Cosegregation of schizophrenia with Becker muscular dystrophy: susceptibility locus for schizophrenia at Xp21 or an effect of the dystrophin gene in the brain?

Cognitive profile and neuropsychiatric disorders in Becker muscular dystrophy: A systematic review of literature

BACKGROUND

Brain co-morbidities in DMD are well-documented, less is known about the cognitive, behavioral and psychosocial functioning of patients with BMD.

METHODS

The systematic review was carried out on two databases (Pubmed and Scopus) according to the PRISMA guidelines. We included all research articles specific to BMD written after 1995.

RESULTS

Studies examining neuropsychological and neurobehavioral functioning in BMD are few and have several methods limitations. BMD population is characterized by high rates of cognitive impairment, with specific involvement of different cognitive areas. Unlike DMD, verbal skills are better preserved. Neurodevelopmental and emotional/behavioral disorders have great importance in BMD, due to their high prevalence. Lack of Dp140 or Dp71 can cause intellectual disability, these isoforms are probably responsible for the other brain-related comorbidities as well.

DISCUSSION

The results suggest that cognitive and neuropsychiatric comorbid symptoms may affect a significant proportion of BMD patients therefore it is important to mental health and neuropsychological screening. Finding tools for an adequate assessment is a priority in order to include brain outcome measures in clinical trials.

Synaptic alterations as a neurodevelopmental trait of Duchenne muscular dystrophy

Dystrophinopaties, e.g., Duchenne muscular dystrophy (DMD), Becker muscular dystrophy and X-linked dilated cardiomyopathy are inherited neuromuscular diseases, characterized by progressive muscular degeneration, which however associate with a significant impact on general system physiology. The more severe is the pathology and its diversified manifestations, the heavier are its effects on organs, systems, and tissues other than muscles (skeletal, cardiac and smooth muscles). All dystrophinopaties are characterized by mutations in a single gene located on the X chromosome encoding dystrophin (Dp427) and its shorter isoforms, but DMD is the most devasting: muscular degenerations manifests within the first 4 years of life, progressively affecting motility and other muscular functions, and leads to a fatal outcome between the 20s and 40s. To date, after years of studies on both DMD patients and animal models of the disease, it has been clearly demonstrated that a significant percentage of DMD patients are also afflicted by cognitive, neurological, and autonomic disorders, of varying degree of severity. The anatomical correlates underlying neural functional damages are established during embryonic development and the early stages of postnatal life, when brain circuits, sensory and motor connections are still maturing. The impact of the absence of Dp427 on the development, differentiation, and consolidation of specific cerebral circuits (hippocampus, cerebellum, prefrontal cortex, amygdala) is significant, and amplified by the frequent lack of one or more of its lower molecular mass isoforms. The most relevant aspect, which characterizes DMD-associated neurological disorders, is based on morpho-functional alterations of selective synaptic connections within the affected brain areas. This pathological feature correlates neurological conditions of DMD to other severe neurological disorders, such as schizophrenia, epilepsy and autistic spectrum disorders, among others. This review discusses the organization and the role of the dystrophin-dystroglycan complex in muscles and neurons, focusing on the neurological aspect of DMD and on the most relevant morphological and functional synaptic alterations, in both central and autonomic nervous systems, described in the pathology and its animal models.

Abnormalities in the copper transporter CTR1 in postmortem hippocampus in schizophrenia: A subregion and laminar analysis

Dysbindin-1 modulates copper transport, which is crucial for cellular homeostasis. Several brain regions implicated in schizophrenia exhibit decreased levels of dysbindin-1, which may affect copper homeostasis therein. Our recent study showed decreased levels of dysbindin-1, the copper transporter-1 (CTR1) and copper in the substantia nigra in schizophrenia, providing the first evidence of disrupted copper transport in schizophrenia. In the present study, we hypothesized that there would be lower levels of dysbindin-1 and CTR1 in the hippocampus in schizophrenia versus a comparison group. Using semi-quantitative immunohistochemistry for dysbindin1 and CTR1, we measured the optical density in a layer specific fashion in the hippocampus and entorhinal cortex in ten subjects with schizophrenia and ten comparison subjects. Both regions were richly immunolabeled for CTR1 and dysbindin1 in both groups. In the superficial layers of the entorhinal cortex, CTR1 immunolabeled neuropil and cells showed lower optical density values in patients versus the comparison group. In the molecular layer of the dentate gyrus, patients had higher optical density values of CTR1 versus the comparison group. The density and distribution of dysbindin-1 immunolabeling was similar between groups. These laminar specific alterations of CTR1 in schizophrenia suggest abnormal copper transport in those locations.

Impaired copper transport in schizophrenia results in a copper-deficient brain state: A new side to the dysbindin story

Objectives: Several schizophrenia brain regions exhibit decreased dysbindin. Dysbindin modulates copper transport crucial for myelination, monoamine metabolism and cellular homeostasis. Schizophrenia patients (SZP) exhibit increased plasma copper, while copper-decreasing agents produce schizophrenia-like behavioural and pathological abnormalities. Therefore, we sought to determine dysbindin and copper transporter protein expression and copper content in SZP.Methods: We studied the copper-rich substantia nigra (SN) using Western blot and inductively-coupled plasma mass spectrometry. We characterised specific protein domains of copper transporters ATP7A, CTR1, ATP7B and dysbindin isoforms 1 A and 1B/C in SZP (n = 15) and matched controls (n = 11), and SN copper content in SZP (n = 14) and matched controls (n = 11). As a preliminary investigation, we compared medicated (ON; n = 11) versus unmedicated SZP (OFF; n = 4).Results: SZP exhibited increased C terminus, but not N terminus, ATP7A. SZP expressed less transmembrane CTR1 and dysbindin 1B/C than controls. ON exhibited increased C terminus ATP7A protein versus controls. OFF exhibited less N terminus ATP7A protein than controls and ON, suggesting medication-induced rescue of the ATP7A N terminus. SZP exhibited less SN copper content than controls.Conclusions: These results provide the first evidence of disrupted copper transport in schizophrenia SN that appears to result in a copper-deficient state. Furthermore, copper homeostasis may be modulated by specific dysbindin isoforms and antipsychotic treatment.

Variations in Dysbindin-1 are associated with cognitive response to antipsychotic drug treatment

Antipsychotics are the most widely used medications for the treatment of schizophrenia spectrum disorders. While such drugs generally ameliorate positive symptoms, clinical responses are highly variable in terms of negative symptoms and cognitive impairments. However, predictors of individual responses have been elusive. Here, we report a pharmacogenetic interaction related to a core cognitive dysfunction in patients with schizophrenia. We show that genetic variations reducing dysbindin-1 expression can identify individuals whose executive functions respond better to antipsychotic drugs, both in humans and in mice. Multilevel ex vivo and in vivo analyses in postmortem human brains and genetically modified mice demonstrate that such interaction between antipsychotics and dysbindin-1 is mediated by an imbalance between the short and long isoforms of dopamine D2 receptors, leading to enhanced presynaptic D2 function within the prefrontal cortex. These findings reveal one of the pharmacodynamic mechanisms underlying individual cognitive response to treatment in patients with schizophrenia, suggesting a potential approach for improving the use of antipsychotic drugs.

Contribution of copy number variants to schizophrenia from a genome-wide study of 41,321 subjects

Copy number variants (CNVs) have been strongly implicated in the genetic etiology of schizophrenia (SCZ). However, genome-wide investigation of the contribution of CNV to risk has been hampered by limited sample sizes. We sought to address this obstacle by applying a centralized analysis pipeline to a SCZ cohort of 21,094 cases and 20,227 controls. A global enrichment of CNV burden was observed in cases (odds ratio (OR) = 1.11, P = 5.7 × 10-15), which persisted after excluding loci implicated in previous studies (OR = 1.07, P = 1.7 × 10-6). CNV burden was enriched for genes associated with synaptic function (OR = 1.68, P = 2.8 × 10-11) and neurobehavioral phenotypes in mouse (OR = 1.18, P = 7.3 × 10-5). Genome-wide significant evidence was obtained for eight loci, including 1q21.1, 2p16.3 (NRXN1), 3q29, 7q11.2, 15q13.3, distal 16p11.2, proximal 16p11.2 and 22q11.2. Suggestive support was found for eight additional candidate susceptibility and protective loci, which consisted predominantly of CNVs mediated by nonallelic homologous recombination.

Mosaic Turner syndrome associated with schizophrenia

Turner syndrome is a sex-chromosome disorder; occurring in 1 in 2,500 female births. There are sporadic few case reports of concomitant Turner syndrome with schizophrenia worldwide. Most Turner females had a 45,X monosomy, whereas the majority of comorbidity between Turner syndrome and schizophrenia had a mosaic karyotype (45,X/46,XX). We present a case of a 21-year-old woman with Turner syndrome, mosaic karyotype (45,X/46,XX), showing mental retardation, hypothyroidism, and schizophrenia. HOPA gene within Xq13 is related to mental retardation, hypothyroidism, and schizophrenia. Our case may be a potential clue which supports the hypothesis for involvement of genes on X chromosome in development of schizophrenia. Further studies including comorbid cases reports are need in order to discern the cause of schizophrenia in patients having Turner syndrome.

Genetic variation in the 6p22.3 gene DTNBP1, the human ortholog of the mouse dysbindin gene, is associated with schizophrenia

Prior evidence has supported the existence of multiple susceptibility genes for schizophrenia. Multipoint linkage analysis of the 270 Irish high-density pedigrees that we have studied, as well as results from several other samples, suggest that at least one such gene is located in region 6p24-21. In the present study, family-based association analysis of 36 simple sequence-length-polymorphism markers and of 17 SNP markers implicated two regions, separated by approximately 7 Mb. The first region, and the focus of this report, is 6p22.3. In this region, single-nucleotide polymorphisms within the 140-kb gene DTNBP1 (dystrobrevin-binding protein 1, or dysbindin) are strongly associated with schizophrenia. Uncorrected, empirical P values produced by the program TRANSMIT were significant (P<.01) for a number of individual SNP markers, and most remained significant when the data were restricted to include only one affected offspring per nuclear family per extended pedigree; multiple three-marker haplotypes were highly significant (P=.008-.0001) under the restricted conditions. The pattern of linkage disequilibrium is consistent with the presence of more than one susceptibility allele, but this important issue is unresolved. The number of markers tested in the adjacent genes, all of which are negative, is not sufficient to rule out the possibility that the dysbindin gene is not the actual susceptibility gene, but this possibility appears to be very unlikely. We conclude that further investigation of dysbindin is warranted.

Investigation of Turner syndrome in schizophrenia

Both Turner syndrome and schizophrenia are relatively infrequent conditions. Consequently, individuals having both illnesses are rare. Previous reviews of sex chromosome abnormalities in schizophrenia have focused primarily on the presence of supernumerary X-chromosomes. After identifying two female patients with schizophrenia and Turner syndrome, we reevaluated the available literature that survey female schizophrenics for the presence of chromosomal abnormalities. Eleven patients with Turner syndrome were identified among 6,483 females with schizophrenia in non-case-report studies. These survey results indicate that Turner syndrome occurs approximately three-fold more frequently in schizophrenic females than in the general female population (P < 0.02). Including 6 other case reports and our 2 cases, a total of 19 females with both schizophrenia and Turner syndrome were reported. Interestingly, whereas most Turner syndrome patients have the 45,X karyotype, the majority (18/19) of women with both illnesses have a mosaic karyotype (P < 0.0002). Given the potential role of genes on the X-chromosome in the pathogenesis of schizophrenia, the study of unique populations with abnormalities in this chromosome, such as women with Turner syndrome, may offer clues into this illness.

Chromosomal fragility may be indicative of altered higher-order DNA organization as the underlying genetic diathesis in complex neurobehavioral disorders

Preliminary observations concerning increased chromosomal fragility in association with behavioural disorders in humans allow an opportunity to suggest a cohesive theory regarding the possible importance of higher-order DNA modifications in the coordination of gene function in brain evolution and during development. Visible or submicroscopic acentric chromosomal fragments are formed as an accompaniment to chromosomal breakage and are associated with sequence amplification. During genomic reintegration of extrachromosomally amplified repeat sequence elements, functional consequences could include unequal crossing over with gain-of-function, and/or deletion with loss-of-function. This process could result in regulatory changes in gene function in association with normal coding regions, since fragile sites appear to be located at or near upstream DNaseI-hypersensitive areas. Earlier research on chromosomal breakage in relation to transposon behaviour in maize has set a precedent by which many elements in a network could be coordinately controlled, a principle which may allow transcriptional control over multiple areas in the genome simultaneously. The hypothesis proposed in this paper implies that a small number of fundamental higher-order changes may be responsible for influencing a wide range of genetic alterations leading to complex phenotypes, sometimes segregating as distinct entities within pedigrees, or alternatively, and perhaps more commonly, presenting with several overlapping phenotypes in some other families. Studying only pure multiplex families in psychiatric genetics may not be sufficient for an understanding of the underlying genetic diathesis in this group of disorders. Validation of the fragile site hypothesis for complex neurobehavioural disorders may offer additional avenues for gene therapy based either on preferential integration of exogenous DNA at fragile sites, or utilizing the acentric fragments to modify sequence amplification extrachromosomally.

Social adjustment in adult males affected with progressive muscular dystrophy

Adult male patients affected with Becker (BMD, N = 22), limb girdle (LGMD, N = 22) and facioscapulohumeral (FSHMD, N = 18) muscular dystrophy were interviewed to assess for the first time how the disease's severity and recurrence risk (RR) magnitude alter their social adjustment. BMD (X-linked recessive) is the severest form and confers an intermediate RR because all daughters will be carriers, LGMD (autosomal-recessive) is moderately severe with a low RR in the absence of consanguineous marriage, and FSHMD (autosomal-dominant) is clinically the mildest of these three forms of MD but with the highest RR, of 50%. Results of the semistructured questionnaire [WHO (1988): Psychiatric Disability Assessment Schedule] showed no significant difference between the three clinical groups, but more severely handicapped patients as well as patients belonging to lower socioeconomic levels from all clinical groups showed poorer social adjustment. Taken together, myopathic patients displayed intermediate social dysfunction compared to controls and schizophrenics studied by Jablensky [1988: WHO Psychiatric Disability Assessment Schedule]. Since the items of major dysfunction proportion among myopathic patients concern intimate relationships (70%), interest in working among those unemployed (67%), and social isolation (53%), emotional support and social and legal assistance should concentrate on these aspects. Interestingly, the results of this study also suggest that high RRs do not affect relationships to the opposite sex.

The genetics of schizophrenia: past, present, and future concepts

Although a genetic susceptibility for schizophrenia has been long established and even noted by Kraepelin in 1907, the mechanisms for its inheritance remains unknown. No candidates have proven to be correct and while many weakly positive chromosomal linkages have been reported, none have yet been consistently replicated. The following review examines the present status of these findings. The conclusion is that the field must move on to finding a consistently replicable mutation segregating with schizophrenia in families, before any of the present linkage results can be resolved.

Constitutive heterochromatin of chromosome 1 and Duffy blood group alleles in schizophrenia

Cytogenetic analysis was carried out in unrelated schizophrenic patients, unrelated controls and patients and family members in multiplex families. The size distribution of chromosome 1 heterochromatic region (1qH, C-band variants) among 21 unrelated schizophrenic patients was different from that found in a group of 46 controls. The patient group had 1qH variants of smaller size than the control group (P < 0.01). Incubation of phytohemagglutinin-treated blood lymphocytes with 5-azacytidine (which causes decondensation and extension of the heterochromatin) led to a lesser degree of heterochromatin decondensation in a group of patients than in the controls (7 schizophrenic, 9 controls, P < 0.01). The distribution of phenotypes of Duffy blood group system [whose locus is linked to the 1qH region (Donahue et al.: Proc Natl Acad Sci USA 61:949-955, 1968; Rouleau et al.: Genomics 7:313-318, 1990)] among 28 schizophrenic patients was also different from that in the general population. Cosegregation of schizophrenia with a 1qH (C-band) variant and Duffy blood group allele was observed in one of six multiplex families. The overall results suggest that alterations within the Duffy/1qH region are involved in schizophrenia in some cases. This region contains the locus of D5 dopamine receptor pseudogene 2 (1q21.1), which is transcribed in normal lymphocytes (Takahashi et al.: FEBS Lett 314:23-25, 1992).

Linkage studies on chromosome 22 in familial schizophrenia

As part of a systematic search for a major genetic locus for schizophrenia we have examined chromosome 22 using 14 highly polymorphic markers in 23 disease pedigrees. The markers were distributed at an average distance of 6.6 cM, covering 70-80% of the chromosome. We analyzed the data by the lod score method using five plausible genetic models ranging from dominant to recessive, after testing the power of our sample under the same genetic parameters. The most positive lod score found was 1.51 under a recessive model for the marker D22S278, which is insufficient to conclude linkage. However, an excess of shared alleles in affected siblings (P < .01) was found for both D22S278 and D22S283. For D22S278, the A statistic was equal to the lod score (1.51) and therefore did not provide additional evidence for linkage allowing for heterogeneity, but the Liang statistic was more significant (P = .002). Our results suggest the possibility that the region around D22S278 and D22S283 contains a gene which contributes to the aetiology of schizophrenia.

Deletion status and intellectual impairment in Duchenne muscular dystrophy

The authors collected Verbal, Performance and Full-scale IQs for 74 patients in whom complete analysis of the dystrophin gene for deletions and duplications had been performed. There was a significant difference in the mean Full-scale IQ between patients with deletions at the 5' and 3' ends of the gene, with no patients with 5' deletions having mental retardation. No relationship was established between mental retardation and the presence or absence of deletions or length of deletions, and similar deletions were observed in the presence and absence of mental retardation. Although distal deletions were more commonly associated with mental retardation, there was no clear evidence for a particular region of the dystrophin gene being specifically responsible for IQ. The intellectual deficit seen in DMD may be a consequence of cerebral hypoxia, ue to malfunction of smooth muscle dystrophin.

Becker and limb-girdle muscular dystrophies: a psychiatric and intellectual level comparative study

There are some indications that Becker muscular dystrophy (BMD) might be related to mental disorders and mental retardation (MR). To investigate this question, we made a standardized psychiatric and intellectual level assessment of 22 BMD patients in comparison with 22 limb-girdle muscular dystrophy (LGMD) patients. There were not significant differences between the two groups. Twelve patients (54.5%) in each group received at least one lifetime psychiatric diagnosis, the most frequent being depressive disorders. The intelligence quotient means for BMD was 85.9 and 87.8 for LGMD. There was one case of mild MR among BMD patients and two cases among LGMD patients.

Screening the dystrophin gene suggests a high rate of polymorphism in general but no exonic deletions in schizophrenics

The dystrophin gene, located at chromosome Xp21, was evaluated as a candidate gene in chronic schizophrenia in response to the report of a large family in which schizophrenia cosegregated with Becker muscular dystrophy [Zatz et al., 1991: Am J Hum Genet 49: A364; 1992: J Med Genet 30(2):131-134]. Genomic DNA from 94 men with chronic schizophrenia was evaluated by Southern blot analysis using cDNA probes that span exons 1-59. No exonic deletions were identified. An unexpectedly high rate of polymorphism was calculated in this study and two novel polymorphisms were found, demonstrating the usefulness of the candidate gene approach even when results of the original study are negative.

Integrated study of 100 patients with Xp21 linked muscular dystrophy using clinical, genetic, immunochemical, and histopathological data. Part 3. Differential diagnosis and prognosis

This report is the third part of a trilogy from a multidisciplinary study which was undertaken to investigate gene and protein expression in a large cohort of patients with well defined and diverse clinical phenotypes. The aim of part 3 was to review which of the analytical techniques that we had used would be the most useful for differential diagnosis, and which would provide the most accurate indication of disease severity. Careful clinical appraisal is very important and every DMD patient was correctly diagnosed on this basis. In contrast, half of the sporadic BMD patients and all of the sporadic female patients had received different tentative diagnoses based on clinical assessments alone. Sequential observations of quantitative parameters (such as the time taken to run a fixed distance) were found to be useful clinical indicators for prognosis. Intellectual problems might modify the impression of physical ability in patients presenting at a young age. Histopathological assessment was accurate for DMD but differentiation between BMD and other disorders was more difficult, as was the identification of manifesting carriers. Our data on a small number of women with symptoms of muscle disease indicate that abnormal patterns of dystrophin labelling on sections may be an effective way of differentiating between female patients with a form of limb girdle dystrophy and those carrying a defective Xp21 gene. Dystrophin gene analysis detects deletions/duplications in 50 to 90% of male patients and is the most effective non-invasive technique for diagnosis. Quantitative Western blotting, however, would differentiate between all Xp21 and non-Xp21 male patients. In this study we found a clear relationship between increased dystrophin abundance (determined by densitometric analysis of blots) and clinical condition, with a correlation between dystrophin abundance and the age at loss of independent mobility among boys with DMD and intermediate D/BMD. This indicates that blotting is the most sensitive and accurate technique for diagnosis and prognosis.