What is a reciprocal translocation?

Understanding Reciprocal Translocation

A reciprocal translocation is defined as an exchange of genetic material between two non-homologous chromosomes, where segments from each chromosome break off and swap places with each other. 1

Key Characteristics of Reciprocal Translocations

• Balanced Exchange: In a balanced reciprocal translocation, there is no net gain or loss of genetic material, just a rearrangement between chromosomes
• Breakpoints: Occurs at specific breakpoints on each chromosome involved
• Nomenclature: Described using cytogenetic notation, e.g., t(9;22)(q34;q11) indicates a translocation between chromosomes 9 and 22 at bands q34 and q11 respectively 1

Clinical Significance

Medical Implications

1. Disease Association: Some reciprocal translocations are associated with specific diseases:

   • The Philadelphia chromosome t(9;22)(q34;q11) results from a reciprocal translocation that creates the BCR-ABL1 fusion gene, which is the hallmark of Chronic Myeloid Leukemia (CML) 1
   • In Ewing Sarcoma, reciprocal translocations involving the EWS gene on chromosome 22 (e.g., t(11;22)(q24;q12)) are characteristic 1

2. Fusion Genes: Often creates fusion genes at the breakpoints that may have altered function:

   • In CML, the BCR-ABL1 fusion protein has deregulated tyrosine kinase activity that drives the pathogenesis of the disease 1

Reproductive Implications

1. Fertility Issues: Carriers of reciprocal translocations may experience:

   • Infertility
   • Recurrent miscarriages
   • Higher risk of having children with congenital anomalies 2

2. Genetic Counseling: Carriers may benefit from:

   • Prenatal diagnosis (PND)
   • Preimplantation genetic diagnosis (PGD) 2

Detection Methods

Reciprocal translocations can be detected through various cytogenetic techniques:

• Conventional Karyotyping: Traditional chromosome analysis that can detect larger rearrangements
• Fluorescence In Situ Hybridization (FISH): Uses fluorescent probes to detect specific chromosome regions involved in translocations 1
• Reverse Transcription Polymerase Chain Reaction (RT-PCR): Detects fusion transcripts resulting from translocations 1
• Next-Generation Sequencing: Can identify breakpoints at the nucleotide level

Important Distinctions

• Reciprocal vs. Robertsonian Translocations: Robertsonian translocations specifically involve acrocentric chromosomes fusing at their centromeres, while reciprocal translocations can occur between any non-homologous chromosomes 3
• Balanced vs. Unbalanced: A balanced translocation has no net gain or loss of genetic material, while an unbalanced translocation results in duplications or deletions of chromosome segments

Clinical Management Considerations

For individuals with reciprocal translocations:

• Disease Monitoring: For disease-associated translocations (like Philadelphia chromosome in CML), regular monitoring of the translocation through molecular techniques is essential 1
• Reproductive Planning: Genetic counseling and possibly assisted reproductive technologies with genetic testing may be recommended 3, 2

Understanding reciprocal translocations is crucial for proper diagnosis, risk assessment, and management of associated conditions, particularly in oncology and reproductive medicine.