U01.01.058 Robertsonian translocation

Robertsonian translocation is a type of chromosomal translocation involving the fusion of the long arms of two acrocentric chromosomes. This type of translocation is commonly associated with specific chromosome pairs and can result in either a balanced or unbalanced chromosomal arrangement.

Key Features

Chromosome Pairs Involved: Most commonly involves chromosomes 21, 22, 13, 14, and 15.
Acrocentric Chromosomes: These chromosomes have centromeres near their ends and are prone to fusion during Robertsonian translocation.
Fusion Mechanism: The long arms of two acrocentric chromosomes fuse at their centromere, while the short arms are lost.

Types of Robertsonian Translocations

Balanced Translocation
- The total genetic material remains unchanged.
- Typically no phenotypic abnormalities in the individual carrying the translocation.
- Carriers can pass the translocation to offspring.
Unbalanced Translocation
- Results in chromosomal imbalance due to the loss of short arms and possible duplication or deletion of genetic material.
- Can lead to miscarriage, stillbirth, or genetic syndromes such as:
  - Down Syndrome (Trisomy 21)
  - Patau Syndrome (Trisomy 13)

Points to Remember

Robertsonian Translocation is common but usually asymptomatic in the carrier due to balanced translocations.
Unbalanced translocations can cause significant developmental issues, including common trisomy disorders.
Chromosome Pairs: The involved pairs are often 13, 14, 15, 21, and 22.
Acrocentric Chromosomes: The two chromosomes involved in the translocation must both be acrocentric, with centromeres near the end of the chromosome.

Table: Types of Robertsonian Translocations

Type of Translocation	Chromosomal Outcome	Potential Effects
Balanced Translocation	No loss or gain of genetic material	Usually no phenotype changes, carrier may pass to offspring
Unbalanced Translocation	Loss of short arms, chromosomal imbalance	Can cause miscarriage, stillbirth, or genetic syndromes (e.g., Down syndrome, Patau syndrome)

Learning Objective

Understand the mechanism, clinical implications, and inheritance patterns of Robertsonian translocations, and recognize their potential role in chromosomal disorders like Down syndrome and Patau syndrome.

USMLE Step 1 Review Series

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