Down syndrome cell adhesion molecule--a common determinant of brain and heart wiring

The Drosophila homolog of APP promotes Dscam expression to drive axon terminal growth, revealing interaction between Down syndrome genes

Down syndrome (DS) is caused by triplication of human chromosome 21 (HSA21). Although several HSA21 genes have been found to be responsible for aspects of DS, whether and how HSA21 genes interact with each other is poorly understood. DS patients and animal models present with a number of neurological changes, including aberrant connectivity and neuronal morphology. Previous studies have indicated that amyloid precursor protein (APP) and Down syndrome cell adhesion molecule (DSCAM) regulate neuronal morphology and contribute to neuronal aberrations in DS. Here, we report the functional interaction between the Drosophila homologs of these two genes, Amyloid precursor protein-like (Appl) and Dscam (Dscam1). We show that Appl requires Dscam to promote axon terminal growth in sensory neurons. Moreover, Appl increases Dscam protein expression post-transcriptionally. We further demonstrate that regulation of Dscam by Appl does not require the Appl intracellular domain or second extracellular domain. This study presents an example of functional interactions between HSA21 genes, providing insights into the pathogenesis of neuronal aberrations in DS.

Advances in understanding the association between Down syndrome and Hirschsprung disease (DS-HSCR)

The clinical association between Trisomy 21 (Down syndrome) and aganglionosis (Hirschsprung disease; DS-HSCR) is well-established, being of the order of 5% and remains the most common congenital association with Hirschsprung disease. However, little consensus exists as to the possible etiologic and genetic factors influencing this association. Recent research has identified a number of levels at which development of the enteric nervous system is potentially affected in Trisomy 21. These include a decreased central pool of available neuroblasts for migration into the enteric nervous system, abnormal neuroblast type, poor synaptic nerve function and early germline gene-related influences on the migrating neuroblasts due to genetic mutations of a number of important developmental genes, and possible somatic mutations resulting from alterations in the local tissue microenvironment. In this paper, we review available evidence for this association. In addition, we provide evidence of both germline and somatic gene mutations suggesting causation. Although the picture is complex, recent associations between specific RET proto-oncogene variations have been shown to be significant in Down syndrome patients with Hirschsprung disease, as they probably interfere with vital RET functions in the development of the autonomic and enteric nervous systems, increasing the risk of disturbed normal function. In addition, we explore potential role of other facilitatory influence of other susceptibility genes as well as potential other chromosome 21 gene actions and the microenvironment on the Down syndrome gastro-intestinal tract. The various ways in which trisomy of chromosome influences the enteric nervous system are becoming clearer. The sum of these effects influences the outcome of surgery in Down syndrome patients with Hirschsprung Disease.

The association of low socioeconomic status and the risk of having a child with Down syndrome: a report from the National Down Syndrome Project

PURPOSE

Advanced maternal age and altered recombination are known risk factors for Down syndrome cases due to maternal nondisjunction of chromosome 21, whereas the impact of other environmental and genetic factors is unclear. The aim of this study was to investigate an association between low maternal socioeconomic status and chromosome 21 nondisjunction.

METHODS

Data from 714 case and 977 control families were used to assess chromosome 21 meiosis I and meiosis II nondisjunction errors in the presence of three low socioeconomic status factors: (i) both parents had not completed high school, (ii) both maternal grandparents had not completed high school, and (iii) an annual household income of <$25,000. We applied logistic regression models and adjusted for covariates, including maternal age and race/ethnicity.

RESULTS

As compared with mothers of controls (n = 977), mothers with meiosis II chromosome 21 nondisjunction (n = 182) were more likely to have a history of one low socioeconomic status factor (odds ratio = 1.81; 95% confidence interval = 1.07-3.05) and ≥2 low socioeconomic status factors (odds ratio = 2.17; 95% confidence interval = 1.02-4.63). This association was driven primarily by having a low household income (odds ratio = 1.79; 95% confidence interval = 1.14-2.73). The same statistically significant association was not detected among maternal meiosis I errors (odds ratio = 1.31; 95% confidence interval = 0.81-2.10), in spite of having a larger sample size (n = 532).

CONCLUSION

We detected a significant association between low maternal socioeconomic status and meiosis II chromosome 21 nondisjunction. Further studies are warranted to explore which aspects of low maternal socioeconomic status, such as environmental exposures or poor nutrition, may account for these results.

Down syndrome and the enteric nervous system

Down syndrome (DS) is the most common chromosomal abnormality occurring in humans. Up to 77% of DS children have associated gastrointestinal (GI) abnormalities, which may be structural or functional in nature. Functional disturbances may, in turn, affect the outcome of corrective surgical procedures, prompting to caution. It is becoming clear that the processes affecting the enteric nervous system (ENS) in DS not only affect the micro-anatomy but also nerve function, and there is some histological evidence of ENS variations in both human and DS animal models. This suggests that developmental disorders of the ENS are probably fundamental to the functional GI disturbances encountered in patients with DS. The anomalous brain development, function and resulting intellectual impairment associated with DS appears to result from the genetic imbalance created by the trisomy of chromosome 21. The possible links between the brain, GI and ENS involvement are not as yet entirely clear. Neurotropic factors affecting brain development during embryogenesis are probably interlinked with ENS development, but the precise mechanism of how this occurs has yet to be established. This study explores what is known about the ENS dysfunction in DS and reviews the possible importance of chromosome 21 located and other genes in its etiology. Functional motor disturbances of the esophagus and colon are not uncommon and may be congenital or acquired in nature. The most prominent of these include esophageal dysmotility syndromes (e.g. achalasia, gastroesophageal reflux, dysphagia) as well as a higher incidence of chronic constipation and Hirschsprung's disease (HSCR) (2-15%) occurring in association with DS. Chromosome 21 itself is thought to be the site of a modifier gene for HSCR. Recently identified candidate genetic mechanisms provide unique insights into the genetic background of the neurological and cognitive disorders associated with DS. Although the role of the triplicated chromosome 21 and genetic dosage remain important, the additional role of other chromosome 21 genes in the etiology of ENS developmental anomalies remains undetermined and requires ongoing research.