Dandy-Walker malformation in an infant with tetrasomy 9p.

An infant with Dandy-Walker malformation and prenatally diagnosed tetrasomy 9p is reported. Chromosomal analysis of primary amniocyte culture revealed true mosaicism for two cell lines: 50% of the cells had an isochromosome 9p (pter-q13::q13-pter), and the other 50% showed a normal female karyotype (46,XX). After birth the same chromosomal abnormality was found in 75% of peripheral blood lymphocytes. Phenotypic features included intrauterine growth retardation, hypotrophy of the left side of the body with left microphthalmus, and progressive hydrocephalus secondary to Dandy-Walker malformation. Although most cases of Dandy-Walker malformation are not associated with chromosomal abnormalities, our case, together with two previously reported cases of the same association, indicates that this chromosomal disorder should be looked for in children with Dandy-Walker malformation and abnormal somatic development.