Diagnosis: Unbalanced Robertsonian Translocation Causing Down Syndrome

ISCN: 46,XY,der(14;21)(q10;q10),+21 or 46,XY,rob(14;21)(q10;q10),+21

Discussion:
This patient has Trisomy 21 or Down syndrome from inheriting a Robertsonian translocation along with a normal chromosome 21 from his mother. Please see unknown 3 for a discussion of Down syndrome.

Robertsonian translocations are chromosomal rearrangements that occur between the short arms of two acrocentric chromosomes (13, 14, 15, 21, 22). Balanced Robertsonian translocations are present in approximately 1/1,000 newborns. The most common Robertsonian translocation involves chromosomes 13 and 14 [rob(13;14)]; this accounts for approximately 75% of all Robertsonian translocations. The second most common is the rob(14;21) which accounts for approximately 10% of all Robertsonian translocations. Newborn balanced carriers of Robertsonian translocations are phenotypically normal, while newborns with an unbalanced karyotype, as in this case, have the same phenotypic findings as newborns with an extra chromosome. Balanced carriers of Robertsonian translocations have an increased risk of infertility and miscarriage, as well as an increased risk for having offspring with an unbalanced Robertsonian translocation.

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