CAG Repeat In Exon Research Articles

Prediction of low ovarian reserve using a multifactorial genetic model

To design a predictive model of poor ovarian response based in several polymorphisms of genes previously reported associated with poor ovarian response (POR). (TA repeat in promoter of Estrogen receptor alpha (ERα), CAG repeat in exon 1 of Androgen receptor (AR) and SNP N680S of FSH receptor (FSHR).

Clearance of the mutant androgen receptor in motoneuronal models of spinal and bulbar muscular atrophy

Spinal and bulbar muscular atrophy (SBMA) is an X-linked motoneuron disease caused by an abnormal expansion of a tandem CAG repeat in exon 1 of the androgen receptor (AR) gene that results in an abnormally long polyglutamine tract (polyQ) in the AR protein. As a result, the mutant AR (ARpolyQ) misfolds, forming cytoplasmic and nuclear aggregates in the affected neurons. Neurotoxicity only appears to be associated with the formation of nuclear aggregates. Thus, improved ARpolyQ cytoplasmic clearance, which indirectly decreases ARpolyQ nuclear accumulation, has beneficial effects on affected motoneurons. In addition, increased ARpolyQ clearance contributes to maintenance of motoneuron proteostasis and viability, preventing the blockage of the proteasome and autophagy pathways that might play a role in the neuropathy in SBMA. The expression of heat shock protein B8 (HspB8), a member of the small heat shock protein family, is highly induced in surviving motoneurons of patients affected by motoneuron diseases, where it seems to participate in the stress response aimed at cell protection. We report here that HspB8 facilitates the autophagic removal of misfolded aggregating species of ARpolyQ. In addition, though HspB8 does not influence p62 and LC3 (two key autophagic molecules) expression, it does prevent p62 bodies formation, and restores the normal autophagic flux in these cells. Interestingly, trehalose, a well-known autophagy stimulator, induces HspB8 expression, suggesting that HspB8 might act as one of the molecular mediators of the proautophagic activity of trehalose. Collectively, these data support the hypothesis that treatments aimed at restoring a normal autophagic flux that result in the more efficient clearance of mutant ARpolyQ might produce beneficial effects in SBMA patients.

Androgen receptor gene and sex-specific Alzheimer's disease

Women are at a 2-fold risk of developing late-onset Alzheimer's disease (AD) (onset at 65 years of age or older) compared with men. During perimenopausal years, women undergo hormonal changes that are accompanied by metabolic, cardiovascular, and inflammatory changes. These all together have been suggested as risk factors for late-onset AD. However, not all perimenopausal women develop AD; we hypothesize that certain genetic factors might underlie the increased susceptibility for developing AD in postmenopausal women. We investigated the Androgen Receptor gene (AR) in a clinical cohort of male and female AD patients and normal control subjects by sequencing all coding exons and evaluating the length and distribution of the CAG repeat in exon 1. We could not establish a correlation between the repeat length, sex, and the disease status, nor did we identify possible pathogenic variants. AR is located on the X chromosome; to assess its role in AD, X-inactivation patterns will need to be studied to directly correlate the actual expressed repeat length to a possible sex-specific phenotypic effect.

Androgen Receptor mRNA Measured by Quantitative Real Time PCR is Decreased in the Urethral Mucosa of Patients with Middle Idiopathic Hypospadias

Androgen action is exerted through the androgen receptor. The normal 46,XY genital virilization depends on androgen receptor gene expression, which is tissue specific, and requires normal androgen receptor mRNA levels in androgen sensitive tissues. Hypospadias is a frequent male genital abnormality, potentially related to reduced androgen sensitivity in genital tissues. The aim of this study was to compare, by quantitative real time PCR, the amount of androgen receptor mRNA in cells obtained from the urethral mucosa of patients with middle idiopathic hypospadias with the androgen receptor mRNA levels observed in control phimosis subjects with eutopic urethral opening. Prepubertal individuals were studied, including 41 controls and 17 hypospadias patients with mean (SD) ages of 4.7 (2.1) years and 4.0 (3.0) years, respectively. We observed significantly less androgen receptor mRNA in the urethral mucosa of patients with hypospadias than in the controls (p=0.002). The correlation between the level of androgen receptor mRNA expression and the penile size was almost statistically significant only in hypospadias patients (r=0.47; p=0.053). We also established the number of CAG repeats in exon 1 of the androgen receptor gene by GeneScan analysis. No significant difference was observed in the number of CAG repeats when patients and controls were compared. A negative correlation between the CAG repeats and penile size was detected in patients with hypospadias, but not in controls. Our data suggest that a critical lower level of androgen receptor mRNA expression could be a determining factor in the development of middle hypospadias.

Insulin sensitivity and early-phase insulin secretion in normoglycemic Huntington's disease patients.

Huntington's disease (HD) is an autosomal dominant neurodegenerative disorder caused by an expanded CAG repeat in exon 1 of the HTT gene. There is increasing evidence pointing towards an involvement of the endocrine system in HD. Recent studies, investigating the increased risk of diabetes mellitus and impaired insulin sensitivity and secretion in HD patients, led to contradictory results. To investigate glucose homeostasis in HD. Twenty-eight consecutive patients with HD and 28 healthy controls were matched for age, sex, and BMI. Diagnosis of HD was confirmed genetically. Clinical tools for assessment were the Unified Huntington's Disease Rating Scale (UHDRS) motor section and the Total Function Capacity (TFC). Basal metabolic and endocrine investigations and a 2-hour 75-g oGTT were performed. We used the homeostasis model assessment of insulin resistance (HOMA-IR) as index of insulin sensitivity and the insulinogenic index to assess insulin secretion. HD patients did not differ from the controls with respect to fasting plasma glucose, insulin sensitivity and secretion. CAG expansion size, disease stage and duration, or BMI did not influence HOMA-IR and insulinogenic index. Patients showed lower serum glucose (-19%) and insulin levels (-48%) at 30 min and higher serum insulin levels at 90 (+132%) and 120 min (+380%). Our data do not support an increased risk of diabetes among HD patients although they show glucose regulation abnormalities with a flat glucose curve and delayed insulin peak after oral glucose load.

L02 Insulin sensitivity and early-phase insulin secretion in normoglycemic patients with huntington's disease

BackgroundHuntington's Disease (HD) is an autosomal dominant neurodegenerative disorder caused by an expanded CAG repeat in exon 1 of the HTT gene. Apart from neurological impairment, there is increasing evidence...

New Perspectives on the Neuropathology in Huntington's Disease in the Human Brain and its Relation to Symptom Variation

We review recent investigations regarding the relationship between selective neurodegeneration in the human brain and the variability in symptom profiles in Huntington's disease. Huntington's disease is a genetic neurodegenerative disorder caused by an expanded CAG repeat in exon 1 of the Huntingtin gene on chromosome 4, encoding a protein called huntingtin. The huntingtin protein is expressed ubiquitously in somatic tissue, however, the major pathology affects the brain with profound degeneration in the striatum and the cerebral cortex. Despite the disease being caused by a single gene, there is a major variability in the neuropathology, as well as major heterogeneity in the symptom profiles observed in Huntington's disease patients. The symptoms may vary throughout the disease course and present as varying degrees of movement disorder, cognitive decline, and mood and behavioral changes. To determine whether there is an anatomical basis underlying symptom variation, recent studies on the post-mortem human brain have shown a relationship between the variable degeneration in the forebrain and the variable symptom profile. In this review, we will summarize the progress relating cell loss in the striatum and cerebral cortex to symptom profile in Huntington's disease.

Clinical and genetic analysis of a pedigree of Kennedy disease

To review the clinical and genetic features of a pedigree of Kennedy disease in China. The clinical data of patients from a Kennedy disease family were collected. The numbers of trinucleotide CAG repeats in exon 1 of the androgen receptor gene were determined by DNA sequencing and repeat fragment analysis. In the pedigree, 4 patients were identified as Kennedy disease. Clinical manifested with adult-onset, progressive proximal limb muscle weakness and atrophy, gynecomastia, oligospermia were also presented. The number of trinucleotide CAG repeats in exon 1 of the androgen receptor gene was 51 in the proband. The electrophysiological study showed sensory and motor involvement and their serum triglycerides values were elevated significantly. Androgen receptors gene testing is the most reliable diagnosing method, the patients suspected as Kennedy disease should have a gene testing of androgen receptors.

Gene expression and behaviour in mouse models of HD.

Huntington's disease (HD) is an autosomal dominant neurodegenerative disease, resulting in expansion of the CAG repeat in exon 1 of the HTT gene. The resulting mutant huntingtin protein has been implicated in the disruption of a variety of cellular functions, including transcription. Mouse models of HD have been central to the development of our understanding of gene expression changes in this disease, and are now beginning to elucidate the relationship between gene expression and behaviour. Here, we review current mouse models of HD and their characterisation in terms of gene expression. In addition, we look at how this can inform behaviours observed in mouse models of disease. The relationship between gene expression and behaviour in mouse models of HD is important, as this will further our knowledge of disease progression and its underlying molecular events, highlight new treatment targets, and potentially provide new biomarkers for therapeutic trials.

Predictors of pilosebaceous unit responsiveness to testosterone therapy in patients with hypogonadotrophic hypogonadism

Testosterone replacement therapy is the mainstay of treatment in male patients with isolated hypogonadotrophic hypogonadism (HH) to achieve virilisation. However, responsiveness of pilosebaceous unit (PSU) to testosterone replacement therapy in these patients is quite variable. Androgen action is inversely proportional to the number of CAG repeats in exon 1 of androgen receptor gene; therefore, we hypothesised that CAG repeat length contributes to testosterone responsiveness in patients with HH. The CAG repeat length in 21 well-virilised men (hair score > 30, responders) and 25 poorly virilised men (hair score ≤ 30, non-responders) with HH on optimal testosterone replacement therapy at least for a period of 1 year was analysed. Serum LH, FSH, testosterone and 17 β oestradiol were estimated. Polymerase chain reaction (PCR) amplification of exon 1 of androgen receptor gene was performed from genomic DNA, and these PCR-amplified products were sequenced for the number of CAG repeats. The difference between number of CAG repeats in responders and non-responders was statistically significant (19.19 ± 3.25 and 22.24 ± 2.65, P = 0.001) and showed a strong negative correlation with total body hair score (r = -0.538 and P = 0.0001). In conclusion, these results suggest that the number of CAG repeats influences the responsiveness of PSU to testosterone treatment in patients with HH.

Expression of Humoral Autoimmunity is Related to Androgen Receptor CAG Repeat Length in Men with Systemic Lupus Erythematosus

We sought to explore whether inherited differences in androgen sensitivity conferred by variation in the length of a CAG repeat in exon 1 of the androgen receptor gene could be correlated with differing manifestations of humoral autoimmunity in men with lupus. In a sample of 15 men with lupus, AR CAG repeat length was linearly correlated with levels of antibodies against extractable nuclear antigens and with the number of diagnostic criteria for lupus. Protein microarrays were used to assess levels of 86 different IgG and IgM autoantibodies in the sera of these patients. IgG autoantibodies were more frequently observed in male lupus patients with longer AR CAG repeat length (>23), while IgM autoantibodies were more prevalent in subjects with shorter CAG repeat length (≤23). These data support a potential role for androgen signaling in the modulation of immunoglobulin class switching processes, with consequent impact on the autoimmune phenotype in men with lupus.

Dysregulated brain creatine kinase is associated with hearing impairment in mouse models of Huntington disease

Huntington disease (HD) is a degenerative disorder caused by expanded CAG repeats in exon 1 of the huntingtin gene (HTT). Patients with late-stage HD are known to have abnormal auditory processing, but the peripheral auditory functions of HD patients have yet to be thoroughly assessed. In this study, 19 HD patients (aged 40-59 years) were assessed for hearing impairment using pure-tone audiometry and assessment of auditory brainstem responses (ABRs). PTA thresholds were markedly elevated in HD patients. Consistent with this, elevated ABR thresholds were also detected in two mouse models of HD. Hearing loss thus appears to be an authentic symptom of HD. Immunohistochemical analyses demonstrated the presence of mutant huntingtin that formed intranuclear inclusions in the organ of Corti of HD mice, which might interfere with normal auditory function. Quantitative RT-PCR and Western blot analyses further revealed reduced expression of brain creatine kinase (CKB), a major enzyme responsible for ATP regeneration via the phosphocreatine-creatine kinase (PCr-CK) system, in the cochlea of HD mice. Treatment with creatine supplements ameliorated the hearing impairment of HD mice, suggesting that the impaired PCr-CK system in the cochlea of HD mice may contribute to their hearing impairment. These data also suggest that creatine may be useful for treating the hearing abnormalities of patients with HD.

A03 Protein localisation studies: where is huntingtin hiding?

BackgroundThe underlying mutation of the neurodegenerative disorder Huntington's disease (HD) is an expanded and unstable CAG repeat in exon 1 of the HD gene. This is translated into an expanded...

Study on clinical manifestation, genotype and genetic characteristics of two Kennedy disease pedigrees

To investigate the clinical manifestations, genotypes, and genetic characteristics of two pedigrees with Kennedy disease. The clinical data of the patients from two Kennedy disease families were collected. The numbers of trinucleotide CAG repeats in exon 1 of the androgen receptor gene were determined by DNA sequencing and repeat fragment analysis. Family A was composed of 58 individuals in 4 generations. The proband had onset at 39 years old. There were two Kennedy disease patients in family B which included 61 individuals in 5 generations. The two patients had onset at 39 and 41 years old, respectively. All the three patients displayed limbs and bulbar muscular weakness because of the damage of lower motor neurons. They had androgen insensitivity syndrome in common, and showed mild or moderate increase in serum creatine kinase level. The electromyogram showed wild damage in anterior horn of spinal cord. Muscle biopsy displayed neurogenic muscular atrophy. The numbers of the CAG repeat expansion in the androgen receptor gene of the three patients were 49, 48, and 47, respectively. X-linked recessive mode of inheritance was demonstrated by pedigree analysis in the two families. Kennedy disease usually occurs in mid-adulthood man. The clinical features are the weakness and wasting of limbs and bulbar muscles. Genetic analysis contributes to diagnosis and identification of carriers, and is beneficial to genetic counseling and prenatal diagnosis.

How vital is sleep in Huntington’s disease?

Huntington's disease (HD) is a fatal neurodegenerative disease caused by an abnormal expansion of a CAG repeat in exon 1 of the HD gene on chromosome 4. The disease runs a debilitating and progressive course with an average survival of 15-25 years after disease onset. HD patients classically develop involuntary movements including chorea, as well as progressive cognitive and psychiatric disturbances, although a number of other features have also been reported, including changes in sleep and circadian rhythms; it is this latter area that forms the focus of this review.

Functional Variation in the Androgen-Receptor Gene Is Associated With Visceral Adiposity and Blood Pressure in Male Adolescents

Intra-abdominal accumulation of fat is a hallmark of male body-fat distribution and a major risk factor for hypertension. Sympathoactivation may be one of the mechanisms linking intra-abdominal obesity to hypertension. The aim of the present study was to investigate whether a functional variation in the androgen-receptor gene (AR, a variable number of CAG repeats in exon 1) is associated with intra-abdominal adiposity, sympathetic modulation of vasomotor tone, and blood pressure in adolescent boys but not girls. We studied 223 boys and 259 girls (age 12 to 18 years) from a French-Canadian founder population. Intra-abdominal fat and subcutaneous-abdominal fat were quantified with an MRI. Blood pressure was recorded beat-to-beat during an hour-long protocol including physical and mental challenges, and these blood pressure time series were used to assess sympathetic modulation of vasomotor tone by power spectral analysis. The results showed that boys with a "low" versus "intermediate" or "high" CAG-repeat number in AR demonstrated higher intra-abdominal fat (by 28% and 48%, respectively) but not subcutaneous-abdominal fat. These intra-abdominal fat differences remained significant after adjusting for serum levels of sex hormones and subcutaneous-abdominal fat. Furthermore, boys with low versus intermediate or high CAG-repeat numbers also showed higher blood pressure, with the differences being most pronounced during mental stress (8.0 and 8.5 mm Hg, respectively) and higher sympathetic modulation of vasomotor tone. As expected, no such differences were seen among girls. In adolescent boys, low CAG-repeat numbers in AR may be a genetic risk factor for intra-abdominal obesity and hypertension; sympathoactivation may be an underlying link between the 2 conditions.

CAG polymorphism of the androgen receptor gene in azoospermic and oligozoospermic men from Ukraine

An analysis of the number of CAG repeats in exon 1 of the gene was conducted in a group of 228 infertile males with azoospermia (n = 68) and oligozoospermia (n = 160), and in a control group (124 proven fathers) by means of polymerase chain reaction with subsequent fragment analysis on an ALF-Express automated fluorescent analyzer. Allele frequency with the number of CAG repeats ≤ 18 was found to be significantly higher (P < 0.01) in the group of patients with azoospermia (17.7%) as compared to the control group (2.4%), and in the group of patients with oligozoospermia (12.5%) as compared to the control group (2.4%). Allele frequency with the number of CAG repeats ≥ 28 was shown to be significantly higher (P < 0.01) in patients with oligozoospermia (12.5%) as compared to the control group (2.4%). Our data suggest an association between the number of CAG repeats and impaired spermatogenesis in azoospermic and oligozoospermic males.

Huntington's disease: Silencing a brutal killer

Huntington’s disease (HD) is a progressive and invariably fatal autosomal dominant neurodegenerative disorder caused by expansion of the CAG repeat in exon 1 of the Huntingtin gene. CAG repeat expansion generates an extended, toxic polyglutamine tract in the mutant Huntingtin protein (The Huntington’s Disease Collaborative Research Group, 1993), which disrupts a stunningly large number of cellular pathways. Mutant Huntingtin is especially damaging to the medium spiny neurons of the striatum (Graveland et al., 1985), and degeneration in this region is thought to underlie the motor disturbances or —chorea that characterize the disease. In parallel, loss of striatal and cortical neurons disrupts patient cognition and alters mood and personality (Heinsen et al., 1994). The age of onset of HD varies with CAG repeat length (Brinkman et al., 1997; Duyao et al., 1993) 36 or more repeats is considered pathological, but some patients with 36 to 39 repeats remain asymptomatic well into old age. The vast majority of patients are heterozygous for the HD mutation; most have 39 to 50 repeats and develop symptoms between age 30 and 50. No current treatment can prevent or delay the progression of HD.

A stable G‐quartet binds to a huntingtin protein fragment containing expanded polyglutamine tracks

Huntington's disease (HD) is a progressive neurodegenerative disorder that is inherited in an autosomal dominant fashion. The disease is the result of an expanded CAG repeat in exon 1 of the HD gene, which encodes an elongated polyglutamine tract in the mutant form of the protein, huntingtin. Disease pathogenesis is linked to intracellular aggregates that form because of the tendency of the mutant protein to misfold. The role of huntingtin aggregates in disease pathology is unclear; it has been proposed that the aggregates themselves are toxic because of their ability to sequester intracellular proteins and disrupt normal cellular function. In addition, the mechanistic steps that lead to aggregate formation appear to be central to HD pathology. We have previously reported that guanosine-rich oligonucleotides with the ability to fold into a G-quartet are effective inhibitors of the aggregation process of a huntingtin protein fragment with an elongated polyglutamine tract, Htn 1-171(Q58). The most active molecule is composed of 20 guanosine residues, which adopt a G-wire conformation. Here we establish that G20 inhibits protein aggregation as judged by native gel electrophoresis, an agarose gel electrophoresis for resolving aggregates (AGERA) assay, and an immunoblotting assay. We also visualize the G20-Htn1-171(Q58) protein complex by using a streptavidin-biotin pull-down assay as well as atomic force microscopy (AFM). The G20 molecule also interacts with Htn1-171(Q23), a fusion protein that contains 23 glutamine residues instead of 58 (Q58), but in a more degenerate and nonspecific fashion. Taken together, our data support the notion that G20 exhibits some selectivity in binding to specific protein species that assemble along the aggregation pathway.

Longer CAG repeat length in the androgen receptor gene is associated with premature ovarian failure

Premature ovarian failure (POF) is a disorder characterized by lack of ovulation and elevated serum gonadotrophin levels before the age of 40 years. The cause of POF in most cases is unknown. As mice lacking the Androgen receptor (Ar) gene reportedly have a POF-like phenotype, we hypothesize that, variations in the AR gene maybe one of the causative factors for POF in humans. Thus the objective of the study is to evaluate the number of CAG repeats in exon 1 of the AR gene in non-familial, non-syndromic cases of POF. A clinic-based case-control study. Seventy-eight patients with non-familial, non-syndromic POF, and 90 controls were recruited to investigate the CAG repeat numbers in exon 1 of the AR gene by PCR and Gene Scan analysis. The mean CAG repeat length in exon 1 of the AR gene of women with POF was 23.6 +/- 3.8, which was significantly higher than controls (20.08 +/- 3.45) (P < 0.001). The biallelic mean CAG repeat ranged from 11 to 32 in the control women, compared to 16 to 30 in the POF patients. The 22 CAG repeat allele followed by the 24 CAG repeat allele was found to be at highest frequency (15.38 and 12.8%) in POF cases, although the 19 CAG repeat allele was observed at highest frequency (12.2%) in controls. The observation suggests that the CAG repeat length is increased in women with POF as compared with controls, and may be pathogenic for POF, at least in a subset of Indian women.