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.

The Fibroblast Growth Factor Receptor 1 (FGFR1, MIM*136350) is a protein member of the fibroblast growth factor receptor (FGFR) family, with various biological functions, such as the normal development control. It contains an extracellular site for the ligand (three Ig-like domains, IgI, IgII, IgIII), a single transmembrane and a cytoplasmic protein tyrosine kinase (TK) domain. Variants in this gene have been associated with a wide spectrum of genetic disorders, including the clinical entity known as FGFR1-related Hartsfield or Hartsfield syndrome (HRTFDS, MIM#615465), which is an autosomal dominant or recessive disorder characterized by the clinical association of split-hand/foot malformation (SHFM) and holoprosencephaly (HPE). Dysmorphic facies, including cleft/lip palate, genitourinary anomalies, cardiovascular defects and intellectual disability/developmental delay (ID/DD) can also be a part of the clinical picture. The malformation phenotype of HRTFDS has been reviewed in 26 previously reported patients in terms of single congenital defects, mutational spectrum, impacted protein domains and inheritance. Molecular basis, clinical management, main differential diagnoses and genetic counseling were also illustrated. SHFM was identified in every patient. The other main associated features included craniofacial defects, skeletal malformation identified at radiography, genitourinary anomalies, HPE and cardiovascular disorders. FGFR1 causative variants mainly impact the TK domain and have a smaller impact on other protein sites (IgII, IgIII). This study extensively recapitulates the malformation phenotype associated with HRTFDS and the underlying molecular perturbations. A multidisciplinary clinical approach is fundamental, in which genetic counseling can have an important role. However, our results are partial and refer to a restricted number of patients, pointing out the necessity of other descriptions and similar research. Additional studies will expand clinical and molecular knowledge as well as further clarify the biological mechanisms.

Split-hand/foot malformation (SHFM) is a rare congenital limb anomaly defined by the absence or hypoplasia of the central rays of the autopod. SHFM occurs as an isolated entity or part of genetic syndromes with several causative copy-number variations or monogenic alterations known to be involved in the disease pathomechanism. On the other hand, cleft lip/palate (CL/P) usually results from polygenic and environmental factors, with the complex interplay of both leading to this malformation. Pathogenic variants in FGFR1 have been linked to phenotypically distinct disorders, including Hartsfield syndrome, Kallmann syndrome, Jackson-Weiss syndrome, osteoglophonic dysplasia, and Pfeiffer syndrome. Although pathogenic variants in FGFR1 can contribute to syndromic SHFM or CL/P, their role in isolated SHFM or CL remains poorly described in the literature. We conducted targeted next-generation sequencing (NGS) in the proband with SHFM, followed by segregation analysis in the family members. In this study, we report an index patient presenting with isolated SHFM and his brother with CL and facial dysmorphism, as well as their father with isolated hyposmia. Targeted next-generation sequencing revealed a previously reported heterozygous missense pathogenic variant in FGFR1 (c.830G>A; p.Cys277Tyr) in both affected siblings and their hyposmic father. This study expands the phenotypic spectrum associated with FGFR1 pathogenic variants, emphasizing their involvement in non-syndromic SHFM and CL or isolated hyposmia. Our findings highlight the importance of considering FGFR1 in the molecular diagnosis of isolated SHFM or orofacial clefting, point to the high intrafamilial variability of FGFR1 pathogenic variants, and demonstrate the diagnostic value of targeted NGS in rare congenital malformations.

Holoprosencephaly (HPE) is the most common aberration of forebrain development, and it leads to a wide spectrum of developmental and craniofacial anomalies. HPE etiology is highly heterogeneous and includes both chromosomal abnormalities and single-gene defects. Here, we report an FGFR1 heterozygous variant detected by prenatal exome sequencing and inherited from the asymptomatic mother, in association with recurrent neurological abnormalities in the HPE spectrum in two consecutive pregnancies. Individuals with germline pathogenic variants in FGFR1 (MIM: 136350) show extensive phenotypic variability, which ranges from asymptomatic carriers to hypogonadotropic hypogonadism, arhinencephaly, Kallmann's syndrome with associated features such as cleft lip and palate, skeletal anomalies, isolated HPE, and Hartsfield syndrome. The presented case supports the role of exome sequencing in prenatal diagnosis when fetal midline structural anomalies are suggestive of a genetic etiology, as early as the first trimester of gestation. The profound heterogeneity of FGFR1 allelic disorders needs to be considered when planning prenatal screening even in asymptomatic carriers.