Tissue limited mosaicism for unbalanced autosomal translocation in a child with congenital anomalies and mental retardation.

We studied a patient with a sporadic mental retardation/multiple congenital anomalies syndrome. Chromosome analysis showed a 46,XX, inv(9)(p 11;q13) karyotype in all lymphocytes. Fibroblasts from two separate skin biopsies revealed a mosaic karyotype. Some 22.5% of fibroblasts had a karyotype like that of the lymphocytes, while 77.5% of fibroblasts had a karyotype 46,XX,inv(9)(p11;q13),der(12),t(12;?)(P13;?). The data in this case emphasize the drawbacks of confining cytogenetic analysis to lymphocytes.