Isochromosome 9p and choroid plexus papilloma: Coincidence or cause?

Abstract

Choroid plexus papilloma (CPP) is a generally benign brain tumor that forms within the ventricle and may lead to hydrocephalus. Two-thirds of patients with CPP are under the age of 2 years. CPP has been associated with von Hippel-Lindau syndrome, Aicardi syndrome and hypomelanosis of Ito. Non-syndromic CPP may be inherited in an autosomal recessive pattern. It has also been proposed that duplication of 9p is associated with hyperplasia of the choroid plexus. Our patients, 1 2/12 year old twin girls, presented for genetic evaluation due to suspected CPP. Both patients had height and weight below the 3rd percentile and head circumference at or just below the 50th percentile. Both patients also had deep-set small eyes, prominent nose, normal appearing mouth and ears, single palmar creases, bilateral 5th finger clinodactyly, hyperconvex nails of fingers 3, 4, and 5, spatutate fingertips, and hypoplastic toenails. One of the twins functioned at the 7-8 month level developmentally, had varus position of the foot and a large anterior fontanelle. The second twin functioned at the 13 month level developmentally with areas of concern being language delay, fine motor skills, and self-help issues. The second twin also had strabismus. Due to the multiplicity of findings, we were suspicious of a chromosomal aberration possibly involving the p arm of chromosome 9. Peripheral blood chromosome analyses using banding and multicolored FISH revealed a karyotype of 47, XX, +idic(9)(q12) or tetrasomy 9p. Review of the literature revealed few cases of tetrasomy 9p and variable expression thereof. Though hydrocephaly and Dandy-Walker malformation had been reported in some individuals, only 2 cases included abnormalities of the choroid plexus, CPP and hyperplasia respectively. Our patients appear to have a less severe expression of tetrasomy 9p. This case demonstrates that CPP may be yet another finding of tetrasomy 9p. In addition, it may further support the suggestion that a gene on 9p controls growth of the choroid plexus.