scholarly journals What Causes Down Syndrome?

2021 ◽  
Author(s):  
Emine Ikbal Atli

Trisomy 21 (Down Syndrome) is the model human phenotype for all genome gain-dosage imbalance situations, including microduplications. Years after the sequencing of chromosome 21, the discovery of functional genomics and the creation of multiple cellular and mouse models provided an unprecedented opportunity to demonstrate the molecular consequences of genome dosage imbalance. It was stated years ago that Down syndrome, caused by meiotic separation of chromosome 21 in humans, is associated with advanced maternal age, but defining and understanding other risk factors is insufficient. Commonly referred to as Down syndrome (DS) in humans, trisomy 21 is the most cited genetic cause of mental retardation. In about 95% of cases, the extra chromosome occurs as a result of meiotic non- nondisjunction (NDJ) or abnormal separation of chromosomes. In most of these cases the error occurs during maternal oogenesis, especially in meiosis I.

2009 ◽  
Vol 26 (4) ◽  
pp. 155-161 ◽  
Author(s):  
N. Fintelman-Rodrigues ◽  
J. C. Corrêa ◽  
J. M. Santos ◽  
M. M. G. Pimentel ◽  
C. B. Santos-Rebouças

Recent evidence shows that almost 92% of the DS children are born from young mothers, suggesting that other risk factors than advanced maternal age must be involved. In this context, some studies demonstrated a possible link between DS and maternal polymorphisms in genes involved in folate metabolism. These polymorphisms, as well as low intake of folate could generate genomic instability, DNA hypomethylation and abnormal segregation, leading to trisomy 21. We compared the frequency ofCBS844ins68,MTR2756A>G,RFC-1 80G&gt A andTC776C>G polymorphisms among 114 case mothers and 110 matched controls, in order to observe whether these variants act as risk factors for DS. The genotype distributions revealed that there were not significant differences between both samples. However, when we proceed the multiplicative interaction analyses between the four polymorphisms described above together with the previously studiedMTHFR677C>T,MTHFR1298A>C andMTRR66A>G polymorphisms, our results show that the combined genotypeTC776CC /MTHFR677TT andTC776CC /MTR2756AG were significantly higher in the control sample. Nevertheless, there was no significant association after Bonferroni correction. Our results suggest that maternal folate-related polymorphisms studied here have no influence on trisomy 21 susceptibility in subjects of Brazilian population.


Author(s):  
Loly Anastasya Sinaga ◽  
Dwi Kartika Apriyono ◽  
Masniari Novita

Background: Down Syndrome is a genetic disorder that occurs because of chromosome 21 has three chromosome (trisomy 21). The extra chromosome changes the genetic balance, physical characteristic, intellectual abilities, and physiological body function. Tooth eruption in Down Syndrome children typically delayed in both the timing and sequence of eruption up to two or three years. Objective: To observe the permanent teeth eruption in Down syndrome children at age 10-16 years old, boys and girls in Special Needs School in Jember. Materials and Methods: This research was a descriptive study with 7 subjects. Each subject was examined then calculated teeth that had emerged or functionally eruption with articualting paper. Result and Conclusion:  Both permanent teeth that is still partially erupted tooth (emerged/ EM) and had erupted perfectly (functionally eruption/ FE) delayed in eruption in Down Syndrome boys and girls at age 10-16 years old.


2021 ◽  
Vol 21 (04) ◽  
Author(s):  
Disha Sawhney

ABSTRACT Down syndrome (DS) has been prevalent worldwide, for centuries now. Despite the fact that tremendous research has been done on DS ever since the early 1950s, most results obtained, are on the basis of etiological and demographic factors and predominantly of the western data. Every year in India, >30,000 children are born with DS. This survey has been done keeping the Indian population in mind and to analyze the outlook of parents having children with DS, understand the comorbidities and their management. The study was conceptualized to create an exhaustive and comprehensive questionnaire to study the pattern of inheritance of Trisomy 21, analyze influence and correlation of advanced maternal age, sex ratio, order of birth, hypothyroidism, common comorbidities, abortions, Attention deficit hyperactivity disorder (ADHD) and sleeping difficulties in individuals diagnosed with DS. 50 family triads were interviewed. The results showed that incidence of DS was more in males compared to females. The analysis revealed that mean maternal age of 25-28 years showed increased incidence of DS. 2.5 percent showed severe ID and 27.5 percent had severe ADHD symptoms, while 10-13 percent showed mild to moderate ADHD. The most and least prevalent comorbidity seen was the presence of heart disease (45%) and hearing impairment (10 percent) respectively. It was found that about 40 percent of parents strongly agreed to the idea that Genetic Counseling (GC) is helpful and wanted to reinforce it to others who find it difficult to cope up with their DS child.


Author(s):  
George T Capone

People with Down syndrome (trisomy 21) are distinguished by having an extra copy of chromosome 21. Chromosome 21 contains an estimated 562 genes, including 161 known to code for functional proteins, and at least 396 considered novel. Gene dosage imbalance is the primary mechanism, which results in the molecular, cellular, histological, and anatomical features characteristic of the condition. Throughout brain development, major neurobiological events go awry, resulting in a differently organized brain and characteristic developmental delays noted during infancy and the preschool years. The consequences of gene dosage imbalance continue to have repercussions on neurobiological function throughout childhood and adult life.


2018 ◽  
Vol 159 (28) ◽  
pp. 1146-1152
Author(s):  
Dániel Horányi ◽  
Lilla Éva Babay ◽  
Balázs Győrffy ◽  
Gyula Richárd Nagy

Abstract: Down syndrome is the most common autosomal chromosomal abnormality. According to the classical interpretation, it is the result of meiotic nondisjunction. Its occurrence is more common in advanced maternal age. Despite intensive research, pathophysiology of this genetic disorder is not fully understood. According to recent studies, a different kind of mechanism may be found in the background of trisomy 21 than was previously considered. Based on the ovarian mosaicism model, the cause of trisomy 21 (or any common trisomy) is a segregation error of a chromosome in premeiotic mitosis. The cell entering meiosis will be an oocyte with preexisting trisomy, where its (so-called “secondary”) nondisjunction is essential. Maturation of the trisomic oocytes appears to fall behind the disomic oocytes, resulting in their relative accumulation in the ovaries as time progresses. The ratio of trisomic/disomic cells becomes less favorable in maternal maturity. If ovulation is inhibited – although the number of oocytes will continue to decline due to apoptosis – it can be assumed that the trisomic/disomic oocyte ratio remains more favorable with the progression of age. In our summary report, presenting and updating our previous data, we would like to propose that – according to ovarian mosaicism model – long-term oral contraception in the anamnesis may be beneficial in pregnancies with advanced maternal age. Orv Hetil. 2018; 159(28): 1146–1152.


Dawn syndrome Trisomy 21 means there’s an extra copy of chromosome 21 in every cell. This is the most common form of Down syndrome, there is three types of Down syndrome. Trisomy 21 which there is an extra copy of chromosome 21 in every cell. Mosaicism occurs when a child is born with an extra chromosome in some but not all of their cells. Translocation in this type of Down syndrome, children have only an extra part of chromosome 21. There are 46 total chromosomes. However, one of them has an extra piece of chromosome 21 attached. Down syndrome is associated with a lots of complication like congenital heart disease. Vision. Hearing behavior and mental problem. Our case is Down syndrome with congenital chylothorax which is rare complication. Neonatal chylothorax results from the accumulation of chyle in the pleural space and may be either congenital or an acquired condition. Congenital chylothorax is most likely due to abnormal development or obstruction of the lymphatic system. It is often associated with hydrops fetalis. It can be idiopathic or may be associated with various chromosomal anomalies including Trisomy 21, Turner syndrome, Noonan syndrome, and other genetic abnormalities [1]. Treatment of chylothorax is multidisplenery need insertion of chest tube to decrease respiratory distress, diet management and pediatric surgery.


2018 ◽  
Vol 2018 ◽  
pp. 1-5
Author(s):  
Diamond Ling ◽  
Jonathan G Dayan

Trisomy 21, or Down syndrome (DS), is a genetic disorder affecting approximately 1 in 500–750 live births. The prevalence of DS has increased over the past two decades, correlating with a rise in the proportion of pregnancies complicated by advanced maternal age. There is also a correlation between advanced maternal age and dizygotic twinning rates. There is an increased risk of at least one twin being affected in dizygotic pregnancies compared to singletons. However, despite this greater relative risk, reports of concordance of DS in both dizygotic twins are very rare. Congenital heart disease (CHD) occurs in roughly 40% of individuals with DS, but there can be considerable phenotypic variation. The most common, atrioventricular septal defect accounts for only 40% of CHD seen in DS. There is also a higher incidence of CHD in twins, but also with a low incidence of concordance. There have been only five reported cases of concordant DS in dizygotic twins with confirmed chromosomal analyses; none of which describe concordant congenital heart disease. Here, we describe an unusual case of dizygotic twins of differing genders concordant for both Down syndrome and congenital heart disease of a strikingly similar presentation.


PLoS Genetics ◽  
2021 ◽  
Vol 17 (3) ◽  
pp. e1009462
Author(s):  
Upamanyu Pal ◽  
Pinku Halder ◽  
Anirban Ray ◽  
Sumantra Sarkar ◽  
Supratim Dutta ◽  
...  

Altered patterns of recombination on 21q have long been associated withthe nondisjunction chromosome21within oocytes and the increased risk of having a child with Down syndrome. Unfortunately the genetic etiology of these altered patterns of recombination have yet to be elucidated. We for the first time genotyped the gene MCM9, a candidate gene for recombination regulation and DNA repair in mothers with or without children with Down syndrome. In our approach, we identified the location of recombination on the maternal chromosome 21 using short tandem repeat markers, then stratified our population by the origin of meiotic error and age at conception. We observed that twenty-five out of forty-one single nucleotide polymorphic sites within MCM9 exhibited an association with meiosis I error (N = 700), but not with meiosis II error (N = 125). This association was maternal age-independent. Several variants exhibited aprotective association with MI error, some were neutral. Maternal age stratified characterization of cases revealed that MCM9 risk variants were associated with an increased chance of reduced recombination on 21q within oocytes. The spatial distribution of single observed recombination events revealed no significant change in the location of recombination among women harbouring MCM9 risk, protective, or neutral variant. Additionally, we identified a total of six novel polymorphic variants and two novel alleles that were either risk imparting or protective against meiosis I nondisjunction. In silico analyses using five different programs suggest the risk variants either cause a change in protein function or may alter the splicing pattern of transcripts and disrupt the proportion of different isoforms of MCM9 products within oocytes. These observations bring us a significant step closer to understanding the molecular basis of recombination errors in chromosome 21 nondisjunction within oocytes that leads to birth of child with Down syndrome.


2021 ◽  
Vol 21 (1) ◽  
Author(s):  
Hui Zhu ◽  
Xiaoxiao Jin ◽  
Yuqing Xu ◽  
Weihua Zhang ◽  
Xiaodan Liu ◽  
...  

Abstract Background Non-invasive prenatal screening (NIPS) is widely used as the alternative choice for pregnant women at high-risk of fetal aneuploidy. However, whether NIPS has a good detective efficiency for pregnant women at advanced maternal age (AMA) has not been fully studied especially in Chinese women. Methods Twenty-nine thousand three hundred forty-three pregnant women at AMA with singleton pregnancy who received NIPS and followed-up were recruited. The sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV), receiver operating characteristic (ROC) curves and the Youden Index for detecting fetal chromosomal aneuploidies were analyzed. The relationship between maternal age and common fetal chromosomal aneuploidy was observed. Results The sensitivity, specificity, PPV, NPV of NIPS for detecting fetal trisomy 21 were 99.11, 99.96, 90.98, and 100%, respectively. These same parameters for detecting fetal trisomy 18 were 100, 99.94, 67.92, and 100%, respectively. Finally, these parameters for detecting trisomy 13 were 100, 99.96, 27.78, and 100%, respectively. The prevalence of fetal trisomy 21 increased exponentially with maternal age. The high-risk percentage incidence rate of fetal trisomy 21 was significantly higher in the pregnant women at 37 years old or above than that in pregnant women at 35 to 37 years old. (Youden index = 37). Conclusion It is indicated that NIPS is an effective prenatal screening method for pregnant women at AMA.


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