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ACCME/DisclosuresThe USCAP requires that anyone in a position to influence or control the content of CME disclose

any relevant financial relationship WITH COMMERCIAL INTERESTS which they or their

spouse/partner have, or have had, within the past 12 months, which relates to the content of

this educational activity and creates a conflict of interest.

Dr. Jennifer O. Black declares she has no conflict(s) of interest to disclose.

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 91:452-459, 2015


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


Squamous Cell Carcinoma

Robbins and Cotran Pathologic Basis of Disease. Lazar, Alexander J.F.; Murphy, George F. Pages 1141-1178


Basal Cell Carcinoma

Robbins and Cotran Pathologic Basis of Disease. Lazar, Alexander J.F.; Murphy, George F. Pages 1141-1178.


Melanoma

Pigment Cell & Melanoma Research Volume 27, Issue 3, pages 454-464

Introduction: Xeroderma Pigmentosum Ocular Manifestations of Disease

Brooks et al. Ophthalmology. 2013 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. 2008 Aug;131:1979-89

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

Gene Normal Protein Function Disease 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 defects Photosensitivity, 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


Nucleotide Excision Repair Pathway

DiGiovanna. J Invest Dermatol. 2012 Mar; 132(3): 785–796.

Gene Normal Protein Function Clinical Syndrome Disease Characteristics

XPB/ERCC3 Helicase involved with DNA unwinding XP-B, CS, TTD Photosensitivity, poikiloderma, lentigines, skin cancer, neurodegeneration

XPD/ERCC2 Helicase involved with DNA unwinding XP-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/ERCC8 DNA excision repair protein involved in the TCR pathways CS Growth failure, impaired neurodevelopment, photosensitivity, eye disorders, premature aging

CSB/ERCC6 DNA excision repair protein involved in the TCR pathway CS, 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

TTD Brittle hair, intellectual impairment, photosensitivity

TTDN1/C7orf11 Regulates mitosis and cytokinesis TTD Non-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


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;45:564-571

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: oAggressive photoprotection recommended

• Surgical resection of skin cancers o Early resection important for long-term survival

• Systemic Therapy: oRetinoids oAntioxidant therapy oVitamin 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 oXP 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, 2011 2. DiGiovanna JJ, Kraemer KH: Shining a light on xeroderma pigmentosum. J Invest Dermatol 132:785–796, 2012 3. 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, 2011 4. 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 34:120-127, 2015 5. 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 7:454-464, 2014 6. Tamura D, DiGiovanna JJ, Khan SG, et al: Living with xeroderma pigmentosum: comprehensive photoreception for highly photosensitive patients. Photodermatol Photoimmunol Photomed 30:146-152, 2014 7. Anttinen A, Koulu L, Nikoskelainen E, et al: Neurological symptoms and natural course of xeroderma pigmentosum. Brain 131: 1979-1989, 2008 8. Masutani C, Kusumoto R, Yamada A, et al: The XPV (xeroderma pigmentosum variant) gene encodes human DNA polymerase eta. Nature 399:700–704, 1999 9. 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, 2002 10. 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, 2013 11. Shabbir SH: DNA repair dysfunction and neurodegeneration: lessons from rare pediatric disorders. J Child Neurol, 1-5, 2015. 12. Suzumura H, Arisaka O. Cerebro-oculo-facio-skeletal syndrome. Adv Exp Med Biol 685, 210-214, 2010 13. Kraemer KH, DiGiovann JJ. Forty years of research on xeroderma pigmentosum at the US National Institutes of Health. Photochemistry and Photobiology 91:452-459, 2015 14. 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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