Peek-a-boo fragile site at 16d associated with Tourette syndrome, bipolar disorder, autistic disorder, and mental retardation

Progress in Genetic Studies of Tourette's Syndrome

Tourette's Syndrome (TS) is a complex disorder characterized by repetitive, sudden, and involuntary movements or vocalizations, called tics. Tics usually appear in childhood, and their severity varies over time. In addition to frequent tics, people with TS are at risk for associated problems including attention deficit hyperactivity disorder (ADHD), obsessive-compulsive disorder (OCD), anxiety, depression, and problems with sleep. TS occurs in most populations and ethnic groups worldwide, and it is more common in males than in females. Previous family and twin studies have shown that the majority of cases of TS are inherited. TS was previously thought to have an autosomal dominant pattern of inheritance. However, several decades of research have shown that this is unlikely the case. Instead TS most likely results from a variety of genetic and environmental factors, not changes in a single gene. In the past decade, there has been a rapid development of innovative genetic technologies and methodologies, as well as significant progresses in genetic studies of psychiatric disorders. In this review, we will briefly summarize previous genetic epidemiological studies of TS and related disorders. We will also review previous genetic studies based on genome-wide linkage analyses and candidate gene association studies to comment on problems of previous methodological and strategic issues. Our main purpose for this review will be to summarize the new genetic discoveries of TS based on novel genetic methods and strategies, such as genome-wide association studies (GWASs), whole exome sequencing (WES) and whole genome sequencing (WGS). We will also compare the new genetic discoveries of TS with other major psychiatric disorders in order to understand the current status of TS genetics and its relationship with other psychiatric disorders.

Fragility Extraordinaire: Unsolved Mysteries of Chromosome Fragile Sites

Chromosome fragile sites are a fascinating cytogenetic phenomenon now widely implicated in a slew of human diseases ranging from neurological disorders to cancer. Yet, the paths leading to these revelations were far from direct, and the number of fragile sites that have been molecularly cloned with known disease-associated genes remains modest. Moreover, as more fragile sites were being discovered, research interests in some of the earliest discovered fragile sites ebbed away, leaving a number of unsolved mysteries in chromosome biology. In this review we attempt to recount some of the early discoveries of fragile sites and highlight those phenomena that have eluded intense scrutiny but remain extremely relevant in our understanding of the mechanisms of chromosome fragility. We then survey the literature for disease association for a comprehensive list of fragile sites. We also review recent studies addressing the underlying cause of chromosome fragility while highlighting some ongoing debates. We report an observed enrichment for R-loop forming sequences in fragile site-associated genes than genomic average. Finally, we will leave the reader with some lingering questions to provoke discussion and inspire further scientific inquiries.

Tourette syndrome and bipolar disorder: unique problems with pediatric comorbidity

Tourette syndrome and bipolar disorder are frequent comorbidities in pediatric age group. They provide a clinician with certain unique challenges. While on one hand the tics mask manifestation of affective symptomatology, the latter makes it difficult to elicit tics with certainty. Data suggest that they might share genetic and neurobiological basis and this is currently an area of extensive research. These clinical and biological overlaps provide grey areas in our understanding, which not only complicates the diagnosis, but also poses problems with management.

Adolescent with tourette syndrome and bipolar disorder: a case report

Tourette syndrome consists of multiple motor tics and one or more vocal tics. Psychopathology occurs in approximately 90% of Tourette syndrome patients, with attention-deficit/hyperactivity, mood, and obsessive-compulsive disorders being common. Additionally, Tourette syndrome and bipolar disorder may be related in some individuals. However, it is unclear why bipolar disorder may be overrepresented in Tourette syndrome patients, and more research is needed. Herein, we report the case of a 15-year-old boy diagnosed with both Tourette syndrome and bipolar disorder, whose symptoms improved with aripiprazole, atomoxetine, and valproate. The patient was diagnosed with Tourette syndrome at 8 years of age when he developed tics and experienced his first depressive episode. The patient had a poor response to a variety of antidepressants and anti-tic medications. A combination of valproate and aripiprazole stabilized both the patient's tics and mood symptoms. It is important to assess individuals with Tourette syndrome for other disorders, including bipolar disorder. The treatment of children and adolescents with both Tourette syndrome and bipolar disorder is an important clinical issue.

Analysis of the MRPL3, DNAJC13 and OFCC1 variants in Chinese Han patients with TS-CTD

Tourette syndrome/chronic tic phenotype (TS-CTD) is a neurological disorder manifested particularly by motor and vocal tics and associated with a variety of behavioral abnormalities. Recently, the mitochondrial ribosomal protein L3 gene (MRPL3) S75N, the DnaJ (Hsp40) homolog subfamily C member 13 gene (DNAJC13) A2057S, the orofacial cleft 1 candidate 1 gene (OFCC1) R129G and c.-5A>G variants are reported to be associated with Tourette syndrome/chronic tic phenotype (TS-CTD) in patients of European ancestry. To evaluate whether these variants are associated with TS-CTD in Chinese Han patients, we screened 132 Chinese Han patients from Mainland China. None of the 132 samples from patients with TS-CTD showed the MRPL3 S75N, DNAJC13 A2057S, OFCC1 R129G and c.-5A>G variants, and these variants probably are a rare cause of TS-CTD in a Chinese Han ethnic group. Genetic heterogeneity of TS should be considered and tests designed to detect these variants in Chinese Han ethnic group probably will not have a diagnostic utility in clinical practice.

Diagnosis and treatment of comorbidities of Tourette's syndrome and bipolar disorder in a 10-year-old boy

Changes in moods are one of the comorbid psychiatric manifestations that frequently occur in patients with Tourette's syndrome. The assessment of a manic episode in children with Tourette's syndrome is challenging. Furthermore, the treatment of children with comorbid mania and Tourette's syndrome has not been extensively studied. We present a 10-year-old boy who suffered from both Tourette's syndrome and mania, whose symptoms improved after using lithium and risperidone. The child was diagnosed with Tourette's syndrome at 7 years of age when he suffered from tics and experienced his first manic episode. He received monotherapy, including haloperidol, risperidone and aripiprazole, and the response was poor. When the combination of lithium and risperidone was used, the tics and mania subsided. It is important to assess individuals with Tourette's syndrome for associated bipolar disorder. The treatment of children with both disorders is a major clinical issue, and our case may serve as an example for successful treatment strategies.

Tourette syndrome and comorbid pervasive developmental disorders

We examined the rates of comorbid pervasive developmental disorders in participants with Tourette syndrome. We used 7288 participants from the Tourette Syndrome International Database Consortium Registry. We found 334 (4.6%; 1 of every 22 participants) with Tourette syndrome had a comorbid pervasive developmental disorder. In participants with Tourette syndrome and comorbid pervasive developmental disorders, 98.8% had one or more comorbidities (pervasive developmental disorder was not counted) compared to 13.2% in the group of participants with Tourette syndrome only. Variables from logistic modeling that were significant predictors of Tourette syndrome and pervasive developmental disorders were: male gender; no family history of tics/Tourette syndrome; and an increased number of comorbidities (P < .001). We found rates of comorbid Tourette syndrome and pervasive developmental disorders to be increased by 13 times. Identification of differences between subgroups of patients with Tourette syndrome may increase understanding of syndromal susceptibility, severity, and outcome.

Candidate locus for chorea and tic disorders at 15q?

Cases of chromosomal aberrations are known to be associated with specific phenotypic abnormalities, including tics and chorea. We report the case of a 10-year-old caucasian boy with tics, chorea, and a de novo chromosome 15 paracentric inversion, 46,XY,inv(15) (q13;q22.3) identified with G-banding chromosome analysis (trypsin-Giemsa staining). Subsequent fluorescence in situ hybridization with locus-specific small nuclear ribonucleoprotein polypeptide N gene probe confirmed that the breakpoints of the inversion were distal to 15q12. Mutation analysis showed no mutation or polymorphism in the thyroid transcription factor 1 gene (TITF1). The results suggest that 15q is a region to explore for candidate genes of etiologic importance in the development of tics and chorea.

Mood disorders and Gilles de la Tourette's syndrome: An update on prevalence, etiology, comorbidity, clinical associations, and implications

Gilles de la Tourette's syndrome (GTS) consists of multiple motor tics and one or more phonic tics. Psychopathology occurs in approximately 90% of GTS patients, with attention-deficit/hyperactivity disorder (ADHD) and obsessive-compulsive disorder (OCD) being common. Depression is common, with a lifetime risk of 10% and a prevalence of between 1.8% and 8.9%. Depression and depressive symptoms are found to occur in 13% and 76% of GTS patients attending specialist clinics, respectively. In controlled studies embracing over 700 GTS patients, the patients were significantly more depressed than controls in all but one instance. In community and epidemiological studies, depression in GTS individuals was evident in two of five investigations. Clinical correlates of depression in people with GTS appear to be: tic severity and duration, the presence of echophenomena and coprophenomena, premonitory sensations, sleep disturbances, obsessive-compulsive behaviors/OCD, self-injurious behaviors, aggression, conduct disorder (CD) in childhood, and, possibly, ADHD. Depression in people with GTS has been shown to result in a lower quality of life, potentially leading to hospitalization and suicide. The etiology of depression appears to be multifactorial. Bipolar affective disorder (BAD) and GTS may be related in some individuals. However, it is noted that sample sizes in most of these studies were small, and it is unclear at the present time as to why BAD may be overrepresented among GTS patients.

Chromosomal fragility, structural rearrangements and mobile element activity may reflect dynamic epigenetic mechanisms of importance in neurobehavioural genetics

Advances in human genome analyses have not yet allowed identification of specific genetic mechanisms underlying the expression of human neurobehavioural disorders. There is an increasing awareness that several genes may contribute to behavioural phenotypes and these genes appear to interact in as yet undetermined ways. It has been suggested that the problem needs elucidation from an epigenetic, gene expression perspective. Cytogenetic instability manifesting as chromosomal fragile sites, translocations, duplications, deletions and inversions, when co-occurring with neurobehavioural disorders, may offer a doorway to the investigation of such chromatin level, regulatory region, epigenetic processes. Due to earlier indications of non-specificity of chromosomal aberrations, poor phenotype:genotype correlations and a shift to analysing candidate coding regions on high resolution map level, the only utility of chromosomal breakpoints came to be seen as harbouring possible candidate genes of interest when segregating together with particular neurobehavioural disorders. More recent findings of the expression of highly specific subsets of fragile sites in association with Tourette and Rett syndromes need to be extended to other neurobehavioural disorders to ascertain whether observed patterns can be considered representative of 'chromatin endophenotypes' correlating with discrete sets of neurobehavioural symptoms. Environmental/epigenetic factors could affect the chromatin characteristics of the genome arising through DNA strand breakage, mobile element activity and retroinsertion, establishing new architectural features of regulatory control networks very rapidly in comparison to coding region evolution rates. Microarray-based techniques for the genome-wide mapping of in vivo protein-DNA interactions offer increasingly comprehensive views of genetic and epigenetic regulatory networks. It may be informative to include functionally significant chromatin structural variation analyses when considering candidate genes for neurobehavioural disorders.

[Alpha-thalassemias and bipolar disorders: a genetic link?]

After a previous paper discussing the possible association between beta-thalassemias and bipolar disorder, this article considers a possible association between alpha-thalassemia and the bipolar disorder. We report the case of a 36 year old woman with bipolar disorder and alpha-thalassemia. The patient, native of Reunion Island, has a family history of bipolar disorder (both parents, one brother, and a paternal uncle). The severity of the bipolar disorder type I in her family, is illustrated by the suicides of both parents, one brother and the paternal uncle, in intervals of only a few years. After a Medline review (1980-2004) we found only two studies suggesting a possible relationship between bipolar disorders and alpha-thalassemias, but without clinical case report information. Some genetic studies described the existence of possible genetic susceptibility for bipolar disorder on the short arm of chromosome 16, close to the gene involved in certain alpha-thalassemias, on the region 16p13.3. An interesting finding is that the sequencing of 258 kb of the chromosome region 16p13.3 not only allowed the identification of genes involved in the alpha-thalassemia and in the vulnerability to bipolar disorders, but also the identification of genes implicated in tuberous sclerosis, in polycystic kidney disease, in cataract with microophtalmia, and in vulnerability genetic factors for ATR-16 syndrome, asthma, epilepsy, certain forms of autism and mental retardation. Numerous clinical descriptions and some familial studies on linkage suggested a possible relationship between tuberous sclerosis, polycystic kidney disease, cataract with microophtalmia, ATR-16 syndrome, asthma, epilepsy, certain forms of autism, mental retardation and bipolar disorder, given the closeness of these vulnerability genes on the short arm of the chromosome 16. A vulnerability gene of alcohol dependence was also identified on this same chromosome region (16p13.3), by a study concerning 105 families. Taking into account the methodological difficulties due to the clinical and genetic heterogeneity of bipolar disorder, we suggest that linkage techniques should be used to confirm the presence of susceptibility genetic factor for bipolar disorders on chromosome 16. Thus a known genetic disease (alpha-thalassemia) could contribute to confirming the presence on the short arm of chromosome 16 of a susceptibility genetic factor for bipolar disorders. Linkage studies should be performed in families with a strong association for both diseases. Thanks to linkage techniques, one could hope for an improvement in understanding the physiopathology of bipolar disorder, with possible implications at a therapeutic level.

Clinical significance of tics and attention-deficit hyperactivity disorder (ADHD) in children with pervasive developmental disorder

The goal of this study was to examine the clinical significance of co-occurring tics and attention-deficit hyperactivity disorder (ADHD) as indicators of a more complex symptomatology in children with and without pervasive developmental disorder. Parents and teachers completed a Diagnostic and Statistical Manual of Mental Disorders-IV-referenced rating scale for 3- to 5- (n = 182/135) and 6- to 12- (n = 301/191) year-old children with pervasive developmental disorder and clinic controls, respectively. The percentage of children with tic behaviors varied with age: preschoolers (25%, 44%) versus elementary schoolchildren (60%, 66%) (parent and teacher ratings, respectively). For many psychiatric symptoms, screening prevalence rates were highest for the ADHD + tics group and lowest for the group with symptoms of neither, but the pattern of group differences varied by age group and informant. In general, there were few differences between the ADHD only and tics only groups. The pattern of ADHD/tic group differences was similar for both children with and without pervasive developmental disorder. We concluded that these findings support the notion that the co-occurrence of ADHD and tics is an indicator of a more complex psychiatric symptomatology in children with pervasive developmental disorder.

Association between 7q31 markers and Tourette syndrome

Tourette syndrome (TS) is a complex neuropychiatric disorder with a strong genetic basis. Although no specific susceptibility genes have been identified for TS, cytogenetic studies in selected cases suggest the existence of a predisposing gene located in the 7q31 chromosomal region. In order to test the hypothesis of a possible relationship between this region and TS at the population level, we undertook a family based association study in a sample of French Canadian patients from Quebec. For this purpose, markers D7S522, D7S523, and D7S1516 were tested using the extended transmission disequilibrium test (e-TDT). Marker D7S522 showed a biased transmission of alleles from heterozygote parents to their TS offsprings (allele-wise TDT chi(2) = 12.61, 4 df, P = 0.013, genotype-wise TDT chi(2) = 15.49, 7 df, P = 0.030). When the analysis was restricted to patients without ADHD or OCD comorbidity, similar results were observed both allele and genotype-wise (chi(2) = 10.68, 4 df, P = 0.03 and chi(2) = 12.55, 5 df, P = 0.028, respectively). In addition, marker D7S523 was also associated (allele-wise TDT chi(2) = 18.37, 7 df, P = 0.01 and genotype-wise TDT chi(2) = 46.26, 17 df, P = 0.00016), and showed a tendency for association in the comorbidity-free subgroup (genotype-wise TDT chi(2) = 18.7, 10 df, P = 0.044). Finally, marker D7S1516, contained in the inner mitochondrial membrane peptidase 2 like (IMMP2L) gene, also showed a tendency for association (genotype-wise TDT chi(2) = 32.87, 21 df, P = 0.048). These results may reflect the proximity of markers D7S522, D7S523, and possibly D7S1516 to a gene or regulatory region relevant to TS predisposition.

Chromosomal abnormalities and mental illness

Linkage studies of mental illness have provided suggestive evidence of susceptibility loci over many broad chromosomal regions. Pinpointing causative gene mutations by conventional linkage strategies alone is problematic. The breakpoints of chromosomal abnormalities occurring in patients with mental illness may be more direct pointers to the relevant gene locus. Publications that describe patients where chromosomal abnormalities co-exist with mental illness are reviewed along with supporting evidence that this may amount to an association. Chromosomal abnormalities are considered to be of possible significance if (a) the abnormality is rare and there are independent reports of its coexistence with psychiatric illness, or (b) there is colocalisation of the abnormality with a region of suggestive linkage findings, or (c) there is an apparent cosegregation of the abnormality with psychiatric illness within the individual's family. Breakpoints have been described within many of the loci suggested by linkage studies and these findings support the hypothesis that shared susceptibility factors for schizophrenia and bipolar disorder may exist. If these abnormalities directly disrupt coding regions, then combining molecular genetic breakpoint cloning with bioinformatic sequence analysis may be a method of rapidly identifying candidate genes. Full karyotyping of individuals with psychotic illness especially where this coexists with mild learning disability, dysmorphism or a strong family history of mental disorder is encouraged.

Tourette syndrome: clinical characteristics and current management strategies

Tourette Syndrome (TS) is a disorder comprised of involuntary motor and phonic tics often associated with psychiatric conditions. The etiology for TS is unclear, with both genetic and immunological theories being studied to date. When pharmacotherapy is considered by the patient and physician to be required, owing to either functional impairment from tics or comorbid psychiatric illness, dopamine receptor antagonists are commonly used. Our first-line agents for tic suppression include clonidine, guanfacine, clonazepam and baclofen. Should these agents be ineffective, we would recommend pimozide, fluphenazine, risperidone or haloperidol. The potential benefit of other agents, such as olanzapine, ziprasidone, pergolide and botulinum toxin, is encouraging. Despite many years of concern, we have found little exacerbation of tics with stimulant medications for attention deficit hyperactivity disorder, but clearly clonidine and guanfacine can ameliorate both comorbid conditions. Obsessive compulsive disorder, when associated with TS, may be treated with either a selective serotonin reuptake inhibitor in association with a dopamine receptor antagonist or risperidone alone. New therapies for all aspects of TS and its comorbid conditions are in active clinical trials.