NExt pathology: chromosomal abnormalities

Chromatin is the complex of DNA, histone proteins, and other proteins that make up the genetic material within the nucleus of a cell. Structural abnormalities in chromatin can lead to various genetic disorders and diseases. Here are some common structural abnormalities in chromatin:

**1. Chromosomal Deletions:**

Chromosomal deletions involve the loss of a segment of DNA from a chromosome. This can result in the loss of important genes, leading to developmental disorders. Examples include:

- Cri-du-chat syndrome: Caused by a deletion on chromosome 5, leading to developmental and intellectual disabilities.

**2. Chromosomal Duplications:**

Chromosomal duplications involve the presence of extra copies of a segment of DNA. This can disrupt normal gene dosage and regulation. Examples include:

- Charcot-Marie-Tooth disease type 1A: Caused by a duplication on chromosome 17, leading to peripheral neuropathy.

**3. Chromosomal Inversions:**

Chromosomal inversions involve the reversal of a segment of DNA within a chromosome. This can disrupt gene order and regulation. Examples include:

- Hemophilia A: Inversions in the factor VIII gene can lead to hemophilia A.

**4. Translocations:**

Translocations involve the movement of genetic material from one chromosome to another, leading to changes in gene expression. There are two types:

- Reciprocal translocations: Exchange of genetic material between two chromosomes.

- Robertsonian translocations: Fusion of two acrocentric chromosomes, often involving chromosomes 13, 14, 15, 21, or 22.

**5. Fragile Sites:**

Fragile sites are regions of the genome that are prone to breakage under certain conditions. Fragile X syndrome is caused by a CGG repeat expansion in the FMR1 gene, leading to chromosomal fragility.

**6. Trinucleotide Repeat Expansions:**

These involve the expansion of trinucleotide repeats within certain genes. These expanded repeats can disrupt gene function and lead to diseases such as:

- Huntington's disease: Caused by an expanded CAG repeat in the HTT gene.

- Fragile X syndrome: As mentioned earlier, caused by an expanded CGG repeat in the FMR1 gene.

These chromatin structural abnormalities can lead to a wide range of genetic disorders and diseases, affecting various aspects of development, growth, and physiological function. Understanding these abnormalities is crucial for diagnosing and managing genetic conditions and providing appropriate genetic counseling.

Certainly! Here are 10 multiple-choice questions (MCQs) related to common structural abnormalities in chromatin, along with their answers:

**Common Structural Abnormalities in Chromatin:**

**Question 1:** What genetic disorder is caused by the presence of an extra copy of a segment of DNA within a chromosome?

a) Cri-du-chat syndrome

b) Charcot-Marie-Tooth disease type 1A

c) Hemophilia A

d) Huntington's disease

**Answer:** b) Charcot-Marie-Tooth disease type 1A

**Question 2:** Which type of chromosomal abnormality involves the loss of a segment of DNA from a chromosome?

a) Chromosomal duplications

b) Chromosomal inversions

c) Chromosomal deletions

d) Chromosomal translocations

**Answer:** c) Chromosomal deletions

**Question 3:** Fragile X syndrome is caused by:

a) Chromosomal duplication

b) Chromosomal inversion

c) Trinucleotide repeat expansion

d) Chromosomal deletion

**Answer:** c) Trinucleotide repeat expansion

**Question 4:** What is the term for the fusion of two acrocentric chromosomes, often involving chromosomes 13, 14, 15, 21, or 22?

a) Reciprocal translocation

b) Robertsonian translocation

c) Chromosomal inversion

d) Chromosomal deletion

**Answer:** b) Robertsonian translocation

**Question 5:** Hemophilia A can be caused by:

a) Chromosomal deletion

b) Chromosomal duplication

c) Chromosomal inversion

d) Chromosomal translocation

**Answer:** d) Chromosomal translocation

**Question 6:** Which genetic disorder is characterized by an expanded CGG repeat in the FMR1 gene, leading to chromosomal fragility?

a) Huntington's disease

b) Charcot-Marie-Tooth disease type 1A

c) Fragile X syndrome

d) Cri-du-chat syndrome

**Answer:** c) Fragile X syndrome

**Question 7:** What type of chromosomal abnormality involves the reversal of a segment of DNA within a chromosome?

a) Chromosomal translocation

b) Chromosomal inversion

c) Chromosomal duplication

d) Chromosomal deletion

**Answer:** b) Chromosomal inversion

**Question 8:** Which disorder is caused by an expanded CAG repeat in the HTT gene?

a) Huntington's disease

b) Charcot-Marie-Tooth disease type 1A

c) Fragile X syndrome

d) Cri-du-chat syndrome

**Answer:** a) Huntington's disease

**Question 9:** Cri-du-chat syndrome is caused by:

a) Chromosomal inversion

b) Chromosomal duplication

c) Trinucleotide repeat expansion

d) Chromosomal deletion

**Answer:** d) Chromosomal deletion

**Question 10:** What term is used to describe regions of the genome that are prone to breakage under certain conditions?

a) Trinucleotide repeats

b) Translocations

c) Fragile sites

d) Inversions

**Answer:** c) Fragile sites

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