Tandem duplication chromosome 21 in the offspring of a ring chromosome 21 carrier

Area of Science:

• Genetics
• Human Genetics
• Chromosomal Abnormalities

Background:

• Down syndrome is a genetic disorder caused by the presence of all or part of a third copy of chromosome 21.
• Ring chromosome 21 is a rare chromosomal abnormality where the ends of chromosome 21 fuse, forming a ring structure.

Observation:

• A case study identified a direct tandem duplication of chromosome 21 in a male infant diagnosed with Down syndrome.
• The proband's maternal lineage revealed the presence of a ring chromosome 21 in both his mother and grandmother.

Findings:

• The direct tandem duplication in the proband is hypothesized to arise from two potential mechanisms involving the maternal ring chromosome 21.
• These mechanisms include recombination between the maternal ring chromosome and the mother's normal chromosome 21, or a breakage event within a doubled-sized ring chromosome 21.

Implications:

• This case highlights the complex inheritance patterns of chromosomal abnormalities and their contribution to Down syndrome.
• Understanding the mechanisms behind such duplications is crucial for genetic counseling and accurate diagnosis in families with ring chromosome variants.