Xeroderma Pigmentosum: An Insight into DNA Repair Processes Jennifer O. Black, MD Assistant Professor Division of Pediatric Pathology and Laboratory Medicine Children’s Hospital Colorado University of Colorado Anschutz Medical Campus Aurora, Colorado

Introduction: Xeroderma Pigmentosum Xeroderma Pigmentosum (XP): Initially described 1874 Rare autosomal recessive disorder Prevalence: 1-45/million, variable ethnic frequency UV radiation sensitivity disorder characterized by: Severe skin burning following minimal sun exposure Early freckling (before 2 years of age) Skin cancer at an early age Kraemer KH, DiGiovann JJ. Photochemistry and Photobiology 91: , 2015

Introduction: Xeroderma Pigmentosum XP Clinical Spectrum: Skin Changes: o Early freckling and subsequent checkered pigmentation o Thin, dry, contracted skin o Telangiectasias o Skin cancers: o Squamous cell carcinoma o Basal cell carcinoma o Melanoma Courtesy Dr. Bahig M. Shehata, Children’s Healthcare of Atlanta

Introduction: Xeroderma Pigmentosum Squamous Cell Carcinoma Robbins and Cotran Pathologic Basis of Disease. Lazar, Alexander J.F.; Murphy, George F. Pages

Introduction: Xeroderma Pigmentosum Basal Cell Carcinoma Robbins and Cotran Pathologic Basis of Disease. Lazar, Alexander J.F.; Murphy, George F. Pages

Introduction: Xeroderma Pigmentosum Melanoma Pigment Cell & Melanoma Research Volume 27, Issue 3, pages

Introduction: Xeroderma Pigmentosum Ocular Manifestations of Disease Brooks et al. Ophthalmology Jul; 120(7): 1324–1336. OCULAR ABNORMALITIES Structural Eyelid Abnormalities:Entropion Ectropion* Lagophthalmos Blepharitis Keratinization Loss of Eyelashes Neoplasms of the Ocular Surface and Eyelids: Squamous Cell Carcinoma Basal Cell Carcinoma Ocular Surface Disease and Inflammation: Conjunctivitis Melanosis* Xerosis Corneal Abnormalities:Neovascularization Pterygium Scarring Opacification Other:Photophobia * More frequent in patients with non-burning phenotype

Introduction: Xeroderma Pigmentosum Neurologic Manifestations of Disease 24% XP Patients Progressive Neurologic Degeneration: o Cognitive deterioration o Impaired hearing o Abnormal speech o Areflexia o Progressive ataxia o Spasticity o Peripheral neuropathy Brain tumors: Glial tumors Pontine glioma, glioblastoma, spinal cord astrocytoma Anttinen, et al. Brain Aug;131:

Xeroderma Pigmentosum: Disease Pathophysiology

Xeroderma Pigmentosum: Pathophysiology BER: Base excision repair NER: Nucleotide excision repair DSBR: Double stranded break repair MMR: Mismatch repair

Xeroderma Pigmentosum: Pathophysiology Historical Studies: XP cells demonstrate UV radiation hypersensitivity (Gartler 1964) Deficient excision repair observed in cultured XP skin fibroblasts (Cleaver 1968) Stable DNA photoproducts identified following UV radiation (Setlow 1962), not removed by XP cells ( Setlow 1969, Cleaver and Trosko 1970) Defective excision repair in XP cells demonstrated in vitro (Reed 1969) and in vivo (Epstein 1970) Cell fusion studies demonstrated heterogeneity of XP molecular defects ( De Weerd-Kastelein 1972)  Fusion of fibroblasts from different XP patients form heterokaryons that demonstrate corrected DNA repair mechanisms.  Characterization of different complementation groups, A-G (Kramer 1975, Arase 1979, Keijer 1979)

Xeroderma Pigmentosum: Complementation Groups Complementation Group GeneNormal Protein FunctionDisease Characteristics XP-A XPA Protein that assists with DNA unwinding Photosensitivity, poikiloderma, lentigines, skin cancer, neurodegeneration XP-B XPB/ERCC3 Helicase involved with DNA unwinding Photosensitivity, poikiloderma, lentigines, skin cancer, neurodegeneration XP-C XPC Protein recognizing global genome defectsPhotosensitivity, poikiloderma, lentigines, skin cancer XP-D XPD/ERCC2 Helicase involved with DNA unwinding Photosensitivity, poikiloderma, lentigines, skin cancer, neurodegeneration, brain tumors XP-E XPE/DDB2 Protein recognizing global genome defects Photosensitivity, poikiloderma, lentigines, skin cancer, neurodegeneration XP-F XPF/ERCC4 Forms an endonuclease together with ERCC1 that incises damaged DNA for repair Photosensitivity, poikiloderma, lentigines, skin cancer, neurodegeneration, brain tumors XP-G XPG/ERCC5 Endonuclease that incise damaged DNA Photosensitivity, poikiloderma, lentigines, skin cancer, neurodegeneration XP-Variant XPV/POLH DNA-polymerase eta (pol-eta) which performs trans-lesion DNA synthesis past ultraviolet (UV) Milder photosensitivity and poikiloderma

Xeroderma Pigmentosum: Pathophysiology Nucleotide Excision Repair Pathway DiGiovanna. J Invest Dermatol Mar; 132(3): 785–796.

Xeroderma Pigmentosum: Pathophysiology

GeneNormal Protein FunctionClinical SyndromeDisease Characteristics XPB/ERCC3Helicase involved with DNA unwindingXP-B, CS, TTD Photosensitivity, poikiloderma, lentigines, skin cancer, neurodegeneration XPD/ERCC2Helicase involved with DNA unwindingXP-D, TTD, COFS, CS Photosensitivity, poikiloderma, lentigines, skin cancer, neurodegeneration, brain tumors XPF/ERCC4 Forms an endonuclease together with ERCC1 that incises damaged DNA for repair XP-F, XFE progeroid syndrome, Fanconi anemia Photosensitivity, poikiloderma, lentigines, skin cancer, neurodegeneration, brain tumors ERCC1 Forms an endonuclease together with XPF/ERCC4 that incises damaged DNA for repair XP, CS, COFS Photosensitivity, poikiloderma, lentigines, skin cancer, neurodegeneration CSA/ERCC8DNA excision repair protein involved in the TCR pathwaysCS Growth failure, impaired neurodevelopment, photosensitivity, eye disorders, premature aging CSB/ERCC6DNA excision repair protein involved in the TCR pathwayCS, COFS Growth failure, severely impaired neurodevelopment, photosensitivity, eye disorders, premature aging GTF2H5 TTDA protein stabilizes the DNA/protein complex during unwinding of DNA strand for repair TTDBrittle hair, intellectual impairment, photosensitivity TTDN1/C7orf11Regulates mitosis and cytokinesisTTDNon-photosensitive TTD Xeroderma Pigmentosum: Overlap Syndromes CS = Cockayne Syndrome; TTD = Trichothiodystrophy; COFS = Cerebro-Oculo-Facio-Skeletal Syndrome

Xeroderma Pigmentosum: Overlap Syndromes Trichothiodystrophy (TTD): Features: Photosensitivity (with XPD, XPB, TTDA but not TTDN1 mutations) Abnormal hair Decreased fertility Short stature Ichthyosis Normal skin pigmentation Intellectual impairment without neurodegeneration Neuroimaging: demyelination, cortical heterotopia, partial agenesis of the corpus callosum, perimedullary fibrosis of the spinal cord, intracranial calcifications DiGiovanna. J Invest Dermatol Mar; 132(3): 785–796.

Xeroderma Pigmentosum: Overlap Syndromes Cockayne Syndrome (CS) Results from mutations in the CSA and CSB genes of the NER pathway Features: Short stature Microcephaly Pigmentary retinal degeneration Kyphoscoliosis Gait defects Sensorineural deafness Distinct facial features (deep-set eyes, prominent ears, “wizened appearance”) Neurodegenerative Features; Demyelination (increased DTRs), Neuroimaging: cerebral atrophy, ventricular dilation, calcification of basal ganglia and cortex, neuronal loss Multiple Types: Type I: moderate phenotype, normal prenatal development, abnormalities evident in first 2 years of life Type II: Severe phenotype, growth failure at birth, death first decade Type III: Mild symptoms, late onset; photosensitivity with normal pigmentation, no increased risk of cutaneous malignancy Laugel. Mechanisms of Ageing and Development 134 (2013) 161–170

Xeroderma Pigmentosum: Overlap Syndromes Cerebro-Oculo-Facio-Skeletal Syndrome (COFS): Autosomal recessive disorder\ Mutations involve CSB, XPD, XPG, and ERCC1 genes Features: Microcephaly Congenital cataracts Arthrogryposis Severe developmental delay Severe postnatal growth failure Photosensitivity Facial dysmorphism (prominent nasal root and overhanging upper lip) Laugel. J Med Genet 2008;45:

Xeroderma Pigmentosum Disease Course

Xeroderma Pigmentosum: Long Term Survival Leading Cause of Death: Skin cancer and metastasis  Lifetime Cancer Risk: 33% XP patients do not develop cancer Squamous Cell and Basal Cell Carcinoma: o Median age at first cancer = 9 years (range 1-32 years) o XP patients have 58-year reduction in age at first non-melanocytic skin cancer o 10,000 fold lifetime risk compared to general population Melanoma: o Median age at first cancer = 22 years (range 2-47 years) o XP patients have a 33-year reduction in age at first non-melanocytic skin cancer o 2,000 fold lifetime risk compared to general population o PTEN mutations more common (53%) compared to general population (16%) Other Cancer: Increased risk of lung cancer in XP smokers Brain tumors  Neurodegeneration: More common in XPA, XPB, XPD, XPF, XPG (Rare in XPC, XPE) Associated with decreased median age of death compared to XP patients without neurodegeneration (29 vs 37 years) Second leading cause of death in XP patients

Xeroderma Pigmentosum: Disease Treatment and Prevention Prevention: o Aggressive photoprotection recommended Surgical resection of skin cancers o Early resection important for long-term survival Systemic Therapy: o Retinoids o Antioxidant therapy o Vitamin D supplementation Gene therapy

Xeroderma Pigmentosum: Conclusions Patients with XP have mutations in genes that are necessary for nucleotide excision repair of damaged DNA: o Exploration of the disease pathogenesis has elucidated DNA repair processes o XP patients exhibit: -Photosensitivity with a tendency for skin burning -Markedly increased risk of developing cutaneous malignancy among other cancers -Susceptibility for neurodegenerative problems Long term survival is improved by avoidance of UV radiation and photoprotection

Selected References 1. Lehmann AR, McGibbon D, Stefanini M: Xeroderma pigmentosum. Orphanet J Rare Dis 6:70-45, DiGiovanna JJ, Kraemer KH: Shining a light on xeroderma pigmentosum. J Invest Dermatol 132:785–796, Bradford PT, Goldstein AM, Tamura D, et al: Cancer and neurologic degeneration in xeroderma pigmentosum: long term follow-up characterises the role of DNA repair. J Med Genet 48:168–176, Karass M, Naguib MN, Elawabdeh N, et al: Xeroderma pigmentosa: three new cases with an in depth review of the genetic and clinical characteristics of the disease. Fetal and Pediatr Pathol 34: , Masaki T, Wang Y, DiGiovanna JJ, et al: High frequency of pTEN mutations in nevi and melanomas from xeroderma pigmentosum patients. Pigment Cell Melanoma Res 7: , Tamura D, DiGiovanna JJ, Khan SG, et al: Living with xeroderma pigmentosum: comprehensive photoreception for highly photosensitive patients. Photodermatol Photoimmunol Photomed 30: , Anttinen A, Koulu L, Nikoskelainen E, et al: Neurological symptoms and natural course of xeroderma pigmentosum. Brain 131: , Masutani C, Kusumoto R, Yamada A, et al: The XPV (xeroderma pigmentosum variant) gene encodes human DNA polymerase eta. Nature 399:700–704, Broughton BC, Cordonnier A, Kleijer WJ, et al: Molecular analysis of mutations in DNA polymerase eta in xeroderma pigmentosum-variant patients. Proc Natl Acad Sci USA 99:815–820, Brooks BP, Thompson AH, Bishop RJ, et al: Ocular manifestations of xeroderma pigmentosum: long-term follow-up highlights the role of DNA repair in protection from sun damage. Ophthalmology 120:1324–1336, Shabbir SH: DNA repair dysfunction and neurodegeneration: lessons from rare pediatric disorders. J Child Neurol, 1-5, Suzumura H, Arisaka O. Cerebro-oculo-facio-skeletal syndrome. Adv Exp Med Biol 685, , Kraemer KH, DiGiovann JJ. Forty years of research on xeroderma pigmentosum at the US National Institutes of Health. Photochemistry and Photobiology 91: , Dupuy A, Sarasin A: DNA damage and gene therapy of xeroderma pigmentosum, a human DNA repair-deficient disease. Mutat Res 776:2-8, 2015

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