|Year : 2021 | Volume
| Issue : 2 | Page : 98-102
Association of Down syndrome with major congenital anomalies in the North Indian population
Kanchan Bisht1, Rakesh Kumar Verma1, Navneet Kumar1, Shakal Narayan Singh2, Baibhav Bhandari3
1 Department of Anatomy, KGMU, Lucknow, Uttar Pradesh, India
2 Department of Pediatrics, KGMU, Lucknow, Uttar Pradesh, India
3 UCHC, Lucknow, Uttar Pradesh, India
|Date of Submission||26-Nov-2020|
|Date of Acceptance||24-Jun-2021|
|Date of Web Publication||10-Feb-2022|
Dr. Rakesh Kumar Verma
Department of Anatomy, KGMU Lucknow - 226 003, Uttar Pradesh
Source of Support: None, Conflict of Interest: None
Context: Down syndrome (DS), which usually occurs due to an extra chromosome 21 or a partial trisomy, is the most common genetic cause of intellectual disability. The affected individuals usually present with characteristic clinical manifestations and are seen to be associated with various systemic defects. Aim: The aim of our study was to determine the major congenital anomalies associated with DS in the North Indian population. Methods: Blood samples of 51 children (0–10 years) who were screened for the suspicion of DS were collected. Karyotyping was conducted. Data were analyzed using the Statistical Package for the Social Sciences (SPSS) software version 21.0. Results: Out of the 51 suspected participants, karyotypes could be successfully obtained only for 40. Among these 40 participants, karyotypes of 35 were confirmed to be DS. Of these 35 confirmed cases, 21 (60%) were found to be associated with at least one major congenital anomaly, of which cardiac anomalies (34.2%) were most common, followed by gastrointestinal tract and genitourinary anomalies (11.4% each). Central nervous system and musculoskeletal anomalies constituted 5.7% each. Mosaic variant of DS was found to be least associated with congenital anomalies. Conclusion: The patients with DS should be carefully examined for systemic anomalies. Most cases are usually associated with at least one congenital anomaly.
Keywords: Anomalies, congenital, cytogenetics, Down syndrome, karyogram, translocation, trisomy
|How to cite this article:|
Bisht K, Verma RK, Kumar N, Singh SN, Bhandari B. Association of Down syndrome with major congenital anomalies in the North Indian population. J Mahatma Gandhi Inst Med Sci 2021;26:98-102
|How to cite this URL:|
Bisht K, Verma RK, Kumar N, Singh SN, Bhandari B. Association of Down syndrome with major congenital anomalies in the North Indian population. J Mahatma Gandhi Inst Med Sci [serial online] 2021 [cited 2022 May 20];26:98-102. Available from: https://www.jmgims.co.in/text.asp?2021/26/2/98/337461
| Introduction|| |
Down syndrome (DS), which usually occurs due to an extra chromosome 21 or a partial trisomy, is the most common genetic cause of intellectual disability. John Langdon Down was a British physician who first recognized the syndrome in 1866. In 1932, Waardenberg and Davenport suggested that DS could be the result of some chromosomal anomaly. In 1959, it was finally concluded that an extra copy of chromosome 21 is the root cause of this syndrome.
DS is the most common genetic cause of mental retardation in the world. Patients with DS have a characteristic phenotype such as protruding tongue, microgenia, short stature, brachycephaly, flat facies, upward slanting palpebral fissures, epicanthus, low-set ears with abnormal folds, and simian crease. Some patients may present with nasal hypoplasia, shortening of the femur and sandal gap (a large space between the big toe and the rest of the toes), and clinodactyly or middle phalanx hypoplasia of the fifth finger. The characteristic presentation of DS patients makes their clinical diagnosis relatively easy.
DS is commonly associated with systemic anomalies such as mental retardation, cardiac anomalies, gastrointestinal anomalies, ophthalmological errors, hearing loss, skin problems, and genitourinary abnormalities. Males with DS are usually sterile, in contrast to DS females, who can still be fertile, although menstrual irregularities have been reported in them. Congenital heart diseases (CHDs) are seen in most of the patients of DS in the form of atrioventricular septal defects (AVSDs), ventricular septal defect (VSD), atrial septal defect (ASD), etc.
Various risk factors have been associated with the occurrence of DS such as advanced maternal age, consanguineous marriage, use of contraceptive pills, early induced abortion, socioeconomic conditions, cigarette smoking, alcohol intake, and radiation exposure.
The three main cytogenetic variants of DS are as follows: (a) Free trisomy 21, where an extra chromosome 21 is present in all the cells, (b) mosaic trisomy 21, in which two types of cell lineages are present, one is normal and another cell line with trisomy 21, and (c) Robertsonian translocation trisomy 21, where the long arm of chromosome 21 is attached to another chromosome (usually an acrosome). All the variants of DS do not present with similar features. One of the variants of DS, mosaicism, shows milder phenotypes in comparison to free trisomy.
This study was conducted to determine the major congenital anomalies associated with DS in the North Indian population.
| Methods|| |
This study was approved by the ethics committee of the institute. Blood samples were collected from 51 children, ranging from 0 to 10 years. [Figure 1] represents the distribution of Down's syndrome with/ without associated congenital anomaly. These children were screened in the department of pediatrics for suspicion of DS, after taking written informed consent from their parents/guardians. Detailed personal and family histories were taken, and a thorough clinical examination was done in these children. Peripheral venous blood samples were collected in BD Vacutainer sodium heparin vials and brought in an ice pack to the department of anatomy. [Figure 2] represents the distribution of Down's syndrome according to the type of associated anomalies. Further processing was carried out in the cytogenetics laboratory of the department. [Figure 3] and [Figure 4] represent the karyotype of a trisomy male (47, XY) and a trisomy female (47, XX) respectively.
|Figure 1: Distribution of Down syndrome with/without associated congenital anomaly|
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|Figure 2: Distribution of Down syndrome according to associated anomalies|
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0.5 ml of blood sample was taken in 5 ml of culture media (PB MAX) in a test tube, under laminar air flow and was incubated at 37°C temperature, 85% humidity, and 5% concentration of CO2 for 72 h in slanting position in CO2 incubator (YORCO). Then three drops of karyoMAX colcemid solution (0.1 μg/ml) were added, and test tube was centrifuged at 1000 rpm for 10 min. The supernatant was discarded leaving behind a little cell button. The cell button was suspended in 5 ml of hypotonic solution (potassium chloride) and was incubated at 37°C for 30 min. The test tube was then centrifuged at 1000 rpm for 10 min. Leaving the cell button, test tube was re-suspended in 5 ml of fixative (methanol: Acetic acid ratio 3:1). This process of centrifugation, discarding the supernatant, and adding the fixative was repeated 2–3 times, until button at the bottom of the test tube became white. Finally, the tube was kept at 2°C–3°C for 2 h before the harvested blood cells became ready for slide preparation. Slides were prepared by dropping method, and then treated with trypsin for better banding. Adequately aged slides were stained with Giemsa stain. These slides were observed under a microscope (Olympus BX51) attached with a computer. Fields showing a good spread of metaphase were photographed. Karyograms were prepared from slides using Cytovision software. Karyograms were then analyzed for different cytogenetic variants of DS, in the Cytogenetic laboratory of the anatomy department of our institute. For each case, at least 20 metaphase fields were analyzed before obtaining the karyotype. In cases where mosaicism is suspected, the observation was extended to a total of 30 fields. The karyotypes were reported as per the international system for human cytogenetic nomenclature (ISCN, 2013) guidelines. Statistical analysis was performed using the SPSS software version 21.0
| Results|| |
A total of 51 participants were screened. However, karyogram could be obtained for only 40 (78.4%) participants. Among those 40 children, 35 children had DS, of which 32 (91.4%) had free trisomy, two (5.7%) had Robertsonian translocation, and one (2.9%) had mosaic pattern on karyogram. Among the 32 free trisomy cases, 20 had genotype 47, XY + 21 while remaining 12 had genotype 47, XX + 21. Among the two cases with Robertsonian translocation, one each had genotype 46, XY + 21, t (14;21) and 46, XX + 21, t (14;21), respectively. The single case with mosaic pattern had genotype 47, XY + 21/46, XY. Twenty-one (60%) children had at least one congenital anomaly, whereas 14 (40%) had no congenital anomaly, as shown in [Table 1].
|Table 1: Distribution of Down syndrome with/without associated congenital anomaly (n=35)|
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Among congenital anomalies, cardiac anomalies were the most commonly reported and responsible for 34.2% cases, followed by gastrointestinal tract (GIT) and urinary tract anomalies, each seen in 11.4% of children. Central nervous system (CNS) and musculoskeletal anomalies were each reported in 5.7% of children, whereas respiratory tract anomalies and lymphoma were each reported in 2.9% of children [Table 2].
|Table 2: Distribution of Down syndrome according to associated anomalies (n=35)|
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Mosaic pattern was seen in only one child, but this was not accompanied by any congenital anomaly. Cardiac abnormalities were more commonly seen with Robertsonian translocations (100%) than with free trisomy (32.3%), but it was not statistically significant (P = 0.106). Urinary anomalies were more common in Robertsonian translocation (50% v/s 9.4%) but was statistically insignificant (P = 0.202). The karyotype of a Robertsonian translocation 46, XY t (14; 21) is shown in [Figure 5]. All the other congenital anomalies (GIT, musculoskeletal, and respiratory) and lymphoma were seen only in free trisomy cases [Table 3]. Statistically, there was no significant association between the variant of DS and type of congenital anomaly (P > 0.05).
|Table 3: Distribution of anomalies in different variants of Down syndrome (n=35)|
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Out of 12 children having congenital cardiac anomalies, 66% had ASD, 25% had tetralogy of Fallot (TOF), whereas patent ductus arteriosus (PDA) and VSD were each reported in 8% children [Table 4].
| Discussion|| |
Free trisomy was the most common cytogenetic variant of DS, constituting 91.4% of all DS cases in this study, followed by translocation and mosaicism, which accounted for 5.7% and 2.9% cases, respectively. Kadotani et al. in their study conducted on the population in Hiroshima reported the frequencies of these variants as 78.64%, 6.8%, and 5.8%, respectively. A retrospective analysis performed by Kava et al. on DS cases in Mumbai also revealed an almost similar pattern: 95%, 3.2%, and 1.8%, respectively. Similarly, free trisomy was again reported to be the most common variant by Kolgeci et al. in Prishtina with 93.4% cases, followed by translocation (5.6%) and then mosaicism (1%).
Wahab et al. in their study in a Qatari population observed that almost half of the DS cases (48.3%) had some sort of CHD. In a study conducted by El Gilany in Egypt, CHDs were diagnosed in 18.9% of DS cases, although not much difference was seen in their frequencies among different variants of DS. The most common cardiac anomalies in their study were VSD (7.9%) and ASD (5.6%). Stoll et al. conducted a study in a French population and found that 36% had no major associated anomalies and 64% had at least one major associated anomaly. The most common type of anomalies associated with DS in their study was also observed to be cardiac anomalies (44%), among which AVSD (30%) was most commonly seen, followed by ASD (25%), VSD (22%), PDA (5%), coarctation of aorta (CoA) (5%), TOF (3%), and other CHDs (9%). In a study conducted by Tubman et al. on DS patients of Ireland, cardiac anomalies were observed in 42% cases, of which 38% had AVSDs, 15% had VSD, 21% with ASD, and 18% with PDA. Frid et al. reported cardiac anomalies in Swedish patients with DS as 47% AVSD, 33% VSD, 8% ASD, 2% TOF, 1% COA, and 9% with PDA. Freeman et al. observed major cardiac defects in 44% of DS patients in Atlanta, of which 39% had AVSD, 42% had secundum ASD, 43% had VSD, and 6% had TOF.
We observed that 60% of DS patients were associated with at least one major congenital anomaly, among which congenital cardiac anomalies were the most common (34.2%) followed by GIT and urinary tract anomalies (each 11.4%), followed by CNS and musculoskeletal anomalies (each 5.7%) and lastly respiratory tract anomalies and lymphoma (each 2.9%). The findings of our study are consistent with the above-mentioned studies.
Congenital cardiac anomalies were found to be the most common congenital anomaly associated with DS. The most common congenital cardiac anomaly seen in this study was ASD (66%). It was followed by TOF (25%), VSD, and PDA (8% each). These findings, however, were slightly different from the above-mentioned studies. Only one case of mosaicism was detected in our study which was devoid of any congenital anomaly. Congenital cardiac abnormalities were more common with Robertsonian translocations than with free trisomy, but it was not statistically significant (P = 0.106). Urinary anomalies were also more common with Robertsonian translocation as compared to free trisomy, but this was not statistically significant (P = 0.202). All the other congenital anomalies (GIT, musculoskeletal, and respiratory) and lymphoma were present exclusively in free trisomy cases.
Patients with DS should be carefully examined for the presence of any systemic anomalies. As we have seen most cases are usually associated with at least one congenital anomaly. Cytogenetic studies are crucial not only to confirm the diagnosis but also to differentiate between the variants of DS for genetic counseling, since different variants are associated with different risks of recurrence. This information, together with advancement in diagnostic techniques might help the parents in taking decisions and thus reducing the burden of DS in our society.
| Conclusion|| |
Free trisomy was the most common cytogenetic variant of Down's syndrome, constituting 91.4% of all DS cases in this study, followed by translocation and mosaicism, which accounted for 5.7% and 2.9% cases respectively. Out of total confirmed cases of DS, 60% were associated with at least one congenital anomaly, most common anomaly being congenital cardiac anomalies (34.2%). Most common cardiac anomaly seen with DS patients in the study was ASD (66%).Mosaic variant of DS was found to be least associated with congenital anomalies. Congenital cardiac anomalies were present in Robertsonian translocation as well as in free trisomies. The patients with DS should thus be carefully examined for any systemic anomaly as most of the cases are usually associated with at least one congenital anomaly. Cytogenetic study is crucial not only to confirm the diagnosis but also to differentiate the variants of DS for genetic counselling purpose since different variants are associated with different risks of recurrence. This information, together with advancement in diagnostic techniques might help the parents in making decision and thus reducing the burden of DS in our society.
We wish to thank faculty and residents of pediatrics department for the permission to collect the blood samples from the suspected patients. We would also like to thank Dr. Brijesh Kumar, Dr. Priyanka Pandey, and other seniors for their valuable suggestions and help.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]
[Table 1], [Table 2], [Table 3], [Table 4]