De novo mutations in MLL cause Wiedemann-Steiner syndrome

Excessive growth of terminal hair around the elbows (hypertrichosis cubiti) has been reported both in isolation and in association with a variable spectrum of associated phenotypic features. We identified a cohort of six individuals with hypertrichosis cubiti associated with short stature, intellectual disability, and a distinctive facial appearance, consistent with a diagnosis of Wiedemann-Steiner syndrome (WSS). Utilizing a whole-exome sequencing approach, we identified de novo mutations in MLL in five of the six individuals. MLL encodes a histone methyltransferase that regulates chromatin-mediated transcription through the catalysis of methylation of histone H3K4. Each of the five mutations is predicted to result in premature termination of the protein product. Furthermore, we demonstrate that transcripts arising from the mutant alleles are subject to nonsense-mediated decay. These findings define the genetic basis of WSS, provide additional evidence for the role of haploinsufficency of histone-modification enzymes in multiple-congenital-anomaly syndromes, and further illustrate the importance of the regulation of histone modification in development.

Impaired natural killer cell phenotype and function in idiopathic and heritable pulmonary arterial hypertension

BACKGROUND

Beyond their role as innate immune effectors, natural killer (NK) cells are emerging as important regulators of angiogenesis and vascular remodeling. Pulmonary arterial hypertension (PAH) is characterized by severe pulmonary vascular remodeling and has long been associated with immune dysfunction. Despite this association, a role for NK cells in disease pathology has not yet been described.

METHODS AND RESULTS

Analysis of whole blood lymphocytes and isolated NK cells from PAH patients revealed an expansion of the functionally defective CD56(-)/CD16(+) NK subset that was not observed in patients with chronic thromboembolic pulmonary hypertension. NK cells from PAH patients also displayed decreased levels of the activating receptor NKp46 and the killer immunoglobulin-like receptors 2DL1/S1 and 3DL1, reduced secretion of the cytokine macrophage inflammatory protein-1β, and a significant impairment in cytolytic function associated with decreased killer immunoglobulin-like receptor 3DL1 expression. Genotyping patients (n=222) and controls (n=191) for killer immunoglobulin-like receptor gene polymorphisms did not explain these observations. Rather, we show that NK cells from PAH patients exhibit increased responsiveness to transforming growth factor-β, which specifically downregulates disease-associated killer immunoglobulin-like receptors. NK cell number and cytotoxicity were similarly decreased in the monocrotaline rat and chronic hypoxia mouse models of PAH, accompanied by reduced production of interferon-γ in NK cells from hypoxic mice. NK cells from PAH patients also produced elevated quantities of matrix metalloproteinase 9, consistent with a capacity to influence vascular remodeling.

CONCLUSIONS

Our work is the first to identify an impairment of NK cells in PAH and suggests a novel and substantive role for innate immunity in the pathobiology of this disease.

Combined analysis of genome-wide association studies for Crohn disease and psoriasis identifies seven shared susceptibility loci

Psoriasis (PS) and Crohn disease (CD) have been shown to be epidemiologically, pathologically, and therapeutically connected, but little is known about their shared genetic causes. We performed meta-analyses of five published genome-wide association studies on PS (2,529 cases and 4,955 controls) and CD (2,142 cases and 5,505 controls), followed up 20 loci that showed strongest evidence for shared disease association and, furthermore, tested cross-disease associations for previously reported PS and CD risk alleles in additional 6,115 PS cases, 4,073 CD cases, and 10,100 controls. We identified seven susceptibility loci outside the human leukocyte antigen region (9p24 near JAK2, 10q22 at ZMIZ1, 11q13 near PRDX5, 16p13 near SOCS1, 17q21 at STAT3, 19p13 near FUT2, and 22q11 at YDJC) shared between PS and CD with genome-wide significance (p < 5 × 10(-8)) and confirmed four already established PS and CD risk loci (IL23R, IL12B, REL, and TYK2). Three of the shared loci are also genome-wide significantly associated with PS alone (10q22 at ZMIZ1, p(rs1250544) = 3.53 × 10(-8), 11q13 near PRDX5, p(rs694739) = 3.71 × 10(-09), 22q11 at YDJC, p(rs181359) = 8.02 × 10(-10)). In addition, we identified one susceptibility locus for CD (16p13 near SOCS1, p(rs4780355) = 4.99 × 10(-8)). Refinement of association signals identified shared genome-wide significant associations for exonic SNPs at 10q22 (ZMIZ1) and in silico expression quantitative trait locus analyses revealed that the associations at ZMIZ1 and near SOCS1 have a potential functional effect on gene expression. Our results show the usefulness of joint analyses of clinically distinct immune-mediated diseases and enlarge the map of shared genetic risk loci.

BMPR-II deficiency elicits pro-proliferative and anti-apoptotic responses through the activation of TGFβ-TAK1-MAPK pathways in PAH

Pulmonary arterial hypertension (PAH) is a cardiovascular disorder associated with enhanced proliferation and suppressed apoptosis of pulmonary arterial smooth muscle cells (PASMCs). Heterozygous mutations in the type II receptor for bone morphogenetic protein (BMPR2) underlie the majority of the inherited and familial forms of PAH. The transforming growth factor β (TGFβ) pathway is activated in both human and experimental models of PAH. However, how these factors exert pro-proliferative and anti-apoptotic responses in PAH remains unclear. Using mouse primary PASMCs derived from knock-in mice, we demonstrated that BMPR-II dysfunction promotes the activation of small mothers against decapentaplegia-independent mitogen-activated protein kinase (MAPK) pathways via TGFβ-associated kinase 1 (TAK1), resulting in a pro-proliferative and anti-apoptotic response. Inhibition of the TAK1-MAPK axis rescues abnormal proliferation and apoptosis in these cells. In both hypoxia and monocrotaline-induced PAH rat models, which display reduced levels of bmpr2 transcripts, this study further indicates that the TGFβ-MAPK axis is activated in lungs following elevation of both expression and phosphorylation of the TAK1 protein. In ex vivo cell-based assays, TAK1 inhibits BMP-responsive reporter activity and interacts with BMPR-II receptor. In the presence of pathogenic BMPR2 mutations observed in PAH patients, this interaction is greatly reduced. Taken together, these data suggest dysfunctional BMPR-II responsiveness intensifies TGFβ-TAK1-MAPK signalling and thus alters the ratio of apoptosis to proliferation. This axis may be a potential therapeutic target in PAH.

Allele-specific cytokine responses at the HLA-C locus: implications for psoriasis

Psoriasis is an inflammatory skin disorder that is inherited as a complex trait. Genetic studies have repeatedly highlighted HLA-C as the major determinant for psoriasis susceptibility, with the Cw*0602 allele conferring significant disease risk in a wide range of populations. Despite the potential importance of HLA-C variation in psoriasis, either via an effect on peptide presentation or immuno-inhibitory activity, allele-specific expression patterns have not been investigated. Here, we used reporter assays to characterize two regulatory variants, which virtually abolished the response to tumor necrosis factor (TNF)-α (rs2524094) and IFN-γ (rs10657191) in HLA-Cw*0602 and a cluster of related alleles. We validated these findings through the analysis of HLA-Cw*0602 expression in primary keratinocytes treated with TNF-α and IFN-γ. Finally, we showed that HLA-Cw*0602 transcripts are not increased in psoriatic skin lesions, despite highly elevated TNF-α levels. Thus, our findings demonstrate the presence of allele-specific differences in HLA-C expression and indicate that HLA-Cw*0602 is unresponsive to upregulation by key proinflammatory cytokines in psoriasis. These data pave the way for functional studies into the pathogenic role of the major psoriasis susceptibility allele.

Psoriasis and other complex trait dermatoses: from Loci to functional pathways

Driven by advances in molecular genetic technologies and statistical analysis methodologies, there have been huge strides taken in dissecting the complex genetic basis of many inflammatory dermatoses. One example is psoriasis, for which application of classical linkage analysis and genome-wide association investigation has identified genetic loci of major and minor effect. Although most loci independently have modest genetic effects, they identify important biological pathways potentially relevant to disease pathogenesis and therapeutic intervention. In the case of psoriasis, these appear to involve the epidermal barrier, NF-κB mechanisms, and T helper type 17 adaptive immune responses. The advent of next-generation sequencing methods will permit a more detailed and complete map of disease genetic architecture, a key step in developing personalized medicine strategies in the clinical management of the complex inflammatory dermatoses.

Mutations in KIF11 cause autosomal-dominant microcephaly variably associated with congenital lymphedema and chorioretinopathy

We have identified KIF11 mutations in individuals with syndromic autosomal-dominant microcephaly associated with lymphedema and/or chorioretinopathy. Initial whole-exome sequencing revealed heterozygous KIF11 mutations in three individuals with a combination of microcephaly and lymphedema from a microcephaly-lymphedema-chorioretinal-dysplasia cohort. Subsequent Sanger sequencing of KIF11 in a further 15 unrelated microcephalic probands with lymphedema and/or chorioretinopathy identified additional heterozygous mutations in 12 of them. KIF11 encodes EG5, a homotetramer kinesin motor. The variety of mutations we have found (two nonsense, two splice site, four missense, and six indels causing frameshifts) are all predicted to have an impact on protein function. EG5 has previously been shown to play a role in spindle assembly and function, and these findings highlight the critical role of proteins necessary for spindle formation in CNS development. Moreover, identification of KIF11 mutations in patients with chorioretinopathy and lymphedema suggests that EG5 is involved in the development and maintenance of retinal and lymphatic structures.

Genome-wide association study identifies a variant in HDAC9 associated with large vessel ischemic stroke

Genetic factors have been implicated in stroke risk, but few replicated associations have been reported. We conducted a genome-wide association study (GWAS) for ischemic stroke and its subtypes in 3,548 affected individuals and 5,972 controls, all of European ancestry. Replication of potential signals was performed in 5,859 affected individuals and 6,281 controls. We replicated previous associations for cardioembolic stroke near PITX2 and ZFHX3 and for large vessel stroke at a 9p21 locus. We identified a new association for large vessel stroke within HDAC9 (encoding histone deacetylase 9) on chromosome 7p21.1 (including further replication in an additional 735 affected individuals and 28,583 controls) (rs11984041; combined P = 1.87 × 10(-11); odds ratio (OR) = 1.42, 95% confidence interval (CI) = 1.28-1.57). All four loci exhibited evidence for heterogeneity of effect across the stroke subtypes, with some and possibly all affecting risk for only one subtype. This suggests distinct genetic architectures for different stroke subtypes.

Molecular genetic characterization of SMAD signaling molecules in pulmonary arterial hypertension

Heterozygous germline mutations of BMPR2 contribute to familial clustering of pulmonary arterial hypertension (PAH). To further explore the genetic basis of PAH in isolated cases, we undertook a candidate gene analysis to identify potentially deleterious variation. Members of the bone morphogenetic protein (BMP) pathway, namely SMAD1, SMAD4, SMAD5, and SMAD9, were screened by direct sequencing for gene defects. Four variants were identified in SMADs 1, 4, and 9 among a cohort of 324 PAH cases, each not detected in a substantial control population. Of three amino acid substitutions identified, two demonstrated reduced signaling activity in vitro. A putative splice site mutation in SMAD4 resulted in moderate transcript loss due to compromised splicing efficiency. These results demonstrate the role of BMPR2 mutation in the pathogenesis of PAH and indicate that variation within the SMAD family represents an infrequent cause of the disease.

Promoter mutation is a common variant in GJC2-associated Pelizaeus-Merzbacher-like disease

Pelizaeus-Merzbacher-like disease (PMLD) is a clinically and genetically heterogeneous neurological disorder of cerebral hypomyelination. It is clinically characterised by early onset (usually infantile) nystagmus, impaired motor development, ataxia, choreoathetoid movements, dysarthria and progressive limb spasticity. We undertook autozygosity mapping studies in a large consanguineous family of Pakistani origin in which affected children had progressive lower limb spasticity and features of cerebral hypomyelination on MR brain imaging. SNP microarray and microsatellite marker analysis demonstrated linkage to chromosome 1q42.13-1q42.2. Direct sequencing of the gap junction protein gamma-2 gene, GJC2, identified a promoter region mutation (c.-167A>G) in the non-coding exon 1. The c.-167A>G promoter mutation was identified in a further 4 individuals from two families (who were also of Pakistani origin) with clinical and radiological features of PMLD in whom previous routine diagnostic screening of GJC2 had been reported as negative. A common haplotype was identified at the GJC2 locus in the three mutation-positive families, consistent with a common origin for the mutation and likely founder effect. This promoter mutation has only recently been reported in GJC2-PMLD but it has been postulated to affect the binding of the transcription factor SOX10 and appears to be a prevalent mutation, accounting for ~29% of reported patients with GJC2-PMLD. We propose that diagnostic screening of GJC2 should include sequence analysis of the non-coding exon 1, as well as the coding regions to avoid misdiagnosis or diagnostic delay in suspected PMLD.

Interaction between ERAP1 and HLA-B27 in ankylosing spondylitis implicates peptide handling in the mechanism for HLA-B27 in disease susceptibility

Ankylosing spondylitis is a common form of inflammatory arthritis predominantly affecting the spine and pelvis that occurs in approximately 5 out of 1,000 adults of European descent. Here we report the identification of three variants in the RUNX3, LTBR-TNFRSF1A and IL12B regions convincingly associated with ankylosing spondylitis (P < 5 × 10(-8) in the combined discovery and replication datasets) and a further four loci at PTGER4, TBKBP1, ANTXR2 and CARD9 that show strong association across all our datasets (P < 5 × 10(-6) overall, with support in each of the three datasets studied). We also show that polymorphisms of ERAP1, which encodes an endoplasmic reticulum aminopeptidase involved in peptide trimming before HLA class I presentation, only affect ankylosing spondylitis risk in HLA-B27-positive individuals. These findings provide strong evidence that HLA-B27 operates in ankylosing spondylitis through a mechanism involving aberrant processing of antigenic peptides.

Functional analysis of the RNF114 psoriasis susceptibility gene implicates innate immune responses to double-stranded RNA in disease pathogenesis

Psoriasis is an immune-mediated skin disease, the aetiology of which remains poorly understood. In recent years, genome-wide association studies (GWAS) have helped to illuminate the molecular basis of this condition, by demonstrating the pathogenic involvement of multiple genes from the IL-23 and NF-κB pathways. A GWAS carried out by our group also identified RNF114, a gene encoding a novel ubiquitin binding protein, as a determinant for psoriasis susceptibility. Although the function of RNF114 is unknown, its paralogue RNF125 has been shown to regulate the RIG-I/MDA5 innate antiviral response. This signalling cascade, which is activated by the presence of double-stranded RNA (dsRNA) within the cytoplasm, induces the production of type I interferon (IFN) through the activation of the IRF3 and NF-κB transcription factors. Here, we explore the hypothesis that RNF114 may also modulate RIG-I/MDA5 signalling. We show that RNF114 associates with ubiquitinated proteins and that it is a soluble cytosolic protein that can be induced by interferons and synthetic dsRNA. Moreover, we demonstrate that RNF114 over-expression enhances NF-κb and IRF3 reporter activity and increases type I and type III IFN mRNA levels. These results indicate that RNF114 regulates a positive feedback loop that enhances dsRNA induced production of type I IFN. Thus, our data point to a novel pathogenic pathway, where dysregulation of RIG-I/MDA5 signalling leads to the over-production of type I IFN, a key early mediator of epithelial inflammation.

Dymeclin, the gene underlying Dyggve-Melchior-Clausen syndrome, encodes a protein integral to extracellular matrix and golgi organization and is associated with protein secretion pathways critical in bone development

Dyggve-Melchior-Clausen syndrome (DMC), a severe autosomal recessive skeletal disorder with mental retardation, is caused by mutation of the gene encoding Dymeclin (DYM). Employing patient fibroblasts with mutations characterized at the genomic and, for the first time, transcript level, we identified profound disruption of Golgi organization as a pathogenic feature, resolved by transfection of heterologous wild-type Dymeclin. Collagen targeting appeared defective in DMC cells leading to near complete absence of cell surface collagen fibers. DMC cells have an elevated apoptotic index (P< 0.01) likely due to a stress response contingent upon Golgi-related trafficking defects. We performed spatiotemporal mapping of Dymeclin expression in zebrafish embryos and identified high levels of transcript in brain and cartilage during early development. Finally, in a chondrocyte cDNA library, we identified two novel secretion pathway proteins as Dymeclin interacting partners: GOLM1 and PPIB. Together these data identify the role of Dymeclin in secretory pathways essential to endochondral bone formation during early development.

Mutations in NOTCH2 cause Hajdu-Cheney syndrome, a disorder of severe and progressive bone loss

We used an exome-sequencing strategy and identified an allelic series of NOTCH2 mutations in Hajdu-Cheney syndrome, an autosomal dominant multisystem disorder characterized by severe and progressive bone loss. The Hajdu-Cheney syndrome mutations are predicted to lead to the premature truncation of NOTCH2 with either disruption or loss of the C-terminal proline-glutamate-serine-threonine-rich proteolytic recognition sequence, the absence of which has previously been shown to increase Notch signaling.

The IL23R R381Q gene variant protects against immune-mediated diseases by impairing IL-23-induced Th17 effector response in humans

IL-23 and Th17 cells are key players in tissue immunosurveillance and are implicated in human immune-mediated diseases. Genome-wide association studies have shown that the IL23R R381Q gene variant protects against psoriasis, Crohn's disease and ankylosing spondylitis. We investigated the immunological consequences of the protective IL23R R381Q gene variant in healthy donors. The IL23R R381Q gene variant had no major effect on Th17 cell differentiation as the frequency of circulating Th17 cells was similar in carriers of the IL23R protective (A) and common (G) allele. Accordingly, Th17 cells generated from A and G donors produced similar amounts of Th17 cytokines. However, IL-23-mediated Th17 cell effector function was impaired, as Th17 cells from A allele carriers had significantly reduced IL-23-induced IL-17A production and STAT3 phosphorylation compared to G allele carriers. Our functional analysis of a human disease-associated gene variant demonstrates that IL23R R381Q exerts its protective effects through selective attenuation of IL-23-induced Th17 cell effector function without interfering with Th17 differentiation, and highlights its importance in the protection against IL-23-induced tissue pathologies.

Novel SPG11 mutations in Asian kindreds and disruption of spatacsin function in the zebrafish

Autosomal recessive hereditary spastic paraplegia with thin corpus callosum (HSP-TCC) maps to the SPG11 locus in the majority of cases. Mutations in the KIAA1840 gene, encoding spatacsin, have been shown to underlie SPG11-linked HSP-TCC. The aim of this study was to perform candidate gene analysis in HSP-TCC subjects from Asian families and to characterize disruption of spatacsin function during zebrafish development. Homozygosity mapping and direct sequencing were used to assess the ACCPN, SPG11, and SPG21 loci in four inbred kindreds originating from the Indian subcontinent. Four novel homozygous SPG11 mutations (c.442+1G>A, c.2146C>T, c.3602_3603delAT, and c.4846C>T) were identified, predicting a loss of spatacsin function in each case. To investigate the role of spatacsin during development, we additionally ascertained the complete zebrafish spg11 ortholog by reverse transcriptase PCR and 5′ RACE. Analysis of transcript expression through whole-mount in situ hybridization demonstrated ubiquitous distribution, with highest levels detected in the brain. Morpholino antisense oligonucleotide injection was used to knock down spatacsin function in zebrafish embryos. Examination of spg11 morphant embryos revealed a range of developmental defects and CNS abnormalities, and analysis of axon pathway formation demonstrated an overall perturbation of neuronal differentiation. These data confirm loss of spatacsin as the cause of SPG11-linked HSP-TCC in Asian kindreds, expanding the mutation spectrum recognized in this disorder. This study represents the first investigation in zebrafish addressing the function of a causative gene in autosomal recessive HSP and identifies a critical role for spatacsin during early neural development in vivo.

Dissection of the genetics of Parkinson's disease identifies an additional association 5' of SNCA and multiple associated haplotypes at 17q21

We performed a genome-wide association study (GWAS) in 1705 Parkinson's disease (PD) UK patients and 5175 UK controls, the largest sample size so far for a PD GWAS. Replication was attempted in an additional cohort of 1039 French PD cases and 1984 controls for the 27 regions showing the strongest evidence of association (P< 10⁻⁴). We replicated published associations in the 4q22/SNCA and 17q21/MAPT chromosome regions (P< 10⁻¹⁰) and found evidence for an additional independent association in 4q22/SNCA. A detailed analysis of the haplotype structure at 17q21 showed that there are three separate risk groups within this region. We found weak but consistent evidence of association for common variants located in three previously published associated regions (4p15/BST1, 4p16/GAK and 1q32/PARK16). We found no support for the previously reported SNP association in 12q12/LRRK2. We also found an association of the two SNPs in 4q22/SNCA with the age of onset of the disease.

A genome-wide association study identifies new psoriasis susceptibility loci and an interaction between HLA-C and ERAP1

To identify new susceptibility loci for psoriasis, we undertook a genome-wide association study of 594,224 SNPs in 2,622 individuals with psoriasis and 5,667 controls. We identified associations at eight previously unreported genomic loci. Seven loci harbored genes with recognized immune functions (IL28RA, REL, IFIH1, ERAP1, TRAF3IP2, NFKBIA and TYK2). These associations were replicated in 9,079 European samples (six loci with a combined P < 5 × 10⁻⁸ and two loci with a combined P < 5 × 10⁻⁷). We also report compelling evidence for an interaction between the HLA-C and ERAP1 loci (combined P = 6.95 × 10⁻⁶). ERAP1 plays an important role in MHC class I peptide processing. ERAP1 variants only influenced psoriasis susceptibility in individuals carrying the HLA-C risk allele. Our findings implicate pathways that integrate epidermal barrier dysfunction with innate and adaptive immune dysregulation in psoriasis pathogenesis.

Common variants near CAV1 and CAV2 are associated with primary open-angle glaucoma

We conducted a genome-wide association study for primary open-angle glaucoma (POAG) in 1,263 affected individuals (cases) and 34,877 controls from Iceland. We identified a common sequence variant at 7q31 (rs4236601[A], odds ratio (OR) = 1.36, P = 5.0 × 10⁻¹⁰). We then replicated the association in sample sets of 2,175 POAG cases and 2,064 controls from Sweden, the UK and Australia (combined OR = 1.18, P = 0.0015) and in 299 POAG cases and 580 unaffected controls from Hong Kong and Shantou, China (combined OR = 5.42, P = 0.0021). The risk variant identified here is located close to CAV1 and CAV2, both of which are expressed in the trabecular meshwork and retinal ganglion cells that are involved in the pathogenesis of POAG.

Elevated Levels of Inflammatory Cytokines Predict Survival in Idiopathic and Familial Pulmonary Arterial Hypertension

Background— Inflammation is a feature of pulmonary arterial hypertension (PAH), and increased circulating levels of cytokines are reported in patients with PAH. However, to date, no information exists on the significance of elevated cytokines or their potential as biomarkers. We sought to determine the levels of a range of cytokines in PAH and to examine their impact on survival and relationship to hemodynamic indexes.

Methods and Results— We measured levels of serum cytokines (tumor necrosis factor-α, interferon-γ and interleukin-1β, -2, -4, -5, -6, -8, -10, -12p70, and -13) using ELISAs in idiopathic and heritable PAH patients (n=60). Concurrent clinical data included hemodynamics, 6-minute walk distance, and survival time from sampling to death or transplantation. Healthy volunteers served as control subjects (n=21). PAH patients had significantly higher levels of interleukin-1β, -2, -4, -6, -8, -10, and -12p70 and tumor necrosis factor-α compared with healthy control subjects. Kaplan-Meier analysis showed that levels of interleukin-6, 8, 10, and 12p70 predicted survival in patients. For example, 5-year survival with interleukin-6 levels of >9 pg/mL was 30% compared with 63% for patients with levels ≤9 pg/mL ( P =0.008). In this PAH cohort, cytokine levels were superior to traditional markers of prognosis such as 6-minute walk distance and hemodynamics.

Conclusions— This study illustrates dysregulation of a broad range of inflammatory mediators in idiopathic and familial PAH and demonstrates that cytokine levels have a previously unrecognized impact on patient survival. They may prove to be useful biomarkers and provide insight into the contribution of inflammation in PAH.

Mutations in FLVCR2 are associated with proliferative vasculopathy and hydranencephaly-hydrocephaly syndrome (Fowler syndrome)

Proliferative vasculopathy and hydranencephaly-hydrocephaly syndrome (PVHH), also known as Fowler syndrome, is an autosomal-recessively inherited prenatal lethal disorder characterized by hydranencephaly; brain stem, basal ganglia, and spinal cord diffuse clastic ischemic lesions with calcifications; glomeruloid vasculopathy of the central nervous system and retinal vessels; and a fetal akinesia deformation sequence (FADS) with muscular neurogenic atrophy. To identify the molecular basis for Fowler syndrome, we performed autozygosity mapping studies in three consanguineous families. The results of SNP microarrays and microsatellite marker genotyping demonstrated linkage to chromosome 14q24.3. Direct sequencing of candidate genes within the target interval revealed five different germline mutations in FLVCR2 in five families with Fowler syndrome. FLVCR2 encodes a transmembrane transporter of the major facilitator superfamily (MFS) hypothesized to be involved in regulation of growth, calcium exchange, and homeostasis. This is the first gene to be associated with Fowler syndrome, and this finding provides a basis for further studies to elucidate the pathogenetic mechanisms and phenotypic spectrum of associated disorders.

A novel PCFT gene mutation (p.Cys66LeufsX99) causing hereditary folate malabsorption

Hereditary folate malabsorption (HFM) is a rare autosomal recessive disorder which is characterized by impaired intestinal folate malabsorption and impaired folate transport into the central nervous system. Mutations in the intestinal folate transporter PCFT have been reported previously in only 10 individuals with this disorder. The purpose of the current study was to describe the clinical phenotype and determine the molecular basis for this disorder in a family with four affected individuals. A consanguineous family of Pakistani origin with autosomal recessive HFM was ascertained and clinically phenotyped. After genetic linkage studies all coding exons of the PCFT gene were screened for mutations by direct sequencing. The clinical phenotype of four affected patients is described. Direct sequencing of PCFT revealed a novel homozygous frameshift mutation (c.194dupG) at a mononucleotide repeat in exon 1 predicted to result in a truncated protein (p.Cys66LeufsX99). This report extends current knowledge on the phenotypic manifestations of HFM and the PCFT mutation spectrum.