Disorders of collagen

Published on 08/03/2015 by admin

Filed under Pathology

Last modified 22/04/2025

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11 Disorders of Collagen

Collagen “basics” 236

Scleroderma 237

Localized scleroderma overall 237

Linear morphea 237

Diffuse systemic scleroderma 238

Limited systemic scleroderma 238

Mixed connective tissue disease 238

Eosinophilic fasciitis 239

Perforating collagenoses 250

Reactive perforating collagenosis 250

Perforating verruciform “collagenoma” 251

Chondrodermatitis nodularis helicis 251

Variable collagen changes 251

Ehlers–Danlos syndrome 251

Osteogenesis imperfecta 252

Marfan’s syndrome 252

Syndromes of premature aging 252

Werner’s syndrome 252

Poikiloderma congenitale 252

Cockayne syndrome 252

Collagen “basics”

• Major constituent of connective tissue (70% of dry weight)

• Repeating triplet of amino acids glycine-X-Y (X is usually proline)

Transcription step = produces collagen mRNA, regulator of collagen production:

• Stimulated by TGF-β, retinoids, IL-4

• Decreased production by TNF-α, IFN-γ

Translation step = occurs in rough endoplasmic reticulum:

• Hydroxylation of lysine and proline amino acids (stabilizes helix)

– requires vitamin C and iron

– scurvy = ascorbic acid deficiency reduces hydroxylation of proline

– helix unstable and breakdown before excretion

• Glycosylation = add glucose and galactose residues (role in protein folding and assembly in ER)

• Synthesis of interchain disulfide bond (lines up chains so triple helix can form)

• Triple helix procollagen molecule (“the zipper” forms from C-terminus to N-terminus)

• Secretion of procollagen

Extracellular step:

• Cleavage of C- and N-terminal extensions

• Crosslinking of covalent bonds between triple helices (lysyl oxidase enzyme and others)

– lysyl oxidase requires copper and oxygen

• Assembly into helix … then fibril … then fibers … then bundles

Major types of collagen = location (associated disorders):

• Type I (80%) = skin, bone, tendon; has two identical chains (osteogenesis imperfecta)

• Type II = cartilage (relapsing polychondritis)

• Type III (10%) = GI and vascular, first deposited in wound, contains three identical chains (Ehlers-Danlos, vascular type)

• Type IV = basement membrane

• Type V = skin (classic type of Ehlers-Danlos syndrome, previously type 1 & 2)

• Type VI = beaded filament collagen; increased in keloids and morphea

• Type VII = anchoring fibrils in basement membrane (EBA, bullous SLE, linear IgA)

• Type VIII = endothelium

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