Repeat length variations in polyglutamine disease-associated genes affect body mass index.

BACKGROUND: The worldwide prevalence of obesity, a major risk factor for numerous debilitating chronic disorders, is increasing rapidly. Although a substantial amount of the variation in body mass index (BMI) is estimated to be heritable, the largest meta-analysis of genome-wide association studies (GWAS) to date explained only ~2.7% of the variation. To tackle this 'missing heritability' problem of obesity, here we focused on the contribution of DNA repeat length polymorphisms which are not detectable by GWAS. SUBJECTS AND METHODS: We determined the cytosine-adenine-guanine (CAG) repeat length in the nine known polyglutamine disease-associated genes (ATXN1, ATXN2, ATXN3, CACNA1A, ATXN7, TBP, HTT, ATN1 and AR) in two large cohorts consisting of 12,457 individuals and analyzed their association with BMI, using generalized linear mixed-effect models. RESULTS: We found a significant association between BMI and the length of CAG repeats in seven polyglutamine disease-associated genes (including ATXN1, ATXN2, ATXN3, CACNA1A, ATXN7, TBP and AR). Importantly, these repeat variations could account for 0.75% of the total BMI variation. CONCLUSIONS: Our findings incriminate repeat polymorphisms as an important novel class of genetic risk factors of obesity and highlight the role of the brain in its pathophysiology.

Primary Ovarian Failure in Addition to Classical Clinical Features of Coats Plus Syndrome in a Female Carrying 2 Truncating Variants of CTC1.

Coats plus syndrome is an autosomal recessive multisystemic and pleiotropic disorder affecting the eyes, brain, bone, and gastrointestinal tract, usually caused by compound heterozygous variants of the conserved telomere maintenance component 1 gene (CTC1), involved in telomere homeostasis and replication. So far, most reported patients are compound heterozygous for a truncating mutation and a missense variant. The phenotype is believed to result from telomere dysfunction, with accumulation of DNA damage, cellular senescence, and stem cell depletion. Here, we report a 23-year-old female with prenatal and postnatal growth retardation, microcephaly, osteopenia, recurrent fractures, intracranial calcification, leukodystrophy, parenchymal brain cysts, bicuspid aortic valve, and primary ovarian failure. She carries a previously reported maternally inherited pathogenic variant in exon 5 (c.724_727del, p.(Lys242Leufs*41)) and a novel, paternally inherited splice site variant (c.1617+5G>T; p.(Lys480Asnfs*17)) in intron 9. CTC1 transcript analysis showed that the latter resulted in skipping of exon 9. A trace of transcripts was normally spliced resulting in the presence of a low level of wild-type CTC1 transcripts. We speculate that ovarian failure is caused by telomere shortening or chromosome cohesion failure in oocytes and granulosa cells, with early decrease in follicular reserve. This is the first patient carrying 2 truncating CTC1 variants and the first presenting primary ovarian failure.

Quantification of sequence exchange events between PMS2 and PMS2CL provides a basis for improved mutation scanning of Lynch syndrome patients.

Heterozygous mutations in PMS2 are involved in Lynch syndrome, whereas biallelic mutations are found in Constitutional mismatch repair-deficiency syndrome patients. Mutation detection is complicated by the occurrence of sequence exchange events between the duplicated regions of PMS2 and PMS2CL. We investigated the frequency of such events with a nonspecific polymerase chain reaction (PCR) strategy, co-amplifying both PMS2 and PMS2CL sequences. This allowed us to score ratios between gene and pseudogene-specific nucleotides at 29 PSV sites from exon 11 to the end of the gene. We found sequence transfer at all investigated PSVs from intron 12 to the 3' end of the gene in 4 to 52% of DNA samples. Overall, sequence exchange between PMS2 and PMS2CL was observed in 69% (83/120) of individuals. We demonstrate that mutation scanning with PMS2-specific PCR primers and MLPA probes, designed on PSVs, in the 3' duplicated region is unreliable, and present an RNA-based mutation detection strategy to improve reliability. Using this strategy, we found 19 different putative pathogenic PMS2 mutations. Four of these (21%) are lying in the region with frequent sequence transfer and are missed or called incorrectly as homozygous with several PSV-based mutation detection methods.

Repeat variations in polyglutamine disease-associated genes and cognitive function in old age.

Although the heritability of cognitive function in old age is substantial, genome-wide association studies have had limited success in elucidating its genetic basis, leaving a considerable amount of "missing heritability." Aside from single nucleotide polymorphisms, genome-wide association studies are unable to assess other large sources of genetic variation, such as tandem repeat polymorphisms. Therefore, here, we studied the association of cytosine-adenine-guanine (CAG) repeat variations in polyglutamine disease-associated genes (PDAGs) with cognitive function in older adults. In a large cohort consisting of 5786 participants, we found that the CAG repeat number in 3 PDAGs (TBP, HTT, and AR) were significantly associated with the decline in cognitive function, which together accounted for 0.49% of the variation. Furthermore, in an magnetic resonance imaging substudy, we found that CAG repeat polymorphisms in 4 PDAGs (ATXN2, CACNA1A, ATXN7, and AR) were associated with different imaging characteristics, including brain stem, putamen, globus pallidus, thalamus, and amygdala volumes. Our findings indicate that tandem repeat polymorphisms are associated with cognitive function in older adults and highlight the importance of PDAGs in elucidating its missing heritability.

Prevalence of Carriers of Intermediate and Pathological Polyglutamine Disease-Associated Alleles Among Large Population-Based Cohorts.

Importance: Nine hereditary neurodegenerative diseases are known as polyglutamine diseases, including Huntington disease, 6 spinocerebellar ataxias (SCAs) (SCA1, SCA2, SCA3, SCA6, SCA7, and SCA17), dentatorubral-pallidoluysion atrophy, and spinal bulbar muscular atrophy. Objective: To determine the prevalence of carriers of intermediate and pathological polyglutamine disease-associated alleles among the general population. Design, Setting, and Participants: This observational cross-sectional study included data from 5 large European population-based cohorts that were compiled between 1997 and 2012, and the analyses were conducted in 2018. In total, 16 547 DNA samples were obtained from participants of the 5 cohorts. Individuals with a lifetime diagnosis of major depression were excluded (n = 2351). In the remaining 14 196 participants without an established polyglutamine disease diagnosis, the CAG repeat size in both alleles of all 9 polyglutamine disease-associated genes (PDAGs) (ie, ATXN1, ATXN2, ATXN3, CACNA1A, ATXN7, TBP, HTT, ATN1, and AR) was determined. Exposure: The number of CAG repeats in the alleles of the 9 PDAGs. Main Outcomes and Measures: The number of individuals with alleles within the intermediate or pathological range per PDAG, as well as differences in sex, age, and body mass index between individuals carrying alleles within the normal or intermediate range and individuals carrying alleles within the pathological range of PDAGs. Results: In the 14 196 analyzed participants (age range, 18-99 years; 56.3% female), 10.7% had a CAG repeat number within the intermediate range of at least 1 PDAG. Moreover, up to 1.3% of the participants had a CAG repeat number within the disease-causing range, predominantly in the lower pathological range associated with elderly onset. No differences in sex, age, or body mass index were found between individuals with CAG repeat numbers within the pathological range and individuals with CAG repeat numbers within the normal or intermediate range. Conclusions and Relevance: These results indicate a high prevalence of individuals carrying intermediate and pathological ranges of polyglutamine disease-associated alleles among the general population. Therefore, a substantially larger proportion of individuals than previously estimated may be at risk of developing a polyglutamine disease later in life or bearing children with a de novo mutation.

Generation of 5 induced pluripotent stem cell lines, LUMCi007-A and B and LUMCi008-A, B and C, from 2 patients with Huntington disease.

Huntington disease (HD) is an autosomal dominant, neurodegenerative disease caused by a CAG repeat expansion within the coding sequence of the HTT gene, resulting in a highly toxic protein with an expanded polyglutamine stretch that forms typical protein aggregates throughout the brain. We generated human induced pluripotent stem cells (hiPSCs) from two HD patients using non-integrating Sendai virus (SeV). The hiPSCs display a normal karyotype, express all pluripotency markers, have the same CAG repeat expansion as the original fibroblasts and are able to differentiate into the three germ layers in vitro.

Repeat length variations in ATXN1 and AR modify disease expression in Alzheimer's disease.

Genomewide association studies (GWASs) have contributed greatly to unraveling the genetic basis of Alzheimer's disease (AD). However, a large amount of "missing heritability" remains. In this exploratory study, we investigated the effect of cytosine-adenine-guanine (CAG) repeats in polyglutamine disease-associated genes (PDAGs) on the risk of AD and its expression. In a cohort of 959 patients diagnosed with AD (Amsterdam Dementia cohort) and 4106 cognitively healthy participants (Leiden 85-plus Study and the Prospective Study of Pravastatin in the Elderly at Risk), we determined the CAG repeat sequences in ATXN1, ATXN2, ATXN3, CACNA1A, ATXN7, TBP, HTT, ATN1, and AR. We did not find a significant association between the risk of AD and variations in CAG repeat numbers of PDAGs. However, we found that differences in CAG repeat numbers in ATXN1, ATXN2, and AR were significantly associated with several clinical and imaging features in AD patients. Specifically, the association between memory performance in patients with AD and the CAG repeat size in the longer ATXN1 allele, and the association between atrophy in the medial temporal lobes and the CAG repeat number in the longer AR allele remained significant after correction for multiple testing. Our findings suggest that repeat polymorphisms in ATXN1 and AR can act as important genetic modifiers of AD, warranting further scrutiny of their role in its missing heritability and pathogenesis.

Bioenergetics in fibroblasts of patients with Huntington disease are associated with age at onset.

OBJECTIVE: We aimed to assess whether differences in energy metabolism in fibroblast cell lines derived from patients with Huntington disease were associated with age at onset independent of the cytosine-adenine-guanine (CAG) repeat number in the mutant allele. METHODS: For this study, we selected 9 pairs of patients with Huntington disease matched for mutant CAG repeat size and sex, but with a difference of at least 10 years in age at onset, using the Leiden Huntington disease database. From skin biopsies, we isolated fibroblasts in which we (1) quantified the ATP concentration before and after a hydrogen-peroxide challenge and (2) measured mitochondrial respiration and glycolysis in real time, using the Seahorse XF Extracellular Flux Analyzer XF24. RESULTS: The ATP concentration in fibroblasts was significantly lower in patients with Huntington disease with an earlier age at onset, independent of calendar age and disease duration. Maximal respiration, spare capacity, and respiration dependent on complex II activity, and indices of mitochondrial respiration were significantly lower in patients with Huntington disease with an earlier age at onset, again independent of calendar age and disease duration. CONCLUSIONS: A less efficient bioenergetics profile was found in fibroblast cells from patients with Huntington disease with an earlier age at onset independent of mutant CAG repeat size. Thus, differences in bioenergetics could explain part of the residual variation in age at onset in Huntington disease.

Generation of 3 spinocerebellar ataxia type 1 (SCA1) patient-derived induced pluripotent stem cell lines LUMCi002-A, B, and C and 2 unaffected sibling control induced pluripotent stem cell lines LUMCi003-A and B.

Spinocerebellar ataxia type 1 (SCA1) is a hereditary neurodegenerative disease caused by a CAG repeat expansion in exon 8 of the ATXN1 gene. We generated induced pluripotent stem cells (hiPSCs) from a SCA1 patient and his non-affected sister by using non-integrating Sendai Viruses (SeV). The resulting hiPSCs are SeVfree, express pluripotency markers, display a normal karyotype, retain the mutation (length of the CAG repeat expansion in the ATXN1 gene) and are able to differentiate into the three germ layers in vitro.

Huntingtin gene repeat size variations affect risk of lifetime depression.

Huntington disease (HD) is a severe neuropsychiatric disorder caused by a cytosine-adenine-guanine (CAG) repeat expansion in the HTT gene. Although HD is frequently complicated by depression, it is still unknown to what extent common HTT CAG repeat size variations in the normal range could affect depression risk in the general population. Using binary logistic regression, we assessed the association between HTT CAG repeat size and depression risk in two well-characterized Dutch cohorts─the Netherlands Study of Depression and Anxiety and the Netherlands Study of Depression in Older Persons─including 2165 depressed and 1058 non-depressed persons. In both cohorts, separately as well as combined, there was a significant non-linear association between the risk of lifetime depression and HTT CAG repeat size in which both relatively short and relatively large alleles were associated with an increased risk of depression (ß = -0.292 and ß = 0.006 for the linear and the quadratic term, respectively; both P < 0.01 after adjustment for the effects of sex, age, and education level). The odds of lifetime depression were lowest in persons with a HTT CAG repeat size of 21 (odds ratio: 0.71, 95% confidence interval: 0.52 to 0.98) compared to the average odds in the total cohort. In conclusion, lifetime depression risk was higher with both relatively short and relatively large HTT CAG repeat sizes in the normal range. Our study provides important proof-of-principle that repeat polymorphisms can act as hitherto unappreciated but complex genetic modifiers of depression.

Microsatellite analysis of voided-urine samples for surveillance of low-grade non-muscle-invasive urothelial carcinoma: feasibility and clinical utility in a prospective multicenter study (Cost-Effectiveness of Follow-Up of Urinary Bladder Cancer trial [CEFUB]).

BACKGROUND: Microsatellite analysis (MA) of voided-urine samples has been promoted as an alternative for cystoscopy surveillance (UCS) of patients with low-grade non-muscle-invasive papillary urothelial carcinoma (UC). OBJECTIVE: To assess the feasibility and clinical utility of MA on voided-urine samples in a routine setting to detect or predict bladder cancer recurrences. DESIGN, SETTING, AND PARTICIPANTS: We evaluated 228 patients monitored by MA of voided-urine samples and synchronous UCS who participated in a longitudinal prospective study in 10 hospitals. Follow-up started after diagnosis of a primary or recurrent pTa, pT1, grade 1 or grade 2 papillary UC. MEASUREMENTS: Clinico-pathological parameters and fibroblast growth factor receptor 3 (FGFR3) gene mutation status of the inclusion tumour were determined. MA outcome was analysed in 1012 urine samples during a mean follow-up of 41 mo. Poor DNA quality prevented MA in 19% (197/1012) of the samples, leaving 815 visits for a cross-sectional analysis of sensitivity and specificity. We determined the predictive value (PPV) in a longitudinal analysis for 458 series with persistent MA results. Factors influencing diagnostic quality of MA were investigated. Kaplan-Meier analysis was performed to relate MA results to recurrence. RESULTS AND LIMITATIONS: Cross-sectional sensitivity and specificity of MA for detection of a recurrence were 58% (49/84) and 73% (531/731), respectively. One pT1 grade 3 UC was missed. In a longitudinal analysis, the 2-yr risk to develop a recurrence reached 83% if MA outcome was persistently positive and 22% when MA was persistently negative. PPV of MA was higher with wild-type FGFR3 gene status and smoking habits. All four upper urinary tract tumours detected were preceded by a positive MA test. CONCLUSIONS: Consecutive positive MA results are a strong predictor for future recurrences, but sensitivity needs to be improved, for example, by patient selection and testing of additional genetic markers in urine samples.