A genetic mechanism implicates chromosome 11 in schizophrenia and bipolar diseases

DRDs and Brain-Derived Neurotrophic Factor Share a Common Therapeutic Ground: A Novel Bioinformatic Approach Sheds New Light Toward Pharmacological Treatment of Cognitive and Behavioral Disorders

Cognitive and behavioral disorders are subgroups of mental health disorders. Both cognitive and behavioral disorders can occur in people of different ages, genders, and social backgrounds, and they can cause serious physical, mental, or social problems. The risk factors for these diseases are numerous, with a range from genetic and epigenetic factors to physical factors. In most cases, the appearance of such a disorder in an individual is a combination of his genetic profile and environmental stimuli. To date, researchers have not been able to identify the specific causes of these disorders, and as such, there is urgent need for innovative study approaches. The aim of the present study was to identify the genetic factors which seem to be more directly responsible for the occurrence of a cognitive and/or behavioral disorder. More specifically, through bioinformatics tools and software as well as analytical methods such as systemic data and text mining, semantic analysis, and scoring functions, we extracted the most relevant single nucleotide polymorphisms (SNPs) and genes connected to these disorders. All the extracted SNPs were filtered, annotated, classified, and evaluated in order to create the "genomic grammar" of these diseases. The identified SNPs guided the search for top suspected genetic factors, dopamine receptors D and neurotrophic factor BDNF, for which regulatory networks were built. The identification of the "genomic grammar" and underlying factors connected to cognitive and behavioral disorders can aid in the successful disease profiling and the establishment of novel pharmacological targets and provide the basis for personalized medicine, which takes into account the patient's genetic background as well as epigenetic factors.

A rare case of schizophrenia coexistence with antiphospholipid syndrome, β-thalassemia, and monoclonal gammopathy of undetermined significance

A patient with schizophrenia who was treated with chlorpromazine developed lupus anticoagulant (LA) and antiphospholipid syndrome (APS). On protein electrophoresis, a monoclonal immunoglobulin A peak was seen in this patient, defining a condition of monoclonal gammopathy of undetermined significance. Additionally, β-thalassemia was diagnosed with the CD41-42 genotype. This condition is extremely rare, particularly in patients with schizophrenia and APS. We present a case of a patient with schizophrenia and secondary APS who had a positive LA, a significantly prolonged activated partial thromboplastin time, endogenous coagulation factor deficiency and inhibitor, no bleeding, and an unexpected finding of β-thalassemia and monoclonal IgA. Following that, a literature review on the disorders was presented.

Association Between ApoA1 Gene Polymorphisms and Antipsychotic Drug-Induced Dyslipidemia in Schizophrenia

PURPOSE

Dyslipidemia frequently occurs in schizophrenia patients treated with antipsychotic drugs (APDs), especially atypical APDs. Apolipoprotein A1 (ApoA1) plays a key role in lipid metabolism. The aim of this study was to investigate whether ApoA1 gene polymorphisms are associated with APD-induced dyslipidemia in schizophrenia patients.

PATIENTS AND METHODS

A total of 1987 patients with schizophrenia were enrolled in this study. Serum lipid profiles were determined with a biochemistry analyzer. Genotyping for the rs5072 polymorphism of ApoA1 was performed with TaqMan assay. Logistic regression analysis was carried out to evaluate the relationship between ApoA1 gene polymorphisms and APD-induced dyslipidemia. The effects of drug classification (typical vs atypical APD) and drug regimen (monotherapy vs combination therapy) on serum lipid levels were also analyzed.

RESULTS

A significant association was found between rs5072 and triglyceride (TG) levels in the recessive model of the logistic regression analysis (adjusted odds ratio [OR]=1.50, 95% confidence interval [CI]: 1.03, 2.17; P<0.05). TG level was significantly higher in patients treated with combination therapy (1.03 (0.71, 1.51) mmol/l) compared to monotherapy (0.93 (0.67, 1.43) mmol/l) and was also associated with sex. There were significant differences in TG levels among the three genotypes of ApoA1 rs5072 (GG, GA, and AA) in the whole study population and in patients treated with atypical APDs.

CONCLUSION

The ApoA1 rs5072 variant is associated with dysregulated TG metabolism in schizophrenia patients treated with APDs, which may increase susceptibility to dyslipidemia.

Split hand/foot malformation genetics supports the chromosome 7 copy segregation mechanism for human limb development

Genetic aberrations of several unlinked loci cause human congenital split hand/foot malformation (SHFM) development. Mutations of the DLX5 (distal-less) transcription factor-encoding gene in chromosome 7 cause SHFM through haploinsufficiency, but the vast majority of cases result from heterozygous chromosomal aberrations of the region without mutating the DLX5 gene. To resolve this paradox, we invoke a chromosomal epigenetic mechanism for limb development. It is composed of a monochromatid gene expression phenomenon that we discovered in two fission yeasts with the selective chromosome copy segregation phenomenon that we discovered in mouse cells. Accordingly, one daughter cell inherits both expressed DLX5 copies while the other daughter inherits both epigenetically silenced ones from a single deterministic cell of the developing limb. Thus, differentiated daughter cells after further proliferation will correspondingly produce proximal/distal-limb tissues. Published results of a Chr. 7 translocation with a centromere-proximal breakpoint situated over 41 million bases away from the DLX locus, centromeric and DLX5-region inversions have satisfied key genetic and developmental biology predictions of the mechanism. Further genetic tests of the mechanism are proposed. We propose that the DNA double helical structure itself causes the development of sister cells' gene regulation asymmetry. We also argue against the conventionally invoked morphogen model of development.This article is part of the themed issue 'Provocative questions in left-right asymmetry'.

Selective chromatid segregation mechanism proposed for the human split hand/foot malformation development by chromosome 2 translocations: A perspective

Three unrelated chromosome 2q14.1-14.2 region translocations caused the split hand/foot limb malformation development in humans by an unknown mechanism. Their etiology was described by the autosomal dominant inheritance with incomplete penetrance genetic model although authors stated, "the understanding of the genotype-to-phenotype relationship has been most challenging". The conundrums are that no mutation was found in known genes located at or near the translocation breakpoints, some limbs were malformed while others were not in the same patient and surprisingly breakpoints lie at relatively large distance of more than 2.5 million bases to have caused disorder-causing gene mutations in a single gene. To help understand translocations etiology for limb development, we invoke the selective DNA strand/chromatid-specific epigenetic imprinting and segregation mechanism employed by the two highly diverged fission yeasts to produce daughter cells of different cell types by mitosis. By this mechanism, an anterior- and posterior-limb-tissues-generating pair of daughter cells is produced by a single deterministic cell dividing in the anlagen of the limb bud. Accordingly, malformation develops simply because translocations hinder the proper distribution of chromatid-specific epialleles of a limb developmental gene during the deterministic cell's mitosis. It is tempting to speculate that such a mechanism might involve the HOXD-cluster genes situated centromere-distal to the translocation breakpoints many million bases away at the 2q31.1 region. Further genetic tests of the hypothesis are proposed for the human and mouse limb development. In sum, genetic analysis of translocations suggests that the sequence asymmetry of strands in the double-helical DNA structure of a developmental gene forms the physical basis of daughter cells' developmental asymmetry, thus opposing the morphogen-gradient research paradigm of limb development.

A Unique DNA Recombination Mechanism of the Mating/Cell-type Switching of Fission Yeasts: a Review

Cells of the highly diverged Schizosaccharomyces (S.) pombe and S. japonicus fission yeasts exist in one of two sex/mating types, called P (for plus) or M (for minus), specified by which allele, M or P, resides at mat1. The fission yeasts have evolved an elegant mechanism for switching P or M information at mat1 by a programmed DNA recombination event with a copy of one of the two silent mating-type genes residing nearby in the genome. The switching process is highly cell-cycle and generation dependent such that only one of four grandchildren of a cell switches mating type. Extensive studies of fission yeast established the natural DNA strand chirality at the mat1 locus as the primary basis of asymmetric cell division. The asymmetry results from a unique site- and strand-specific epigenetic "imprint" at mat1 installed in one of the two chromatids during DNA replication. The imprint is inherited by one daughter cell, maintained for one cell cycle, and is then used for initiating recombination during mat1 replication in the following cell cycle. This mechanism of cell-type switching is considered to be unique to these two organisms, but determining the operation of such a mechanism in other organisms has not been possible for technical reasons. This review summarizes recent exciting developments in the understanding of mating-type switching in fission yeasts and extends these observations to suggest how such a DNA strand-based epigenetic mechanism of cellular differentiation could also operate in diploid organisms.

Selective chromatid segregation mechanism invoked for the human congenital mirror hand movement disorder development by RAD51 mutations: a hypothesis

The vertebrate body plan externally is largely symmetrical across the midline but internal organs develop asymmetrically. The biological basis of asymmetric organ development has been investigated extensively for years, although the proposed mechanisms remain controversial. By comparison, the biological origin of external organs symmetry has not been extensively investigated. Bimanual hand control is one such external organs symmetry allowing independent motor control movements of both hands to a person. This gap in our knowledge is illustrated by the recent reports of heterozygous rad51 mutations causing mysterious symptoms of congenital mirror hand movement disorder (MM) in humans with 50% penetrance by an unknown mechanism. The analysis of mutations that vary symmetry or asymmetry could be exploited to decipher the mechanisms of laterality development. Here I present a hypothesis for explaining 50% penetrance of the rad51 mutation. The MM's origin is explained with the Somatic Strand-specific Imprinting and selective sister chromatid Segregation (SSIS) hypothesis proposed originally as the mechanism of asymmetric cell division to promote visceral organs body plan laterality development in vertebrates. By hypothesis, random sister chromatid segregation in mitosis occurs for a specific chromosome due to rad51/RAD51 constitution causing MM disorder development in 50% of subjects.

Unbiased segregation of fission yeast chromosome 2 strands to daughter cells

The base complementarity feature (Watson and Crick in Nature 171(4356):737-738, 1953) and the rule of semi-conservative mode of DNA replication (Messelson and Stahl in Proc Natl Acad Sci U S A 44:671-682, 1958) dictate that two identical replicas of the parental chromosome are produced during replication. In principle, the inherent strand sequence differences could generate nonequivalent daughter chromosome replicas if one of the two strands were epigenetically imprinted during replication to effect silencing/expression of developmentally important genes. Indeed, inheritance of such a strand- and site-specific imprint confers developmental asymmetry to fission yeast sister cells by a phenomenon called mating/cell-type switching. Curiously, location of DNA strands with respect to each other at the centromere is fixed, and as a result, their selected segregation to specific sister chromatid copies occurs in eukaryotic cells. The yeast system provides a unique opportunity to determine the significance of such biased strand distribution to sister chromatids. We determined whether the cylindrical-shaped yeast cell distributes the specific chromosomal strand to the same cellular pole in successive cycles of cell division. By observing the pattern of recurrent mating-type switching in progenies of individual cells by microscopic analyses, we found that chromosome 2 strands are distributed by the random mode in successive cell divisions. We also exploited unusual "hotspot" recombination features of this system to investigate whether there is selective segregation of strands such that oldest Watson-containing strands co-segregate in the diploid cell at mitosis. Our data suggests that chromosome 2 strands are segregated independently to those of the homologous chromosome.

T102C polymorphism of serotonin 2A type receptor gene confers susceptibility to (early onset) schizophrenia in Han Chinese: an association study and meta-analysis

INTRODUCTION

Several lines of evidence have indicated that serotonin 2A receptor (HTR2A) may be involved in the pathophysiology of schizophrenia. One functional polymorphism in HTR2A (T102C) has been widely investigated; however, the results have been inconsistent. The purpose of this study was to evaluate the association between HTR2A T02C polymorphism and schizophrenia in a Chinese Han population.

METHODS

We performed a case-control study, using an early onset sample, which may be an attractive subgroup for genetic studies. In addition, we performed a meta-analysis of the combined sample groups in Han Chinese.

RESULTS

Our study, based on 385 schizophrenic patients and 399 controls, found a significant genotype-wise association of T102C and schizophrenia (P = 0.02). After applying stratified analyses, the dominant model for T allele produced significant association (OR = 1.60, 95%CI = 1.11-2.30, P = 0.01). In the meta-analysis including all of the published population-based association studies in Han Chinese and the present association study, the pooled genotype-wise result in a dominant model was statistically significant with a summary OR of 1.25 (95%CI = 1.04-1.50, P = 0.02).

DISCUSSION

Our results suggest that the HTR2A T102C polymorphism may confer susceptibility to schizophrenia in Han Chinese.

Npas4: a neuronal transcription factor with a key role in social and cognitive functions relevant to developmental disorders

Npas4 is a transcription factor, which is highly expressed in the brain and regulates the formation and maintenance of inhibitory synapses in response to excitatory synaptic activity. A deregulation of the inhibitory-excitatory balance has been associated with a variety of human developmental disorders such as schizophrenia and autism. However, not much is known about the role played by inhibitory synapses and inhibitory pathways in the development of nervous system disorders. We hypothesized that alterations in the inhibitory pathways induced by the absence of Npas4 play a major role in the expression of the symptoms observed in psychiatric disorders. To test this hypothesis we tested mice lacking the transcription factor (Npas4 knock-out mice (Npas4-KO)) in a battery of behavioral assays focusing on general activity, social behaviors, and cognitive functions. Npas4-KO mice are hyperactive in a novel environment, spend less time exploring an unfamiliar ovariectomized female, spend more time avoiding an unfamiliar male during a first encounter, show higher social dominance than their WT littermates, and display pre-pulse inhibition, working memory, long-term memory, and cognitive flexibility deficits. These behavioral deficits may replicate schizophrenia-related symptomatology such as social anxiety, hyperactivity, and cognitive and sensorimotor gating deficits. Immunohistochemistry analyses revealed that Npas4 expression is induced in the hippocampus after a social encounter and that Npas4 regulates the expression of c-Fos in the CA1 and CA3 regions of the hippocampus after a cognitive task. Our results suggest that Npas4 may play a major role in the regulation of cognitive and social functions in the brain with possible implications for developmental disorders such as schizophrenia and autism.

R, Elston R. Some capabilities for model-based and model-free linkage analysis using the program package S.A.G.E. (Statistical Analysis for Genetic Epidemiology)

For both model-free and model-based linkage analysis the S.A.G.E. (Statistical Analysis for Genetic Epidemiology) program package has some unique capabilities in analyzing both continuous traits and binary traits with variable age of onset. Here we highlight model-based linkage analysis of a quantitative trait (plasma dopamine β hydroxylase) that is known to be largely determined by monogenic inheritance, using a prior segregation analysis to produce the best fitting model for the trait. For a binary trait with variable age of onset (schizophrenia), we illustrate how using age of onset information to obtain a quantitative susceptibility trait leads to more statistically significant linkage signals, suggesting better power.

Functional characterization of stem cell activity in the mouse mammary gland

Any portion of the mouse mammary gland is capable of recapitulating a clonally derived complete and functional mammary tree upon transplantation into an epithelial divested mammary fat-pad of a recipient host. As such, it is an ideal model tissue for the study somatic stem cell function. This review will outline what is known regarding the function of stem/progenitor cells in the mouse mammary gland, including how progenitor populations can be functionally defined, the evidence for and potential role of selective DNA strand segregation, and the role of the niche in maintaining and controlling stem cell function.

Discovery of the mitotic selective chromatid segregation phenomenon and its implications for vertebrate development

The asymmetric cell division process is required for cellular differentiation and embryonic development. Recent evidence obtained in Drosophila and C. elegans suggest that this process occurs by non-equivalent distribution of proteins or mRNA (intrinsic factors) to daughter cells, or by their differential exposure to cell extrinsic factors. In contrast, haploid fission yeast sister cells developmentally differ by inheriting sister chromatids that are differentiated by epigenetic means. Specifically, the act of DNA replication at the mating-type locus in yeast switches it's alternate alleles only in one specific member of chromosome 2 sister chromatids in nearly every chromosome replication cycle. To employ this kind of mechanism for cellular differentiation, strictly based on Watson-Crick structure of DNA in diploid organism, selective segregation mechanism is required to coordinate distribution of potentially differentiated sister chromatids to daughter cells. Genetic evidence to this postulate was fortuitously provided by the analysis of mitotic recombinants of chromosome 7 in mouse cells. Remarkably, the biased segregation occurs in some cell types but not in others and the process seems to be chromosome-specific. This review summarizes the discovery of selective chromatid segregation phenomenon and it suggests that such a process of Somatic Sister chromatid Imprinting and Selective chromatid Segregation (SSIS model) might explain development in eukaryotes, such as that of the body axis left-right visceral organs laterality specification in mice.

Asymmetric cell divisions and asymmetric cell fates

The regulation of self-renewal, cell diversity, and differentiation can occur by modulating symmetric and asymmetric cell divisions. Remarkably, asymmetric cell divisions can arise through multiple processes in which molecules in the cytoplasm and nucleus, as well as template "immortal" DNA strands, can segregate to one daughter cell during cell division. Explaining how these events direct distinct daughter cell fates is a major challenge to understanding how the organism is assembled and maintained for a lifetime. Numerous technical issues that are associated with assessing how distinct cell fates are executed in vivo have resulted in divergent interpretations of experimental findings. This review addresses some of these points and considers different developmental model systems that attempt to investigate how cell fate decisions are determined, as well as the molecules that guide these choices.

Asymmetric strand segregation: epigenetic costs of genetic fidelity?

Asymmetric strand segregation has been proposed as a mechanism to minimize effective mutation rates in epithelial tissues. Under asymmetric strand segregation, the double-stranded molecule that contains the oldest DNA strand is preferentially targeted to the somatic stem cell after each round of DNA replication. This oldest DNA strand is expected to have fewer errors than younger strands because some of the errors that arise on daughter strands during their synthesis fail to be repaired. Empirical findings suggest the possibility of asymmetric strand segregation in a subset of mammalian cell lineages, indicating that it may indeed function to increase genetic fidelity. However, the implications of asymmetric strand segregation for the fidelity of epigenetic information remain unexplored. Here, I explore the impact of strand-segregation dynamics on epigenetic fidelity using a mathematical-modelling approach that draws on the known molecular mechanisms of DNA methylation and existing rate estimates from empirical methylation data. I find that, for a wide range of starting methylation densities, asymmetric—but not symmetric—strand segregation leads to systematic increases in methylation levels if parent strands are subject to de novo methylation events. I found that epigenetic fidelity can be compromised when enhanced genetic fidelity is achieved through asymmetric strand segregation. Strand segregation dynamics could thus explain the increased DNA methylation densities that are observed in structured cellular populations during aging and in disease.

Through my investigations of the fidelity of epigenetic inheritance, I became intrigued by the interplay of genetic and epigenetic fidelities. Cairns proposed in 1975 that the lifetime risk of epithelial cancers would be reduced if chromosomes containing the oldest DNA strands were selectively segregated to somatic stem cells. I wondered about the implications of such asymmetric strand segregation for the fidelity of epigenetic information. To address this issue, I modelled the partitioning of DNA molecules after replication, with special attention to the molecule that contained the oldest strand. I found that the enhanced genetic fidelity that may be achieved through asymmetric strand segregation could, under some scenarios, compromise epigenetic fidelity. I am excited to pursue these studies as they apply to epigenetic changes observed to occur during aging and in human diseases, including several cancers.

Support for the selective chromatid segregation hypothesis advanced for the mechanism of left-right body axis development in mice

The somatic DNA strand-specific imprinting to effect gene regulation and selective chromatid segregation model was previously proposed to produce developmentally nonequivalent sister cells in mitosis. Such a mechanism might explain generation of stem-cell pattern of cell division in eukaryotes. The developmentally controlled process involves a pair of homologous chromosomes at a specific cell division to establish embryonic left-right body axis asymmetry. As a result, visceral organs in the two sides of vertebrate's body develop asymmetrically. The model was specifically proposed to explain the well-known axis randomization phenotype of the left-right dynein mutant mice where one-half of animals develop with standard visceral organ's positioning and the balance develops with the inverted arrangement. The model postulated that the specific dynein, a microtubule-based molecular motor protein, promotes the selective chromatid segregation process in mitosis. Thus, random segregation involving sister chromatids of a pair of specific chromosomes leads to axis randomization of the mutant. Moreover, the model uniquely predicts that 50 percent mutant embryos should produce symmetrical cell divisions because of random segregation; consequently, their either visceral side would develop as mirror image of the other side resulting in embryonic lethality. In view of this prediction, validity of prominent body axis-determination models is scrutinized here. Results supporting the cell-type regulated chromosome 6 and chromosome 7 selective chromatids segregation phenomenon existing in mouse cells are reviewed. Published results with the mutant mice are consistent with the chromosome segregation model for axis determination.

Scalp hair-whorl orientation of Japanese individuals is random; hence, the trait's distribution is not genetically determined

Because the features of clockwise versus anti-clockwise orientation of hair-whorl coiling developed on a person's scalp is (partially, albeit significantly) correlated with that individual's right- versus left-hand-use preference (i.e., handedness) in the US and British subjects, these traits have been recently suggested to be determined biologically and through a common genetic mechanism. Here I report results of a serendipitously made observation with the Japanese population that helps to scrutinize validity of partial correlation between these attributes and to ascertain whether the underlying gene's frequency variations exist in different gene pools. Surprisingly, the whorl orientation in the Japanese individuals was found to be random, although their handedness variation is similar to that of the US population. Therefore, the whorl orientation trait is not genetically determined in the Japanese population. This result supports the idea that separate decisions must be made during embryogenesis for developing handedness and hair-whorl features at least in Japanese individuals. A recent study found the lack of association between whorl orientation and handedness in the German population, yet previous studies suggested that their scalp hair orientation is genetically determined. Therefore, pronounced genetic variation for the hair-whorl trait exists between individuals of different geographical regions. As hand preference exhibits "complex correlation" with brain hemispheric functional specialization, implications of these findings are discussed here with the goal to define biology of brain hemispheric laterality determination.

Schizophrenia and beta-thalassemia: a genetic link?

This report of two cases in which schizophrenia and beta-thalassemia occurred simultaneously in several family members may suggest that a genetic link exists between these two disorders. A known genetic disease (beta-thalassemia) could help confirm the presence, on the short arm of chromosome 11, of a genetic susceptibility factor for schizophrenia.

A hypothesis for how chromosome 11 translocations cause psychiatric disorders

Despite extensive effort for many years, the etiology of major psychiatric diseases remains unknown. A recent study by Baysal et al. has argued against the ALG9 gene variants in causing psychosis. Due to its disruption by a balanced t(9p24;11q23) translocation that segregates with the disorder in a family, it was proposed to be a primary candidate gene causing psychosis. In addition, a recent review article by Pickard et al., entitled "Cytogenetics and gene discovery in psychiatric disorders," highlighted the importance of studies of chromosome rearrangements in finding disease-causing mutations. However, achieving the goal of finding genes by conventional association studies and by investigating chromosome rearrangements remains elusive. Here we discuss a fundamentally different explanation from the usual one considered by workers in the field concerning chromosome aberrations and psychoses etiology. We hypothesize how chromosome aberrations might cause disease but the gene at the rearrangement breakpoint is irrelevant for the etiology. Moreover, we discuss subsequently published findings that help scrutinize validity of the two very different hypotheses considered in the psychiatric genetics field. In sum, we alert the readers to the complexities of interpreting phenotypes associated with rearrangements.

Left-right dynein motor implicated in selective chromatid segregation in mouse cells

During cell division, copies of mouse chromosome 7 are segregated selectively or randomly to daughter cells depending on the cell type. The mechanism for differential segregation is unknown. Because mouse left-right dynein (LRD) gene mutations result in randomization of visceral organs' laterality, we hypothesized that LRD may also function in selective chromatid segregation. Indeed, upon knock-down by RNA interference methods, LRD depletion disrupts biased segregation. LRD messenger RNA presence or absence correlates with the observed segregation patterns. This work supports the claim that LRD functions in a mechanism for selective chromatid segregation.

Cell type regulates selective segregation of mouse chromosome 7 DNA strands in mitosis

After chromosome replication, sister chromatid copies are generally thought to segregate randomly to daughter cells. However, sister chromatids differ in their DNA strands, with each chromatid inheriting one older strand that is paired to a newly synthesized strand. Genetic analysis with a homologous chromosome pair indicated nonrandom chromatid distribution in embryonic stem cells. Biased segregation pattern was also found in all 100 endoderm cells examined, but not in any of the 165 neuroectoderm cells. In contrast, the mesoderm, cardiomyocyte, and pancreatic cells exhibited a random mode of segregation. Strand distribution mechanisms regulated by cell type may have consequences for cellular differentiation and for evolving strategies for developmental mechanisms.

Schizophrenia genetics: uncovering positional candidate genes

The efforts to decipher the genetic causes of schizophrenia, one of the most devastating mental illnesses, have reached a turning point. Several linkage findings in schizophrenia have been replicated and, in the last few years, have been followed by systematic fine-mapping efforts to identify positional susceptibility genes. Here, we outline the evidence supporting each of the proposed positional candidate genes and identify some general areas of caution in their interpretation. Several of these findings hold considerable promise both for understanding the neuropathology of this brain disorder, the causes of which remain a mystery, but also for development of novel, mechanism-based treatments for the patients.

The genetic basis of hair whorl, handedness, and other phenotypes

Evidence is presented that RHD, RHCE, and other RH genes, may be interesting candidates to consider when searching for the genetic basis of hair whorl rotation (i.e., clockwise or counterclockwise), handedness (i.e., right handed, left handed or ambidextrous), speech laterality (i.e., right brained or left brained), speech dyslexia (e.g., stuttering), sexual orientation (i.e., heterosexual, homosexual, bisexual, or transsexual), schizophrenia, bipolar disorder, and autism spectrum disorder. Such evidence involves the need for a genetic model that includes maternal immunization to explain some of the empirical results reported in the literature. The complex polymorphisms present among the maternally immunizing RH genes can then be used to explain other empirical results. Easily tested hypotheses are suggested, based upon genotypic (but not phenotypic) frequencies of the RH genes. In particular, homozygous dominant individuals are expected to be less common or lacking entirely among the alternative phenotypes. If it is proven that RH genes are involved in brain architecture, it will have a profound effect upon our understanding of the development and organization of the asymmetrical vertebrate brain and may eventually lead to a better understanding of the developmental processes which occur to produce the various alternative phenotypes discussed here. In addition, if RH genes are shown to be involved in the production of these phenotypes, then the evolutionary studies can be performed to demonstrate the beneficial effect of the recessive alleles of RHD and RHCE, and why human evolution appears to be selecting for the recessive alleles even though an increase in the frequency of such alleles may imply lower average fecundity among some individuals possessing them.

A 1927 study supports a current genetic model for inheritance of human scalp hair-whorl orientation and hand-use preference traits

The basis of right- vs. left-hand-use preference in humans has been debated for a long time. Culturally learned, birth stress, and biologically specified causes are the prominent etiologies under consideration. A 2003 (Klar 2003) study reported a correlation between a person's preferred hand and the scalp hair-whorl orientation developed on the head. By reinterpreting results of a 1927 (Schwarzburg 1927) study on the genetics of the hair-whorl trait, support for a recent single gene, two-allele "random-recessive model" for both hair-whorl orientation and handedness trait inheritance is demonstrated.