Ashkenazi Jewish population frequency of the Bloom syndrome gene 2281 delta 6ins7 mutation

Social determinants of health and primary immunodeficiency

OBJECTIVE

Inborn errors of immunity (IEI) are rare genetic conditions affecting the immune system. The rate of IEI and their presentation, course, and treatment are all affected by a multitude of social determinants, eventually affecting prognosis. This review summarizes the current knowledge of the social determinants affecting infectious susceptibility, genetic predisposition, diagnosis, and treatment of IEI.

DATA SOURCES

PubMed.

STUDY SELECTIONS

Search terms included "consanguinity," "social determinants," and "founder effect." Further studies were selected based on relevant citations.

RESULTS

Changes in climate and human behavior have modulated the spread of disease vectors and infectious organisms. Consanguinity increases the rate of autosomal recessive conditions, changes the distribution, and affects the severity of IEI. Access to sophisticated genetic and immunologic diagnostic modalities affects genetic counseling and timely diagnosis. Effective genetic counseling should address to the patient's genetic background and ethical code. Access to appropriate and timely treatment of immunodeficiencies is scarce in some regions of the world.

CONCLUSION

High consanguinity rate and reduced access to prophylactic measures increase the burden of immunodeficiencies in many low- and medium-income countries. Furthermore, poor access to diagnostic and treatment modalities in these regions adversely affects patients' prognosis. Increased awareness among health care professionals and the public and increased collaboration with Western countries aid in diagnosis of these conditions. Further advancements require improved public funding to the prevention, diagnosis, and treatment of IEI.

Bloom syndrome and the underlying causes of genetic instability

Autosomal hereditary recessive diseases characterized by genetic instability are often associated with cancer predisposition. Bloom syndrome (BS), a rare genetic disorder, with <300 cases reported worldwide, combines both. Indeed, patients with Bloom's syndrome are 150 to 300 times more likely to develop cancers than normal individuals. The wide spectrum of cancers developed by BS patients suggests that early initial events occur in BS cells which may also be involved in the initiation of carcinogenesis in the general population and these may be common to several cancers. BS is caused by mutations of both copies of the BLM gene, encoding the RecQ BLM helicase. This review discusses the different aspects of BS and the different cellular functions of BLM in genome surveillance and maintenance through its major roles during DNA replication, repair, and transcription. BLM's activities are essential for the stabilization of centromeric, telomeric and ribosomal DNA sequences, and the regulation of innate immunity. One of the key objectives of this work is to establish a link between BLM functions and the main clinical phenotypes observed in BS patients, as well as to shed new light on the correlation between the genetic instability and diseases such as immunodeficiency and cancer. The different potential implications of the BLM helicase in the tumorigenic process and the use of BLM as new potential target in the field of cancer treatment are also debated.

Bloom syndrome with myelodysplastic syndrome that was converted into acute myeloid leukaemia, with new ophthalmologic manifestations: the first report from Syria

Bloom syndrome is a rare autosomal recessive disease, in which BLM gene is mutated, leading to genome instability and proneness to malignancy. It is characterized by short stature, sun-sensitive rash and immunodeficiency. We present a case of bloom syndrome with myelodysplasia complicated by acute myeloid leukaemia. This case has new ophthalmologic manifestations. We confirmed the diagnosis by detection of high rate of sister chromatid exchange. The patient received chemotherapy but did not tolerate it well and developed fungal pneumonia.

Rare Genetic Diseases with Defects in DNA Repair: Opportunities and Challenges in Orphan Drug Development for Targeted Cancer Therapy

A better understanding of mechanistic insights into genes and enzymes implicated in rare diseases provide a unique opportunity for orphan drug development. Advances made in identification of synthetic lethal relationships between rare disorder genes with oncogenes and tumor suppressor genes have brought in new anticancer therapeutic opportunities. Additionally, the rapid development of small molecule inhibitors against enzymes that participate in DNA damage response and repair has been a successful strategy for targeted cancer therapeutics. Here, we discuss the recent advances in our understanding of how many rare disease genes participate in promoting genome stability. We also summarize the latest developments in exploiting rare diseases to uncover new biological mechanisms and identify new synthetic lethal interactions for anticancer drug discovery that are in various stages of preclinical and clinical studies.

First Two Cases of Bloom Syndrome in Russia: Lack of Skin Manifestations in a BLM c.1642C>T (p.Q548X) Homozygote as a Likely Cause of Underdiagnosis

Bloom syndrome (BS) is an exceptionally rare hereditary disease. Typical manifestations of BS usually include growth deficiency, a characteristic facial appearance, skin hypersensitivity to ultraviolet irradiation, and a strong predisposition to early-onset cancers. We have previously described a recurrent BLM c.1642C>T (p.Q548X) mutation, which is present in heterozygous state in 0.2-0.6% of individuals of Slavic origin. Despite the high occurrence of this founder allele, BS has not yet been described in patients of Slavic ethnicity. Here, we present 2 cases of BS, which were missed by standard genetic counseling and were eventually identified entirely due to chance. Our patients show the need for further investigations to confirm whether the atypical appearance of BS is indeed characteristic for biallelic carriers of the c.1642C>T (p.Q548X) allele and whether the absence of skin manifestations contributes to the underdiagnosis of the disease in Russia. Therefore, we suggest that all Slavic patients with only one single clinical feature of BS are to be screened for this allele and subjected to further analysis wherever appropriate. In addition to identifying new BS patients, this effort will help to clarify the frequency of "atypical BS" with incomplete phenotypic manifestations.

Bloom's Syndrome: Clinical Spectrum, Molecular Pathogenesis, and Cancer Predisposition

Bloom's syndrome is an autosomal recessive disorder characterized by prenatal and postnatal growth deficiency, photosensitive skin changes, immune deficiency, insulin resistance, and a greatly increased risk of early onset of cancer and for the development of multiple cancers. Loss-of-function mutations of BLM, which codes for a RecQ helicase, cause Bloom's syndrome. The absence of a functional BLM protein causes chromosome instability, excessive homologous recombination, and a greatly increased number of sister chromatid exchanges that are pathognomonic of the syndrome. A common founder mutation designated blmAsh is present in about 1 in 100 persons of Eastern European Jewish ancestry, and there are additional recurrent founder mutations among other populations. Missense, nonsense, and frameshift mutations as well as multiexonic deletions have all been observed. Bloom's syndrome is a prototypical chromosomal instability syndrome, and the somatic mutations that occur as a result of that instability are responsible for the increased cancer risk. Although there is currently no treatment aimed at the underlying genetic abnormality, persons with Bloom's syndrome benefit from sun protection, aggressive treatment of infections, surveillance for insulin resistance, and early identification of cancer.

Genetic predispositions to childhood leukemia

While the majority of leukemia cases occur in the absence of any known predisposing factor, there are germline mutations that significantly increase the risk of developing hematopoietic malignancies in childhood. In this review article, we describe a number of these mutations and their clinical features. These predispositions can be broadly classified as those leading to bone marrow failure, those involving tumor suppressor genes, DNA repair defects, immunodeficiencies or other congenital syndromes associated with transient myeloid disorders. While leukemia can develop as a secondary event in the aforementioned syndromes, there are also several syndromes that specifically lead to the development of leukemia as their primary phenotype. Many of the genes discussed in this review can also be somatically mutated in other cancers, highlighting the importance of understanding shared alterations and mechanisms underpinning syndromic and sporadic leukemia.

Human pyruvate kinase M2: a multifunctional protein

Glycolysis, a central metabolic pathway, harbors evolutionary conserved enzymes that modulate and potentially shift the cellular metabolism on requirement. Pyruvate kinase, which catalyzes the last but rate-limiting step of glycolysis, is expressed in four isozymic forms, depending on the tissue requirement. M2 isoform (PKM2) is exclusively expressed in embryonic and adult dividing/tumor cells. This tetrameric allosterically regulated isoform is intrinsically designed to downregulate its activity by subunit dissociation (into dimer), which results in partial inhibition of glycolysis at the last step. This accumulates all upstream glycolytic intermediates as an anabolic feed for synthesis of lipids and nucleic acids, whereas reassociation of PKM2 into active tetramer replenishes the normal catabolism as a feedback after cell division. In addition, involvement of this enzyme in a variety of pathways, protein-protein interactions, and nuclear transport suggests its potential to perform multiple nonglycolytic functions with diverse implications, although multidimensional role of this protein is as yet not fully explored. This review aims to provide an overview of the involvement of PKM2 in various physiological pathways with possible functional implications.

Review and hypothesis: syndromes with severe intrauterine growth restriction and very short stature--are they related to the epigenetic mechanism(s) of fetal survival involved in the developmental origins of adult health and disease?

Diagnosing the specific type of severe intrauterine growth restriction (IUGR) that also has post-birth growth restriction is often difficult. Eight relatively common syndromes are discussed identifying their unique distinguishing features, overlapping features, and those features common to all eight syndromes. Many of these signs take a few years to develop and the lifetime natural history of the disorders has not yet been completely clarified. The theory behind developmental origins of adult health and disease suggests that there are mammalian epigenetic fetal survival mechanisms that downregulate fetal growth, both in order for the fetus to survive until birth and to prepare it for a restricted extra-uterine environment, and that these mechanisms have long lasting effects on the adult health of the individual. Silver-Russell syndrome phenotype has recently been recognized to be related to imprinting/methylation defects. Perhaps all eight syndromes, including those with single gene mutation origin, involve the mammalian mechanism(s) of fetal survival downsizing. Insights into those mechanisms should provide avenues to understanding the natural history, the heterogeneity and possible therapy not only for these eight syndromes, but for the common adult diseases with which IUGR is associated.

Bloom syndrome in two siblings

Bloom syndrome (congenital telangiectatic erythema) is a rare autosomal recessive disorder characterized by telangiectasias and photosensitivity, growth deficiency of prenatal onset, variable degrees of immunodeficiency, and increased susceptibility to neoplasms of many sites and types. We are reporting Bloom syndrome in two brothers from Kashmir (India), 8 and 6 years of age, who presented with erythematous rashes on the face, photosensitivity, and growth retardation.

Carrier Testing for Autosomal- Recessive Disorders

The aim of carrier testing is to identify carrier couples at risk of having offspring with a serious genetic (autosomal recessive) disorder. Carrier couples are offered genetic consultation where their reproductive options, including prenatal diagnosis, are explained. The Ashkenazi Jewish population is at increased risk for several recessively inherited disorders (Tay-Sachs disease, Cystic fibrosis, Canavan disease, Gaucher disease, Familial Dysautonomia, Niemann-Pick disease, Fanconi anemia, and Bloom syndrome). Unlike Tay-Sachs disease, there is no simple biochemical or enzymatic test to detect carriers for these other disorders. However, with the rapid identification of disease-causing genes in recent years, DNA-based assays are increasingly available for carrier detection. Approximately 5% of the world's population carries a mutation affecting the globin chains of the hemoglobin molecule. Among the most common of these disorders are the thalassemias. The global birth rate of affected infants is at least 2 per 1000 (in unscreened populations), with the greatest incidence in Southeast Asian, Indian, Mediterranean, and Middle Eastern ethnic groups. Carriers are detected by evaluation of red cell indices and morphology, followed by more sophisticated hematological testing and molecular analyses. The following issues need to be considered in the development of a carrier screening program: (1) test selection based on disease severity and test accuracy; (2) funding for testing and genetic counselling; (3) definition of the target population to be screened; (4) development of a public and professional education program; (5) informed consent for screening; and (6) awareness of community needs.

Sarcoma epidemiology and etiology: potential environmental and genetic factors

Sarcomas are a heterogeneous group of tumors that may have many etiologies. The incidence of histologic subtypes differs significantly between children and adults. The increase in incidence may be due to improved registry systems, diagnostic tools, and pathologic definitions. Environmental causes may contribute to increased incidence. Genetic alternations may play a role in sarcoma development. As a result of rapidly evolving genomic and proteomic technologies, increased knowledge of the oncogenic mechanisms underlying sarcomagenesis is being generated. Understanding the mechanisms involved in sarcomagenesis is rudimentary. Insight into the molecular basis of sarcoma inception, proliferation, and dissemination hopefully will lead to more effective therapies.

Molecular pathogenesis of osteosarcoma

Osteosarcoma is a devastating but rare disease, whose study has illuminated both the basic biology and clinical management of cancer over the past 30 years. These contributions have included insight into the roles of key cancer genes such as the retinoblastoma tumor suppressor gene and TP53, the identification of familial cancer syndromes implicating DNA helicases, and dramatic improvements in survival by the use of adjuvant chemotherapy. This review provides a synoptic overview of our current understanding of the molecular causes of osteosarcoma, and suggests future directions for study.

Molecular screening for diseases frequent in Ashkenazi Jews: lessons learned from more than 100,000 tests performed in a commercial laboratory

PURPOSE

To determine the frequency of carriers of Ashkenazi Jewish (AJ) genetic diseases in the US population and compare these numbers with previously published frequencies reported in smaller more isolated cohorts.

METHODS

A database containing more than 100,000 genotyping assays was queried. Assays for 10 separate AJ genetic diseases where comparisons were made with published data.

RESULTS

As expected, we observed lower carrier frequencies in a general, US population than those reported in literature. In 2427 patients tested for a panel of 8 AJ diseases, 20 (1:121) were carriers of two diseases and 331 (1:7) were carriers of a single disease. Fifty-three of 7184 (1:306) individuals tested for Gaucher disease had 2 Gaucher Disease mutations indicating a potentially affected phenotype.

CONCLUSIONS

As the number of AJ diseases increases, progressively more individuals will be identified as carriers of at least one disease.

Nemaline myopathy in the Ashkenazi Jewish population is caused by a deletion in the nebulin gene

Nemaline myopathy (NM) is a neuromuscular disorder that is clinically diverse and can be attributed to mutations in any of several genes. The Ashkenazi Jewish population, which represents a relatively genetically homogeneous group, has an increased frequency of several genetic disorders and has been the beneficiary of genetic screening programs that have reduced the incidence of these diseases. The identification of individuals with NM in this population has prompted a study of its cause. Our study has revealed that five NM patients from five families bear an identical 2,502-bp deletion that lies in the nebulin gene and that includes exon 55 and parts of introns 54 and 55. The absence of this exon results in the generation of a transcript that encodes 35 fewer amino acids. An analysis of the gene frequency of this mutation in a random sample of 4,090 Ashkenazi Jewish individuals has revealed a carrier frequency of one in 108.

Bloom syndrome: multiple retinopathies in a chromosome breakage disorder

AIM

To describe multiple retinal abnormalities in a patient with Bloom syndrome, including early macular drusen, diabetic retinopathy, and the onset of leukaemic retinopathy.

METHODS

Clinical data were collected over 1 year of follow up, and ocular abnormalities in Bloom syndrome were reviewed from the literature.

RESULTS

A 39 year old man with a rare autosomal recessive "chromosome breakage" syndrome was followed. A variety of ocular findings have been reported in Bloom syndrome; this patient had hard drusen in both maculae, non-proliferative diabetic retinopathy, and haemorrhagic retinopathy as a herald of acute lymphocytic leukaemia.

CONCLUSIONS

Bloom syndrome is a rare disorder of genomic instability, in which a variety of ocular abnormalities have been found. Described here are multiple retinal manifestations arising from characteristic systemic associations of diabetes mellitus and leukaemia, as well as macular hard drusen.

Meta-analysis of indels causing human genetic disease: mechanisms of mutagenesis and the role of local DNA sequence complexity

A relatively rare type of mutation causing human genetic disease is the indel, a complex lesion that appears to represent a combination of micro-deletion and micro-insertion. In the absence of meta-analytical studies of indels, the mutational mechanisms underlying indel formation remain unclear. Data from the Human Gene Mutation Database (HGMD) were therefore used to compare and contrast 211 different indels underlying genetic disease in an attempt to deduce the processes responsible for their genesis. Each indel was treated as if it were the result of a two-step insertion/deletion process and was assessed in the context of 10 base-pairs DNA sequence flanking the lesion on either side. Several indel hotspots were noted and a GTAAGT motif was found to be significantly over-represented in the vicinity of the indels studied. Previously postulated mechanisms underlying micro-deletions and micro-insertions were initially explored in terms of local DNA sequence regularity as measured by its complexity. The change in complexity consequent to a mutation was found to be indicative of the type of repeat sequence involved in mediating the event, thereby providing clues as to the underlying mutational mechanism. Complexity analysis was then employed to examine the possible intermediates through which each indel could have occurred and to propose likely mechanisms and pathways for indel generation on an individual basis. Manual analysis served to confirm that the majority of indels (>90%) are explicable in terms of a two-step process involving established mutational mechanisms. Indels equivalent to double base-pair substitutions (22% of the total) were found to be mechanistically indistinguishable from the remainder and may therefore be regarded as a special type of indel. The observed correspondence between changes in local DNA sequence complexity and the involvement of specific mutational mechanisms in the insertion/deletion process, and the ability of generated models to account for both the number and identity of the bases deleted and/or inserted, makes this approach invaluable not only for the analysis of indel formation, but also for the study of other types of complex lesion.

Genetic insights into familial cancers-- update and recent discoveries

While the vast majority of cancers are believed to occur sporadically, most forms of cancer, both adult and paediatric, have a hereditary equivalent. In the case of adult malignancies, these include hereditary breast and ovarian cancer and syndromes such as the multiple endocrine neoplasias types 1 and 2 characterised by specific tumours of the endocrine gland system. In the case of paediatric malignancies, these include syndromes such as retinoblastoma and Wilms tumour. In a little over a single decade, we have seen a tremendous increase in the knowledge of the primary genetic basis of many of the familial cancer syndromes. The majority of familial syndromes are inherited as autosomal dominant traits including hereditary colon cancer and familial malignant melanoma, however, the genetics behind autosomal recessive disorders such as Bloom syndrome and Fanconi anaemia are also being elucidated. A third mode of inheritance less well understood in the setting of familial cancer is that of imprinting recently observed in a subset of families with inherited paraganglioma. In this review, we discuss 31 genes inherited in an autosomal dominant manner associated with 20 familial cancer syndromes. Genes inherited in an autosomal recessive manner linked to familial cancer syndromes are also discussed. The identification of genes associated with familial cancer syndromes has in some families enabled a 'molecular diagnosis' that complements clinical assessment and allows directed cancer surveillance for those individuals determined to be at-risk of disease.

Complex SNP-based haplotypes in three human helicases: implications for cancer association studies

We have initiated a candidate gene approach to study variation and predisposition to cancer in the four major ethnic groups that constitute the U.S. population (African Americans, Caucasians, Hispanics, and Asians). We resequenced portions of three helicase genes (BLM, WRN, and RECQL) identifying a total of 37 noncoding single nucleotide polymorphisms (SNPs). Haplotype inference predicted 50 haplotypes in BLM, 56 in WRN, and 47 in RECQL in a sample of 600 chromosomes. Approximately 10% of the predicted haplotypes were shared among all ethnic groups. Linkage disequilibrium and recombination effects showed that each locus has taken a diverse evolutionary path. Primate DNA analysis of the same loci revealed one human haplotype per gene shared with the great apes, indicating that the observed diversity occurred since the divergence of humans from the last common ancestor. In BLM, we confirmed the presence of a founder haplotype among Ashkenazi Jews homozygous for the blm(Ash) mutation. The cosegregating haplotype was seen in all (6/6) samples of Ashkenazi descent, whereas in the general population it has a low frequency (0.02) and was not found in African Americans. In WRN, ethnic samples were studied for their haplotype content and the presence or absence of six previously described coding SNPs (cSNPs). Hispanic individuals carrying two of these cSNPs showed a 60% increase in the frequency of a common haplotype (haplotype No. 28). In the pooled sample, no association was found. Because (1) the majority of the haplotypes are population specific and (2) the patterns of linkage disequilibrium, recombination, and haplotype diversity are markedly different between gene regions, these data show the importance of either ethnically matched controls or within-family-based disease-gene association studies.

DNA helicases, genomic instability, and human genetic disease

DNA helicases are a highly conserved group of enzymes that unwind DNA. They function in all processes in which access to single-stranded DNA is required, including DNA replication, DNA repair and recombination, and transcription of RNA. Defects in helicases functioning in one or more of these processes can result in characteristic human genetic disorders in which genomic instability and predisposition to cancer are common features. So far, different helicase genes have been found mutated in six such disorders. Mutations in XPB and XPD can result in xeroderma pigmentosum, Cockayne syndrome, or trichothiodystrophy. Mutations in the RecQ-like genes BLM, WRN, and RECQL4 can result in Bloom syndrome, Werner syndrome, and Rothmund-Thomson syndrome, respectively. Because XPB and XPD function in both nucleotide excision repair and transcription initiation, the cellular phenotypes associated with a deficiency of each one of them include failure to repair mutagenic DNA lesions and defects in the recovery of RNA transcription after UV irradiation. The functions of the RecQ-like genes are unknown; however, a growing body of evidence points to a function in restarting DNA replication after the replication fork has become stalled. The genomic instability associated with mutations in the RecQ-like genes includes spontaneous chromosome instability and elevated mutation rates. Mouse models for nearly all of these entities have been developed, and these should help explain the widely different clinical features that are associated with helicase mutations.