Adducted thumb may not be mandatory for prenatal diagnosis of X-linked hydrocephalus in early second trimester.

Objective: X-linked hydrocephalus (XLH), the most common genetic hydrocephalus, is caused by mutation of the L1 cell adhesion molecule (L1CAM). A fetus/neonate with this disorder frequently shows an adducted thumb, which has been employed as a helpful finding in the prenatal diagnosis of XLH.
Materials and Methods: We describe a male fetus with hydrocephalus without an adducted thumb: the pregnancy was terminated at 21 weeks' gestation on the parents' request. Direct sequencing of the umbilical cord revealed L1CAM mutation, which confirmed the diagnosis of XLH.
Results: Our literature review demonstrated that while an adducted thumb was observed in almost all fetuses with this disorder after 24 weeks' gestation, it was noted in only 57% (8/14) of fetuses/neonates at less than 24 weeks: it was absent in 43%.
Conclusion: Even if an adducted thumb is not observed, XLH should not be ruled out, especially in early gestation.
Competing Interests: Declaration of competing interest The authors report no conflict of interest.
(Copyright © 2022. Published by Elsevier B.V.)