Translocation Down syndrome
46,XX,der(14;21)(q10;q10),+21
Also known as: translocation trisomy 21, der(14;21) trisomy 21, familial Down syndrome
46,XX,der(14;21)(q10;q10),+21 is Down syndrome caused by an unbalanced Robertsonian translocation: the count stays at 46, but the der(14;21) plus a free chromosome 21 add up to three copies of 21q. When a parent carries the balanced rob(14;21), the recurrence risk is far higher than after free trisomy 21, which is why the distinction matters for counseling.
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What the notation means
46- total chromosome count (the normal human number)
XX- sex chromosomes: two X (usual female karyotype)
der(14;21)(q10;q10)- an abnormal (“derivative”) chromosome that has chromosome 14’s centromere.
+21- an EXTRA copy of chromosome 21 (three copies = trisomy 21)