Bloom syndrome (OMIM 210900) is an autosomal recessive disorder caused by mutation of a DNA helicase. Among the principal symptoms of the disease are chromosome instability and a propensity to develop cancer. Explain these symptoms on the basis of the helicase mutation.

Verified step by step guidance

1. Understand the role of DNA helicase: DNA helicase is an enzyme responsible for unwinding the double-stranded DNA during replication, repair, and recombination. It separates the two strands of DNA by breaking the hydrogen bonds between complementary bases, allowing other enzymes to access the DNA strands.
2. Explain the impact of helicase mutation: A mutation in the DNA helicase gene can impair the enzyme's ability to unwind DNA properly. This can lead to stalled replication forks, incomplete DNA replication, and errors during DNA repair processes.
3. Connect helicase dysfunction to chromosome instability: When DNA replication and repair are compromised, it can result in structural abnormalities in chromosomes, such as breaks, deletions, or rearrangements. This is referred to as chromosome instability, which is a hallmark of Bloom syndrome.
4. Relate chromosome instability to cancer development: Chromosome instability increases the likelihood of mutations and genomic alterations, which can activate oncogenes or inactivate tumor suppressor genes. These changes promote uncontrolled cell growth and contribute to the development of cancer.
5. Summarize the connection: The symptoms of Bloom syndrome, including chromosome instability and cancer predisposition, can be explained by the defective DNA helicase. This defect disrupts normal DNA replication and repair, leading to genomic instability and an increased risk of tumorigenesis.

Key Concepts

DNA Helicase Function

DNA helicases are essential enzymes that unwind the DNA double helix during replication and repair processes. They separate the two strands of DNA, allowing other proteins to access the genetic information. Mutations in helicase genes can disrupt this unwinding process, leading to errors in DNA replication and repair, which are critical for maintaining genomic stability.

Chromosome Instability

Chromosome instability refers to an increased rate of chromosomal alterations, such as breaks, rearrangements, or aneuploidy. This instability can arise from defective DNA repair mechanisms, often due to mutations in genes like those encoding helicases. In Bloom syndrome, the inability to properly unwind and repair DNA leads to frequent chromosomal abnormalities, contributing to the disease's symptoms.

Cancer Propensity

The propensity to develop cancer in individuals with Bloom syndrome is linked to the accumulation of genetic mutations resulting from chromosome instability. When DNA repair processes fail, mutations can accumulate in oncogenes and tumor suppressor genes, leading to uncontrolled cell growth. This increased mutation rate is a hallmark of many cancers, making individuals with Bloom syndrome more susceptible to various malignancies.