Beyond finding individual genes that are involved in medical disorders, an important challenge is the integration of sets of disease genes with the complexities of basic biological processes. We examine this issue by focusing on neuronal multiprotein complexes and their components encoded on the human X chromosome. Multiprotein signaling complexes in the postsynaptic terminal of central nervous system synapses are essential for the induction of neuronal plasticity and cognitive processes in animals. The prototype complex is the N-methyl-D-aspartate receptor complex/membrane-associated guanylate kinase-associated signaling complex (NRC/MASC) comprising 185 proteins and embedded within the postsynaptic density (PSD), which is a set of complexes totaling approximately 1,100 proteins. It is striking that 86% (6 of 7) of X-linked NRC/MASC genes and 49% (19 of 39) of X-chromosomal PSD genes are already known to be involved in human psychiatric disorders. Moreover, of the 69 known proteins mutated in X-linked mental retardation, 19 (28%) encode postsynaptic proteins. The high incidence of involvement in cognitive disorders is also found in mouse mutants and indicates that the complexes are functioning as integrated entities or molecular machines and that disruption of different components impairs their overall role in cognitive processes. We also noticed that NRC/MASC genes appear to be more strongly associated with mental retardation and autism spectrum disorders. We propose that systematic studies of PSD and NRC/MASC genes in mice and humans will give a high yield of novel genes important for human disease and new mechanistic insights into higher cognitive functions.

Many complex human diseases are highly sexually dimorphic, suggesting a potential contribution of the X chromosome to disease risk. However, the X chromosome has been neglected or incorrectly analyzed in most genome-wide association studies (GWAS). We present tailored analytical methods and software that facilitate X-wide association studies (XWAS), which we further applied to reanalyze data from 16 GWAS of different autoimmune and related diseases (AID). We associated several X-linked genes with disease risk, among which (1) ARHGEF6 is associated with Crohn's disease and replicated in a study of ulcerative colitis, another inflammatory bowel disease (IBD). Indeed, ARHGEF6 interacts with a gastric bacterium that has been implicated in IBD. (2) CENPI is associated with three different AID, which is compelling in light of known associations with AID of autosomal genes encoding centromere proteins, as well as established autosomal evidence of pleiotropy between autoimmune diseases. (3) We replicated a previous association of FOXP3, a transcription factor that regulates T-cell development and function, with vitiligo; and (4) we discovered that C1GALT1C1 exhibits sex-specific effect on disease risk in both IBDs. These and other X-linked genes that we associated with AID tend to be highly expressed in tissues related to immune response, participate in major immune pathways, and display differential gene expression between males and females. Combined, the results demonstrate the importance of the X chromosome in autoimmunity, reveal the potential of extensive XWAS, even based on existing data, and provide the tools and incentive to properly include the X chromosome in future studies.

Genetically engineered pigs play an indispensable role in the study of rare monogenic diseases. Pigs harboring a gene responsible for a specific disease can be efficiently generated via somatic cell cloning. The generation of somatic cell-cloned pigs from male cells with mutation(s) in an X chromosomal gene is a reliable and straightforward method for reproducing X-linked genetic diseases (XLGDs) in pigs. However, the severe symptoms of XLGDs are often accompanied by impaired growth and reproductive disorders, which hinder the reproduction of these valuable model animals. Here, we generated unique chimeric boars composed of mutant cells harboring a lethal XLGD and normal cells. The chimeric boars exhibited the cured phenotype with fertility while carrying and transmitting the genotype of the XLGD. This unique reproduction system permits routine production of XLGD model pigs through the male-based breeding, thereby opening an avenue for translational research using disease model pigs.

X-linked hypophosphatemia (XLH) is caused by inactivating mutations in the phosphate-regulating endopeptidase homolog, X-linked (PHEX) gene, resulting in an excess of circulating intact fibroblast growth factor-23 (iFGF-23) and a waste of renal phosphate. In the present study, we retrospectively reviewed the clinical and molecular features of 153 Chinese patients, representing 87 familial and 66 sporadic cases with XLH. A total of 153 patients with XLH presented with signs or symptoms at a median age of 18.0 months (range, 9.0 months-26.0 years). Lower-limb deformity was the most frequent clinical manifestation, accounting for 79.1% (121/153). Biochemical screening showed increased serum levels of iFGF23 in patients with XLH, with a wide variation ranging from 14.39 to 730.70 pg/ml. Median values of serum iFGF23 in pediatric and adult patients were 94.87 pg/ml (interquartile range: 74.27-151.86 pg/ml) and 72.82 pg/ml (interquartile range: 39.42-136.00 pg/ml), respectively. Although no difference in circulating iFGF23 levels between these two groups was observed (P = 0.062), the proportion of patients with high levels of circulating iFGF23 (>42.2 pg/ml) was greater in the pediatric group than in the adult group (P = 0.026). Eighty-eight different mutations in 153 patients were identified, with 27 (30.7%) being novel. iFGF23 levels and severity of the disease did not correlate significantly with truncating and non-truncating mutations or N-terminal and C-terminal PHEX mutations. This study provides a comprehensive description of the clinical profiles, circulating levels of iFGF23 and gene mutation features of patients with XLH, further enriching the genotypic spectrum of the diseases. The findings show no evident correlation of circulating iFGF23 levels with the age or disease severity in patients with XLH.

Autoimmune diseases often share common susceptibility genes. Most genetic variants associated with susceptibility to systemic lupus erythematosus are also associated with other autoimmune diseases. The X-linked variant rs2294020 is positioned in exon 7 of the CCDC22 gene. The encoded protein functions in the regulation of NF-κB, a master regulator in immune response. The aim of this study is to investigate whether the rs2294020 polymorphism may be a general susceptibility factor for autoimmunity. We evaluated case-control association between the occurrence of rs2294020 and different autoimmune diseases, including new data for systemic lupus erythematosus and previous genome-wide association studies (GWAS) (though most did not analyse the X chromosome) of psoriasis, celiac disease, Crohn's disease, ulcerative colitis, multiple sclerosis, vitiligo, type-1 diabetes, rheumatoid arthritis, and ankylosing spondylitis. Cases from patients affected by amyotrophic lateral sclerosis and type-2 diabetes were also included in the study. We detected nominal significant associations of rs2294020 with systemic lupus erythematosus (additive model test: p=0.01), vitiligo (p=0.016), psoriasis (p=0.038), and in only one of two studies of multiple sclerosis (p=0.03). Our results suggest that rs2294020 is associated with the risk of several autoimmune diseases in European populations, specifically with diseases that present themselves, among else, in the skin.

X-linked hyper-IgM syndrome (XHIGM) is one type of primary immunodeficiency diseases, resulting from defects in the CD40 ligand/CD40 signaling pathways. We retrospectively analyzed the clinical and molecular features of 20 Chinese patients diagnosed and followed up in hospitals affiliated to Shanghai Jiao Tong University School of Medicine from 1999 to 2013. The median onset age of these patients was 8.5 months (range: 20 days-21 months). Half of them had positive family histories, with a shorter diagnosis lag. The most common symptoms were recurrent sinopulmonary infections (18 patients, 90%), neutropenia (14 patients, 70%), oral ulcer (13 patients, 65%), and protracted diarrhea (13 patients, 65%). Six patients had BCGitis. Six patients received hematopoietic stem cell transplantations and four of them had immune reconstructions and clinical remissions. Eighteen unique mutations in CD40L gene were identified in these 20 patients from 19 unrelated families, with 12 novel mutations. We compared with reported mutation results and used bioinformatics software to predict the effects of mutations on the target protein. These mutations reflected the heterogeneity of CD40L gene and expanded our understanding of XHIGM.

Spondyloepimetaphyseal dysplasias (SEMDs) comprise a heterogeneous group of autosomal-dominant and autosomal-recessive disorders. An apparent X-linked recessive (XLR) form of SEMD in a single Italian family was previously reported. We have been able to restudy this family together with a second family from Korea by segregating a severe SEMD in an X-linked pattern. Exome sequencing showed missense mutations in BGN c.439A>G (p.Lys147Glu) in the Korean family and c.776G>T (p.Gly259Val) in the Italian family; the c.439A>G (p.Lys147Glu) mutation was also identified in a further simplex SEMD case from India. Biglycan is an extracellular matrix proteoglycan that can bind transforming growth factor beta (TGF-β) and thus regulate its free concentration. In 3-dimensional simulation, both altered residues localized to the concave arc of leucine-rich repeat domains of biglycan that interact with TGF-β. The observation of recurrent BGN mutations in XLR SEMD individuals from different ethnic backgrounds allows us to define "XLR SEMD, BGN type" as a nosologic entity.

Males with X-linked adrenoleukodystrophy (ALD) are at high risk for developing adrenal insufficiency and/or progressive leukodystrophy (cerebral ALD) at an early age. Pathogenic variants in ABCD1 result in elevated levels of very long-chain fatty acids (VLCFA), including C26:0-lysophosphatidylcholine (C26:0-LPC). Newborn screening for ALD enables prospective monitoring and timely therapeutic intervention, thereby preventing irreversible damage and saving lives. The Dutch Health Council recommended to screen only male newborns for ALD without identifying untreatable conditions associated with elevated C26:0-LPC, like Zellweger spectrum disorders and single peroxisomal enzyme defects. Here, we present the results of the SCAN (Screening for ALD in the Netherlands) study which is the first sex-specific newborn screening program worldwide. Males with ALD are identified based on elevated C26:0-LPC levels, the presence of one X-chromosome and a variant in ABCD1, in heel prick dried bloodspots. Screening of 71 208 newborns resulted in the identification of four boys with ALD who, following referral to the pediatric neurologist and confirmation of the diagnosis, enrolled in a long-term follow-up program. The results of this pilot show the feasibility of employing a boys-only screening algorithm that identifies males with ALD without identifying untreatable conditions. This approach will be of interest to countries that are considering ALD newborn screening but are reluctant to identify girls with ALD because for girls there is no direct health benefit. We also analyzed whether gestational age, sex, birth weight and age at heel prick blood sampling affect C26:0-LPC concentrations and demonstrate that these covariates have a minimal effect.

Cellular identity in multicellular organisms is maintained by characteristic transcriptional networks, nutrient consumption, energy production and metabolite utilization. Integrating these cell-specific programs are epigenetic modifiers, whose activity is often dependent on nutrients and their metabolites to function as substrates and co-factors. Emerging data has highlighted the role of the nutrient-sensing enzyme O-GlcNAc transferase (OGT) as an epigenetic modifier essential in coordinating cellular transcriptional programs and metabolic homeostasis. OGT utilizes the end-product of the hexosamine biosynthetic pathway to modify proteins with O-linked β-D-N-acetylglucosamine (O-GlcNAc). The levels of the modification are held in check by the O-GlcNAcase (OGA). Studies from model organisms and human disease underscore the conserved function these two enzymes of O-GlcNAc cycling play in transcriptional regulation, cellular plasticity and mitochondrial reprogramming. Here, we review these findings and present an integrated view of how O-GlcNAc cycling may contribute to cellular memory and transgenerational inheritance of responses to parental stress. We focus on a rare human genetic disorder where mutant forms of OGT are inherited or acquired de novo. Ongoing analysis of this disorder, OGT- X-linked intellectual disability (OGT-XLID), provides a window into how epigenetic factors linked to O-GlcNAc cycling may influence neurodevelopment.

X-linked adrenoleukodystrophy (X-ALD) is a genetic disorder of X-linked inheritance caused by a mutation in the ABCD1 gene which determines an accumulation of long-chain fatty acids in plasma and tissues. Recent evidence shows that oxidative stress may be a hallmark in the pathogenesis of X-ALD and glutathione plays an important role in the defense against free radicals. In this study we have analyzed glutathione homeostasis in lymphocytes of 14 patients with X-ALD and evaluated the balance between oxidized and reduced forms of glutathione, in order to define the role of this crucial redox marker in this condition.

X-linked adrenoleukodystrophy (ALD) is a progressive neurodegenerative disease that is caused by mutations in the ABCD1 gene and characterized by elevated levels of very long-chain fatty acids (VLCFA) in plasma and tissues, with the most pronounced increase in the central nervous system. Virtually all male patients develop adrenal insufficiency and myelopathy (adrenomyeloneuropathy), but a subset develops a fatal cerebral demyelinating disease (known as cerebral ALD). Female patients may also develop myelopathy, but adrenal insufficiency or leukodystrophy are very rare. ALD has been associated with mitochondrial dysfunction, oxidative stress and bioenergetic failure, but the mechanism by which VLCFA accumulation triggers these effects has not been resolved thus far. In this study, we used primary human fibroblasts from normal subjects and ALD patients to investigate whether VLCFA can induce endoplasmic reticulum stress. We show that saturated VLCFA (C26:0) induce endoplasmic reticulum stress in fibroblasts from ALD patients, but not in controls. Furthermore, there is a clear correlation between the chain-length of the fatty acid and the induction of endoplasmic reticulum stress. Exposure of ALD fibroblasts to C26:0, resulted in increased expression of additional endoplasmic reticulum stress markers (EDEM1, GADD34 and CHOP) and in lipoapoptosis. This new insight into the underlying mechanism of VLCFA-induced toxicity is of great importance for the development of a disease modifying treatment for ALD aimed at the normalization of VLCFA levels in tissues.

Pf62-Y and Pf62-X is a pair of allelic Y chromosome-linked and X chromosome-linked markers, and have been used to identify YY super-males, XY males and XX females for commercial production of all-male populations in yellow catfish (Pelteobagrus fulvidraco). However, the SCAR primers used previously have only two nucleotide difference, which restricts the wide utility because of nucleotide polymorphism. In this study, a continuous 8102 bp Pf62-Y sequence and a 5362 bp Pf62-X sequence have been cloned by genome walking, and significant genetic differentiation has been revealed between the corresponding X and Y chromosome allele sequences. Moreover, three pairs of primers were designed to efficiently identify YY super-males, XY males and XX females in an artificial breeding population, and to distinguish XY males and XX females in various wild populations. Together, the three new sex-specific genetic markers develop a highly stable and efficient method for genetic sex identification and sex control application in sustainable aquaculture of all-male yellow catfish.

POU3F4 is the causative gene for X-linked deafness-2 (DFNX2), characterized by incomplete partition type III (IP-III) malformation of the inner ear. The purpose of this study was to investigate the clinical characteristics and molecular findings in IP-III patients by Sanger or nanopore single-molecule sequencing.

Over 80% of women with X-linked adrenoleukodystrophy (ALD) develop spinal cord disease in adulthood for which treatment is supportive only. For future clinical trials quantitative data on disease progression rates are essential. Moreover, diagnosis can be challenging in ALD women, as the most important diagnostic biomarker is normal in 15-20%. Better biomarkers are needed. The purpose of this single centre cross-sectional follow-up study in women with ALD was to assess whether Expanded Disability Status Scale (EDSS), AMC Linear Disability Scale (ALDS) and Short Form (36) Health Survey (SF-36) can detect disease progression and to model the effect of age and duration of symptoms on the rate of progression. Moreover, we performed a pilot study to assess if a semi-targeted lipidomics approach can identify possible new diagnostic biomarkers.

Maturation arrest (MA) is a subtype of non-obstructive azoospermia, and male infertility is a known risk factor for testicular tumors. However, the genetic basis for many affected individuals remains unknown. Here, we identified a deleterious hemizygous variant of X-linked retinoblastoma-binding protein 7 (RBBP7) as a potential key cause of MA, which was also found to be associated with the development of Leydig cell tumors. This mutation resulted in premature protein translation termination, affecting the sixth WD40 domain of the RBBP7 and the interaction of the mutated RBBP7 with histone H4. Decreased BRCA1 and increased γH2AX were observed in the proband. In mouse spermatogonial and pachytene spermatocyte-derived cells, deprivation of rbbp7 led to cell cycle arrest and apoptosis. In Drosophila, knockdown of RBBP7/Caf1-55 in germ cells resulted in complete absence of germ cells and reduced testis size, whereas knockdown of RBBP7/Caf1-55 in cyst cells resulted in hyperproliferative testicular cells. Interestingly, male infertility caused by Caf1-55 deficiency was rescued by ectopic expression of wild-type human RBBP7 but not mutant variants, suggesting the importance of RBBP7 in spermatogenesis. Our study provides insights into the mechanisms underlying the co-occurrence of MA and testicular tumors and may pave the way for innovative genetic diagnostics of these 2 diseases.

Rheumatoid arthritis (RA) is an autoimmune disease that predominantly affects women. MicroRNAs have emerged as crucial regulators of the immune system, whose expression is deregulated in RA. We aimed at quantifying the expression level of 14 miRNAs located on the X chromosome and at identifying whether differences are associated with disease and/or sex. A case-control study of 21 RA patients and 22 age- and sex-matched healthy controls was performed on peripheral blood mononuclear cells. The expression level of five miRNAs (miR-221, miR-222, miR-532, miR-106a, and miR-98) was significantly different between RA and controls when stratifying by sex, and the expression level of four miRNAs (miR-222, miR-532, miR-98, and miR-92a) was significantly different between RA females and males. The expression quantitative trait loci (eQTL) analysis revealed a significant gender effect of the FoxP3 promoter polymorphism rs3761548A/C on miR-221, miR-222 and miR-532 expression levels, and of the FoxP3 polymorphism rs2232365A/G on miR-221 expression levels in PBMC of RA patients. These data further support the involvement of the X chromosome in RA susceptibility. X-linked miRNAs, in the context of sex differences, might provide novel insight into new molecular mechanisms and potential therapeutic targets in RA for disease treatment and prevention.

X-linked hydrocephalus (XLH), characterized by mental retardation and bilateral adducted thumbs, often come out to be a genetic disorder of L1CAM. It codes the protein L1 cell adhesion molecule (L1CAM), playing a crucial role in the development of the nervous system. The objective of the study was to report a new disease-causing mutation site of L1CAM, and gain further insight into the pathophysiology of hydrocephalus.

To identify the causal gene in a multi-incident U.S. kindred with Parkinson's disease (PD).

To identify a pharmacological compound targeting macrophages, the most affected immune cells in inflammatory X-linked adrenoleukodystrophy (cerebral X-ALD) caused by ABCD1 mutations and involved in the success of hematopoietic stem cell transplantation and gene therapy.

X-linked intellectual deficiency (XLID) is a widely heterogeneous group of genetic disorders that involves more than 100 genes. The mediator of RNA polymerase II subunit 12 (MED12) is involved in the regulation of the majority of RNA polymerase II-dependent genes and has been shown to cause several forms of XLID, including Opitz-Kaveggia syndrome also known as FG syndrome (MIM #305450), Lujan-Fryns syndrome (MIM #309520) and the X-linked Ohdo syndrome (MIM #300895). Here, we report on two first cousins with X-linked Ohdo syndrome with a missense mutation in MED12 gene, identified through whole exome sequencing. The probands had facial features typical of X-linked Ohdo syndrome, including blepharophimosis, ptosis, a round face with a characteristic nose and a narrow mouth. Nextera DNA Exome kit (Illumina Inc., San Diego, CA, USA) was used for exome capture. The variant identified was a c.887G > A substitution in exon 7 of the MED12 gene leading to the substitution of a glutamine for a highly conserved arginine (p. Arg296Gln). Although the variant described has been previously reported in the literature, our study contributes to the expanding phenotypic spectrum of MED12-related disorders and above all, it demonstrates the phenotypic variability among different affected patients despite harboring identical mutations.