Biomedical subjects

B D Gelb

Publications and source records attributed to B D Gelb.

At least 19 recordsLinked to original sources

PubMed2003

Cathepsin K deficiency in pycnodysostosis results in accumulation of non-digested phagocytosed collagen in fibroblasts.

The rare osteosclerotic disease, pycnodysostosis, is characterized by decreased osteoclastic bone collagen degradation due to the absence of active cathepsin K. Although this enzyme is primarily expressed by osteoclasts, there is increasing evidence that it may also be present in other cells, including fibroblasts. Since fibroblasts are known to degrade collagen intracellularly following phagocytosis, we analyzed various soft connective tissues (periosteum, perichondrium, tendon, and synovial membrane) from a 13-week-old human fetus with pycnodysostosis for changes in this collagen digestion pathway. In addition, the same tissues from cathepsin K-deficient and control mice were analyzed. Microscopic examination of the human fetal tissues showed that cross-banded collagen fibrils had accumulated in lysosomal vacuoles of fibroblasts. Morphometric analysis of periosteal fibroblasts revealed that the volume density of collagen-containing vacuoles was 18 times higher than in fibroblasts of control patients. A similar accumulation was seen in periosteal fibroblasts of three children with pycnodysostosis. In contrast to the findings in humans, an accumulation of internalized collagen was not apparent in fibroblasts of mice with cathepsin K deficiency. Our observations indicate that the intracellular digestion of phagocytosed collagen by fibroblasts is inhibited in humans with pycnodysostosis, but probably not in the mouse model mimicking this disease. The data strongly suggest that cathepsin K is a crucial protease for this process in human fibroblasts. Murine fibroblasts may have other proteolytic activities that are expressed constitutively or up regulated in response to a deficiency of cathepsin K. This may explain why cathepsin K-deficient mice lack the dysostotic features that are prominent in patients with pycnodysostosis.

Animals↗

PubMed2003

Exclusion of PTPN11 mutations in Costello syndrome: further evidence for distinct genetic etiologies for Noonan, cardio-facio-cutaneous and Costello syndromes.

Costello syndrome (CS) is a rare, multiple congenital anomaly syndrome with characteristic dysmorphic features, cardiac anomalies and a tendency to develop certain cancers. Phenotypically there is some overlap with other genetic disorders, notably cardio-facio-cutaneous (CFC) syndrome and Noonan syndrome (NS), suggesting that these syndromes may be allelic. We recently identified PTPN11, which encodes the non-receptor protein tyrosine phosphatase, SHP-2, as a major NS disease gene. In this report, we screened a cohort of 27 patients, with the clinical diagnosis of CS, for PTPN11 mutations using denaturing high performance liquid chromatography analysis. No mutations of the PTPN11 gene were found in the CS patients. Common polymorphisms in introns 6 and 7 and exon 8 were identified in four individuals. With our previous exclusion of PTPN11 mutations in CFC syndrome, these data suggest distinct genetic etiologies for Noonan, CFC and Costello syndromes.

Abnormalities, Multiple↗

PubMed2001

Cloning and characterization of a novel mouse AP-2 transcription factor, AP-2delta, with unique DNA binding and transactivation properties.

AP-2 transcription factors are sequence-specific DNA-binding proteins expressed in neural crest and other tissues during mammalian development. Three mammalian genes, AP-2alpha, AP-2beta, and AP-2gamma, have been reported previously. A partial predicted AP-2 gene was identified in tandem with AP-2beta on human chromosome 6p12-p21.1. The orthologous mouse gene, which we named Ap-2delta, was identified from a fetal mouse head cDNA library. Northern analysis revealed two transcripts in embryonic and newborn mouse brain, with markedly higher steady-state levels in the former. The predicted Ap-2delta protein comprised 452 amino acids and was highly similar to other AP-2 proteins across the DNA-binding and dimerization domains. Ap-2delta formed homodimers and heterodimers in vitro, bound an optimized AP-2 consensus DNA sequence, and transactivated gene expression in eukaryotic cells. Ap-2delta dimers bound poorly to an AP-2 binding sequence from the human metallothionein IIa promoter in vitro, revealing a sequence specificity not previously observed among other AP-2 proteins. The PY motif and critical residues in the transactivation domain, which are highly conserved in the AP-2 family and believed necessary for transactivation, were divergent in Ap-2delta. The unique protein sequence and functional features of Ap-2delta suggest mechanisms, besides tissue-specific AP-2 gene expression, for specific control of target gene activation.

Amino Acid Sequence↗

PubMed2001

Novel TFAP2B mutations that cause Char syndrome provide a genotype-phenotype correlation.

To elucidate further the role, in normal development and in disease pathogenesis, of TFAP2B, a transcription factor expressed in neuroectoderm, we studied eight patients with Char syndrome and their families. Four novel mutations were identified, three residing in the basic domain, which is responsible for DNA binding, and a fourth affecting a conserved PY motif in the transactivation domain. Functional analyses of the four mutants disclosed that two, R225C and R225S, failed to bind target sequence in vitro and that all four had dominant negative effects when expressed in eukaryotic cells. Our present findings, combined with data about two previously identified TFAP2B mutations, show that dominant negative effects consistently appear to be involved in the etiology of Char syndrome. Affected individuals in the family with the PY motif mutation, P62R, had a high prevalence of patent ductus arteriosus but had only mild abnormalities of facial features and no apparent hand anomalies, a phenotype different from that associated with the five basic domain mutations. This genotype-phenotype correlation supports the existence of TFAP2 coactivators that have tissue specificity and are important for ductal development but less critical for craniofacial and limb development.

3T3 Cells↗

PubMed2001

Impact of the reduced folate carrier on the accumulation of active thiamin metabolites in murine leukemia cells.

The thiamin transporter encoded by SLC19A2 and the reduced folate carrier (RFC1) share 40% homology at the protein level, but the thiamin transporter does not mediate transport of folates. By using murine leukemia cell lines that express no, normal, or high levels of RFC1, we demonstrate that RFC1 does not mediate thiamin influx. However, high level RFC1 expression substantially reduced accumulation of the active thiamin coenzyme, thiamin pyrophosphate (TPP). This decreased level of TPP, synthesized intracellularly from imported thiamin, resulted from RFC1-mediated efflux of TPP. This conclusion was supported by the following observations. (i) Efflux of intracellular TPP was increased in cells with high expression of RFC1. (ii) Methotrexate inhibits TPP influx. (iii) TPP competitively inhibits methotrexate influx. (iv) Loading cells, which overexpress RFC1 to high levels of methotrexate to inhibit competitively RFC1-mediated TPP efflux, augment TPP accumulation. (v) There was an inverse correlation between thiamin accumulation and RFC1 activity in cells grown at a physiological concentration of thiamin. The modulation of thiamin accumulation by RFC1 in murine leukemia cells suggests that this carrier may play a role in thiamin homeostasis and could serve as a modifying factor in thiamin nutritional deficiency as well as when the high affinity thiamin transporter is mutated.

Animals↗

PubMed2001

Slc19a2: cloning and characterization of the murine thiamin transporter cDNA and genomic sequence, the orthologue of the human TRMA gene.

Recently, our group and others cloned the TRMA disease gene, SLC19A2, which encodes a thiamin transporter. Here, we report the cloning and characterization of the full-length cDNA and genomic sequences of mouse Slc19a2. The Slc19a2 cDNA contained a 1494-bp open-reading frame, and had 5'- and 3'-untranslated regions of 189 and 1857 bp, respectively. A putative GC-rich, TATA-less promoter was identified in genomic sequence directly upstream of the identified 5' end. The Slc19a2 gene spanned 16.3 kb and was organized into six exons, a gene structure conserved with the human orthologue. The predicted Slc19a2 protein, like SLC19A2, was predicted to have 12 transmembrane domains and shared a number of other conserved sequence motifs with the human orthologue, including one potential N-glycosylation site (N(63)) and several potential phosphorylation sites. Comparison of the Slc19a2 amino acid sequence with those of the other known SLC19A solute carriers highlighted interesting patterns of conservation and divergence in various domains, allowing insight into potential structure-function relationships. The identification of the mouse Slc19a2 cDNA and genomic sequences will facilitate the generation of an animal model of TRMA, permitting future studies of disease pathogenesis.

Amino Acid Sequence↗

PubMed2001

Mutations in PTPN11, encoding the protein tyrosine phosphatase SHP-2, cause Noonan syndrome.

Noonan syndrome (MIM 163950) is an autosomal dominant disorder characterized by dysmorphic facial features, proportionate short stature and heart disease (most commonly pulmonic stenosis and hypertrophic cardiomyopathy). Webbed neck, chest deformity, cryptorchidism, mental retardation and bleeding diatheses also are frequently associated with this disease. This syndrome is relatively common, with an estimated incidence of 1 in 1,000-2,500 live births. It has been mapped to a 5-cM region (NS1) [corrected] on chromosome 12q24.1, and genetic heterogeneity has also been documented. Here we show that missense mutations in PTPN11 (MIM 176876)-a gene encoding the nonreceptor protein tyrosine phosphatase SHP-2, which contains two Src homology 2 (SH2) domains-cause Noonan syndrome and account for more than 50% of the cases that we examined. All PTPN11 missense mutations cluster in interacting portions of the amino N-SH2 domain and the phosphotyrosine phosphatase domains, which are involved in switching the protein between its inactive and active conformations. An energetics-based structural analysis of two N-SH2 mutants indicates that in these mutants there may be a significant shift of the equilibrium favoring the active conformation. This implies that they are gain-of-function changes and that the pathogenesis of Noonan syndrome arises from excessive SHP-2 activity.

Chromosomes, Human, Pair 12↗

PubMed2001

Genetic basis of syndromes associated with congenital heart disease.

Numerous syndromes affecting patients have phenotypes that include congenital heart defects (CHDs). These disorders have fascinated physicians for many years, raising questions about how seemingly disparate aspects of human development can be perturbed together in striking, but consistent, ways. Paralleling the major advances in human genetics during recent decades, we have come to understand that some of these syndromes arise from gross defects in chromosomal number, some from subtler alterations in genomic regions, and still others from point mutations in specific genes. These disorders, largely mendelian in nature, have provided researchers with the wherewithal to discover disease genes underlying CHD. Although some of these medical conditions are relatively rare, their solution has often provided insights that could be applied toward understanding the basis of nonsyndromic CHD. In this review, recent progress toward uncovering the molecular basis of several forms of syndromic CHD is discussed.

Heart Defects, Congenital↗

PubMed2000

Char syndrome: an additional family with polythelia, a new finding.

This report describes a father and daughter with Char syndrome, a rare autosomal dominant disorder. Both affected individuals had typical face, strabismus, and foot anomalies. The girl also had a patent ductus arteriosus. In addition, both patients had polythelia (supernumerary nipples), a finding not described before in the Char syndrome.

Abnormalities, Multiple↗

PubMed2000

Gaucher disease: the origins of the Ashkenazi Jewish N370S and 84GG acid beta-glucosidase mutations.

Type 1 Gaucher disease (GD), a non-neuronopathic lysosomal storage disorder, results from the deficient activity of acid beta-glucosidase (GBA). Type 1 disease is panethnic but is more prevalent in individuals of Ashkenazi Jewish (AJ) descent. Of the causative GBA mutations, N370S is particularly frequent in the AJ population, (q approximately .03), whereas the 84GG insertion (q approximately .003) occurs exclusively in the Ashkenazim. To investigate the genetic history of these mutations in the AJ population, short tandem repeat (STR) markers were used to map a 9.3-cM region containing the GBA locus and to genotype 261 AJ N370S chromosomes, 60 European non-Jewish N370S chromosomes, and 62 AJ 84GG chromosomes. A highly conserved haplotype at four markers flanking GBA (PKLR, D1S1595, D1S2721, and D1S2777) was observed on both the AJ chromosomes and the non-Jewish N370S chromosomes, suggesting the occurrence of a founder common to both populations. Of note, the presence of different divergent haplotypes suggested the occurrence of de novo, recurrent N370S mutations. In contrast, a different conserved haplotype at these markers was identified on the 84GG chromosomes, which was unique to the AJ population. On the basis of the linkage disequilibrium (LD) delta values, the non-Jewish European N370S chromosomes had greater haplotype diversity and less LD at the markers flanking the conserved haplotype than did the AJ N370S chromosomes. This finding is consistent with the presence of the N370S mutation in the non-Jewish European population prior to the founding of the AJ population. Coalescence analyses for the N370S and 84GG mutations estimated similar coalescence times, of 48 and 55.5 generations ago, respectively. The results of these studies are consistent with a significant bottleneck occurring in the AJ population during the first millennium, when the population became established in Europe.

Algorithms↗

PubMed2000

Recent advances in the understanding of genetic causes of congenital heart defects.

The clinical approach to children with congenital heart defects (CHD) has been revolutionized during the past four decades by developments in diagnostics and therapeutics. In contrast, a profound understanding of the causes of the majority of CHD has only begun to emerge within the past few years. Prior epidemiological studies suggested that Mendelian disorders constituted a very small percentage of CHD and that polygenic inheritance was responsible for the majority of cases. Recent discoveries, largely achieved with molecular genetic studies, have provided new insights into the genetic basis of heart malformations. These studies have shown that CHD caused by single gene or single locus defects is more common than had been suspected. In addition, a higher percentage of heart malformations occur in the context of familial disease than was evident previously. In this review, molecular genetic studies of specific heart lesions and syndromes with CHD are reviewed. Progress on the Human Genome Project has accelerated identification of genes for Mendelian traits with heart defects, and it is anticipated that disease genes for most single gene traits will be known within a few years. Future challenges include utilizing this emerging genetic information to improve diagnosis and treatment of children with CHD, and harnessing the power of genomics to analyze isolated heart defects with complex inheritance patterns.

Animals↗

PubMed2000

Mutations in TFAP2B cause Char syndrome, a familial form of patent ductus arteriosus.

Char syndrome is an autosomal dominant trait characterized by patent ductus arteriosus, facial dysmorphism and hand anomalies. Using a positional candidacy strategy, we mapped TFAP2B, encoding a transcription factor expressed in neural crest cells, to the Char syndrome critical region and identified missense mutations altering conserved residues in two affected families. Mutant TFAP2B proteins dimerized properly in vitro, but showed abnormal binding to TFAP2 target sequence. Dimerization of both mutants with normal TFAP2B adversely affected transactivation, demonstrating a dominant-negative mechanism. Our work shows that TFAP2B has a role in ductal, facial and limb development and suggests that Char syndrome results from derangement of neural-crest-cell derivatives.

3T3 Cells↗

PubMed2000

Genetics of peanut allergy: a twin study.

BACKGROUND: The role of genetics in the etiology of peanut allergy is unknown. For complex genetic traits, twin studies can provide information on the relative contribution of genetic factors to a disease, as the relative confounding effects of environmental factors are markedly decreased. OBJECTIVE: This study was performed to search for evidence that genetic factors influence peanut allergy by comparing the concordance rate for this allergy among monozygotic and dizygotic twins. METHODS: Twin pairs with at least one member with peanut allergy were ascertained through the Food Allergy Network by advertisements in the organization's newsletters and Web site. Individuals with peanut allergy or parental surrogates were interviewed by telephone. A full atopic history was obtained, and peanut allergy and zygosity were determined using previously validated questionnaires. Heritability of peanut allergy was determined using univariate genetic model fitting by maximum likelihood with the Mx statistical modeling software package. RESULTS: Seventy-five twin pairs were recruited. Seventeen pairs were excluded because of unconvincing peanut allergy histories (9 pairs, including 4 of uncertain zygosity) or because one twin had reportedly never ingested peanut (8 pairs). The median age of the 58 remaining twin pairs was 5 years (range 1 to 58 years). Seventy individuals had peanut allergy. In addition to convincing histories of peanut allergy, 52 (74%) had been tested (skin prick testing with or without radioallergosorbent assay) and all had positive reactions to peanut. Twenty-nine of the 70 had experienced >1 reaction to peanut; 29 of 70 had multisystem reactions. Among the monozygotic pairs (n = 14), 9 were concordant for peanut allergy (pairwise concordance, 64.3%) and among dizygotic pairs (n = 44), 3 were concordant for peanut allergy (pairwise concordance, 6.8%; chi(2) = 21.38, P <.0001). Heritability of peanut allergy was estimated at 81. 6% (95% confidence interval 41.6% to 99.7%) with model fitting using a population prevalence of peanut allergy of 0.4%. CONCLUSIONS: The significantly higher concordance rate of peanut allergy among monozygotic twins suggests strongly that there is a significant genetic influence on peanut allergy.

Adolescent↗

PubMed2000

Malignant fibrous histiocytoma: inherited and sporadic forms have loss of heterozygosity at chromosome bands 9p21-22-evidence for a common genetic defect.

Hereditary cancers represent a unique opportunity to investigate the genetic etiology of their more common sporadic forms. We recently established genetic linkage for the rare autosomal-dominant bone dysplasia/cancer syndrome, diaphyseal medullary stenosis with malignant fibrous histiocytoma (DMS-MFH), to a 3-cM region on chromosome bands 9p21-22. This hereditary cancer syndrome is characterized by bone infarctions, cortical growth abnormalities, pathologic fractures, and painful debilitation. Most notably, 35% of affected individuals develop bone MFH, a sarcoma that, in its sporadic form, accounts for 6% of all bone cancers. To determine whether the hereditary and sporadic forms of bone MFH are genetically linked, we performed loss of heterozygosity (LOH) studies of the DMS-MFH critical region. In addition to the hereditary specimen, 71% (5/7) of informative sporadic bone MFH specimens displayed LOH for markers within that same region. Definition of the minimal region of LOH overlap effectively limited the DMS-MFH gene to a 2-cM region between markers D9S736 and D9S171. In summary, these studies suggest that a common genetic etiology underlies the autosomal-dominant and sporadic forms of this sarcoma and provide the basis for identifying the putative MFH tumor suppressor gene. Genes Chromosomes Cancer 27:191-195, 2000.

Adolescent↗

PubMed1999

Familial patent ductus arteriosus and bicuspid aortic valve with hand anomalies: a novel heart-hand syndrome.

The association between cardiac and limb defects, particularly those affecting the hand, has been well documented by the delineation of several heart-hand syndromes. Based on observations with a three-generation family with seven affected individuals, we describe a novel heart-hand syndrome comprising patent ductus arteriosus, bicuspid aortic valve, 5th metacarpal hypoplasia, and brachydactyly. The inheritance pattern was consistent with autosomal dominance, although X-linked dominance could not be excluded. Penetrance appeared to be complete, but there was variability of the cardiac and hand phenotypes. Because this new syndrome closely resembled Char syndrome (patent ductus arteriosus, 5th finger middle phalangeal hypoplasia, and minor facial anomalies), multipoint linkage analysis was performed using polymorphic DNA markers spanning the recently identified Char syndrome critical region at chromosomal bands 6p12-p21.1. This analysis formally excluded this 3-cM region, documenting that the two traits are not allelic. In sum, a novel heart-hand syndrome involving left ventricular outflow and aortic arch as well as an ulnar ray derivative has been identified. Because the hand anomalies can be subtle, thorough evaluation is suggested for families inheriting these cardiac defects as a mendelian trait.

Alleles↗

PubMed1999

Sanjad-Sakati and autosomal recessive Kenny-Caffey syndromes are allelic: evidence for an ancestral founder mutation and locus refinement.

The Sanjad-Sakati syndrome (SSS; MIM241410), an autosomal recessive trait characterized by congenital hypoparathyroidism, growth and mental retardation, seizures, and a characteristic physiognomy, was recently linked to chromosome area 1q42-q43. SSS resembles the autosomal recessive form of Kenny-Caffey syndrome (KCS; MIM244460), with similar manifestations but lacking osteosclerosis. Since KCS was recently linked to the region 1q42-q43, the possibility that this disorder is allelic with SSS was considered. Eight Sanjad-Sakati families from Saudi Arabia were genotyped with polymorphic short tandem repeat markers from the SSS/KCS critical region. A maximum multipoint LOD score of 14.32 was obtained at marker D1S2649, confirming linkage of SSS to the same region as autosomal recessive KCS. Haplotype analysis refined the critical region to 2.6 cM and identified a rare haplotype present in all the SSS disease alleles, indicative of a common founder. In addition to the assignment of the Saudi SSS and Kuwaiti KCS syndromes to overlapping genetic intervals, comparison of the haplotypes unexpectedly demonstrated that the diseases shared an identical haplotype. This finding, combined with the clinical similarity between the two syndromes, suggests that the two conditions are not only allelic but are also caused by the same ancestral mutation.

Abnormalities, Multiple↗

PubMed1999

Char syndrome, an inherited disorder with patent ductus arteriosus, maps to chromosome 6p12-p21.

BACKGROUND: Patent ductus arteriosus (PDA) is a relatively common form of congenital heart disease. Although polygenic inheritance has been implicated, no specific gene defects causing PDA have been identified to date. Thus, a positional cloning strategy was undertaken to determine the gene responsible for the Char syndrome, an autosomal dominant disorder characterized by PDA, facial dysmorphism, and hand anomalies. METHODS AND RESULTS: A genome scan was performed with 46 members of 2 unrelated families in which the disease was fully penetrant but the phenotype differed. Significant linkage was achieved with several polymorphic DNA markers mapping to chromosome 6p12-p21 (maximal 2-point LOD score of 8.39 with D6S1638 at theta=0.00). Haplotype analysis identified recombinant events that defined the Char syndrome locus with high probability to a 3. 1-cM region between D6S459/D6S1632/D6S1541 and D6S1024. CONCLUSIONS: A familial syndrome in which PDA is a common feature was mapped to a narrow region of chromosome 6p12-p21. Additional analysis with other families and polymorphic markers as well as evaluation of potential candidate genes should lead to the identification of the Char syndrome gene, which will provide insights into cardiogenesis as well as limb and craniofacial development.

Chromosome Mapping↗

PubMed1999

Localization of the thiamine-responsive megaloblastic anemia syndrome locus to a 1.4-cM region of 1q23.

Thiamine-responsive megaloblastic anemia (TRMA) is a rare autosomal recessive syndrome characterized by megaloblastic anemia, deafness, and diabetes mellitus. A genome scan previously established linkage of this disorder to 1q23 and haplotype analysis defined a 16-cM critical region. Molecular genetic analyses of four unrelated multiplex Iranian families inheriting TRMA confirmed linkage to the same region and identified recombinant chromosomes which permitted refinement of the critical region to a narrow 1.4-cM interval. The haplotypes of the families differed, consistent with at least two independent mutational events. This refinement of the TRMA locus to less than 10% of that previously published should markedly facilitate the identification and evaluation of positional candidate and novel genes which may cause this disorder.

Anemia, Megaloblastic↗