down syndrome diagnosed by chromosomal analysis. Of the 196 patients, 99 (50.5%) had congenital heart disease. The incidence increased during study period: 35.4% (1981–1983), 44.9% (1984–1986), 46.4% (1987–1989), 69.0% (1990–1992), 53.8% (1993–1995), and 81.3% (1996–1998). The number and the mean age of new outpatients were found to decrease. The incidence of Down syndrome patients whose disease was chromosomally proven by other institutions was increasing. The incidence of congenital heart disease in patients with Down syndrome is currently increasing in our outpatient clinic. However many factors might contribute to this phenomenon.
ABSTRACT In order to clarify the incidence and types of cardiovascular malformations in Japanese trisomy 21 fetuses, seventeen cases were investigated at around 20 weeks of pregnancy. Cardiovascular malformations were observed in 8 of 17 cases (47.1%). The incidence of cardiovascular malformations was not greatly different from the estimated incidence (50%) in Japanese children with Down syndrome. The preferential elimination would not exist in trisomy 21 fetuses around 20 weeks relevance to cardiovascular malformations. Atrioventricular (AV) septal defect, tetralogy of Fallot and Ebstein's anomaly were observed in one case each. Bicuspid aortic valve and abnormal branching of the aortic arch were present in three and two cases, respectively. AV septal defect, which is perceived as a specific malformation of trisomy 21, was not recognized in high frequency in the present fetal study. A 13-week-old fetus showed multiple malformations; AV septal defect, tetralogy of Fallot and dysplastic bicuspid aortic valve. This case displayed an early morphology of AV septal defect which has rarely been reported in trisomy 21 fetuses. Possible pathogenesis of AV septal defect was discussed in relation to animal models of human trisomy 21. The present study indicated that fetopathological examination of trisomy 21 fetuses would provide useful information on the development of cardiovascular malformations.
ABSTRACT We present an autopsy case of cyclopia and alobar holoprosencephaly and Polydactyly with 13 trisomy. A 27 year-old Japanese female at the 27th gestational week was diagnosed as hydramnios and the fetus showed hydrocephalus and intrauterine growth retardation. The fetus was suspected to be cyclopic and holoproscncephalic by ultrasonograph and MRI images. The mother delivered a stillborn male baby at the 30th week of gestation. At autopsy, the baby showed true cyclopia having one eyeball and two irides in a single ocular opening, and one proboscis. On histological analysis of the eye, there was marked dysplastic hyperplasia of the retina with rosettes, focal degeneration of the retina with calcification, and prominent proliferation of glial cells beneath the hyperplastic retina. Multiple glomerular structures in the cerebral cortex and aplasia of the corticospinal tract were observed. In the spinal cord, a few neurons with pyknosis were observed in the ventral horn. Although no mutation was detected in the Sonic hedgehog in the present case, we reviewed recent studies concerning the molecular mechanisms of cyclopia and holoprosencephaly.
ABSTRACT In order to perform precise chromo- some analysis, we have to have enough knowledge of cyto- genetics, refined techniques and good communication be- tween clinicians and cytogeneticists. This short note shows several examples of easily misdiagnosed chromosome ab- normality and several suggestions for precise cytogenetic diagnosis.