Unbalanced segregation of a complex four-break 5q23-31 insertion in the 5p13 band in a malformed child

Area of Science:

• Genetics
• Molecular Biology
• Developmental Biology

Background:

• Reciprocal translocations and insertions can lead to copy number variations, impacting gene dosage and potentially causing developmental abnormalities.
• Understanding the precise chromosomal rearrangements is crucial for correlating genotype with phenotype, aiding in genetic counseling and diagnosis.
• The 5q23.2-31.3 region is known to harbor genes critical for normal development, making duplications in this area of significant clinical interest.

Observation:

• A 4-month-old male infant presented with hypotonia, microcephaly, cardiac defects, pulmonary issues, kidney abnormalities, and dysmorphisms.
• Genetic analysis revealed a dup(5q)(q23.2q31.3) inherited from the mother's complex insertion ins(5)(p13.1q23.2q31.3).
• Fluorescence in situ hybridization (FISH) identified four breakpoints in the maternal insertion, indicating a complex rearrangement involving inversion and insertion.

Findings:

• The child's phenotype is consistent with previously reported dup(5q) cases, suggesting a specific syndrome associated with this chromosomal abnormality.
• The maternal balanced rearrangement, ins(5)(pter --> p13.1:q23.3 --> q23.2:q31.3 --> q23.3:p13.1 --> q23.2:q31.3 --> qter), did not result in any clinical phenotype in her or other carriers.
• Clusters of Alu sequences at the breakpoints suggest their potential role in mediating this complex chromosomal rearrangement.

Implications:

• This case underscores the phenotypic variability associated with dup(5q) and the importance of detailed cytogenetic analysis for accurate diagnosis.
• The identification of Alu sequences at the breakpoints provides insights into the molecular mechanisms underlying complex chromosomal rearrangements.
• Understanding such rearrangements is vital for accurate genetic counseling, risk assessment for future pregnancies, and potential therapeutic strategies.