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Adducted thumb in the first trimester of pregnancy: An early clue to prenatal diagnosis of L1 syndrome

1 Department of Ultrasound, The Sixth Affiliated Hospital of Sun Yat-Sen University, Guangzhou, Guangdong, China
2 Prenatal Diagnostic Center, Guangzhou Women and Children's Medical Center, Guangzhou, Guangdong, China

Correspondence Address:
Dong-Zhi Li,
Prenatal Diagnostic Center, Guangzhou Women and Children's Medical Center, Jinsui Road 9, Guangzhou, Guangdong 510623
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Source of Support: None, Conflict of Interest: None

A pregnant woman was revealed to have an unusual position of the fetal hand by a routine 12-week ultrasound. Bilateral adducted thumbs and a male phenotype were confirmed by another ultrasound at 14 weeks' gestation. A structural survey at 18 weeks revealed fetal hydrocephalus with severe bilateral ventriculomegaly. The pregnancy was terminated, and postnatal examination with trio exome sequencing detected a hemizygous deletion (1,511 bp in size) variant of L1CAM gene in the fetus, inherited from the mother. The fetus was diagnosed as L1 syndrome (X-linked hydrocephalus). A family study found that this was a familial mutant allele. This study demonstrates that fetal hand abnormalities can be identified in the first trimester. Adducted thumbs might indicate the maldevelopment of the fetal brain, and therefore, examination of fetal hands and fingers should be integrated into fetal anomaly scans.

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