Síndrome de Edwards o trisomía 18

Introduction to Edwards Syndrome

In this section, Michelle introduces Edwards Syndrome, also known as Trisomy 18. She explains that it is a chromosomal disorder where a person inherits an extra copy of chromosome 18.

Understanding Edwards Syndrome

• Edwards Syndrome is also referred to as Trisomy 18 due to the presence of an extra copy of chromosome 18.

• The prevalence of Edwards Syndrome in newborns is estimated to be between 1 in 6,000 and 1 in 8,000. Unfortunately, patients with this syndrome have a high mortality rate.

• There are three main causes of Edwards Syndrome: non-disjunction, translocation, and mosaicism. Non-disjunction refers to a defect in the separation of chromosomes during meiosis. Translocation occurs when a part of one chromosome breaks off and attaches to another chromosome. Mosaicism refers to cells originating from the same zygote having different genotypes.

• Non-disjunction accounts for approximately 95% of cases, translocation for about 3-5% of cases, and mosaicism for around 1% of cases.

Genetic Mechanisms

• DNA contains our genetic information stored in chromosomes. Normally, humans have 46 chromosomes (23 pairs).

• Trisomies occur when there are three copies instead of two copies of a particular chromosome. For example, in Trisomy 18, there are three copies of chromosome 18.

• Meiosis is the process that produces our sex cells (eggs and sperm). During meiosis, chromosomes replicate and divide into four cells with half the number of chromosomes (23 each).

• Non-disjunction can occur during meiosis I or meiosis II. If non-disjunction occurs in meiosis I, one cell ends up with both chromosomes and the other cell lacks a chromosome, resulting in two cells with an extra chromosome and two cells with a missing chromosome.

• Translocation occurs when chromosomes break and reattach to another chromosome. In Edwards Syndrome, chromosome 18 breaks and attaches to another chromosome, often chromosome 14.

Impact of Genetic Mechanisms

• When DNA replication occurs after translocation, it results in different scenarios. Cells with normal chromosomes (no translocation) will have the correct number of chromosomes.

• In non-disjunction during meiosis II, one cell ends up with an extra chromosome, one cell lacks a chromosome, and two cells have the correct number of chromosomes.

• The presence of three copies of chromosome 18 leads to Trisomy 18. This can happen due to non-disjunction or translocation.

• Mosaicism refers to having different genotypes within cells originating from the same zygote.

Translocation and Robertsonian Translocation

• Translocation occurs before DNA replication during meiosis. Chromosomes break and reattach to another chromosome.

• In Edwards Syndrome, the long arm of chromosome 18 breaks and attaches to the long arm of another chromosome (often chromosome 14).

• The short arms of these chromosomes do not have a partner for attachment and form a hybrid structure.

Meiotic Division and Consequences

Michelle explains how meiotic division affects the distribution of genetic material in Edwards Syndrome.

Meiotic Division and Genetic Material Distribution

• Meiotic division prepares cells for division into gametes (eggs or sperm).

• In meiosis I, cells with normal chromosomes divide, resulting in cells with the correct number of chromosomes.

• Cells with translocation (hybrid structure) may lose genetic material during meiosis II due to the absence of essential genes. This loss occurs at the end of meiosis.

• The second meiotic division results in cells with an extra chromosome, cells lacking a chromosome, and cells with the correct number of chromosomes.

Conclusion

Michelle concludes her discussion on Edwards Syndrome by summarizing the genetic mechanisms and consequences associated with this chromosomal disorder.

Summary

• Edwards Syndrome is a chromosomal disorder characterized by an extra copy of chromosome 18.

• The main causes are non-disjunction, translocation, and mosaicism.

• Non-disjunction accounts for most cases, while translocation and mosaicism are less common.

• Meiotic division plays a crucial role in determining the distribution of genetic material in Edwards Syndrome.

• Understanding these genetic mechanisms helps explain how individuals can end up with three copies of chromosome 18 instead of two.

Timestamps provided are approximate and may vary slightly depending on the source video.

Chromosomal Abnormalities and Symptoms

This section discusses different scenarios of chromosomal abnormalities and their associated symptoms.

Chromosome 14 Abnormality

• In this scenario, a cell duplicates its information, resulting in two chromosomes.

• The chromosome 14 with a short arm hybridizes, leading to division in meiosis 2.

• The result is a loss of chromosome 14.

Monosomy 18

• When genetic information from the parent is received, there is only one chromosome 18 present.

• The hybridization of chromosome 18 with long arms results in obtaining a hybrid with long arms and a certain chromosome here.

• This leads to trisomy as there is an extra copy of chromosome 18.

Trisomy 14

• After DNA duplication and meiosis, the father contributes the necessary genetic information.

• A trisomy occurs when there is an extra copy of chromosome 14 due to the hybridization with long arms.

• This can be observed by color-coding the chromosomes.

Chromosome Loss and Gain

• In another scenario, after DNA duplication and meiosis, a chromosome loss occurs while another hybridizes with long arms.

• The father's genetic information results in monosomy for chromosome 14 due to the absence of another copy.

Chromosomal Abnormalities Continued

This section continues discussing chromosomal abnormalities and their implications.

Mosaic Trisomy

• Mosaic trisomy refers to cells being mixed, some having 46 chromosomes while others have 47 chromosomes.

Developmental Process and Mitosis

• A zygote needs to divide multiple times during development through mitosis, producing various types of cells.

Chromosome Dysfunction during Mitosis

• Chromosome dysfunction can also occur during mitosis, resulting in cells with an extra chromosome 18 (47 chromosomes) or a missing chromosome 18 (45 chromosomes).

• Cells with 47 chromosomes can survive and continue replicating.

Clinical Presentation of Trisomy 18

• Patients with trisomy 18 exhibit specific characteristics.

• These include finger positioning, foot deformities, micrognathia (small chin), coliccephaly (elongated head), microcephaly (underdeveloped brain), prominent occiput, hypertelorism (widely spaced eyes), low-set ears, short neck, and clenched hands.

Clinical Features of Trisomy 18

This section discusses the clinical features associated with trisomy 18.

Physical Characteristics

• The position of fingers shows the second finger on top of the first and the fifth finger on top of the fourth.

• Foot deformities resemble a rocking chair shape or equinus.

• Micrognathia and microcephaly are present, along with a prominent occiput.

• Hypertelorism is observed, along with abnormal ear placement and a short neck.

Other Manifestations

• Other manifestations include sternum abnormalities, cleft palate, gastrointestinal anomalies such as omphalocele (organs protruding through the belly button), renal malformations, cardiac defects like septal defects, respiratory problems due to pulmonary hypoplasia, frequent infections, intellectual disability, and growth failure.

Diagnosis and Treatment Options

This section covers the diagnosis and treatment options for trisomy 18.

Prenatal Diagnosis

• Trisomy 18 is suspected during prenatal ultrasound or biochemical testing.

• Confirmation is done through an invasive procedure called chorionic villus sampling to perform a karyotype analysis.

Postnatal Diagnosis

• After birth, a karyotype analysis of peripheral blood is performed if trisomy 18 is suspected.

Treatment

• Unfortunately, there is no specific treatment available to prevent or improve the life of patients with trisomy 18.

Complications and Causes of Survival in Patients with Cardiac, Renal, and Neurological Issues

In this section, the speaker discusses the complications and causes of survival in patients with cardiac, renal, and neurological issues. The discussion includes factors such as mosaicismo or translocation that are related to cases where patients experience mental retardation and limited autonomy.

Complications and Causes of Survival

• Patients who survive cardiac, renal, and neurological issues face complications due to factors such as mosaicismo or translocation.

• These patients often suffer from mental retardation and have limited autonomy.

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