Tetrasomy 18p: a distinctive syndrome.

A 10-month-old girl with growth and psychomotor retardation and pyramidal signs, was found to have a 47,XX,inv(9)(p11q13),+i(18p) karyotype. Whereas the inverted chromosome was inherited from the father, the isochromosome was of unknown origin. A comparative analysis with 17 similar cases from the literature lead to the conclusion that the tetrasomy 18p actually constitutes a distinctive syndrome.