Expanding the Clinical and Mutational Spectrum of Recessive AEBP1-Related Classical-Like Ehlers-Danlos Syndrome

Abstract

Ehlers-Danlos syndrome (EDS) comprises clinically heterogeneous connective tissue disorders with diverse molecular etiologies. The 2017 International Classification for EDS recognized 13 distinct subtypes caused by pathogenic variants in 19 genes mainly encoding fibrillar collagens and collagen-modifying or processing proteins. Recently, a new EDS subtype, i.e., classical-like EDS type 2, was defined after the identification, in six patients with clinical findings reminiscent of EDS, of recessive alterations in AEBP1, which encodes the aortic carboxypeptidase⁻like protein associating with collagens in the extracellular matrix. Herein, we report on a 53-year-old patient, born from healthy second-cousins, who fitted the diagnostic criteria for classical EDS (cEDS) for the presence of hyperextensible skin with multiple atrophic scars, generalized joint hypermobility, and other minor criteria. Molecular analyses of cEDS genes did not identify any causal variant. Therefore, AEBP1 sequencing was performed that revealed homozygosity for the rare c.1925T>C p.(Leu642Pro) variant classified as likely pathogenetic (class 4) according to the American College of Medical Genetics and Genomics (ACMG) guidelines. The comparison of the patient's features with those of the other patients reported up to now and the identification of the first missense variant likely associated with the condition offer future perspectives for EDS nosology and research in this field.

Keywords: AEBP1; aortic carboxypeptidase-like protein; classical Ehlers-Danlos syndrome; classical-like Ehlers-Danlos syndrome type 2; differential diagnosis; high-frequency ultrasonography; reflectance confocal microscopy.

Figure 1

Clinical and molecular findings of the patient. (A) Old-aging appearance of face and androgenetic alopecia (a,b); laxity of the thumb (c), laxity of the fifth finger (d); hyperextensible skin in different body areas: neck (e), elbow (f), dorsum of the hand (g) and forearm (h); flat feet and piezogenic papules (i); subcutaneous spheroid on elbow (j), diffuse PoC-like dermatitis and easy bruising (k); skin redundancy, atrophic papyraceous scars on knees, postsurgical enlarged scar after right knee capsuloplasty and skin plastic surgery (l). (B) Sequence chromatograms showing the position of the c.1925T>C p.(Leu642Pro) variant (arrow) identified in homozygosity in exon 16 of the AEBP1 gene (seq. Ref.: NM_001129.4, NP_001120.3) and in silico prediction of the pathogenicity of the p.(Leu642Pro) missense substitution by using 13 different algorithms [20,21,22,23,24,25,26,27,28,29,30,31,32].

Figure 2

Instrumental findings on patient’s skin. (A) Ultrasonography (50 MHz) images of the forearm skin from the patient and a representative age- and gender-matched healthy individual (control). E, epidermis, D, dermis, S, subcutaneous adipose tissue (depth of imaging: 4 mm). Disorganization of collagen fibers and elastosis in patient’s skin appears as a significant thinning and hypoechogenicity of the dermal layer both on dorsal (left) and volar side (right) compared to control (B) Reflectance confocal microscopy images of the forearm skin from patient and control (magnification: 500 × 500 µm). Epidermis: typical honey-comb pattern on dorsal (left) and volar (right) side in healthy skin are not detectable in patient’s skin. Dermal-epidermal junction: regular edge papillae [rings of basal keratinocytes surrounding dark circular structures corresponding to dermal papillae (*)] on dorsal and volar side of control skin are reduced both in number and definition in patient’s skin. Dermis: Irregular and fragmented collagen fibers that appear bright and coarse on both dorsal and volar side of patient’s skin compared to control. An increased brightness of all skin structures, corresponding to chronological and photoinduced skin aging, is present on the dorsal side of healthy skin but not on the volar side that usually is not photoexposed, whereas in the patient this pronounced skin aging is present at both sides.