Auditory analysis of xeroderma pigmentosum 1971-2012: hearing function, sun sensitivity and DNA repair predict neurological degeneration

Physical, oral, and swallowing functions of three patients with type a xeroderma pigmentosum: a report of three cases

BACKGROUND

Xeroderma pigmentosum (XP) is an extremely rare and severe form of photosensitivity. It is classified into types A-G or V according to the gene responsible for the disease. The progression and severity of symptoms vary depending on the type. Although dysphagia caused by decreased swallowing function and dental malposition due to stenosis of the dentition in the facial and oral regions is common, it has not been reported in detail. We report three cases of type A XP, in which central and peripheral neurological symptoms appeared early on and progressed rapidly. We describe the oral function of these patients, focusing on the swallowing function and dentition malposition.

CASE PRESENTATION

Two males (27 and 25 years old) and one female (28 years old) presented with diverse neurological symptoms. We focused on the relationship between the changes in swallowing and oral functions and conditions due to decline in physical function. Some effects were observed by addressing the decline in swallowing and oral functions. In particular, a dental approach to manage the narrowing of the dentition, which was observed in all three patients, improved the swallowing and oral functions and maintained the current status of these functions.

CONCLUSIONS

In type A XP, early decline in oral and swallowing functions is caused by the early decline in physical function, and it is necessary to monitor the condition at an early stage.

Neurological disease in xeroderma pigmentosum: prospective cohort study of its features and progression

Xeroderma pigmentosum (XP) results from biallelic mutations in any of eight genes involved in DNA repair systems, thus defining eight different genotypes (XPA, XPB, XPC, XPD, XPE, XPF, XPG and XP variant or XPV). In addition to cutaneous and ophthalmological features, some patients present with XP neurological disease. It is unknown whether the different neurological signs and their progression differ among groups. Therefore, we aim to characterize the XP neurological disease and its evolution in the heterogeneous UK XP cohort. Patients with XP were followed in the UK National XP Service, from 2009 to 2021. Age of onset for different events was recorded. Cerebellar ataxia and additional neurological signs and symptoms were rated with the Scale for the Assessment and Rating of Ataxia (SARA), the Inventory of Non-Ataxia Signs (INAS) and the Activities of Daily Living questionnaire (ADL). Patients' mutations received scores based on their predicted effects. Data from available ancillary tests were collected. Ninety-three XP patients were recruited. Thirty-six (38.7%) reported neurological symptoms, especially in the XPA, XPD and XPG groups, with early-onset and late-onset forms, and typically appearing after cutaneous and ophthalmological symptoms. XPA, XPD and XPG patients showed higher SARA scores compared to XPC, XPE and XPV. SARA total scores significantly increased over time in XPD (0.91 points/year, 95% confidence interval: 0.61, 1.21) and XPA (0.63 points/year, 95% confidence interval: 0.38, 0.89). Hyporeflexia, hypopallesthaesia, upper motor neuron signs, chorea, dystonia, oculomotor signs and cognitive impairment were frequent findings in XPA, XPD and XPG. Cerebellar and global brain atrophy, axonal sensory and sensorimotor neuropathies, and sensorineural hearing loss were common findings in patients. Some XPC, XPE and XPV cases presented with abnormalities on examination and/or ancillary tests, suggesting underlying neurological involvement. More severe mutations were associated with a faster progression in SARA total score in XPA (0.40 points/year per 1-unit increase in severity score) and XPD (0.60 points/year per 1-unit increase), and in ADL total score in XPA (0.35 points/year per 1-unit increase). Symptomatic and asymptomatic forms of neurological disease are frequent in XP patients, and neurological symptoms can be an important cause of disability. Typically, the neurological disease will be preceded by cutaneous and ophthalmological features, and these should be actively searched in patients with idiopathic late-onset neurological syndromes. Scales assessing cerebellar function, especially walking and speech, and disability can show progression in some of the groups. Mutation severity can be used as a prognostic biomarker for stratification purposes in clinical trials.

Chemiexcitation: Mammalian Photochemistry in the Dark†

Light is one way to excite an electron in biology. Another is chemiexcitation, birthing a reaction product in an electronically excited state rather than exciting from the ground state. Chemiexcited molecules, as in bioluminescence, can release more energy than ATP. Excited states also allow bond rearrangements forbidden in ground states. Molecules with low-lying unoccupied orbitals, abundant in biology, are particularly susceptible. In mammals, chemiexcitation was discovered to transfer energy from excited melanin, neurotransmitters, or hormones to DNA, creating the lethal and carcinogenic cyclobutane pyrimidine dimer. That process was initiated by nitric oxide and superoxide, radicals triggered by ultraviolet light or inflammation. Several poorly understood chronic diseases share two properties: inflammation generates those radicals across the tissue, and cells that die are those containing melanin or neuromelanin. Chemiexcitation may therefore be a pathogenic event in noise- and drug-induced deafness, Parkinson's disease, and Alzheimer's; it may prevent macular degeneration early in life but turn pathogenic later. Beneficial evolutionary selection for excitable biomolecules may thus have conferred an Achilles heel. This review of recent findings on chemiexcitation in mammalian cells also describes the underlying physics, biochemistry, and potential pathogenesis, with the goal of making this interdisciplinary phenomenon accessible to researchers within each field.

Peripheral neuropathies associated with DNA repair disorders

Repair of genomic DNA is a fundamental housekeeping process that quietly maintains the health of our genomes. The consequences of a genetic defect affecting a component of this delicate mechanism are quite harmful, characterized by a cascade of premature aging that injures a variety of organs, including the nervous system. One part of the nervous system that is impaired in certain DNA repair disorders is the peripheral nerve. Chronic motor, sensory, and sensorimotor polyneuropathies have all been observed in affected individuals, with specific physiologies associated with different categories of DNA repair disorders. Cockayne syndrome has classically been linked to demyelinating polyneuropathies, whereas xeroderma pigmentosum has long been associated with axonal polyneuropathies. Three additional recessive DNA repair disorders are associated with neuropathies, including trichothiodystrophy, Werner syndrome, and ataxia-telangiectasia. Although plausible biological explanations exist for why the peripheral nerves are specifically vulnerable to impairments of DNA repair, specific mechanisms such as oxidative stress remain largely unexplored in this context, and bear further study. It is also unclear why different DNA repair disorders manifest with different types of neuropathy, and why neuropathy is not universally present in those diseases. Longitudinal physiological monitoring of these neuropathies with serial electrodiagnostic studies may provide valuable noninvasive outcome data in the context of future natural history studies, and thus the responses of these neuropathies may become sentinel outcome measures for future clinical trials of treatments currently in development such as adeno-associated virus gene replacement therapies.

Adult-Onset Neurodegeneration in Nucleotide Excision Repair Disorders (NERDND ): Time to Move Beyond the Skin

BACKGROUND

Variants in genes of the nucleotide excision repair (NER) pathway have been associated with heterogeneous clinical presentations ranging from xeroderma pigmentosum to Cockayne syndrome and trichothiodystrophy. NER deficiencies manifest with photosensitivity and skin cancer, but also developmental delay and early-onset neurological degeneration. Adult-onset neurological features have been reported in only a few xeroderma pigmentosum cases, all showing at least mild skin manifestations.

OBJECTIVE

The aim of this multicenter study was to investigate the frequency and clinical features of patients with biallelic variants in NER genes who are predominantly presenting with neurological signs.

METHODS

In-house exome and genome datasets of 14,303 patients, including 3543 neurological cases, were screened for deleterious variants in NER-related genes. Clinical workup included in-depth neurological and dermatological assessments.

RESULTS

We identified 13 patients with variants in ERCC4 (n = 8), ERCC2 (n = 4), or XPA (n = 1), mostly proven biallelic, including five different recurrent and six novel variants. All individuals had adult-onset progressive neurological deterioration with ataxia, dementia, and frequently chorea, neuropathy, and spasticity. Brain magnetic resonance imaging showed profound global brain atrophy in all patients. Dermatological examination did not show any skin cancer or pronounced ultraviolet damage.

CONCLUSIONS

We introduce NERD_ND as adult-onset neurodegeneration (_ND ) within the spectrum of autosomal recessive NER disorders (NERD). Our study demonstrates that NERD_ND is probably an underdiagnosed cause of neurodegeneration in adulthood and should be considered in patients with overlapping cognitive and movement abnormalities. © 2022 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Bilateral cochlear implantation in a young patient with xeroderma pigmentosum (XP-D) and progressive sensorineural hearing loss-How to do it?

Xeroderma pigmentosum (XP), a rare genetic skin condition, causes ultraviolet (UV)-induced neoplasms and possible neurological deficits including sensorineural hearingloss.

We present the first case in literature of bilateral cochlear implantation (CI) in a patient with XP-D with neurodegeneration. Multi-disciplinary team members (national XP team, dermatologist, anaesthetist, theatre team, biophysicists) were involved. UV exposure from equipment and areas where the 14-year-old patient would track was measured. Maximum possible surgery was performed under operating headlights to limit higher-UV microscope exposure. Its bulb light intensity was reduced to achieve safe UV level (0–10 μW/cm²). Skin was protected under surgical drapes. Challenges included drilling unpredicted hard thick bone under low-intensity light and requiring bulkier Nucleus®-7 processor due to unanticipated increased scarring. A delayed left facial weakness was resolved with steroids. He is undergoing hearing rehabilitation.

This highlights challenges of CI in XP. Its impact in preserving cognition and on neurodegeneration should also be observed.

Differences in peripheral neuropathy in xeroderma pigmentosum complementation groups A and D as evaluated by nerve conduction studies

Background

Xeroderma pigmentosum (XP) is a rare autosomal recessive genetic disorder with defective DNA nucleotide excision repair and associated with a high frequency of skin cancer. Approximately 25% of patients develop progressive neurological degeneration. Complementation groups XP-A and XP-D are most frequently associated with neurological disorders.

Design/methods

This is a retrospective review of patients with XP who were evaluated at NIH from 1986 to 2015 and had nerve conduction studies (NCS). In the complementation groups with peripheral neuropathy, further comparisons of the NCS were made with audiological, brain imaging, neuropsychological assessments that were also performed on most of the patients. Limited neuropathology of XP-A and XP-D patients were examined..

Results

The 33 patients had NCS: XP-A (9 patients), XP-C (7 patients), XP-D (10 patients), XP-E (1 patient), XP-V (4 patients), and XP-unknown (2 patients). Peripheral neuropathy based on nerve conduction studies was documented only in two complementation groups: 78% (7/9) of XP-A patients had a sensorimotor neuropathy while 50% (5/10) of XP-D patients had a sensory neuropathy only. Analysis of sural sensory nerve amplitude in both complementation groups XP-A and XP-D correlated with sensorineural hearing loss (SNHL), MRI/CT severity, and Full-scale Intelligence Quotient (IQ). Analysis of fibular motor nerve amplitude in complementation XP-A correlated with SNHL and MRI/CT severity. Limited follow-up studies showed gradual loss of NCS responses compared to an earlier and more rapid progression of the hearing loss.

Conclusions

Despite similar brain imaging and audiological findings patients, XP-A and XP-D complementation groups differ in the type of neuropathy, sensorimotor versus sensory alone. A few cases suggest that sensorineural hearing loss may precede abnormal NCS in XP and therefore serve as valuable clinical indicators of XP patients that will later develop peripheral neuropathy.

Genetic hearing loss: the audiologist's perspective

As knowledge regarding the genetic underpinnings of hearing loss has rapidly evolved, the role of the clinician in managing the patient has expanded beyond that of defining the characteristics of the auditory phenotype. The importance and impact of a genetic diagnosis has yet to be fully realized in routine clinical care. However, audiologists are uniquely situated to be front-line healthcare providers for persons of all ages with hereditary hearing loss. Here, we discuss why the combination of genotype and phenotype are necessary for the delivery of personalized and effective clinical care for individuals with genetic hearing loss.

Thyroid nodules in xeroderma pigmentosum patients: a feature of premature aging

PURPOSE

Xeroderma pigmentosum (XP) is an autosomal recessive disease with defective DNA repair, a markedly increased risk of skin cancer, and premature aging. Reports from North Africa have described thyroid nodules in XP patients, but thyroid nodule prevalence has never been determined in XP patients enrolled in our natural history study at the National Institutes of Health (NIH).

METHODS

We performed thyroid ultrasound examinations on all 29 XP patients examined from 2011 to 2019 and assessed nodule malignancy using the Thyroid Imaging Reporting and Data System. Thyroid nodule prevalence was also obtained from comparison cohorts. DNA sequencing was performed on thyroid tissue from XP patients who had surgery for thyroid cancer.

RESULTS

Thyroid nodules were identified in 18/29 XP patients (62%). The median age of patients with thyroid nodules in our XP cohort (20 years) was younger than that of three comparison groups: 36 years (California study-208 subjects), 48 years (Korean study-24,757 subjects), and 52 years (NIH-682 research subjects). Multiple (2-4) thyroid nodules were found in 12/18 (67%) of the patients with nodules. Autopsy examination revealed follicular adenomas in 4/8 (50%) additional XP patients. DNA sequencing revealed rare mutations in two other XP patients with papillary thyroid cancer.

CONCLUSIONS

XP patients have an increased incidence of thyroid nodules at an early age in comparison to the general population. These finding confirm another premature aging feature of XP.

Clinical and Mutational Spectrum of Xeroderma Pigmentosum in Egypt: Identification of Six Novel Mutations and Implications for Ancestral Origins

Xeroderma pigmentosum is a rare autosomal recessive skin disorder characterized by freckle-like dry pigmented skin, photosensitivity, and photophobia. Skin and ocular symptoms are confined to sun exposed areas of the body. Patients have markedly increased risk for UV-induced skin, ocular, and oral cancers. Some patients develop neurodegenerative symptoms, including diminished tendon reflexes and microcephaly. In this study, we describe clinical and genetic findings of 36 XP patients from Egypt, a highly consanguineous population from North Africa. Thorough clinical evaluation followed by Sanger sequencing of XPA and XPC genes were done. Six novel and seven previously reported mutations were identified. Phenotype-genotype correlation was investigated. We report clinical and molecular findings consistent with previous reports of countries sharing common population structure, and geographical and historical backgrounds with implications on common ancestral origins and historical migration flows. Clinical and genetic profiling improves diagnosis, management, counselling, and implementation of future targeted therapies.

Xeroderma Pigmentosum: A Model for Human Premature Aging

Aging results from intrinsic changes (chronologic) and damage from external exposures (extrinsic) on the human body. The skin is ideal to visually differentiate their unique features. Inherited diseases of DNA repair, such as xeroderma pigmentosum (XP), provide an excellent model for human aging due to the accelerated accumulation of DNA damage. Poikiloderma, atypical lentigines, and skin cancers, the primary cutaneous features of XP, occur in the general population but at a much older age. Patients with XP also exhibit ocular changes secondary to premature photoaging, including ocular surface tumors and pterygium. Internal manifestations of premature aging, including peripheral neuropathy, progressive sensorineural hearing loss, and neurodegeneration, are reported in 25% of patients with XP. Internal malignancies, such as lung cancer, CNS tumors, and leukemia and/or lymphoma, occur at a younger age in patients with XP, as do thyroid nodules. Premature ovarian failure is overrepresented among females with XP, occurring 20 years earlier than in the general population. Taken together, these clinical findings highlight the importance of DNA repair in maintaining genomic integrity. XP is a unique model of human premature aging, which is revealing new insights into aging mechanisms.

Hereditary Hearing Impairment with Cutaneous Abnormalities

Syndromic hereditary hearing impairment (HHI) is a clinically and etiologically diverse condition that has a profound influence on affected individuals and their families. As cutaneous findings are more apparent than hearing-related symptoms to clinicians and, more importantly, to caregivers of affected infants and young individuals, establishing a correlation map of skin manifestations and their underlying genetic causes is key to early identification and diagnosis of syndromic HHI. In this article, we performed a comprehensive PubMed database search on syndromic HHI with cutaneous abnormalities, and reviewed a total of 260 relevant publications. Our in-depth analyses revealed that the cutaneous manifestations associated with HHI could be classified into three categories: pigment, hyperkeratosis/nail, and connective tissue disorders, with each category involving distinct molecular pathogenesis mechanisms. This outline could help clinicians and researchers build a clear atlas regarding the phenotypic features and pathogenetic mechanisms of syndromic HHI with cutaneous abnormalities, and facilitate clinical and molecular diagnoses of these conditions.

Novel mutation identified in the DDB2 gene in patients with xeroderma pigmentosum group-E

BACKGROUND

Xeroderma pigmentosum (XP) is a rare photosensitive syndrome, which is divided into eight complementation groups (XP-A to XP-G and XPV) and characterized by skin cancers diagnosed at early age. A family of seven members (age range between 5 and 47 years) with carriers of the novel nonsense mutation that causes XP-E type were included in the current study.

METHODS

DNA was isolated from peripheral blood samples of the proband, and cancer predisposition genes were sequenced with next-generation sequencing. The demographic features and the laboratory, clinical, and histopathological findings of patients were evaluated.

RESULTS

In the proband, squamous cell carcinoma was first diagnosed in the right-eye cornea at the age of 13 years and then in the left-eye cornea at the age of 15 years. Later, the patient was diagnosed with basosquamous cell carcinoma on the dorsum of the nose at the age of 18 years. After genetic analysis, a novel nonsense c.1063C>T(p.Arg355Ter) pathogenic variation that causes XP-E type was detected as homozygous in the DDB2 gene of the proband and her siblings, 11 and 5 years of age, and as heterozygous in her parents and a 22-year-old brother.

CONCLUSION

Because of the occurrence of early termination codon, truncated nonfunctional proteins or proteins with deleterious loss or gain-of-function activities are synthesized in nonsense mutation. Thus, to avoid the development of pathological lesions, it is important that such patients with nonsense mutation stay away from agents that might cause DNA damage and develop an appropriate lifestyle according to this condition.

Reproductive Health in Xeroderma Pigmentosum: Features of Premature Aging

OBJECTIVE

To assess the age at menarche and menopause of women with xeroderma pigmentosum, a DNA repair disease with premature aging, in a longitudinal natural history study.

METHODS

We conducted a natural history study that reviewed medical records for gynecologic and reproductive health of all female patients with xeroderma pigmentosum aged older than 9 years examined at the National Institutes of Health (NIH). We performed gynecologic and laboratory examinations on a subset of the patients. Women in a second subset, who could not be examined, were interviewed using a questionnaire. Women who were deceased or lost to follow-up formed a third subset.

RESULTS

Sixty females with xeroderma pigmentosum aged older than 9 years (median 29 years, range 10-61 years) were evaluated at the NIH from 1971 to 2018. Of these 60, 31 had history, questionnaire, record review, and gynecologic evaluation; 14 had record review and questionnaire interview by telephone; and 15 had only NIH record review. Menarche in females with xeroderma pigmentosum occurred at a median age of 12.0 years (range 9-17 years), which was comparable with the U.S. general population. Among the 18 patients with menopause, the median age at menopause of 29.5 years (range 18-49.5 years) was more than 20 years younger than in the U.S. general population (52.9 years). Premature menopause (before age 40 years) occurred in 14 of the 45 (31%) women aged 18 years or older, and primary ovarian insufficiency was documented in nine of them. There were 32 live births among 21 of the women, five of whom subsequently developed premature menopause.

CONCLUSION

Females with xeroderma pigmentosum in our study had a normal age at menarche and were fertile but had increased incidence of premature menopause. Premature menopause, a symptom of premature aging, should be considered for gynecologic and reproductive health as well as implicating DNA repair in maintaining normal ovarian function.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov, NCT00001813.

Cochlear histopathology in human genetic hearing loss: State of the science and future prospects

Sensorineural hearing loss (SNHL) is an extraordinarily common disability, affecting 466 million people across the globe. Half of these incidents are attributed to genetic mutations that disrupt the structure and function of the cochlea. The human cochlea's interior cannot be imaged or biopsied without damaging hearing; thus, everything known about the morphologic correlates of hereditary human deafness comes from histopathologic studies conducted in either cadaveric human temporal bone specimens or animal models of genetic deafness. The purpose of the present review is to a) summarize the findings from all published histopathologic studies conducted in human temporal bones with known SNHL-causing genetic mutations, and b) compare the reported phenotypes of human vs. mouse SNHL caused by the same genetic mutation. The fact that human temporal bone histopathologic analysis has been reported for only 22 of the nearly 200 identified deafness-causing genes suggests a great need for alternative and improved techniques for studying human hereditary deafness; in light of this, the present review concludes with a summary of promising future directions, specifically in the fields of high resolution cochlear imaging, intracochlear fluid biopsy, and gene therapy.

Characteristics of Xeroderma Pigmentosum in Japan: Lessons From Two Clinical Surveys and Measures for Patient Care

Xeroderma pigmentosum (XP) is a rare autosomal recessive hereditary disease caused by deficiency in repair of DNA lesions generated by ultraviolet radiation and other compounds. Patients with XP display pigmentary change and numerous skin cancers in sun-exposed sites, and some patients show exaggerated severe sunburns even upon minimum sun exposure as well as neurological symptoms. We conducted a nationwide survey for XP since 1980. In Japan, the frequency of the XP complementation group A is the highest, followed by the variant type; while in the Western countries, those of groups C or D are the highest. Regarding skin cancers in XP, basal cell carcinoma was the most frequent cancer that afflicted patients with XP, followed by squamous cell carcinoma, and malignant melanoma. The frequency of these skin cancers in patients with XP has decreased in these 20 years, and the age of onset of developing skin cancers is higher than those previously observed, owing to early diagnosis and education to patients and care takers on strict prevention from sunlight for patients with XP. On the other hand, the effective therapy for neurological XP has not been established yet, and this needs to be done urgently.

Macular and Retinal Nerve Fibre Layer Thinning in Xeroderma Pigmentosum: A Cross-sectional Study

The purpose of this study was to evaluate retinal thickness in different Xeroderma Pigmentosum (XP) complementation groups using spectral-domain optical coherence tomography (SD-OCT). This was a cross-sectional pilot study of 40 patients with XP. All patients had healthy-looking retinae and optic nerves on slit lamp biomicroscopy, and subtle or no neurological deficits. Patients were divided into two groups based on the known tendency for neurodegeneration associated with certain XP complementation groups. A third control group was obtained from a normative database. Using SD-OCT, we compared peripapillary retinal nerve fibre layer (pRNFL) and macular thickness between the groups. XP patients with a known tendency for neurodegeneration were found to have a statistically significant reduction in both pRNFL (p < 0.01) and macular thickness (p < 0.001) compared with healthy controls. In contrast, there was no statistically significant difference between pRNFL and macular thickness in XP patients not expected to develop neurodegeneration compared to the same control group. When both XP groups were compared, a statistically significant reduction in total pRNFL (p = 0.02) and macular thickness (p = 0.002) was found in XP patients predisposed to neurodegeneration. Our results suggest that pRNFL and macular thickness are reduced in XP patients with a known tendency for neurodegeneration, even before any marked neurological deficits become manifest. These findings demonstrate the potential role of retinal thickness as an anatomic biomarker and prognostic indicator for XP neurodegeneration.

Chemiexcitation and Its Implications for Disease

Quantum mechanics rarely extends to molecular medicine. Recently, the pigment melanin was found to be susceptible to chemiexcitation, in which an electron is chemically excited to a high-energy molecular orbital. In invertebrates, chemiexcitation causes bioluminescence; in mammals, a higher-energy process involving melanin transfers energy to DNA without photons, creating the lethal and mutagenic cyclobutane pyrimidine dimer that can cause melanoma. This process is initiated by NO and O₂^- radicals, the formation of which can be triggered by ultraviolet light or inflammation. Several chronic diseases share two properties: inflammation generates these radicals across the tissue, and the diseased cells lie near melanin. We propose that chemiexcitation may be an upstream event in numerous human diseases.

Mutations in Cockayne Syndrome-Associated Genes (Csa and Csb) Predispose to Cisplatin-Induced Hearing Loss in Mice

Cisplatin is a common and effective chemotherapeutic agent, yet it often causes permanent hearing loss as a result of sensory hair cell death. The causes of sensitivity to DNA-damaging agents in nondividing cell populations, such as cochlear hair and supporting cells, are poorly understood, as are the specific DNA repair pathways that protect these cells. Nucleotide excision repair (NER) is a conserved and versatile DNA repair pathway for many DNA-distorting lesions, including cisplatin-DNA adducts. Progressive sensorineural hearing loss is observed in a subset of NER-associated DNA repair disorders including Cockayne syndrome and some forms of xeroderma pigmentosum. We investigated whether either of the two overlapping branches that encompass NER, transcription-coupled repair or global genome repair, which are implicated in Cockayne syndrome and xeroderma pigmentosum group C, respectively, modulates cisplatin-induced hearing loss and cell death in the organ of Corti, the auditory sensory epithelium of mammals. We report that cochlear hair cells and supporting cells in transcription-coupled repair-deficient Cockayne syndrome group A (Csa(-/-)) and group B (Csb(-/-)) mice are hypersensitive to cisplatin, in contrast to global genome repair-deficient Xpc(-/-) mice, both in vitro and in vivo We show that sensory hair cells in Csa(-/-) and Csb(-/-) mice fail to remove cisplatin-DNA adducts efficiently in vitro; and unlike Xpc(-/-) mice, Csa(-/-) and Csb(-/-) mice lose hearing and manifest outer hair cell degeneration after systemic cisplatin treatment. Our results demonstrate that Csa and Csb deficiencies predispose to cisplatin-induced hearing loss and hair/supporting cell damage in the mammalian organ of Corti, and emphasize the importance of transcription-coupled DNA repair in the protection against cisplatin ototoxicity.

SIGNIFICANCE STATEMENT

The utility of cisplatin in chemotherapy remains limited due to serious side effects, including sensorineural hearing loss. We show that mouse models of Cockayne syndrome, a progeroid disorder resulting from a defect in the transcription-coupled DNA repair (TCR) branch of nucleotide excision repair, are hypersensitive to cisplatin-induced hearing loss and sensory hair cell death in the organ of Corti, the mammalian auditory sensory epithelium. Our work indicates that Csa and Csb, two genes involved in TCR, are preferentially required to protect against cisplatin ototoxicity, relative to global genome repair-specific elements of nucleotide excision repair, and suggests that TCR is a major force maintaining DNA integrity in the cochlea. The Cockayne syndrome mice thus represent a model for testing the contribution of DNA repair mechanisms to cisplatin ototoxicity.

Recommendations for Childhood Cancer Screening and Surveillance in DNA Repair Disorders

DNA repair syndromes are heterogeneous disorders caused by pathogenic variants in genes encoding proteins key in DNA replication and/or the cellular response to DNA damage. The majority of these syndromes are inherited in an autosomal-recessive manner, but autosomal-dominant and X-linked recessive disorders also exist. The clinical features of patients with DNA repair syndromes are highly varied and dependent on the underlying genetic cause. Notably, all patients have elevated risks of syndrome-associated cancers, and many of these cancers present in childhood. Although it is clear that the risk of cancer is increased, there are limited data defining the true incidence of cancer and almost no evidence-based approaches to cancer surveillance in patients with DNA repair disorders. This article is the product of the October 2016 AACR Childhood Cancer Predisposition Workshop, which brought together experts from around the world to discuss and develop cancer surveillance guidelines for children with cancer-prone disorders. Herein, we focus on the more common of the rare DNA repair disorders: ataxia telangiectasia, Bloom syndrome, Fanconi anemia, dyskeratosis congenita, Nijmegen breakage syndrome, Rothmund-Thomson syndrome, and Xeroderma pigmentosum. Dedicated syndrome registries and a combination of basic science and clinical research have led to important insights into the underlying biology of these disorders. Given the rarity of these disorders, it is recommended that centralized centers of excellence be involved directly or through consultation in caring for patients with heritable DNA repair syndromes. Clin Cancer Res; 23(11); e23-e31. ©2017 AACRSee all articles in the online-only CCR Pediatric Oncology Series.

Hearing Dysfunction in Xpa-Deficient Mice

Xeroderma pigmentosum (XP) is a rare recessive heredity disease caused by DNA repair impairment characterized by photosensitivity and neurologic symptoms in half of the cases. There are eight subtypes of XP: XP-A–XP-G and XP variant. Among eight subtypes, XP complementation group A (XP-A) display the lowest DNA repair ability and the severest cutaneous and neurologic symptoms. While its pathogenesis of skin symptoms have been well-studied, that of neurological symptoms, including sensorineural hearing loss (SNHL) remains unknown. Basic studies have suggested that SNHL may be caused by inner ear damage, including damage to the spiral ganglion neurons and organ of Corti, and that the XP-A is associated with most severe form of SNHL in humans. Here, we report the occurrence of SNHL in Xpa-deficient mice. Xpa-deficient mice and wild-type mice underwent measurements for auditory brainstem response, and the results revealed that Xpa-deficient mice exhibited significantly greater (p < 0.01) ABR thresholds at 4, 8, and 16 kHz than the wild-type mice. Furthermore, the number of spiral ganglion neurons was reduced in Xpa-deficient mice compared with that in wild-type mice, indicating that hearing loss may be related to spiral ganglion neuron deficiency, consistent with the few reports published in human patients with XP. These results provide important insights into the pathogenesis of SNHL in patients with XP-A.

Noise Stress Induces an Epidermal Growth Factor Receptor/Xeroderma Pigmentosum-A Response in the Auditory Nerve

In response to toxic stressors, cancer cells defend themselves by mobilizing one or more epidermal growth factor receptor (EGFR) cascades that employ xeroderma pigmentosum-A (XPA) to repair damaged genes. Recent experiments discovered that neurons within the auditory nerve exhibit basal levels of EGFR+XPA co-expression. This finding implied that auditory neurons in particular or neurons in general have the capacity to mobilize an EGFR+XPA defense. Therefore, the current study tested the hypothesis that noise stress would alter the expression pattern of EGFR/XPA within the auditory nerve. Design-based stereology was used to quantify the proportion of neurons that expressed EGFR, XPA, and EGFR+XPA with and without noise stress. The results revealed an intricate neuronal response that is suggestive of alterations to both co-expression and individual expression of EGFR and XPA. In both the apical and middle cochlear coils, the noise stress depleted EGFR+XPA expression. Furthermore, there was a reduction in the proportion of neurons that expressed XPA-alone in the middle coils. However, the noise stress caused a significant increase in the proportion of neurons that expressed EGFR-alone in the middle coils. The basal cochlear coils failed to mobilize a significant response to the noise stress. These results suggest that EGFR and XPA might be part of the molecular defense repertoire of the auditory nerve.

DNA Repair Dysfunction and Neurodegeneration: Lessons From Rare Pediatric Disorders

Nucleotide excision repair disorders display a wide range of clinical syndromes and presentations, all associated at the molecular level by dysfunction of genes participating in the nucleotide excision repair pathway. Genotype-phenotype relationships are remarkably complex and not well understood. This article outlines neurodegenerative symptoms seen in nucleotide excision repair disorders and explores the role that nucleotide excision repair dysfunction can play in the pathogenesis of chronic neurodegenerative diseases.

Forty years of research on xeroderma pigmentosum at the US National Institutes of Health

In 1968, Dr. James Cleaver reported defective DNA repair in cultured cells from patients with xeroderma pigmentosum. This link between clinical disease and molecular pathophysiology has sparked interest in understanding not only the clinical characteristics of sun sensitivity, damage and cancer that occurred in XP patients but also the mechanisms underlying the damage and repair. While affected patients are rare, their exaggerated UV damage provides a window into the workings of DNA repair. These studies have clarified the importance of a functioning DNA repair system to the maintenance of skin and neurologic health in the general population. Understanding the role of damage in causing cancer, neurologic degeneration, hearing loss and internal cancers provides an opportunity for prevention and treatment. Characterizing complementation groups pointed to the importance of different underlying genes. Studying differences in cancer age of onset and underlying molecular signatures in cancers occurring either in XP patients or the general population has led to insights into differences in carcinogenic mechanisms. The accelerated development of cancers in XP has been used as a model to discover new cancer chemopreventive agents. An astute insight can be a "tipping point" triggering decades of productive inquiry.

Cell-autonomous progeroid changes in conditional mouse models for repair endonuclease XPG deficiency

As part of the Nucleotide Excision Repair (NER) process, the endonuclease XPG is involved in repair of helix-distorting DNA lesions, but the protein has also been implicated in several other DNA repair systems, complicating genotype-phenotype relationship in XPG patients. Defects in XPG can cause either the cancer-prone condition xeroderma pigmentosum (XP) alone, or XP combined with the severe neurodevelopmental disorder Cockayne Syndrome (CS), or the infantile lethal cerebro-oculo-facio-skeletal (COFS) syndrome, characterized by dramatic growth failure, progressive neurodevelopmental abnormalities and greatly reduced life expectancy. Here, we present a novel (conditional) Xpg^−/− mouse model which -in a C57BL6/FVB F1 hybrid genetic background- displays many progeroid features, including cessation of growth, loss of subcutaneous fat, kyphosis, osteoporosis, retinal photoreceptor loss, liver aging, extensive neurodegeneration, and a short lifespan of 4–5 months. We show that deletion of XPG specifically in the liver reproduces the progeroid features in the liver, yet abolishes the effect on growth or lifespan. In addition, specific XPG deletion in neurons and glia of the forebrain creates a progressive neurodegenerative phenotype that shows many characteristics of human XPG deficiency. Our findings therefore exclude that both the liver as well as the neurological phenotype are a secondary consequence of derailment in other cell types, organs or tissues (e.g. vascular abnormalities) and support a cell-autonomous origin caused by the DNA repair defect itself. In addition they allow the dissection of the complex aging process in tissue- and cell-type-specific components. Moreover, our data highlight the critical importance of genetic background in mouse aging studies, establish the Xpg^−/− mouse as a valid model for the severe form of human XPG patients and segmental accelerated aging, and strengthen the link between DNA damage and aging.

Accumulation of DNA damage has been implicated in aging. Many premature aging syndromes are due to defective DNA repair systems. The endonuclease XPG is involved in repair of helix-distorting DNA lesions, and XPG defects cause the cancer-prone condition xeroderma pigmentosum (XP) alone or combined with the severe neurodevelopmental progeroid disorder Cockayne syndrome (CS). Here, we present a novel (conditional) Xpg^−/− mouse model which -in a C57BL6/FVB F1 hybrid background- displays many progressive progeroid features, including early cessation of growth, cachexia, kyphosis, osteoporosis, neurodegeneration, liver aging, retinal degeneration, and reduced lifespan. In a constitutive mutant with a complex phenotype it is difficult to dissect cause and consequence. We have therefore generated liver- and forebrain-specific Xpg mutants and demonstrate that they exhibit progressive anisokaryosis and neurodegeneration, respectively, indicating that a cell-intrinsic repair defect in neurons can account for neuronal degeneration. These findings strengthen the link between DNA damage and the complex process of aging.

Histopathology of the inner ear in patients with xeroderma pigmentosum and neurologic degeneration

INTRODUCTION

Xeroderma pigmentosum (XP) is a rare autosomal recessive disease caused by mutations resulting in defective repair of DNA damage. XP patients have a markedly increased risk of ultraviolet-induced neoplasms and premature aging of sun-exposed tissue. Approximately 25% of XP patients in the United States have neurologic abnormalities including progressive sensorineural hearing loss (SNHL).

OBJECTIVE

To describe the temporal bone histopathology in 2 individuals with XP (XPA and XPD) with neurologic degeneration and to discuss the possible causes of deafness in these patients.

METHODS

Temporal bones were removed at autopsy and studied using light microscopy.

RESULTS

In the case with XPD, the organ of Corti was missing throughout the cochlea, whereas the case with XPA demonstrated scattered presence of sensory cells in the middle and apical turns. In both cases, there was moderate-to-severe patchy atrophy of the stria vascularis in all turns, and cochlear neurons were severely atrophied compared with age-matched controls, with loss of both peripheral dendrites and central axons. There was severe degeneration of Scarpa's ganglion in the case with XPA.

CONCLUSION

Two cases of XP with neurologic degeneration are reported. The case with XPD demonstrated a more severe audiologic phenotype than XPA, although both had similar findings such as atrophy of the organ of Corti, stria vascularis, and spiral ganglia leading to severe or profound SNHL by the third decade of life. It is not clear if the neuronal degeneration in the inner ear was primary or secondary to loss of neuroepithelial cells.

A functional Ser326Cys polymorphism in hOGG1 is associated with noise-induced hearing loss in a Chinese population

DNA damage to cochlear hair cells caused by 8-oxoguanine (8-oxoG) is essential for the development of noise-induced hearing loss (NIHL). Human 8-oxoG DNA glycosylase1 (hOGG1) is a key enzyme in the base excision repair (BER) pathway that eliminates 8-oxoG. Many epidemiological and functional studies have suggested that the hOGG1 Ser326Cys polymorphism (rs1052133) is associated with many diseases. The purpose of this investigation was to investigate whether the hOGG1 Ser326Cys polymorphism in the human BER pathway is associated with genetic susceptibility to NIHL in a Chinese population. This polymorphism was genotyped among 612 workers with NIHL and 615 workers with normal hearing. We found that individuals with the hOGG1 Cys/Cys genotype had a statistically significantly increased risk of NIHL compared with those who carried the hOGG1 Ser/Ser genotype (adjusted OR=1.59, 95% CI=1.13-2.25) and this increased risk was more pronounced among the workers in the 15- to 25- and >25-year noise exposure time, 85-92 dB(A) noise exposure level, ever smoking, and ever drinking groups, similar effects were also observed in a recessive model. In summary, our data suggested that the hOGG1 Cys/Cys genotype may be a genetic susceptibility marker for NIHL in the Chinese Han population.

Living with xeroderma pigmentosum: comprehensive photoprotection for highly photosensitive patients

Xeroderma pigmentosum (XP) is a rare autosomal recessive disease of deoxyribonucleic acid (DNA) repair with ultraviolet (UV) radiation sensitivity and a 10 000-fold increased risk of skin cancer. Symptoms include: freckle-like pigmentation in sun-exposed skin before age 2 years, severe burns after minimal sun exposure (50% of patients) and damage to exposed surfaces of the eyes with loss of vision and ocular cancer. About 25% of patients develop a progressive neurodegeneration. The combination of an inherited inability to repair UV-induced DNA damage and environmental exposure to UV must occur for cutaneous and ocular symptoms to develop. There is no cure for XP, but many of its manifestations may be reduced or prevented through consistent UV protection; thus XP serves as a model for sun protection of patients with marked photosenstivity. Sun protective clothing including hats, sunglasses and face shields, sun screen lotions and avoidance of environmental sources of UV are cornerstones of prevention of skin and eye damage and cancer. Although XP is a serious disease with the potential for limitation of life expectancy, XP patients can live active lives while at the same time avoiding UV.

The influence of DNA repair on neurological degeneration, cachexia, skin cancer and internal neoplasms: autopsy report of four xeroderma pigmentosum patients (XP-A, XP-C and XP-D)

Background

To investigate the association of DNA nucleotide excision repair (NER) defects with neurological degeneration, cachexia and cancer, we performed autopsies on 4 adult xeroderma pigmentosum (XP) patients with different clinical features and defects in NER complementation groups XP-A, XP-C or XP-D.

Results

The XP-A (XP12BE) and XP-D (XP18BE) patients exhibited progressive neurological deterioration with sensorineural hearing loss. The clinical spectrum encompassed severe cachexia in the XP-A (XP12BE) patient, numerous skin cancers in the XP-A and two XP-C (XP24BE and XP1BE) patients and only few skin cancers in the XP-D patient. Two XP-C patients developed internal neoplasms including glioblastoma in XP24BE and uterine adenocarcinoma in XP1BE. At autopsy, the brains of the 44 yr XP-A and the 45 yr XP-D patients were profoundly atrophic and characterized microscopically by diffuse neuronal loss, myelin pallor and gliosis. Unlike the XP-A patient, the XP-D patient had a thickened calvarium, and the brain showed vacuolization of the neuropil in the cerebrum, cerebellum and brainstem, and patchy Purkinje cell loss. Axonal neuropathy and chronic denervation atrophy of the skeletal muscles were observed in the XP-A patient, but not in the XP-D patient.

Conclusions

These clinical manifestations and autopsy findings indicate advanced involvement of the central and peripheral nervous system. Despite similar defects in DNA repair, different clinicopathological phenotypes are seen in the four cases, and therefore distinct patterns of neurodegeneration characterize XP-D, XP-A and XP-C patients.