De Novo Deletion of Yq in a Male who is Negative for DYZ1 Sequences

Sex-typing of biological samples can be accomplished using the restriction fragment length polymorphism (RFLP) method and Y-chromosome probes. Many laboratories used cloned or synthetic probes corresponding to locus DYZ1, a class of highly repetitive satellite DNA comprising a major portion of the long arm heterochromatic region of the Y-chromosome (Yq). DYZ1 probes detect a highly repetitive 3.56 kb Hae III in human genomic DNA from males, which normally is absent in DNA from females. This report describes a male infant who is completely negative for DYZ1 sequences due to a de novo deletion of Yq. This is a relatively common cytogenetic variant, with del(Yq) males occurring at frequencies as high as 1 in 1000 live births. For forensic cases in which there is strong evidence that a DYZ1-negative sample originated from a male, the possibility of a Yq deletion should be considered.