Biallelic mutations in FLNB cause a skeletal dysplasia with 46,XY gonadal dysgenesis by activating ß-catenin.

Filamin B (FLNB) functions as a switch that can affect chrondrocyte development and endochondral bone formation through a series of signaling molecules and transcription factors that also affect Sertoli cell development. Here, we report a subject with a novel skeletal dysplasia and co-existing 46,XY gonadal dysgenesis and biallelic mutations in FLNB. Whole exome sequencing was performed to identify mutations. Quantitative polymerase chain reaction (qPCR) and flow variant assays were performed to quantify RNA, proteins and phosphorylated proteins. The TOPFLASH reporter was performed to quantify ß-catenin activity. Mutations were identified in the FLNB gene (FLNB:p.F964L, FLNB:p.A1577V). These mutations increased binding of FLNB protein to the MAP3K1 and RAC1 signal transduction complex and activated ß-catenin and had different effects on phosphorylation of MAP kinase pathway intermediates and SOX9 expression. Direct activation of ß-catenin through the FLNB-MAP3K1-RAC1 complex by FLNB mutations is a novel mechanism for causing 46,XY gonadal dysgenesis. The mechanism of action varies from those reported previously for loss of function mutations in SOX9 and gain-of-function mutations in MAP3K1.

The carrier frequency of the BRCA2 6174delT mutation among Ashkenazi Jewish individuals is approximately 1%.

Certain germline mutations in either BRCA1 or BRCA2 confer a lifetime risk of developing breast cancer that may approach 90%. The BRCA1 185delAG mutation was found in 20% and the BRCA2 6174delT mutation in 8% of Ashkenazi Jewish women with early-onset breast cancer. The 185delAG mutation was observed in 0.9% of 858 Ashkenazi Jews unselected for a personal or family history of cancer. Assuming comparable age-specific penetrances, a carrier frequency of 0.3% was estimated for the 6174delT BRCA2 mutation. To test this hypothesis, we performed a population survey of 1,255 Jewish individuals. In two independent groups, a prevalence of approximately 1% (C.I. 0.6-1.5) was observed for the 6174delT mutation. The relative risk of developing breast cancer by age 42 was estimated to be 9.3 (C.I. 2.5-22.5) for 6174delT, compared to 31 (C.I. 11-77) for 185delAG. Analysis of 107 Ashkenazi Jewish women with breast cancer and a family history of breast or ovarian cancer confirmed a four-fold greater prevalence for the BRCA1 185delAG mutation compared to the BRCA2 6174delT mutation. Our findings suggest a difference in cumulative life-time penetrance for the two mutations. Genetic counseling for the one in 50 Ashkenazi Jewish individuals harbouring specific germline mutations in BRCA1 or BRCA2 must be tailored to reflect the different risks associated with the two mutations.

Familial colorectal cancer in Ashkenazim due to a hypermutable tract in APC.

Approximately 130,000 cases of colorectal cancer (CRC) are diagnosed in the United States each year, and about 15% of these have a hereditary component. Two well-defined syndromes, familial adenomatous polyposis (FAP) and hereditary non-polyposis colorectal cancer (HNPCC), account for up to 5% of the total new cases of CRC. Truncating APC mutations are responsible for FAP, and defective mismatch repair genes cause HNPCC. However, the genes responsible for most of the familial cases are unknown. Here we report a mutation (T to A at APC nucleotide 3920) found in 6% of Ashkenazi Jews and about 28% of Ashkenazim with a family history of CRC. Rather than altering the function of the encoded protein, this mutation creates a small hypermutable region of the gene, indirectly causing cancer predisposition.

The impact of Converso Jews on the genomes of modern Latin Americans.

Modern day Latin America resulted from the encounter of Europeans with the indigenous peoples of the Americas in 1492, followed by waves of migration from Europe and Africa. As a result, the genomic structure of present day Latin Americans was determined both by the genetic structure of the founding populations and the numbers of migrants from these different populations. Here, we analyzed DNA collected from two well-established communities in Colorado (33 unrelated individuals) and Ecuador (20 unrelated individuals) with a measurable prevalence of the BRCA1 c.185delAG and the GHR c.E180 mutations, respectively, using Affymetrix Genome-wide Human SNP 6.0 arrays to identify their ancestry. These mutations are thought to have been brought to these communities by Sephardic Jewish progenitors. Principal component analysis and clustering methods were employed to determine the genome-wide patterns of continental ancestry within both populations using single nucleotide polymorphisms, complemented by determination of Y-chromosomal and mitochondrial DNA haplotypes. When examining the presumed European component of these two communities, we demonstrate enrichment for Sephardic Jewish ancestry not only for these mutations, but also for other segments as well. Although comparison of both groups to a reference Hispanic/Latino population of Mexicans demonstrated proximity and similarity to other modern day communities derived from a European and Native American two-way admixture, identity-by-descent and Y-chromosome mapping demonstrated signatures of Sephardim in both communities. These findings are consistent with historical accounts of Jewish migration from the realms that comprise modern Spain and Portugal during the Age of Discovery. More importantly, they provide a rationale for the occurrence of mutations typically associated with the Jewish Diaspora in Latin American communities.

Rapidly screening variants of uncertain significance in the MAP3K1 gene for phenotypic effects.

DNA sequencing of candidate genes or whole exomes on a diagnostic or investigational basis will yield a plethora of variants of uncertain significance whose potential phenotypic roles cannot be readily demonstrated by prediction programs, SNP databases nor conventional genetic analysis. Many variants may produce phenotypic changes in the encoded proteins by affecting the quantity, post-translational modification or protein interactions. Here, we establish the application of the method of flow cytometry following immunoprecipitation to show that known protein interactions are altered in the B-lymphoblastoid cells of patients with 46,XY gonadal dysgenesis arising from mutations in the MAP3K1 gene. This method can be scaled readily to test multiple interactions for many variants simultaneously from available tissues as well as quantify the effects of variants on protein accumulation and post-translational modification, thus providing an efficient means for screening variants of uncertain significance for phenotypic effects.

TbetaR-I(6A) is a candidate tumor susceptibility allele.

We have previously described a type I transforming growth factor (TGF)-beta receptor (TbetaR-I) polymorphic allele, TbetaR-I(6A), that has a deletion of three alanines from a nine-alanine stretch. We observed a higher than expected number of TbetaR-I(6A) homozygotes among tumor and nontumor DNA from patients with a diagnosis of cancer. To test the hypothesis that TbetaR-I(6A) homozygosity is associated with cancer, we performed a case-control study in patients with a diagnosis of cancer and matched healthy individuals with no history of cancer and who were identical in their gender and their geographical and ethnic background to determine the relative germ-line frequencies of this allele. We found nine TbetaR-I(6A) homozygotes among 851 patients with cancer. In comparison, there were no TbetaR-I(6A) homozygotes among 735 healthy volunteers (P < 0.01). We also observed an excess of TbetaR-I(6A) heterozygotes in cancer cases compared to controls (14.6% versus 10.6%; P = 0.02, Fisher's exact test). A subset analysis revealed that 4 of 112 patients with colorectal cancer were TbetaR-I(6A) homozygotes (P < 0.01). Using mink lung epithelial cell lines devoid of TbetaR-I, we established stably transfected TbetaR-I and TbetaR-I(6A) cell lines. We found that, compared to TbetaR-I, TbetaR-I(6A) was impaired as a mediator of TGF-beta antiproliferative signals. We conclude that TbetaR-I(6A) acts as a tumor susceptibility allele that may contribute to the development of cancer, especially colon cancer, by means of reduced TGF-beta-mediated growth inhibition.

Expression of steroidogenic factor 1 and Wilms' tumour 1 during early human gonadal development and sex determination.

The transcription factors SF-1 and WT1 play pivotal roles in mammalian gonadal development and sexual differentiation. In human embryos, both SF-1 and WT1 are expressed when the indifferent gonadal ridge first forms at 32 days post-ovulation. As the sex cords develop - providing morphological evidence of testis differentiation - SF-1 localises predominantly to developing Sertoli cells in the sex cords, whereas WT1 retains a broader pattern of expression. Later, SF-1 localises predominantly to steroidogenic Leydig cells, and WT1 localises to the sex cords. In the ovary, SF-1 and WT1 transcripts persist in the gonadal ridge from the earliest developmental stages throughout the critical period of sex determination. These studies, which delineate for the first time the sequential expression profiles of SF-1 and WT1 during human gonadal development, provide a framework for understanding human sex reversal phenotypes associated with their mutations.

SRY, SOX9, and DAX1 expression patterns during human sex determination and gonadal development.

SRY, SOX9, and DAX1 are key genes in human sex determination, by virtue of their associated male-to-female sex reversal phenotypes when mutated (SRY, SOX9) or over-expressed (DAX1). During human sex determination, SRY is expressed in 46,XY gonads coincident with sex cord formation, but also persists as nuclear protein within Sertoli cells at 18 weeks gestation. High-level SOX9 expression in the sex cords of the testis parallels that seen during mouse development, however in humans, SOX9 transcripts also are detected in the developing ovary. Low-level DAX1 expression predates peak SRY expression by at least 10 days, and persists in Sertoli cells throughout the entire sex determination period. In Dosage Sensitive Sex reversal, the anti-testis properties of DAX1 over-expression could act prior to the peak effects of SRY and continue during the period of SOX9 expression. These findings highlight expression differences for the SRY, SOX9, and DAX1 genes during sex determination in humans and mice. These results provide a direct framework for future investigation into the mechanisms underlying normal and abnormal human sex determination.

Sry is a transcriptional activator.

The SRY gene functions as a genetic switch in gonadal ridge initiating testis determination. The mouse Sry and human SRY open reading frames (ORFs) share a conserved DNA-binding domain (the HMG-box) yet exhibit no additional homology outside this region. As judged by the accumulation of lacZ-SRY hybrid proteins in the nucleus, both the human and mouse SRY ORFs contain a nuclear localization signal. The mouse Sry HMG-box domain selectively binds the sequence NACAAT in vitro when challenged with a random pool of oligonucleotides and binds AACAAT with the highest affinity. When put under the control of a heterologous promotor, the mouse Sry gene activated transcription of a reporter gene containing multiple copies of the AACAAT binding site. Activation was likewise observed for a GAL4-responsive reporter gene, when the mouse Sry gene was linked to the DNA-binding domain of GAL4. Using this system, the activation function was mapped to a glutamine/histidine-rich domain. In addition, LexA-mouse Sry fusion genes activated a LexA-responsive reporter gene in yeast. In contrast, a GAL4-human SRY fusion gene did not cause transcriptional activation. These studies suggest that both the human and the mouse SRY ORFs encode nuclear, DNA-binding proteins and that the mouse Sry ORF can function as a transcriptional activator with separable DNA-binding and activator domains.

Functional comparison of the Mus musculus molossinus and Mus musculus domesticus Sry genes.

The Sry gene functions as a genetic switch initiating testicular development of the indifferent mammalian gonad. The Mus musculus molossinus Sry open reading frame (ORF) encodes a 395-amino acid transcription factor (mSry) that specifically binds and bends DNA through its N-terminal HMG domain and activates transcription through its long C-terminal (residues 144-366) glutamine/histidine-rich activation domain. The M. m. domesticus Sry ORF encodes a highly homologous, truncated protein (dSry) of approximately 230 amino acids, and the molecular basis for truncation is a point mutation that creates an amber stop codon within the activation domain. The mSry protein activates transcription of a Sry-responsive reporter gene in HeLa cells, but dSry does not. Gene swapping and in vitro DNA binding experiments revealed that lack of transcriptional activation by dSry was not the result of polymorphisms within the first 137 amino acids of the protein. Direct analysis of the C-terminal glutamine/histidine-rich domain revealed that dSry lacked a functional transcriptional activation domain. Fusion of the GAL4 DNA-binding domain to the C-terminal deletion mutants of the GAL4-mSry chimeric protein indicated that residues 263-345 of the glutamine/histidine-rich domain were necessary for high level transactivation. Furthermore, readthrough of the premature amber stop codon by transfer RNA suppression resulted in a strong GAL4-dSry transactivator. This demonstrated that the premature stop codon is the only polymorphism responsible for the inability of the dSry glutamine/histidine-rich region to transactivate.

Carrier screening for cystic fibrosis, Gaucher disease, and Tay-Sachs disease in the Ashkenazi Jewish population: the first 1000 cases at New York University Medical Center, New York, NY.

BACKGROUND: By late 1993, the genes for cystic fibrosis and Gaucher disease and the mutations common among Ashkenazi Jews had been identified. In response to these advances, heterozygote screening for cystic fibrosis and Gaucher disease was added to the more than 20-year-old Tay-Sachs disease screening program at New York University Medical Center, New York, NY. OBJECTIVE: To review the outcomes from the first 1000 patients screened through this program. METHODS: Patients and their referring physicians were informed about the new carrier tests. At the time of screening, patients could choose their tests (hexosaminidase A by enzyme analysis for Tay-Sachs disease or mutation analysis for cystic fibrosis and Gaucher disease). All partners of Tay-Sachs and cystic fibrosis carriers were tested. Prenatal diagnosis was offered and performed for carrier couples or mixed-marriage couples in whom the Ashkenazi Jewish partner was a carrier of Gaucher disease. Outcomes were measured by: (1) choice of tests, (2) decisions regarding prenatal diagnosis, and (3) phenotypes of children born to patients who underwent screening. RESULTS: The majority of Ashkenazi Jewish patients chose to have testing for all 3 diseases. If they previously underwent screening for Tay-Sachs disease, then they chose to undergo testing for cystic fibrosis and Gaucher disease. All carrier couples for each of these diseases went on to have prenatal testing. All mixed-marriage couples in whom the Jewish partner was found to be a carrier for Gaucher disease chose to have prenatal diagnosis. One fetus was identified as having cystic fibrosis. Since the program was initiated, no Ashkenazi Jewish baby has been born with any of these diseases at New York University Medical Center. CONCLUSIONS: New tests can be readily incorporated into established heterozygote screening programs. The Ashkenazi Jewish population described herein tends to choose testing for all conditions for which heterozygote screening is available.

Linkage analysis of a kindred with inherited 46,XY partial gonadal dysgenesis.

We have reported a kindred in which 46,XY gonadal dysgenesis was inherited in an X-linked (or autosomal dominant sex-limited) manner and in which affected subjects did not have a large duplication of the short arm of the X-chromosome. In the present study we used linkage and sequence analyses to test the role of X-linked and various autosomal genes in the etiology of the familial 46,XY partial gonadal dysgenesis. For analysis of X-linkage, 28 microsatellite polymorphisms and 1 restriction fragment length polymorphism were studied. The genotypes of informative family members were determined at each locus, and data were analyzed. Despite the large number of loci tested, our studies did not establish linkage between the trait and an X-chromosomal locus. With respect to the study of autosomal genes, linkage analysis using a polymorphism within the 3'-untranslated region of the WT1 gene excluded involvement of WT-1 in the etiology of the abnormal gonadal differentiation of the family in this study. Similarly, linkage analysis using four microsatellites on the distal short arm of chromosome 9 was not consistent with linkage. Linkage analysis of a locus close to the SOX9 gene as well as analysis of the coding region of the SOX9 gene suggested that this gene was not associated with the trait in the affected subjects we studied. Our data suggest the role of an autosomal gene in the abnormal gonadal differentiation in the family in the study, but do not formally exclude the role of an X-chromosome gene.

Mendelian diseases among Roman Jews: implications for the origins of disease alleles.

The Roman Jewish community has been historically continuous in Rome since pre-Christian times and may have been progenitor to the Ashkenazi Jewish community. Despite a history of endogamy over the past 2000 yr, the historical record suggests that there was admixture with Ashkenazi and Sephardic Jews during the Middle Ages. To determine whether Roman and Ashkenazi Jews shared common signature mutations, we tested a group of 107 Roman Jews, representing 176 haploid sets of chromosomes. No mutations were found for Bloom syndrome, BRCA1, BRCA2, Canavan disease, Fanconi anemia complementation group C, or Tay-Sachs disease. Two unrelated individuals were positive for the 3849 + 10C->T cystic fibrosis mutation; one carried the N370S Gaucher disease mutation, and one carried the connexin 26 167delT mutation. Each of these was shown to be associated with the same haplotype of tightly linked microsatellite markers as that found among Ashkenazi Jews. In addition, 14 individuals had mutations in the familial Mediterranean fever gene and three unrelated individuals carried the factor XI type III mutation previously observed exclusively among Ashkenazi Jews. These findings suggest that the Gaucher, connexin 26, and familial Mediterranean fever mutations are over 2000 yr old, that the cystic fibrosis 3849 + 10kb C->T and factor XI type III mutations had a common origin in Ashkenazi and Roman Jews, and that other mutations prevalent among Ashkenazi Jews are of more recent origin.

Inverted repeats are necessary for circularization of the mouse testis Sry transcript.

Circular non-polyadenylated RNA molecules have been identified as stable transcription products of the human ETS-1 and mouse Sry genes. RNA circularization has been proposed to require two steps. The first step utilizes intramolecular base pairing to produce a transient stem-loop structure. The second step involves splicing a downstream donor splice site (DSS) to a now closely appositioned upstream acceptor splice site (ASS) within the loop. We demonstrate that the presence of long inverted repeats (IR) flanking the mouse Sry gene leads to the formation of the Sry circular transcript in cultured cells. Circularization requires the presence of both IR. As few as 400 complementary nt are necessary for this process. The presence of the IR does not significantly stimulate intermolecular annealing and trans-splicing in vivo.

High-level inducible expression of visual pigments in transfected cells.

A method for high-level expression of a functionally active, recombinant human red cone opsin was developed by adding the coding sequence for the C-terminal epitope of bovine rhodopsin onto the C terminus of the cone opsin and cloning the resulting construct into the vector pMEP4 beta. The recombinant pMEP4 beta vector was transfected stably into 293-EBNA cells, and expression of the cone opsin was induced by the addition of CdCl2 into the medium. The recombinant cone opsin was reconstituted with 11-cis retinal and purified by immunoaffinity chromatography. Spectral analysis prior to and following photobleaching confirmed its identity as a red cone opsin. The protein was targeted to the cell membrane and activated bovine transducin.

Mutation of a conserved cysteine in the X-linked cone opsins causes color vision deficiencies by disrupting protein folding and stability.

PURPOSE: To test the effects of disruption of a conserved cysteine in the green cone opsin molecule on light-activated isomerization, transducin activation, folding, transport, and protein half-life. METHODS: Stable cell lines were established by transfecting 293-EBNA cells with a plasmid containing wild-type or mutant (C203R, C203S, C126S, C126S/C203S) green opsin cDNA molecules. The proteins were induced by culturing the cells in the presence of cadmium chloride and analyzed by spectra, transducin activation, Western blotting, pulse-labeling with immunoprecipitation, and immunocytochemistry. RESULTS: The C203R mutation disrupts the folding and half-life of the green opsin molecule and its abilities to absorb light at the appropriate wavelength and to activate transducin. Similar disruption of folding, half-life, and light activation occurs when Cys203 or its presumed partner for formation of a disulfide bond (Cys126) is replaced by serine residues. CONCLUSIONS: Like rhodopsin, the folding of the cone opsins appears to be dependent on the formation of a disulfide bond between the third transmembrane helix and the second extracellular loop. Disruption of this disulfide bond represents a cause of color vision deficiencies that is unrelated to spectral shifts of the photopigment.

Mutation of a conserved proline disrupts the retinal-binding pocket of the X-linked cone opsins.

PURPOSE: To test the effects of disruption of a conserved proline in the green cone opsin molecule on light-activated isomerization, transducin activation, protein accumulation, glycosylation, and transport. METHODS: Stable cell lines were established by transfecting EBNA-293 cells with a plasmid containing wild-type or mutant (P307L) green opsin cDNA molecules. The proteins were induced by culturing the cells in the presence of CdCl2 and analyzed by spectra, transducin activation, Western blotting, and immunocytochemistry. RESULTS: The P307L mutation diminished ability of the visual pigment to absorb light at the appropriate wavelength and to activate transducin. Protein glycosylation and transport to the cell membrane were unaffected. Although there was some diminution in the accumulation of the opsin, this was insufficient to account for the observed effect. CONCLUSIONS: Like rhodopsin, the formation of the cone opsins visual pigments is dependent on the binding of retinal into a hydrophobic pocket that is formed by the second and fourth transmembranous loops. Disruption of a conserved proline near the retinal binding site represents a cause of color vision deficiency that is unrelated to spectral shifts of the photopigment.

Glycosylation and palmitoylation are not required for the formation of the X-linked cone opsin visual pigments.

PURPOSE: This study was designed to test whether palmitoylation and glycosylation are required for the formation of the green opsin visual pigment. METHODS: Stable cell lines were established by transfecting EBNA-293 cells with a pMEP4ss recombinant plasmid containing wild-type bovine rhodopsin or wild-type or mutant (N32S) green opsin cDNA molecules that included a tag for the eight amino acid residues located at the C-terminus of rhodopsin. The opsins were induced by addition of CdCl2 into the medium and then reconstituted with 11-cis-retinal. The reconstituted opsins were purified by immunoaffinity chromatography, then analyzed by difference spectra, and by binding 35S-GTP in the presence of bovine transducin. Non-reconstituted opsins were analyzed by Western blotting and by pulse-labeling with 3H-palmitic acid followed by immunoprecipitation. RESULTS: Elimination of glycosylation by mutagenesis of the N-linked glycosylation site did not impair the ability of the resulting cone opsin to absorb light at the appropriate wavelength nor to activate transducin. Furthermore, as judged by pulse-labeling with 3H-palmitic acid and immunoprecipitation and by gas chromatography-mass spectroscopy, the wild type green opsin differs from rhodopsin by not being palmitoylated. CONCLUSIONS: Glycosylation and palmitoylation are not required for the formation of cone opsin visual pigments. For the previously described green opsin C203R mutation, disruption of folding and transport, rather than altered glycosylation is sufficient to explain the associated color vision deficiency.

Two chromosome aberrations in the child of a woman with systemic lupus erythematosus treated with azathioprine and prednisone.

A boy with microcephaly, unusual facial features, micropenis, and growth retardation was born to a 30-year-old woman who took azathioprine and prednisone before and during pregnancy for systemic lupus erythematosus. The child has two apparently de novo chromosomal abnormalities: an apparently balanced translocation between chromosomes 6 and 14 and an interstitial deletion of chromosome 7. The karyotype is 46,XY,del(7)(q21);t(6;14)(q21;q12). Use of azathioprine and prednisone in pregnancy has been associated with intrauterine growth retardation, congenital malformations, and transient chromosome breaks in the blood of newborns. To our knowledge, this is the first report of de novo constitutional chromosome abnormalities in such an infant. We suggest that the assessment of infants born to parents treated with azathioprine should include a chromosome study, even if the infants seem to be normal.

Maternal origin of 15q11-13 deletions in Angelman syndrome suggests a role for genomic imprinting.

Six persons with the classical Angelman syndrome (AS) phenotype and de novo deletions of chromosome 15q11-q13 were studied to determine the parental origin of the chromosome deletion. Four of the 6 patients had informative cytogenetic studies and all demonstrated maternal inheritance of the deletion. These findings, together with other reported cases of the origin of the chromosome 15 deletion in AS, suggest that deletion of the maternally contributed chromosome leads to the AS phenotype. This contrasts with the Prader-Willi syndrome (PWS) in which a similar deletion of the paternally contributed chromosome 15 is observed. In deletion cases, a parental gamete effect such as genomic imprinting may be the best model to explain why apparently identical 15q11-q13 deletions may develop the different phenotypes of AS or PWS.