Objective: To explore the clinical phenotypes and genetic characteristics of a pedigree with Distal arthrogryposis type 5D (DA5D) caused by compound heterozygous variants in the ECEL1 gene.

Methods: A child (proband) diagnosed with DA5D and his family members (proband's parents and sister) who was admitted to the Department of Rehabilitation Medicine of Henan Children's Hospital in July 2022 due to "multiplex distal arthrogryposis" were enrolled into this study. Clinical data of the proband were collected and peripheral blood samples were obtained from the proband and members of his family about 3 mL. Trio-whole genome sequencing (trio-WGS) was carried out to detected the genetic variations of the proband and his family members. The candidate's pathogenic gene variants were screened and analyzed by Genome Aggregation Database (gnomAD) and other databases. The screened variants were annotated for clinical phenotypes using databases like the Online Mendelian Inheritance in Man (OMIM). The pathogenicity of the candidate variants was predicted by bioinformatics tools such as Provean. Based on the guidelines of the American College of Medical Genetics and Genomics (ACMG), pathogenicity ratings were conducted for variant sites. The protein conservation and mutation structure prediction of ECEL1 protein among species were carried out though MEGA-X and PyMOL. The research protocol of this study was reviewed by the Ethics Committee of Henan Provincial Children's Hospital (Approval No. 2023-H-H01), and informed consent for clinical research was obtained from the guardians of the probands.

Results: The proband had multiplex distal arthrogryposis involving hands, feet, knees, and ankles, and had right ptosis, micrognathia, low auricular position, and upturned nose. The parents and sister both had normal phenotypes. Trio-WGS and Sanger sequencing revealed that the child had compound heterozygous variants of paternal c.1742_c.1743insT and maternal c.2314T>G, for which the father and sister were carriers of the c.1742_c.1743insT heterozygous variant and the mother was carrier of c.2314T>A. Neither mutation site has been reported. According to guidelines of ACMG, the c.1742_c.1743insT variant was classified as likely pathogenic (PSV1+PM2_Supporting), and c.2314T>G was classified as uncertain (PM2_Supporting+PM3+PP3). The results of conserved analysis of amino acid residue sequences of ECEL1 protein showed that the missense mutation of the maternal c.2314T>G (p.Cys772Gly) was highly conserved among humans and other seven species. The protein structure prediction revealed that the c.1742_c.1743insT frameshift mutation led to the protein truncation, and the c.2314T>G missense mutation resulted in the failure of forming 1 disulfide bond.

Conclusions: The compound heterozygous variants of ECEL1 gene were considered to be pathogenic for this DA5D patient, which have expanded the mutational spectrum of the ECEL1 gene and provided a reference for clinical diagnosis as well as genetic counseling for this family.