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Chapter 15

### INTRODUCTION

The blood vessel is a complex organ with many mechanical and regulatory functions. Abnormalities in the structural characteristics of the extracellular matrix as well as the regulatory functions can results in significant dysfunction. This dysfunction can manifest itself as vascular fragility leading to aneurysms, dissections, and ruptures but it may also result in stenotic lesions.

Many of the conditions have their roots in mutations of the genes responsible for the constitutive proteins of the blood vessel wall, however, probably just as frequently the mutations result in disordered regulation of cell turnover and remodeling. In some cases the underlying abnormality has not been identified, however, the features of the conditions and when they should be suspected are shared with the more definitely identified connective tissue abnormalities and so are included in this chapter.

Beyond the underlying causal abnormality, the primary clinical feature shared by these conditions is the presence of vascular disease in a patient population typically not thought to be a risk: patients who are young and without usually precipitating causes such as hyperlipidemia, hypertension, and diabetes. Typically a familial clustering is also present which should raise concern for these diseases. In addition, the familial nature of these conditions even when a precise genetic syndrome cannot be identified should prompt an evaluation of first-degree relatives.

### EHLERS-DANLOS SYNDROME

Ehlers-Danlos Syndrome (EDS) is a collection of connective diseases characterized by hypermobility of the joints and hyperextensible joints. Following the initial description of the condition several subtypes have been identified with different underlying biochemical and genetic causes and different clinical presentations. Vascular manifestations of EDS are primarily limited to the vascular subtype,1,2 which was known as EDS-IV or Sachs-Barabas syndrome in prior classifications.3 Vascular fragility has been rarely described in other subtypes of EDS (kyphoscoliotic type [EDS-VI] and arthochalasis type [EDS-VII]) and collagen abnormalities, such as osteogenesis imperfecta, but the vast majority of vascular complications in EDS occur in the vascular subtype.4,5,6 The principal clinical manifestations are vessel rupture and dissection with and without preceding blood vessel dilation. Internal organ rupture, uterus, and colon in particular, are also important causes of morbidity and mortality. Overall prevalence of EDS is estimated to be 1 in between 10 000 and 25 000, with vascular EDS constituting 4% of all EDS cases.1,7

#### Pathogenesis

Collagen III is the predominant type of collagen in blood vessel and visceral organ walls.8 Abnormalities in collagen III synthesis were first identified by Pope et al.9 in EDS-IV in 1975. Causative mutations in the COL3A1 gene coding for the procollagen proα1(III) chain of collagen III have been identified in the vast majority of cases. Over 114 different mutations involving the COL3A1 gene hve been documented in the most complete clinical series, with additional mutations described in smaller series and case ...

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