Inv21p12q22del21q22 and intellectual disability

Area of Science:

• Human Genetics
• Cytogenetics
• Reproductive Biology

Background:

• Pericentric inversions, common chromosomal rearrangements, typically do not affect carriers unless breakpoints disrupt genes or cause complex rearrangements.
• These inversions can lead to unbalanced chromosomal content in offspring, increasing risks for genetic disorders.

Observation:

• A family presented with a pericentric inversion of chromosome 21, with the proband experiencing recurrent miscarriages and learning difficulties.
• Cytogenetic analysis revealed a balanced pericentric inversion in four family members, with some offspring exhibiting partial or full trisomy 21.
• Further molecular studies identified a 1.7 Mb deletion on the inverted chromosome 21q22.11 in affected individuals.

Findings:

• The identified deletion on the inverted chromosome 21q22.11 is proposed as the cause of intellectual disability and learning difficulties within the family.
• Recombinant chromosome 21 resulted in partial trisomy, including the Down Syndrome Critical Region (DSCR), without deletion.
• The risk for carriers of this pericentric inversion to have offspring with malformations or intellectual disability is estimated at approximately 30%.

Implications:

• This case highlights the complex genetic risks associated with apparently balanced pericentric inversions, particularly for chromosome 21.
• Accurate cytogenetic and molecular analysis is crucial for identifying cryptic deletions and assessing recurrence risks in families with inversions.
• Understanding these rearrangements aids in genetic counseling and prenatal diagnosis for affected families.