Brain-specific Foxp1 deletion impairs neuronal development and causes autistic-like behaviour.

Neurodevelopmental disorders are multi-faceted and can lead to intellectual disability, autism spectrum disorder and language impairment. Mutations in the Forkhead box FOXP1 gene have been linked to all these disorders, suggesting that it may play a central role in various cognitive and social processes. To understand the role of Foxp1 in the context of neurodevelopment leading to alterations in cognition and behaviour, we generated mice with a brain-specific Foxp1 deletion (Nestin-Cre(Foxp1-/-)mice). The mutant mice were viable and allowed for the first time the analysis of pre- and postnatal neurodevelopmental phenotypes, which included a pronounced disruption of the developing striatum and more subtle alterations in the hippocampus. More detailed analysis in the CA1 region revealed abnormal neuronal morphogenesis that was associated with reduced excitability and an imbalance of excitatory to inhibitory input in CA1 hippocampal neurons in Nestin-Cre(Foxp1-/-) mice. Foxp1 ablation was also associated with various cognitive and social deficits, providing new insights into its behavioural importance.

Identification and functional characterization of rare SHANK2 variants in schizophrenia.

Recent genetic data on schizophrenia (SCZ) have suggested that proteins of the postsynaptic density of excitatory synapses have a role in its etiology. Mutations in the three SHANK genes encoding for postsynaptic scaffolding proteins have been shown to represent risk factors for autism spectrum disorders and other neurodevelopmental disorders. To address if SHANK2 variants are associated with SCZ, we sequenced SHANK2 in 481 patients and 659 unaffected individuals. We identified a significant increase in the number of rare (minor allele frequency<1%) SHANK2 missense variants in SCZ individuals (6.9%) compared with controls (3.9%, P=0.039). Four out of fifteen non-synonymous variants identified in the SCZ cohort (S610Y, R958S, P1119T and A1731S) were selected for functional analysis. Overexpression and knockdown-rescue experiments were carried out in cultured primary hippocampal neurons with a major focus on the analysis of morphological changes. Furthermore, the effect on actin polymerization in fibroblast cell lines was investigated. All four variants revealed functional impairment to various degrees, as a consequence of alterations in spine volume and clustering at synapses and an overall loss of presynaptic contacts. The A1731S variant was identified in four unrelated SCZ patients (0.83%) but not in any of the sequenced controls and public databases (P=4.6 × 10(-5)). Patients with the A1731S variant share an early prodromal phase with an insidious onset of psychiatric symptoms. A1731S overexpression strongly decreased the SHANK2-Bassoon-positive synapse number and diminished the F/G-actin ratio. Our results strongly suggest a causative role of rare SHANK2 variants in SCZ and underline the contribution of SHANK2 gene mutations in a variety of neuropsychiatric disorders.

Pseudoautosomal deletions encompassing a novel homeobox gene cause growth failure in idiopathic short stature and Turner syndrome.

Growth retardation resulting in short stature is a major concern for parents and due to its great variety of causes, a complex diagnostic challenge for clinicians. A major locus involved in linear growth has been implicated within the pseudoautosomal region (PAR1) of the human sex chromosomes. We have determined an interval of 170 kb of DNA within PAR1 which was deleted in 36 individuals with short stature and different rearrangements on Xp22 or Yp11.3. This deletion was not detected in any of the relatives with normal stature or in a further 30 individuals with rearrangements on Xp22 or Yp11.3 with normal height. We have isolated a homeobox-containing gene (SHOX) from this region, which has at least two alternatively spliced forms, encoding proteins with different patterns of expression. We also identified one functionally significant SHOX mutation by screening 91 individuals with idiopathic short stature. Our data suggest an involvement of SHOX in idiopathic growth retardation and in the short stature phenotype of Turner syndrome patients.

New roles of SHOX as regulator of target genes.

The homeobox gene SHOX encodes a transcription factor which is important for normal limb development. Approximately 5 to 10% of short patients exhibit a mutation or deletion in either the SHOX gene or its downstream enhancer regions. In humans, SHOX deficiency has been associated with various short stature syndromes as well as non-syndromic idiopathic short stature. A common feature of these syndromes is disproportionate short stature with a particular shortening of the forearms and lower legs. Madelung deformity, cubitus valgus, high-arched palate and muscular hypertrophy also differed markedly between patients with or without SHOX gene defects. A clinical trial in patients with SHOX deficiency and Turner syndrome demonstrated highly significant growth hormone-stimulated increases in height velocity and height SDS in both groups. Employing microarray analyses and cell culture experiments, a strong effect of SHOX on the expression of the natriuretic peptide BNP and the fibroblast growth factor receptor gene FGFR3 could be demonstrated. We found that BNP was positively regulated, while Fgfr3 was negatively regulated by SHOX. A regulation that occurs mainly in the mesomelic segments, a region where SHOX is known to be strongly expressed, offers a possible explanation for the phenotypes seen in patients with FGFR3 (e.g. achondroplasia) and SHOX defects (e.g. Léri-Weill dyschondrosteosis).

Network-driven discovery yields new insight into Shox2-dependent cardiac rhythm control.

The homeodomain transcription factor SHOX2 is involved in the development and function of the heart's primary pacemaker, the sinoatrial node (SAN), and has been associated with cardiac conduction-related diseases such as atrial fibrillation and sinus node dysfunction. To shed light on Shox2-dependent genetic processes involved in these diseases, we established a murine embryonic stem cell (ESC) cardiac differentiation model to investigate Shox2 pathways in SAN-like cardiomyocytes. Differential RNA-seq-based expression profiling of Shox2+/+ and Shox2-/- ESCs revealed 94 dysregulated transcripts in Shox2-/- ESC-derived SAN-like cells. Of these, 15 putative Shox2 target genes were selected for further validation based on comparative expression analysis with SAN- and right atria-enriched genes. Network-based analyses, integrating data from the Mouse Organogenesis Cell Atlas and the Ingenuity pathways, as well as validation in mouse and zebrafish models confirmed a regulatory role for the novel identified Shox2 target genes including Cav1, Fkbp10, Igfbp5, Mcf2l and Nr2f2. Our results indicate that genetic networks involving SHOX2 may contribute to conduction traits through the regulation of these genes.

A selective difference between human Y-chromosomal DNA haplotypes.

DNA analysis is making a valuable contribution to the understanding of human evolution [1]. Much attention has focused on mitochondrial DNA (mtDNA) [2] and the Y chromosome [3] [4], both of which escape recombination and so provide information on maternal and paternal lineages, respectively. It is often assumed that the polymorphisms observed at loci on mtDNA and the Y chromosome are selectively neutral and, therefore, that existing patterns of molecular variation can be used to deduce the histories of populations in terms of drift, population movements, and cultural practices. The coalescence of the molecular phylogenies of mtDNA and the Y chromosome to recent common ancestors in Africa [5] [6], for example, has been taken to reflect a recent origin of modern human populations in Africa. An alternative explanation, though, could be the recent selective spread of mtDNA and Y chromosome haplotypes from Africa in a population with a more complex history [7]. It is therefore important to establish whether there are selective differences between classes (haplotypes) of mtDNA and Y chromosomes and, if so, whether these differences could have been sufficient to influence the distributions of haplotypes in existing populations. A precedent for this hypothesis has been established for mtDNA in that one mtDNA background increases susceptibility to Leber hereditary optic neuropathy [8]. Although studies of nucleotide diversity in global samples of Y chromosomes have suggested an absence of recent selective sweeps or bottlenecks [9], selection may, in principle, be very important for the Y chromosome because it carries several loci affecting male fertility [10] [11] and as many as 5% of males are infertile [11] [12]. Here, we show that one class of infertile males, PRKX/PRKY translocation XX males, arises predominantly on a particular Y haplotypic background. Selection is, therefore, acting on Y haplotype distributions in the population.

Evolutionary breakpoint analysis on Y chromosomes of higher primates provides insight into human Y evolution.

Comparative FISH mapping of PAC clones covering almost 3 Mb of the human AZFa region in Yq11.21 to metaphases of human and great apes unravels breakpoints that were involved in species-specific Y chromosome evolution. An astonishing clustering of evolutionary breakpoints was detected in the very proximal region on the long arm of the human Y chromosome in Yq11.21. These breakpoints were involved in deletions, one specific for the human and another for the orang-utan Y chromosome, in a duplicative translocation/transposition specific for bonobo and chimpanzee Y chromosomes and in a pericentric inversion specific for the gorilla Y chromosome. In addition, our comparative results allow the deduction of a model for the human Y chromosome evolution.

The evolution of the azoospermia factor region AZFa in higher primates.

Clones of a PAC contig encompassing the human AZFa region in Yq11.21 were comparatively FISH mapped to great ape Y chromosomes. While the orthologous AZFa locus in the chimpanzee, the bonobo and the gorilla maps to the long arm of their Y chromosomes in Yq12.1-->q12.2, Yq13.1-->q13.2 and Yq11.2, respectively, it is found on the short arm of the orang-utan subspecies of Borneo and Sumatra, in Yp12.3 and Yp13.2, respectively. Regarding the order of PAC clones and genes within the AZFa region, no differences could be detected between apes and man, indicating a strong evolutionary stability of this non-recombining region.

Genetic and structural characterization of the human mitochondrial inner membrane translocase.

Translocation of nuclear-encoded mitochondrial preproteins is mediated by translocases in the outer and inner membranes. In the yeast Saccharomyces cerevisiae, translocation of preproteins into the matrix requires the membrane proteins Tim23, Tim17 and Tim44, which drive translocation in cooperation with mtHsp70 and its co-chaperone Mge1p. We have cloned and functionally analyzed the human homologues of Tim17, Tim23 and Tim44. In contrast to yeast, two TIM17 genes were found to be expressed in humans. TIM44, TIM23 and TIM17a genes were mapped to chromosomes 19p13.2-p13.3, 10q11. 21-q11.23 and 1q32. The TIM17b gene mapped to Xp11.23, near the fusion point where an autosomal region was proposed to have been added to the "ancient" part of the X chromosome about 80-130 MY ago. The primary sequences of the two proteins, hTim17a and hTim17b, are essentially identical, significant differences being restricted to their C termini. They are ubiquitously expressed in fetal and adult tissues, and both show expression levels comparable to that of hTim23. Biochemical characterization of the human Tim components revealed that hTim44 is localized in the matrix and, in contrast to yeast, only loosely associated with the inner membrane. hTim23 is organized into two distinct complexes in the inner membrane, one containing hTim17a and one containing hTim17b. Both TIM complexes display a native molecular mass of 110 kDa. We suggest that the structural organization of TIM23.17 preprotein translocases is conserved from low to high eukaryotes.

SHOX: growth, Léri-Weill and Turner syndromes.

Linear growth is a multifactorial trait involving environmental, hormonal and genetic factors. The multitude of growth-affecting genetic factors has recently been supplemented by the discovery of the homeobox gene SHOX. Although originally described as causing idiopathic short stature, SHOX mutations are also responsible for mesomelic growth retardation and Madelung deformity in Léri-Weill dyschondrosteosis and Langer mesomelic dysplasia. Furthermore, recent studies implicate SHOX haploinsufficiency in the etiology of additional somatic stigmata frequently observed in Turner syndrome. Therefore, SHOX has a broad functional scope and leads to a variety of different phenotypes upon mutation.

Interstitial deletion in Xp22.3 is associated with X linked ichthyosis, mental retardation, and epilepsy.

We describe monozygotic male twins with an interstitial deletion of Xp22.3 including the steroid sulphatase gene (STS). The twins had X linked ichthyosis, X linked mental retardation, and epilepsy. A locus for X linked mental retardation has been assigned to a region between STS and DXS31 spanning approximately 3 Mb. Recently the locus was further refined to an approximately 1 Mb region between DXS1060 and GS1. By PCR analysis of flanking STS gene markers in our patients we succeeded in narrowing down the locus to between DXS6837 and GS1.

FISH deletion mapping defines a single location for the Y chromosome stature gene, GCY.

At least 1 in 1000 males lacks part of the long arm of the Y chromosome. This chromosomal aberration is often associated with short stature and infertility. Deletion mapping and genotype-phenotype analysis have previously defined two non-overlapping critical regions for growth controlling gene(s), GCY(s), on the euchromatic portion of the Y chromosome long arm. These initial mapping assignments were based on the analysis of patients carrying a pure 46,XYq- karyotype as defined by classical cytogenetic karyotyping. Four genes have been assigned to the distal one of the two critical regions. To determine whether one or both of these two critical regions harbours GCY and whether one of the four genes assigned to the distal region is involved in determination of stature, nine adult patients with Yq chromosomal abnormalities were studied in detail. By PCR and FISH analysis, we showed that all patients with a previously defined pure 46,XYq- karyotype are actually mosaics with cells containing an idic(Y) or ring(Y) chromosome in association with 45,X0 cells. This leads us to conclude that (1) FISH is an absolute prerequisite for the correct identification of Y chromosomal rearrangements and (2) only patients with interstitial Y deletions are reliable predictors for the physical location of stature gene(s) on Yq. Our molecular analyses of chromosomes from patients with interstitial Yq deletions finally establishes the proximal interval between markers DYZ3 and DYS11 as the only GCY critical interval. No functional gene has so far been identified in this region adjacent to the centromere.

Serotonin receptor gene HTR3A variants in schizophrenic and bipolar affective patients.

Serotonin receptor genes have always been considered excellent candidate genes in the aetiology of neurogenetic diseases. In this study, we assessed sequence variations of the HTR3A gene. For this purpose, we established exon-specific primers and analysed DNA samples from 165 unrelated individuals including 70 schizophrenic patients, 48 patients with bipolar affective disorder and 47 healthy control persons using polymerase chain reaction/single-strand conformational polymorphism analysis. We discovered six sequence variants, five of which represent polymorphisms. These polymorphisms could not be associated with schizophrenia and bipolar affective disorder (P = 0.055-1). We also detected a missense mutation in exon 9 in a schizophrenic patient at a conserved position (Pro391Arg). To determine the incidence of this substitution an extended set of 358 schizophrenic patients and 155 control individuals was investigated. The Pro391Arg mutation was not detected in these schizophrenic patients and controls screened. However, a second missense mutation (Arg344His) was detected in one schizophrenic patient, but not in any of the controls. These results suggest that the observed mutations in HTR3A are rare and therefore do not play a major role in the aetiology of the disorder. Further studies are needed to support the hypothesis that HTR3A may contribute to the schizophrenia in these patients.

Association between the 5' UTR variant C178T of the serotonin receptor gene HTR3A and bipolar affective disorder.

Serotonin receptor type 3 is a ligand-gated ion channel implicated in behavioural disorders. Our objective was to identify nucleotide variants in a specific portion of the 5' region of the serotonin receptor gene (HTR3A) containing upstream open reading frames (uORFs) and to investigate their effect on bipolar disease. Mutations in uORFs have been recently shown to cause disease by changing expression on the translational level. We identified one polymorphism, C195T, and one missense mutation, C178T (Pro16Ser) within an upstream open reading frame. No significant association was found between the C195T polymorphism and bipolar affective disorder. A significant association was, however, found between the variant C178T in 156 patients with bipolar disorder compared to 156 healthy controls (P = 0.00016). To investigate the relevance of this variant on gene expression, luciferase reporter constructs containing the C178T (Pro16Ser) allele were established and compared to the C178T plus C195T and wild-type alleles. Reporter constructs containing the C178T (Pro16Ser) allele drove 245% and 138% expression compared to the wild-type allele. These findings show that the C178T(Pro16Ser) variant in HTR3A may represent a functional variant and affect the susceptibility to bipolar disorder.

Phenotypic variation and genetic heterogeneity in Léri-Weill syndrome.

Léri-Weill syndrome (LWS) or dyschondrosteosis represents a short stature syndrome characterised by the mesomelic shortening of the forearms and lower legs and by bilateral Madelung deformity of the wrists. Recently, mutations in the pseudoautosomal homeobox gene SHOX have been shown to be causative for this disorder. This gene has previously been described as the short stature gene implicated in Turner syndrome (TS). We studied 32 Léri-Weill patients from 18 different German and Dutch families and present clinical, radiological and molecular data. Phenotypic inter- and intrafamilial heterogeneity is a frequent finding in LWS, and phenotypic manifestations are generally more severe in females. In males, muscular hypertrophy is a frequent finding. To test for SHOX mutations we used FISH, Southern blot and SSCP analysis as well as long-range PCR and sequencing. We identified (sub)microscopic deletions encompassing the SHOX gene region in 10 out of 18 families investigated. Deletion sizes varied between 100 kb and 9 Mb and did not correlate with the severity of the phenotype. We did not detect SHOX mutations in almost half (41%) the LWS families studied, which suggests different genetic etiologies.

The Azoospermia region AZFa: an evolutionar y view.

Compared to other regions on the human Y chromosome, the genomic segment encompassing the functionally defined AZFa locus has undergone higher X-Y sequence divergence, which is detectable by fluorescence in-situ hybridisation. This allows an evolutionary definition of an interval enclosing AZFa with a size of about 1.1 Mb. The region includes the genes USP9Y, DBY and UTY and is limited by evolutionary breakpoints within the PAC clones 41L06 and 46M11. These breakpoints restrict an area of possible male specific evolution that may have resulted in the acquisition of male specific functions, including a role in spermatogenesis.

Phenotypic findings due to trisomy 7p15.3-pter including the TWIST locus.

We report on a three-month-old boy with a 46,XY,der(Y)t(Y;7)(p11.32;p15.3) karyotype and growth deficiency, postnatal microcephaly with large fontanels, wide sagittal and metopic sutures, hypertelorism, choanal stenosis, micrognathia, bilateral cryptorchidism, hypospadias, abnormal fingers and toes, and severe developmental delay. FISH studies showed partial trisomy 7p resulting from a de novo unbalanced translocation. The application of molecular probes from the TWIST gene region (7p15.3-p21.1) and probes from the pseudoautosomal region (PAR) demonstrated that the 7p15.3-pter fragment was translocated onto Yp with the breakpoint within approximately 20 kb from the Yp telomere. We discuss the possible role of the TWIST gene in abnormal skull development and suggest that trisomy 7p cases with delayed closure of fontanels can be a result of TWIST gene dosage effect.

Cytogenetic and molecular characterization of two isodicentric Y chromosomes.

We report the results of detailed molecular-cytogenetic studies of two isodicentric Y [idic(Y)] chromosomes identified in patients with complex mosaic karyotypes. We used fluorescence in situ hybridization (FISH) and polymerase chain reaction (PCR) to determine the structure and genetic content of the abnormal chromosomes. In the first patient, classical cytogenetics and FISH analysis with Y chromosome-specific probes showed in peripheral blood lymphocytes a karyotype with 4 cell lines: 45,X[128]/46,X,+idic(Y)(p11.32)[65]/47,XY,+idic(Y)(p11.32)[2]/47,X,+2idic(Y)(p11.32)[1]. No Y chromosome material was found in the removed gonads. For precise characterization of the Yp breakpoint, FISH and fiberFISH analysis, using a telomeric probe and a panel of cosmid probes from the pseudoautosomal region PAR1, was performed. The results showed that the breakpoint maps approximately 1,000 Kb from Ypter. The second idic(Y) chromosome was found in a boy with mild mental retardation, craniofacial anomalies, and the karyotype in lymphocytes 47,X,+idic(Y)(q11.23),+i(Y)(p10)[77]/46,X,+i(Y)(p10)[23]. To our knowledge, such an association has not been previously described. FISH and PCR analysis indicated the presence of at least two copies of the SRY gene in all analyzed cells. Using 17 PCR primers, the Yq breakpoint was shown to map between sY123 (DYS214) and sY121 (DYS212) loci in interval 5O in AZFb region. Possible mechanisms of formation of abnormal Y chromosomes and karyotype-phenotype correlations are discussed.

Effect of 24 months of recombinant growth hormone on height and body proportions in SHOX haploinsufficiency.

Leri-Weill syndrome (LWS) is a skeletal dysplasia with mesomelic short stature, bilateral Madelung deformity (BMD) and SHOX (short stature homeobox-containing gene) haploinsufficiency. The effect of 24 months of recombinant human growth hormone (rhGH) therapy on the stature and BMD of two females with SHOX haploinsufficiency (demonstrated by fluorescence in situ hybridisation) and LWS was evaluated. Both patients demonstrated an increase in height standard deviation score (SDS) and height velocity SDS over the 24 months of therapy. Patient 1 demonstrated a relative increase in arm-span and upper segment measurements with rhGH while patient 2 demonstrated a relative increase in lower limb length. There was appropriate advancement of bone age, no adverse events and no significant deterioration in BMD. In this study, 24 months of rhGH was a safe and effective therapy for the disproportionate short stature of SHOX haploinsufficiency, with no clinical deterioration of BMD.