Prenatal Diagnosis of Hartsfield Syndrome in the Fetus With Isolated Ectrodactyly Caused by a Novel Variant in FGFR1.

Molecular genetic testing was performed on a fetus with ectrodactyly of the right foot to clarify the pathogenic cause and provide evidence for prenatal counseling. Trio whole-exome sequencing (trio-WES) was performed on the fetus and his parents to identify the underlying genetic cause. Candidate variants were validated by Sanger sequencing, and their molecular effects were analyzed through minigene assays. Trio-WES identified a novel heterozygous variant (c.1977+1G>C) in FGFR1, which is consistent with FGFR1-related Hartsfield syndrome (HS; OMIM#615465). Sanger sequencing confirmed that this variant was de novo. The minigene assay revealed that all variants (c.1977+1G>C, c.1977+1G>A, and c.1977+1G>T) at the splice site generated two aberrant splicing events: (1) complete retention of intron 14, leading to a frameshift and premature termination codon; and (2) skipping of exon 14, causing an in-frame deletion of 41 amino acids. These events collectively impaired the function of the FGFR1 protein's tyrosine kinase domain. To our knowledge, prenatal reports of FGFR1-related HS remain extremely limited, and this is the first molecularly confirmed prenatal diagnosis of HS in China. The findings not only expand the mutational spectrum of HS but also provide genetic counseling and reproductive guidance for this family.