Background: Ehler-Danlos syndromes (EDS) is an umbrella term describing 14 types of which 13 are monogenic with overlapping features including joint hypermobility, skin and vascular fragility and connective tissue friability. As DNA analysis has become the gold standard for a diagnosis of EDS, use of transmission electron microscopy (TEM) in clinical practice is decreasing. However, due to increased use of next generation sequencing, the frequency of variants of uncertain significance (VUS) is also increasing. In certain cases of suspected monogenic EDS, TEM analysis of collagen structure may have the potential to contribute to variant classification.

Purpose: To demonstrate the added value of TEM in patients with suspicion on a monogenic EDS type.

Methods: The patient presented clinically with hyperextensible skin, skin fragility, mild atrophic scarring and generalised joint hypermobility, leading to a suspicion on monogenic EDS, in particular on classical or classical-like EDS. Whole Genome Sequencing revealed a COL5A1 variant c.3551C>T; Pro1184Leu which was classified as a cold VUS, unlikely to cause classical EDS. TEM analysis of a skin biopsy was performed to assess collagen fibrils abnormalities.

Results: Transmission electron microscopy studies on the patients' skin biopsy showed ultrastructural alterations in collagen fibril diameter and appearance consistent with collagen flowers. The clinical features of the patient together with the presence of abundant collagen flowers supported the suspicion on a rare EDS type in particular classical EDS or classical-like EDS despite the identified cold COL5A1 VUS. As a result, RNA sequencing in skin fibroblast is undertaken to assess for decreased expression of genes involved in monogenic EDS

Conclusions: Clinical assessment along with TEM analysis of collagen structure may have the potential to aid to identification and/or classification of variants in genes underlying specific rare, monogenic EDS types.