Smallest critical region for microcephaly in a patient with mosaic ring chromosome 13.

A ring chromosome 13 or r(13) exhibits breakage and reunion at breakage points on the long and short arms of chromosome 13, with deletions of the chromosomal segments distal to the breakage points. The r(13) chromosome accounts for approximately 20% of ring chromosomes compatible with life. We describe a female patient with mental retardation, growth retardation, microcephaly, craniofacial dysmorphy, hearing impairment, and prolonged prothrombin time. Chromosomal analysis via GTG banding of peripheral blood lymphocy tes revealed a karyotype of 46,XX,r(13)(p13q34)[71]/45,XX,-13[12]/ 46,XX,dic r(13;13)(p13q34;p13q34)[9]/46,XX,-13,+mar[5]/47, XX,+r(13) (p13q34)×2[2]/46,XX[1] at the age of 6 years and 46,XX,r(13)(p13q34) [82]/45,XX,-13[14]/46,XX,dic r(13;13)(p13q34; p13q34)[2]/46,XX, -13,+mar[2]. Array comparative genomic hybridization analysis of the blood demonstrated a 4.37-Mb deletion on chromosome 13q [arr