- Show more
Causes and clinical manifestations of Down Syndrome
A syndrome is defined as a set of symptoms and signs that form a frame of reference to investigate what characterizes a certain injury, disease or pathology. In this article we will address Down Syndrome.
There are numerous syndromes caused by a chromosomal mutation. The change process generated by reorganization (changes) cell chromosomic is conceived as chromosomal mutation. Many chromosomal mutations occur during a person’s life, most of these mutations are mild, and generated by external or hereditary factors in humans. But there are numerous chromosomal mutations that cause functional anomalies, both at the cellular level and in the body.
To understand a bit on what these mutations are based, it is necessary to have knowledge about what chromosomes are. Chromosomes are structures that contain DNA (deoxyribonucleic acid), these are responsible for storing genetic information in the cell. Chromosomes are formed by genes; while genes are formed by DNA and are the fundamental, physical and functional unit of inheritance (genetic characteristics that are transmitted from parents to children). In the human being there are 22 pairs of autosomes chromosomes and a pair of sex chromosomes in each cell.
In the study of chromosomes and the number of these special techniques are used, so chromosomal maps of the human cell can be developed. There are chromosomes staining techniques to be visualized by the microscope. Chromosomes are grouped according to their size and band pattern. Through these observations, it can be determined if there is the presence of an alteration in terms of the number of chromosomes.
Down syndrome is considered as a chromosomal mutation, and is the best known among chromosomal syndromes both for their frequency in the births of many couples and in the clinical consequences of those affected. It is the most common mutation by aneuploidy (organism whose number of chromosomes differs from normal or paternal) in humans. Occurs at a frequency of 0.15% of all births.
Causes of Down Syndrome
This syndrome is due to the fact that the cells of the affected person have an additional chromosome 21 to the normal torque, or have an additional genetic material from chromosome 21 attached to another chromosome, this is known as trisomy 21. Another cause of Down Syndrome is the trisomy by Robertsonian translocation, in which the long arm of chromosome 21 and the long arm of another acrocentric chromosome are linked by its centromere (central portion constrained by the chromosome that divides it into two), the more common is translocation between pairs 14 and 21.
Approximately 80% of births with Down syndrome starts due to a lack of disjunction in maternal meiosis (cell division). This lack is considered accidental and can happen at any age. However, it has been determined that Down syndrome is produced by a mother -dependent effect; Mothers older or older than 35 have a very high risk of having children with this syndrome.
Regular trisomy cases are not considered hereditary, that is, births of parents who do not possess this mutation. However, in pairs who have already had a child with Down syndrome, there is an increase in the probabilities of happening again with a next pregnancy.
The less frequent causes of Down syndrome include trisomy 21 in mosaic and partial duplication of chromosome 21. Mosaic patients have a mixture of normal cells and trisomic cells. This alteration is generally due to the loss due to anaphasic delay (intermediate phase of the nuclear division during which the chromosomes are directed to the poles of the cells) of the additional chromosome 21, in some of the first divisions of a trisomic zygote ( by the union of an ovule and a sperm, in which there is one or 3 homologous chromosomes respectively instead of 2 normal chromosomes).
The remaining cytogenetic alteration that can cause Down syndrome is the specific duplication of the 21q22 region, this region must contain the main genes (basic inheritance unit found in the chromosome) whose excess gives rise to clinical manifestations.
Clinical manifestations of Down’s disease
Newborns with Down syndrome can be premature. They have food problems, which is due to hypotonia (loss of muscle or arterial tone) and low suction of food, but from adolescence they tend to be obese.
Babies born with Down syndrome have a small skull, with a tendency to brachycephaly (short head). With a flattened facial profile, depressed nasal bridge, short palpebral fissures, oblique up and epicanto.
Patients tend to have lingual protrusion which is due to hypotonia and macroglossia (enlarged language), in the end they suffer from cracking tongue. The atrial pavilions are small and dysplastic, the neck is short and wide. In the abdomen they can develop umbilical hernias; In the extremities, in addition to laxity or fainting, they have wide hands, with brachdactyly (fingers of abnormally short hands), clinodactyly of the fifth finger and transverse palm pear folds; At the feet they present regularly planting and separation between the first and second ortejos.
The skin has a reticulated vascular pattern at cold temperatures; It is also rough in palms and plants. Almost all patients with Down syndrome have intellectual disabilities between moderate and serious, but despite that they can be self-sufficient in daily life activities and integrate properly into society.
Among the malformations in internal organs that may be present, highlights congenital heart disease due to high mortality rates, is present in more than 40% of cases. The most common types of heart disease are those that affect the atrioventricular channel and interventricular communication.
In gastrointestinal tissue, congenital defects such as annular pancreas, duodenal membrane or imperforated anus highlight. They can also present Hirschprung’s disease (dynamic megacolon disease due to the development failure of the mesenteric plexus in the area’s rectosigmoid area), also anal stenosis (narrowing or constriction of the anus). They also have genitourinary congenital defects, including cryptorchidia or hypospadia (abnormal urethral opening, either on the surface below the glans, penile pod or perineum).
Another complication that must be ruled out, in the neonatal period, is transient acute leukemia, present up to 10% of cases, of which 75% note spontaneous resolution around three months. The risk of presenting leukemia persists after this period; Almost half of the cases develop acute lymphocytic leukemia, and the rest of the cases correspond mainly to cases of acute megakarioblastic leukemia or M7 very common in children under three years.
In the immune plane, the patient is expected to have a small thymus and T -cell deficiency, which generates greater susceptibility to infections, they usually suffer constant respiratory infections, this being a cause of mortality in patients with Down syndrome.
In the endocrinologist system, clinical and subclinical hypothyroidism may be present by up to 40% of cases, it can be congenital in 1% or develop throughout its life.
Regarding the vision, it is very common that there are refraction defects, also cataracts (opacity of the lens core), strabismus or nystagmus (involuntary movements of the ocular globe). Hearing is also usually compromised, patients with this syndrome are susceptible to otitis pictures, which can generate a decrease in hearing.
There is a relationship between patients with Down syndrome and the development of Alzheimer 40 years of age.
When adults with Down syndrome approach old age, there is a greater risk that certain mental health disorders, such as depression, anxiety, compulsive disorders and behavioral disorders.
Due to all these symptoms, in addition to others that can develop, the survival of people with Down syndrome can be variable. If the symptoms are not treated with time, patients usually live up to a young age of approximately 30 years. Babies with severe heart heart. However, people with Down who do not develop major complications in any of their symptoms usually live up to 60 years of age.
Down syndrome diagnosis
The clinical diagnosis of Down syndrome is considered simple. In general, in a woman with a pregnancy between 5 and 6 months of gestation, through a morphogenetic ecogram, it can be diagnosed if the baby suffers from this syndrome, in addition to knowing if the fetus is male or female.
Another method for diagnostic confirmation is through a chromosomal characterization, conducting a blood karyotype study. Similarly, these tests are applied to parents’ blood samples to verify that they do not have any other mutation.
The prenatal diagnosis of this syndrome can be performed by studying a karyotype in fetal amniocytes (more internal membrane cells that surrounds the embryo in the uterus) or chorionic hallos (thin filaments of the chorion surface, which are made vascular and form the placenta). The diagnosis of trisomy 21 by a caresting study is recommended for pregnant women with an age older than 35 years, since they have a high risk of births with this syndrome. Also, it is advisable to perform these analyzes whose first pregnancy was a child with Down.
How to treat cases of patients with Down syndrome
Parents are first recommended to provide all possible information about the entity and correct wrong concepts that are on the syndrome. In addition, it is necessary for parents to accept the life and development potential of the born (their son).
It is a priority to perform a cardiological assessment as early as possible, if necessary, surgical treatment to patients can be included. If there is no presence of heart disease, the patient should be performed constant long -term surveillance, to avoid the risk of developing valvulopathy in the heart.
Tests such as neonatal sieve allow to detect the presence of congenital hypothyroidism, semiannual surveillance with hormonal tests must be maintained to verify thyroid functioning. In neonatal stage it is convenient to perform a blood biometry to detect leukemoid reaction data. On the other hand, in addition to discarding gastrointestinal malformations early, digestive symptoms must.
The feeding problems in infants are transitory, so breastfeeding is not contraindicated; The surveillance of the weight and size of the patient is important, for this purpose specific growth curves are used, so it is important to start a caloric and physical activity restriction when it is detected.
Relative immune deficiency does not contraindicates vaccination, and justifies strict attachment treatment in case of infections.
The determination of a possible atlantoaxial instability is only recommended in patients who plan to do sports or activities that involve sudden neck flexion, and in whom they have parstesty data, hyporreflexia, alterations of the march or sphincter control.
It is important, in view of hypotonia and the delay of neurodevelopment, to offer them a comprehensive rehabilitation treatment, both occupational and language. Other periodic valuations that are necessary and relevant are ophthalmological and audiological.
Your learning must be supported and possible behavior problems. Girls parents who have Down syndrome should know the possible risks due to sexual abuse, because although they can have self-sufficiency in everyday activities, they need to be supervised. Polisomnography is indicated when there is suspicion of sleep apnea and many individuals improve considerably with adenoamigdalectomy.
Keep in mind that hypothyroidism or depression can be confused with Alzheimer’s initial symptoms, so these conditions should be ruled out when this problem is suspected. Although Alzheimer has no healing treatment, support can be given and taking measures for incontinence and caregiving assistance.
It is relevant to offer people with Down syndrome the dignity and respect they deserve, so you have to keep in mind their needs; Medical, physical, social, emotional, and personal security.
- Griffiths, A; Miller, J; Susuki, D; Lewontin, R; Gelbart, w. 2002. Genetics. Seventh edition. Inter-American McGraw-Hill Editorial. 568-569 pp.
- Paz, C; López, a. 2014. Molecular and Cytogenetic Genetics Human: Fundamentals, Applications and Research in Ecuador. Editorial Yachay EP. 95-97 pp.
- Kings; H. Quick reference manual in clinical genetics. 13-15 pp.