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

## TL;DR

This paper reviews the physical and genetic features of Hartsfield syndrome, a rare disorder linked to mutations in the FGFR1 gene, and highlights the need for more research.

## Contribution

The study compiles clinical and molecular data from 26 patients to better define the Hartsfield syndrome phenotype and its genetic basis.

## Key findings

- All patients had split-hand/foot malformation, with additional features like craniofacial defects and genitourinary anomalies.
- Most FGFR1 mutations affecting Hartsfield syndrome impact the tyrosine kinase domain of the protein.
- The study emphasizes the importance of a multidisciplinary approach for diagnosis and genetic counseling.

## Abstract

Background/Objectives: 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. Methods: 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. Results: 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). Conclusions: 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.