Prenatal Three-Dimensional Ultrasound Detection of Adducted Thumbs in X-Linked Hydrocephaly: Two Case Reports with Molecular Genetic Studies.

X-linked hydrocephaly is a rare sex-linked genetic recessive condition occurring in 1/30,000 deliveries. Adduction of thumbs and mental retardation are additional associated clinical findings. We describe two cases of X-linked hydrocephaly with associated adducted thumbs that were diagnosed prenatally with the combined use of three-dimensional (3D) ultrasound and fetal blood sampling for cytogenetic and molecular analyses.