REPLY TO LETTER TO THE EDITOR BY MEZA-ESPINOZA AND COLLEAGUES
Meral Yirmibeş Karaoğuz, Ezgi Urtekin, Gülsüm Kayhan, Elvin KazancıoğluDear Editor,
In this journal, we reported a rare live birth case of partial trisomy 9 resulting from a maternal translocation between chromosomes (Chr.) 9 and 22 (1). The affected infant had two normal chromosomes 9 plus a derived/dicentric Chr.9 containing a complete copy of 9pter to 9q22.31 (carrying the centromere regions of both Chr.9 and Chr.22). Meza-Espinoza and colleagues wrote a letter to the editor about this case and the related translocation-derived gametes (2). We appreciate the contributions of the authors.
All possible gametes are shown in Table 1, and there are two options for disomy of 22 products derived from tertiary 3:1 segregation. However, these gametes are also trisomic or monosomic on the long arm of chromosome 9 (q22.31 to 9qter). In the case of tertiary trisomy 3:1 segregation, when normal Chr. 9, normal Chr. 22 and der(22) are transmitted to the next generation, the gamete will be disomic for Chr. 22 and partially trisomic for long arm of Chr.9 (9q22.31 to 9qter). Trisomy of the short arm of chromosome 9 is a rare condition but is compatible with life, as in this case. In contrast, the trisomy of the long arm of chromosome 9 (the product of a tertiary 3:1 segregation) is almost always incompatible with life. In tertiary monosomy 3:1 segregation, when only der(9) is inherited, the offspring will be disomic for Chr.22 but will also have partial monosomy from 9q22.31 to 9qter and will have no chance of a live birth. Two disomy 22 products derived from the segregation of interchange trisomy and interchange monosomy also exist, but the gametes will also be trisomy and monosomy for Chr.9. Additionally, the second option for the adjacent 2 segregation pattern leads to partial monosomy of chromosome 9 (9pter to 9q22.31, our case region) and disomy 22.
