A Homozygous Missense COL1A1 Variant (p.Glu684Lys) Associated with an Arthrochalasia-like Ehlers-Danlos Syndrome Phenotype: A Case Report.

Arthrochalasia Ehlers-Danlos syndrome (aEDS) is a rare connective tissue disorder characterized by severe joint hypermobility, congenital hip dislocation, skin hyperextensibility, and muscle hypotonia. It is typically caused by heterozygous splice-site variants in COL1A1 or COL1A2, leading to exon 6 skipping. Autosomal recessive forms are extremely rare and have been reported predominantly in families from Saudi Arabia carrying the homozygous COL1A1 missense variant c.2050G>A, p.(Glu684Lys), with clinical presentations ranging from severe to mild. Clinical and molecular genetic evaluation of the patient was performed. Whole-exome sequencing was carried out, followed by confirmatory Sanger sequencing in the proband and both parents. A 10-month-old boy presented with severe congenital hypotonia, bilateral hip dislocation, generalized joint hypermobility, skin hyperextensibility and craniofacial dysmorphism. A homozygous likely pathogenic variant NM_000088.4:c.2050G>A, p.(Glu684Lys) was identified in exon 31 of COL1A1; both healthy parents were confirmed to be heterozygous carriers of this variant. To our knowledge this is the first reported case in the Russian population and one of the few cases described worldwide of an autosomal recessive arthrochalasia-like EDS phenotype. This case further refines the phenotypic characterization associated with the recurrent homozygous COL1A1 p.(Glu684Lys) variant, demonstrating an arthrochalasia-like EDS phenotype of intermediate severity between the severe neonatal form with respiratory distress and recurrent fractures and the classical EDS. It further highlights the importance of considering collagenopathies in the differential diagnosis of congenital hypotonia, particularly in cases initially suggestive of neuromuscular disorders.