IPEX is a fatal disorder characterized by immune dysregulation, polyendocrinopathy, enteropathy and X-linked inheritance (MIM 304930). We present genetic evidence that different mutations of the human gene FOXP3, the ortholog of the gene mutated in scurfy mice (Foxp3), causes IPEX syndrome. Recent linkage analysis studies mapped the gene mutated in IPEX to an interval of 17-20-cM at Xp11. 23-Xq13.3.

To determine whether human X-linked neonatal diabetes mellitus, enteropathy and endocrinopathy syndrome (IPEX; MIM 304930) is the genetic equivalent of the scurfy (sf) mouse, we sequenced the human ortholog (FOXP3) of the gene mutated in scurfy mice (Foxp3), in IPEX patients. We found four non-polymorphic mutations. Each mutation affects the forkhead/winged-helix domain of the scurfin protein, indicating that the mutations may disrupt critical DNA interactions.

There is an unmet medical need for anabolic treatments to restore lost bone. Human genetic bone disorders provide insight into bone regulatory processes. Sclerosteosis is a disease typi®ed by high bone mass due to the loss of SOST expression. Sclerostin, the SOST gene protein product, competed with the type I and type II bone morphogenetic protein (BMP) receptors for binding to BMPs, decreased BMP signaling and suppressed mineralization of osteoblastic cells. SOST expression was detected in cultured osteoblasts and in mineralizing areas of the skeleton, but not in osteoclasts. Strong expression in osteocytes suggested that sclerostin expressed by these central regulatory cells mediates bone homeostasis. Transgenic mice overexpressing SOST exhibited low bone mass and decreased bone strength as the result of a signi®cant reduction in osteoblast activity and subsequently, bone formation. Modulation of this osteocyte-derived negative signal is therapeutically relevant for disorders associated with bone loss.

Sclerosteosis is an autosomal recessive sclerosing bone dysplasia characterized by progressive skeletal overgrowth. The majority of affected individuals have been reported in the Afrikaner population of South Africa, where a high incidence of the disorder occurs as a result of a founder effect. Homozygosity mapping in Afrikaner families along with analysis of historical recombinants localized sclerosteosis to an interval of approximately 2 cM between the loci D17S1787 and D17S930 on chromosome 17q12-q21. Here we report two independent mutations in a novel gene, termed "SOST." Affected Afrikaners carry a nonsense mutation near the amino terminus of the encoded protein, whereas an unrelated affected person of Senegalese origin carries a splicing mutation within the single intron of the gene. The SOST gene encodes a protein that shares similarity with a class of cystine knot-containing factors including dan, cerberus, gremlin, prdc, and caronte. The specific and progressive effect on bone formation observed in individuals affected with sclerosteosis, along with the data presented in this study, together suggest that the SOST gene encodes an important new regulator of bone homeostasis.

The expression of the H19 gene is governed by parental imprinting in mammals. H19, an unusual gene encoding an RNA with no known function, is exclusively expressed from the maternal chromosome. In mouse, it lies 90 kb downstream from the lgf2 gene, which encodes a fetal-specific growth factor, insulin-like growth factor II, and is expressed primarily from the paternally inherited chromosome. In this report we have utilized interspecific hybrid mice to identify male-specific DNA methylation of a 7-to 9-kb domain surrounding the 1-119 gene and its promoter. This allele-specific methylation could function as a mark to suppress transcription of the H19 paternal allele. Consistent with this proposal, the H19 promoter displayed an open chromatin conformation only on the relatively unmethylated active maternal allele. In contrast, a cell type-specific enhancer that lies outside the methylation domain is hypersensitive to restriction enzyme digestion in nuclei on both maternal and paternal chromosomes. That the allele-specific methylation domain, coupled to the two H19 enhancers, contains all the information necessary for its imprinting was tested by examining two transgenic lines containing an internally deleted H19 transgene. Both displayed paternal-specific methylation of the transgene and maternal-specific expression. Although neither line has been tested in an inbred genetic background, and therefore the action of complex modifiers cannot be formally excluded, the result suggests that the sequences necessary for the imprinting of H19 have been identified.

Van Buchem disease is an autosomal recessive sclerosing bone dysplasia characterized by skeletal hyperostosis, overgrowth of the mandible, and a liability to entrapment of the seventh and eighth cranial nerves. The genetic determinant maps to chromosome 17q12-q21. We refined the critical interval to the < 1-Mb region between D17S2250 and D17S2253 in 15 affected individuals, all of whom shared a common disease haplotype. Furthermore, we report here the identification of a 52-kb deletion located within the interval and encompassing D17S1789 that is 100% concordant with the disorder. Although the deletion itself does not appear to disrupt the coding region of any known or novel gene(s), the closest flanking genes are MEOX1 on the proximal side, and SOST on the distal side of the deletion. MEOX1 is known to be important for the development of the axial skeleton, whereas the SOST gene is the determinant of sclerosteosis, a disorder that shares many features with van Buchem disease, thus raising the possibility that van Buchem disease results from dysregulation of the expression of one or both of these genes.

The mouse scurfy gene, Foxp3, and its human orthologue, FOXP3, which maps to Xp11.23-Xq13.3, were recently identified by positional cloning. Point mutations and microdeletions of the FOXP3 gene were found in the affected members of eight of nine families with IPEX (immune dysfunction, polyendocrinopathy, enteropathy, X-linked; OMIM 304930). We evaluated a pedigree with clinically typical IPEX in which mutations of the coding exons of FOXP3 were not detected. Our reevaluation of this pedigree identified an A-->G transition within the first polyadenylation signal (AAUAAA-->AAUGAA) after the stop codon. The next polyadenylation signal is not encountered for a further 5.1 kb. This transition was not detected in over 212 normal individuals (approximately 318 X chromosomes), excluding the possibility of a rare polymorphism. We suggest that this mutation is causal of IPEX in this family by a mechanism of nonspecific degradation of the FOXP3 gene message.

We sequenced the genomes of 200 individuals from 41 families multiply affected with bipolar disorder (BD) to identify contributions of rare variants to genetic risk. We initially focused on 3,087 candidate genes with known synaptic functions or prior evidence from genomewide association studies. BD pedigrees had an increased burden of rare variants in genes encoding neuronal ion channels, including subunits of GABA A receptors and voltage-gated calcium channels. Four uncommon coding and regulatory variants also showed significant association, including a missense variant in GABRA6. Targeted sequencing of 26 of these candidate genes in an additional 3,014 cases and 1,717 controls confirmed rare variant associations in ANK3, CACNA1B, CACNA1C, CACNA1D, CACNG2, CAMK2A, and NGF. Variants in promoters and 5′ and 3′ UTRs contributed more strongly than coding variants to risk for BD, both in pedigrees and in the case-control cohort. The genes and pathways identified in this study regulate diverse aspects of neuronal excitability. We conclude that rare variants in neuronal excitability genes contribute to risk for BD. by episodes of mania and depression (1). Episodes of mania are marked by elevated or alternatively irritable mood, grandiosity, racing thoughts, rapid speech, diminished need for sleep, and risk-taking behavior. Depression includes sadness, low energy and motivation, decreased ability to experience pleasure, insomnia, and appetite changes. Psychosis with hallucinations and delusions can occur in either state. BD affects 1-2% of the US population, and if untreated, up to 15% of patients die from suicide. Twin and family studies suggest that heritable causes explain 60-80% of lifetime risk for BD (2), with an approximate eightfold relative risk in the siblings of BD probands (3). Several common genetic markers have shown significant and replicable associations in genome-wide association studies (GWASs), including a region near a voltage-gated calcium channel, CACNA1C, and another near a synaptic scaffolding gene, ANK3 (4). Additive effects of common loci detectable on commercially available genomic arrays may be used to predict about 25% of the risk for BD (5), but typically the function and exact location of the causative variants linked to these loci is unknown.Rare variants may explain additional risk for BD. It is possible that one or a few rare variants of large effect dramatically increase disease risk, resulting in an inheritance model resembling monogenic inheritance in a given family. However, four exomesequencing and whole-genome sequencing (WGS) studies of BD pedigrees have detected few, if any, plausible variants of large effect (6-9). An alternative oligogenic model posits that different combinations of several uncommon or rare variants of moderate effect cluster in affected individuals and collectively cause disease.To test the hypothesis that rare variants contribute to risk for BD, we sequenced the genomes of 200 individuals from 41 multiply affected BD pedigrees of European ancestry. We seque...