Malformation Pattern and Molecular Findings in the FGFR1-Related Hartsfield Syndrome Phenotype

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.