The effect of coal-fired power plants on ambient air quality in Mpumalanga province, South Africa, 2014-2018.

Several coal-fired power plants (CFPPs) were built in South Africa, mainly in the central Mpumalanga Province, due to an increase in the demand for Eskom, the national power utility, to keep up with socio-economic growth. The CFPPs, of which 90% are owned by Eskom, generate a significant share of the country's electricity but contribute to the air pollution experienced in the country. The paper discusses sulphur dioxide (SO2), nitrogen dioxide (NO2) and particulate matter of size less than 10 micrometre (µm) in diameter (PM10), using data from 2014 to 2018. The statistics revealed higher PM10 concentrations during winter than in summer and spring at the Kriel and Komati sites; associated with the higher contribution of domestic burning. The study's results could influence legislation and policies and help to understand the source of poor ambient air quality by assessing the three pollutants within the area of the selected power plants.

Common chromosomal fragile sites (CFS) may be involved in normal and traumatic cognitive stress memory consolidation and altered nervous system immunity.

Previous reports of specific patterns of increased fragility at common chromosomal fragile sites (CFS) found in association with certain neurobehavioural disorders did not attract attention at the time due to a shift towards molecular approaches to delineate neuropsychiatric disorder candidate genes. Links with miRNA, altered methylation and the origin of copy number variation indicate that CFS region characteristics may be part of chromatinomic mechanisms that are increasingly linked with neuroplasticity and memory. Current reports of large-scale double-stranded DNA breaks in differentiating neurons and evidence of ongoing DNA demethylation of specific gene promoters in adult hippocampus may shed new light on the dynamic epigenetic changes that are increasingly appreciated as contributing to long-term memory consolidation. The expression of immune recombination activating genes in key stress-induced memory regions suggests the adoption by the brain of this ancient pattern recognition and memory system to establish a structural basis for long-term memory through controlled chromosomal breakage at highly specific genomic regions. It is furthermore considered that these mechanisms for management of epigenetic information related to stress memory could be linked, in some instances, with the transfer of the somatically acquired information to the germline. Here, rearranged sequences can be subjected to further selection and possible eventual retrotranscription to become part of the more stable coding machinery if proven to be crucial for survival and reproduction. While linkage of cognitive memory with stress and fear circuitry and memory establishment through structural DNA modification is proposed as a normal process, inappropriate activation of immune-like genomic rearrangement processes through traumatic stress memory may have the potential to lead to undesirable activation of neuro-inflammatory processes. These theories could have a significant impact on the interpretation of risks posed by heredity and the environment and the search for neuropsychiatric candidate genes.

Elements of Effective Nutrition Education for Adults with Diabetes Mellitus in Resource-Poor Settings: a Review

This review article highlights the key factors that need consideration in planning an effective nutrition education programme for adults with type 2 diabetes mellitus in resource-poor settings. Type 2 diabetes is increasing to epidemic levels globally. Low socio-economic status is associated with poorer health outcomes and a higher economic burden. Individuals with diabetes cite dietary adherence as the most difficult self-care area. Effective nutrition education achieves the desired goals and outcomes; which include appropriate change in dietary behaviour; improved glycaemic control; plasma lipid levels; blood pressure and body weight; as well as improved potential mediators (knowledge; skills and attitudes). Elements that contribute to a successful nutrition education programme include interventions tailored to the needs; abilities and socio-cultural context of the target group; the active involvement of the patient; a behaviour-focused approach based on appropriate theory; suitable delivery methods and individual/group approaches. Adequate contact time with an educator ( 10 hours); the educator's competence; provision of social support and follow-up intervention are also crucial. Effectively educating diabetic individuals from resource-poor settings in nutrition is a challenging task. It needs innovative and skilled educators who are sensitive to the unique needs of the target group and who use appropriate approaches to address these needs

An integrative view of dynamic genomic elements influencing human brain evolution and individual neurodevelopment.

An increasing number of reports of rearranged and aneuploid chromosomes in brain cells suggest an unexpected link between developmental chromosomal instability and brain genome diversity. Unstable chromosomal fragile sites (FS), endogenously or exogenously induced by replicative stressors, participate in genetic rearrangement and may be key features of epigenetically modified neuroplasticity. Certain common chromosomal FS are known to function as signals for RAG complex targets. Recombinase activation gene RAG-1 directed V(D)J recombination affecting specific recognition sequences allows the immune system to encode memories of a vast array of antigens. The finding that RAG-1 is transcribed in the central nervous system raised the consideration that immunoglobulin-like somatic DNA recombination could be involved in recognition and memory processes in brain development and function. Cognitive stress induced somatic hypermutation in neurons, similar to what happens after antigenic challenge in lymphocytes, could underly a massive increase in the synthesis of novel macromolecules to function as coded information bits which get selected for memory storage. This process may involve mobile element activation, which may also play a role in recombinational repair. As a source of tested, successful new open reading frames, somatic hypermutation may confer a selective advantage if somatically acquired information is fed back to germline V gene arrays and the human brain could have adopted a similar process to manage the information captured in rearranged sequences. In neuroevolution and individual brain development, germline information could thus represent a crucial component. The brain itself may, from an evolutionary genetic point of view, represent nothing more than a highly specialized and individually diversified information accrual and memory system to increase the overall phenotypically validated information content of the immortal germline. In the evolution of rapid evolvability, exceeding the narrow margins within which genetic instability is useful, would be expected to be associated with penalties in terms of neuropathology and malignancy risk. The utilisation of genetic instability to obtain diversification under stress is an ancient principle, but may have reached unprecedented levels in humans, which, in turn, fed back to creation of more unstable environments. Since increased genomic instability is likely to have been introduced to the genomes of other life forms by some of the extremely genotoxic environments created by H sapiens, a better understanding of the implications of borderline genomic instability may be an important priority to ensure long term biological survival, including that of our own species.

Does HIV-1/AIDS-associated frontotemporal neuropathology following perinatal infection influence the development of moral behaviour?

While HIV encephalopathy and the AIDS dementia complex are considered hallmark neurologic manifestations of HIV-1 infection, increasing evidence of a continuum of nervous system involvement indicates the existence of an unrecognized number of individuals with milder, mostly cognitive and/or behavioural effects. Questions are raised whether HIV-related frontotemporal neuropathology during critical developmental stages could affect development of the brain networks documented to be involved in moral decisions, and whether this could contribute to the phenomenon of delinquency in an unknown percentage of the current generation of approximately 18-25 year old survivors of early childhood or vertically acquired HIV infection. Carefully planned and executed long term, prospective controlled studies using environmental, clinical, neurological, behavioural, genetic, immune and functional neuroimaging correlates would be required to elucidate whether HIV-specific neuropathology could indeed act as an independent risk factor for the development of a frontotemporal sociopathy syndrome. If such an association is proven, the accelerated development of neurospecific therapies should be a priority, especially for clinically and immunologically stable HIV-infected children. It may be necessary to institute such treatment as early as possible in perinatally infected cases, and maybe even during intrauterine life if HIV-1 is demonstrated to also act as a neurobehavioural teratogen for the developing fetal brain. It may, however, prove to be difficult to separate primary neurobiological from environmental factors, since the epigenetic effects on the host genome of retroviral insertion influencing behavioural gene expression characteristics, and altered gene expression following early life stresses may involve overlapping neurodevelopmental gene regulatory networks. In the meantime it remains necessary to prevent or ameliorate frequent neuropsychiatric morbidity from whatever causes.

The Role of Long-Chain Polyunsaturated Fatty Acids in the Treatment of Cancer Cachexia and Tumour Growth in Patients with Malignant Diseases : a Review

Recent studies show that u-3 polyunsaturated fatty acids (PUFAs) have the capacity to modulate cancer outcomes. The body responds to cancer in the same way that it responds to inflammation and wound healing. Nutrients with anti-inflammatory effects could therefore be expected to play a role in cancer treatment. This review focuses on the role of u-3 PUFAs in tumourigenesis and cancer cachexia. Studies indicate that eicosapentaenoic acid (EPA) supplementation may promote arrest of tumour growth and reduce cell proliferation. Patients need to consume at least 2 g of EPA per day for it to have a therapeutic effect. Positive outcomes related to cachexia include diminished weight loss; increased appetite; improved quality of life and prolonged survival; although there is controversy regarding these clinical outcomes. The effects of u-3 PUFAs on tumourigenesis and cachexia are viewed in the context of altered lipid and protein metabolism. This altered metabolism usually experienced by cancer patients results in increased formation of proinflammatory eicosanoids and cytokines. Cytokines play an indirect role by stimulating the production of arachidonic acid-derived eicosanoids; which support inflammation; cell proliferation and angiogenesis; and inhibit apoptosis. It can be concluded that u-3 PUFA supplementation offers a means of augmenting cancer therapy; inhibiting tumouri- genesis and possibly contributing to cachexia alleviation

Is there an emerging endosymbiotic relationship between mycobacteria and the human host based on horizontal transfer of genetic sequences?

While not negating the seriousness of tuberculosis and the need to prevent and combat the disease effectively, the large percentage of infected, apparently healthy individuals who harbour latent infections warrants consideration whether an endosymbiotic relationship is being established between mycobacteria and man. By means of a gene decay process eliminating their most metabolically important pathogenic genes associated with an increasing need for host gene products during prolonged intracellular survival, mycobacteria appears to be undergoing a process of establishing a less dangerous relationship with its host. To have tolerated this relationship over time, humans must have benefited. This is suggested to have occurred via changes in DNA higher order structure altering combinatorially regulated gene expression allowing increased cerebrodiversity. It can be expected that, beyond a certain threshold, negative effects ensued, leading to neuropathology and increased susceptibility for certain psychiatric disorders. These processes have probably been happening since the earliest contact with mycobacteria, but recently may have become modified by the emergence of epidemic tuberculosis and waves of increased oxidative stress following the circumstances associated with the Industrial Revolution and the more recent AIDS pandemic. The organism seems to have uniquely exploited the normal stress reaction of the host. Genomic stresses include changes associated with glucocorticoid effects as well as upregulated reactive oxygen species and stress/(heat shock) protein production, the latter two of which result in host cell cycle delay. Subsequently replication dependent chromosomal fragile sites appear in the host genome and together with upregulated chaperonins and mobile element activation, the scene is set for sequence exchange between the organism and host. If proven, these events raise the possibility of modifying chromatin epigenetically to retain the proposed advantages while silencing pathogenicity factors.

Reactive oxygen species and related haem pathway components as possible epigenetic modifiers in neurobehavioural pathology.

The neuroendocrine response to stress utilizes several bio-communicative pathways which also play a role in neurodevelopmental plasticity. The mechanism of action of steroidal compounds includes DNA alteration by reactive oxygen species (ROS) arising through redox cycling of reactive hormone derivatives. ROS and reactive nitrogen species play a significant role in signaling networks affecting gene transcriptional regulation during normal as well as stress-induced responses. ROS-associated synaptic and regulatory region plasticity may have been important for normal brain evolution, but probably simultaneously lowered the threshold for inducing neuropathology. A shift from 'plasticity' to 'instability' is likely to be associated with the emergence of complex effects depending on the timing, duration and intensity of the ROS insult, and is suggested to include heritable epigenetic chromatin/regulatory region remodeling differentially influencing expression levels of significant neuropsychiatric genes and their variant alleles. Neurobehavioural disorder clinical manifestations have been linked with ROS effects. The concepts discussed here relate to ROS-associated instability of DNA regulatory region sequences and a proposal that it may play an important modifying role in brain and neuro-behaviourally related gene expression. Genes encoding key steps in mitochondrial, haem, iron and bilirubin ROS metabolic pathways have been used as examples to illustrate how ROS-modified regulatory networks could possibly alter the context within which (even ostensibly unrelated) neuropsychiatric gene candidates may sometimes be recruited. Furthermore, reactions of certain radicals release sufficient energy to generate UV-photons. DNA conformational changes accompanied by changes in photon emission suggest that functional neuroimaging findings probably reflect interaction on the level of ROS/biophoton/genome regulatory region domains rather than the signatures of individual neurobehavioural disorder candidate genes.

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.

The National Food Consumption Survey (NFCS): South Africa, 1999.

OBJECTIVE: The aim of the National Food Consumption Survey (NFCS) in South Africa was to determine the nutrient intakes and anthropometric status of children (1-9 years old), as well as factors that influence their dietary intake. DESIGN: This was a cross-sectional survey of a nationally representative sample of all children aged 1-9 years in South Africa. A nationally representative sample with provincial representation was selected using 1996 Census information. SUBJECTS: Of the 3120 children who were originally sampled data were obtained from 2894, a response rate of 93%. METHODS: The sociodemographic status of each household was assessed by a questionnaire. Dietary intake was assessed by means of a 24-hour recall and a food-frequency questionnaire from the caregivers of the children. Food purchasing practices were determined by means of a food procurement questionnaire. Hunger was assessed by a modified hunger scale questionnaire. Nutritional status was determined by means of anthropometric measurements: height, weight, head circumference and arm circumference. RESULTS: At the national level, stunting (height-for-age below minus two standard deviations (< -2SD) from the reference median) was by far the most common nutritional disorder, affecting nearly one in five children. The children least affected (17%) were those living in urban areas. Even with regard to the latter, however, children living in informal urban areas were more severely affected (20%) compared with those living in formal urban areas (16%). A similar pattern emerged for the prevalence of underweight (weight-for-age < -2SD), with one in 10 children being affected at the national level. Furthermore, one in 10 (13%) and one in four (26%) children aged 1-3 years had an energy intake less than half and less than two-thirds of their daily energy needs, respectively. For South African children as a whole, the intakes of energy, calcium, iron, zinc, selenium, vitamins A, D, C and E, riboflavin, niacin, vitamin B6 and folic acid were below two-thirds of the Recommended Dietary Allowances. At the national level, data from the 24-hour recalls indicated that the most commonly consumed food items were maize, sugar, tea, whole milk and brown bread. For South African children overall, one in two households (52%) experienced hunger, one in four (23%) were at risk of hunger and only one in four households (25%) appeared food-secure. CONCLUSION: The NFCS indicated that a large majority of households were food-insecure and that energy deficit and micronutrient deficiencies were common, resulting in a high prevalence of stunting. These results were used as motivation for the introduction of mandatory fortification in South Africa.

A qualitative exploration of rural feeding and weaning practices, knowledge and attitudes on nutrition.

AIM: An exploratory qualitative investigation was done to determine the feeding and weaning practices, knowledge and attitudes towards nutrition of mothers/caregivers of children up to 3 years old attending baby clinics in the Moretele district (South Africa). METHODOLOGY: Qualitative data collection on six relevant nutrition topics was done using focus group interviews. Trained moderators, using a pre-tested, structured interview schedule, interviewed participants in six age groups. Focus group interviews were taped, transcribed and translated. Content analysis produced systematic data descriptions and ethnography provided descriptive data. RESULTS: Breast-feeding was the choice feed and bottle-feeding was only given when breast-feeding was impossible. Solid food was introduced early (at 2-3 months) and a mixed family diet at 7-9 months. Milk feeds were stopped completely from 18-24 months. Weaning diets were compromised due to poor food choices, preparation practices and limited variety. The participant's nutrition knowledge regarding specific foods, their functions and recommended quantities was poor. The women adhered to their cultural beliefs regarding food choices and preparation practices. CONCLUSION: The data analysis revealed that inadequate nutrition knowledge and adherence to cultural practices lead to poor-quality feeding practices. Cultural factors and taboos have a powerful influence on feeding practices and eating patterns. Young mothers often find it impossible to ignore their ill-informed elders or peer group. Nutrition knowledge needs to be changed in a first step towards implementing improved feeding practices. Facilitated group discussions could focus on possible solutions for the identified nutrition-related problems.

Further evidence for linkage of Gilles de la Tourette syndrome (GTS) susceptibility loci on chromosomes 2p11, 8q22 and 11q23-24 in South African Afrikaners.

Utilizing DNA samples from 91 Afrikaner nuclear families with one or more affected children, five genomic regions on chromosomes 2p, 8q, 11q, 20q, and 21q that gave evidence for association with GTS in previous case-control association studies were investigated for linkage and association with GTS. Highly polymorphic markers with mean heterozygosity of 0.77 were typed and resulting genotypes evaluated using single marker transmission disequilibrium (TDT), single marker haplotype relative risk (HRR), and multi-marker "extended" TDT and HRR methods. Single marker TDT analysis showed evidence for linkage or association, with p-values near 0.05, for markers D2S139, GATA28F12, and D11S1377 on chromosomes 2p11, 8q22 and 11q23-24, respectively. Extended, two-locus TDT and HRR analysis provided further evidence for linkage or association on chromosome 2 with p-values of 0.007 and 0.025, and chromosome 8 with p-values of 0.059 and 0.013, respectively. These results provide important additional evidence for the location of GTS susceptibility loci.

Risperidone versus pimozide in Tourette's disorder: a comparative double-blind parallel-group study.

BACKGROUND: The treatment of Tourette's disorder with classical neuroleptics is limited by their side effects. Risperidone is a new efficacious antipsychotic with a low propensity for extrapyramidal side effects. To establish risperidone's therapeutic potential in Tourette's disorder, we studied the safety and efficacy of risperidone in comparison with pimozide in patients with Tourette's disorder diagnosed according to DSM-III-R. METHOD: In a 12-week, multicenter, double-blind, parallel-group study, 26 patients were treated with risperidone (mean daily dose = 3.8 mg), and 24 patients were treated with pimozide (mean daily dose = 2.9 mg). RESULTS: There was significant improvement of tics with respect to the Tourette's Symptom Severity Scale (TSSS) for both groups. Forty-one patients completed the study. At endpoint, 54% (14/26) of the risperidone patients and 38% (9/24) of the pimozide patients had only very mild or no symptoms on the global severity rating of the TSSS. Both treatment groups had improved significantly at endpoint in regard to Global Assessment of Functioning and Clinical Global Impressions scale outcomes. Symptoms of anxiety and depressive mood improved significantly from baseline in both groups. Obsessive-compulsive behavior improvement reached significance only in the risperidone group. Although the severity of extrapyramidal side effects was low in both groups, fewer patients in the risperidone group reported extrapyramidal side effects (N = 4) compared with the pimozide group (N = 8). Depression, fatigue, and somnolence were reported as the most prominent side effects in both treatment groups. CONCLUSION: Both drugs were efficacious and well tolerated in patients with Tourette's disorder. Risperidone may become the first-line drug in the treatment of Tourette's disorder owing to a more favorable efficacy and tolerability profile.

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

Preliminary observations concerning increased chromosomal fragility in association with certain behavioural disorders in humans allow an opportunity to suggest a cohesive theory regarding the possible importance of higher-order DNA modification 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 such extra chromosomally 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 DNase-I 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. Current emphasis on the investigation of only pure multiplex families in psychiatric genetics may assist with identification of a number of discrete behaviour-modifying genes, but may not be sufficient for an understanding of the broad underlying genetic diathesis in these, and perhaps other 'multifactorial type' disorders. Validation of a role for altered fragile site expression and the molecular consequences thereof as proposed in this paper may offer additional avenues for gene therapy based either on preferential integration of exogenous DNA at fragile sites, or utilizing the acentric fragments formed during chromosome breakage to modify sequence amplification extrachromosomally.

Effects of iron deprivation on the pathology and stress protein expression in murine X-linked muscular dystrophy.

Duchenne muscular dystrophy (DMD) is caused by dystrophin deficiency, which results in muscle necrosis and the upregulation of heat shock/stress proteins (HSP). We hypothesized that reactive oxygen species, and in particular hydroxyl radicals (.OH), participate in muscle necrosis and HSP expression. It was assumed that iron deprivation decreases .OH generation, restraining the disease process and reducing the oxidant-induced expression of HSP. The role of iron-catalyzed free radical reactions in the pathology of dystrophin-deficient muscle was evaluated in the murine model for Duchenne muscular dystrophy (mdx), by examining the effects of dietary deficiency and supplementation of iron on serum creatine kinase (CK), muscle morphology, lipid peroxidation and HSP levels in mice maintained on diets deficient in or supplemented with iron for 6 weeks. Iron-deprived mdx mice showed a significant decrease in the number of macrophage-invaded necrotic fibers and the expression of the 70-kDa heat shock protein (Hsp70). This suggests that the iron-dependent generation of .OH relates to muscle necrosis in the mdx mouse and modulates the expression of Hsp70 in vivo. In contrast, iron deprivation had no influence on other HSP or on lipid peroxidation in mdx mice, while maintenance on either diet caused a significant decrease in serum creatine kinase activity. The potential therapeutic effects of iron deprivation in mdx should be considered.

Fluorescence-imaging assay for cytotoxic plaque formation and for growth toward confluency of adherent cells.

A nondestructive fluorescence-imaging assay is described for quantitating the number and size of plaques formed over time by cytotoxic effector cells in a monolayer of target cells. It can also be used to assay the growth of adherent cells toward confluence. The method involves the use of fluorescein conjugated to high molecular weight dextran. The dextran is excluded by adherent cells, thereby making the medium around cells more fluorescent than the cells themselves. The area of the plate that is fluorescent can be determined by confocal fluorescence imaging microscopy. With this new method, changes in the confluency of adherent cells or in the number and area of cytotoxic plaques can be assayed repeatedly over an extended period of time, without manipulation of the cells or of the medium.

Identification of genetic markers associated with Gilles de la Tourette syndrome in an Afrikaner population.

Because gene-mapping efforts, using large kindreds and parametric methods of analysis, for the neurologic disorder Tourette syndrome have failed, efforts are being redirected toward association studies in young, genetically isolated populations. The availability of dense marker maps makes it feasible to search for association throughout the entire genome. We report the results of such a genome scan using DNA samples from Tourette patients and unaffected control subjects from the South African Afrikaner population. To optimize mapping efficiency, we chose a two-step strategy. First, we screened pools of DNA samples from both affected and control individuals, using a dense collection of 1,167 short tandem-repeat polymorphisms distributed throughout the genome. Second, we typed those markers displaying evidence of allele frequency-distribution shifts, along with additional tightly linked markers, using DNA from each affected and unaffected individual. To reduce false positives, we tested two independent groups of case and control subjects. Strongest evidence for association (P values 10-2 to 10-5) were obtained for markers within chromosomal regions encompassing D2S1790 near the chromosome 2 centromere, D6S477 on distal 6p, D8S257 on 8q, D11S933 on 11q, D14S1003 on proximal 14q, D20S1085 on distal 20q, and D21S1252 on 21q.

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.