Comparison of cellular sensitivity to UV killing with neuropsychological impairment in Cockayne syndrome patients

A mild case of Cockayne syndrome with a novel start-loss variant of ERCC8

Cockayne syndrome (CS) is a progressive multisystem disorder characterized by growth failure, microcephaly, developmental delay, and photosensitivity. The characteristic symptoms appear during early childhood in most patients with CS. Herein, we report a mild case of CS with a novel start-loss variant in ERCC8 that did not show the characteristic symptoms of CS during early childhood and exhibited sudden growth failure after the age of 10 years.

Identification of two novel homozygous mutations in ERCC8 gene in two unrelated consanguineous families with Cockayne syndrome from Iran

BACKGROUND

Cockayne syndrome (CS) is a rare autosomal recessive disorder with characteristic multisystem involvement including pre- or post-natal growth failure, progressive neurological dysfunction, psychomotor retardation, cerebral atrophy, microcephaly and mental retardation, due to mutations in either the ERCC8/CSA or ERCC6/CSB gene.

METHOD

We present two Iranian patients with remarkable growth failure, developmental delay, microcephaly, severe speech delay, vision problem, sun sensitivity, hearing loss, dental anomalies, unstable gait, mild contractures in knees, kyphosis and spasticity in lower limbs, balance disorders and typical dysmorphic features including long nose, aged face, large ears and sunken eyes. Clinical evaluation, magnetic resonance imaging, Peripheral blood karyotype, Multiplex ligation-dependent probe amplification (MLPA), and whole-exome sequencing were used to characterize etiology in two patients from two unrelated consanguineous families of Iranian descent with Cockayne syndrome.

RESULTS

We detected two novel pathogenic mutations in two unrelated families, a homozygous duplication mutation (c.317_320dupAGTG, p.Trp107Ter) and a splicing variant (c.481 + 1G > A) in ERCC8 gene.

CONCLUSION

WES results together with the characteristic clinical manifestations of Cockayne syndrome, provided an accurate diagnosis for two patients. Also, our study identified two novel variants in Iranian families.

Functional and clinical relevance of novel mutations in a large cohort of patients with Cockayne syndrome

BACKGROUND

Cockayne syndrome (CS) is a rare, autosomal recessive multisystem disorder characterised by prenatal or postnatal growth failure, progressive neurological dysfunction, ocular and skeletal abnormalities and premature ageing. About half of the patients with symptoms diagnostic for CS show cutaneous photosensitivity and an abnormal cellular response to UV light due to mutations in either the ERCC8/CSA or ERCC6/CSB gene. Studies performed thus far have failed to delineate clear genotype-phenotype relationships. We have carried out a four-centre clinical, molecular and cellular analysis of 124 patients with CS.

METHODS AND RESULTS

We assigned 39 patients to the ERCC8/CSA and 85 to the ERCC6/CSB genes. Most of the genetic variants were truncations. The missense variants were distributed non-randomly with concentrations in relatively short regions of the respective proteins. Our analyses revealed several hotspots and founder mutations in ERCC6/CSB. Although no unequivocal genotype-phenotype relationships could be made, patients were more likely to have severe clinical features if the mutation was downstream of the PiggyBac insertion in intron 5 of ERCC6/CSB than if it was upstream. Also a higher proportion of severely affected patients was found with mutations in ERCC6/CSB than in ERCC8/CSA.

CONCLUSION

By identifying >70 novel homozygous or compound heterozygous genetic variants in 124 patients with CS with different disease severity and ethnic backgrounds, we considerably broaden the CSA and CSB mutation spectrum responsible for CS. Besides providing information relevant for diagnosis of and genetic counselling for this devastating disorder, this study improves the definition of the puzzling genotype-phenotype relationships in patients with CS.

Tracking the Cognitive, Social, and Neuroanatomical Profile in Early Neurodegeneration: Type III Cockayne Syndrome

Cockayne syndrome (CS) is an autosomal recessive disease associated with premature aging, progressive multiorgan degeneration, and nervous system abnormalities including cerebral and cerebellar atrophy, brain calcifications, and white matter abnormalities. Although several clinical descriptions of CS patients have reported developmental delay and cognitive impairment with relative preservation of social skills, no previous studies have carried out a comprehensive neuropsychological and social cognition assessment. Furthermore, no previous research in individuals with CS has examined the relationship between brain atrophy and performance on neuropsychological and social cognition tests. This study describes the case of an atypical late-onset type III CS patient who exceeds the mean life expectancy of individuals with this pathology. The patient and a group of healthy controls underwent a comprehensive assessment that included multiple neuropsychological and social cognition (emotion recognition, theory of mind, and empathy) tasks. In addition, we compared the pattern of atrophy in the patient to controls and to its concordance with ERCC8 gene expression in a healthy brain. The results showed memory, language, and executive deficits that contrast with the relative preservation of social cognition skills. The cognitive profile of the patient was consistent with his pattern of global cerebral and cerebellar loss of gray matter volume (frontal structures, bilateral cerebellum, basal ganglia, temporal lobe, and occipito-temporal/occipito-parietal regions), which in turn was anatomically consistent with the ERCC8 gene expression level in a healthy donor’s brain. The study of exceptional cases, such as the one described here, is fundamental to elucidating the processes that affect the brain in premature aging diseases, and such studies provide an important source of information for understanding the problems associated with normal and pathological aging.

Molecular analysis of mutations in the CSB (ERCC6) gene in patients with Cockayne syndrome

Cockayne syndrome is a multisystem sun-sensitive genetic disorder associated with a specific defect in the ability to perform transcription-coupled repair of active genes after UV irradiation. Two complementation groups (CS-A and CS-B) have been identified, and 80% of patients have been assigned to the CS-B complementation group. We have analyzed the sites of the mutations in the CSB gene in 16 patients, to determine the spectrum of mutations in this gene and to see whether the nature of the mutation correlates with the type and severity of the clinical symptoms. In nine of the patients, the mutations resulted in truncated products in both alleles, whereas, in the other seven, at least one allele contained a single amino acid change. The latter mutations were confined to the C-terminal two-thirds of the protein and were shown to be inactivating by their failure to restore UV-irradiation resistance to hamster UV61 cells, which are known to be defective in the CSB gene. Neither the site nor the nature of the mutation correlated with the severity of the clinical features. Severe truncations were found in different patients with either classical or early-onset forms of the disease.

Cataract in early onset and classic Cockayne syndrome

PURPOSE

To describe cataracts in classic and early onset Cockayne syndrome (CS). Classic CS typically has an onset after the first year of life; intrauterine growth failure and severe neurologic dysfunction from birth distinguishes the less common early onset CS from the classic form.

METHODS

A complete ophthalmic evaluation was performed in four affected patients, one with the early onset and three with classic CS.

RESULTS

We report cataract in all patients and glaucoma in one, the latter never previously reported in CS.

CONCLUSION

CS should be considered in babies with low birth weight and congenital cataract.

Involvement of antipain-sensitive protease activity in the interferon-beta-induced UV-refractoriness of Cockayne syndrome fibroblasts

Fibroblast cells obtained from two siblings and a female patient with Cockayne syndrome (CS), when pretreated with human interferon (HuIFN)-beta prior to irradiation with UV light (254 nm wavelength), exhibited transiently induced fibrinolytic protease activity immediately after the irradiation in association with increased refractoriness to UV cell-killing. A protease inhibitor, antipain, inhibited the induction of protease activity in lysates of the CS fibroblasts from these 3 cases after the combination of HuIFN-beta pretreatment and UV irradiation, whereas elastatinal and 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB) inhibited the activity less than antipain did. Antipain also suppressed the increase in UV-refractoriness of HuIFN-beta-pretreated CS fibroblasts, as revealed by culturing cells for 24 h in medium containing the inhibitor immediately after UV exposure and thereafter evaluating the ability of colony formation by the cells. Thus, an antipain-sensitive protease may be involved in the UV-refractoriness induced by HuIFN-beta in CS fibroblast strains.

Xeroderma pigmentosum, Cockayne syndrome and trichothiodystrophy: do the genes explain the diseases?

Xeroderma pigmentosum, Cockayne syndrome and trichothiodystrophy are three distinct human syndromes associated with sensitivity to ultraviolet radiation. We review evidence that these syndromes overlap with each other and arise from mutations in genes involved in nucleotide-excision repair and RNA transcription. Attempts have been made to explain the syndromes in terms of defects in repair and transcription. These two biochemical pathways do not easily account for all the features of the syndromes. Therefore, we propose a third pathway, in which the syndromes are due, in part, to defects in a demethylation mechanism involving the excision of methylated cytosine. Perturbation of demethylation could affect the developmentally regulated expression of some genes.

Comparison of MRI white matter changes with neuropsychologic impairment in Cockayne syndrome

The neuropsychologic function and white matter changes observed on magnetic resonance imaging (MRI) in Cockayne syndrome were studied. MRI with T2-weighted sequences revealed periventricular hyperintensity and white matter hyperintensity in all 3 Cockayne syndrome patients examined; in contrast, 8 age-matched controls had no periventricular or white matter hyperintensity. MRI scans were graded according to the severity of periventricular or white matter hyperintensity using a scale applied to an elderly patient population. There was no difference in the severity of MRI white matter changes in these 3 Cockayne syndrome patients, 2 of whom had severe neuropsychologic functions and one a relatively milder one. There was no correlation between neuropsychologic impairment and MRI white matter changes.

Pelizaeus-Merzbacher disease: cellular hypersensitivity to ultraviolet light

We report two connatal cases of Pelizaeus-Merzbacher disease (PMD) with cellular ultraviolet (UV)-hypersensitivity. We studied the UV-sensitivity of cultured fibroblast cells derived from these PMD cases, as compared with UV-sensitive Cockayne syndrome (CS) and xeroderma pigmentosum (XP) cells as positive controls. The ability of the PMD cells to form colonies after UV irradiation was intermediate between those of CS cells and normal controls. There were no differences in both colony-forming ability after x-ray irradiation and unscheduled DNA synthesis (UDS) activity after UV irradiation between the PMD cells and the control cells. These cytological results suggest the possibility that a DNA defect might be involved in PMD.