Fragile X syndrome and fragile XE mental retardation

There are two forms of mental handicap associated with fragile sites on the end of the long arm of the X chromosome. The well known common disorder Fragile X syndrome is associated with FRAXA and a rare non-specific form of mental handicap is associated with FRAXE. The cytogenetics of these fragile sites is considered. For Fragile X syndrome details are given of the molecular genetics, inheritance patterns, genetic counselling, methods for diagnosis of index cases, carrier detection and prenatal diagnosis. Series of prenatal diagnoses are briefly reviewed and technical and biological problems associated with this procedure are considered. Prenatal diagnosis of Fragile X syndrome using molecular genetic techniques is now a well established procedure, with the only significant problem being the inability to accurately predict phenotype in female fetuses with full mutations. Few prenatal diagnoses of Fragile XE non-specific mental retardation have been recorded. In principle the technical aspects of such a prenatal diagnosis should be little different from those for Fragile X syndrome. Incomplete knowledge of the phenotypic effect of the full mutation in males and females would make phenotypic prediction for any fetus shown to have such a mutation very difficult. At this stage all that could be determined with precision is that the mutation was present or absent in the fetus. Possible consequences of this are discussed.     

Enzymatic and molecular diagnosis of Gaucher disease

Advances in the knowledge of the molecular genetics of Gaucher disease has made diagnosis more certain. Carrier detection in kindreds in which the responsible mutation has been defined is completely reliable now. Coupled with enzymatic assays, the diagnostic capabilities are greater than before. Use of these methods provides important information to individuals at risk and allows them to make critical decisions. The new, simplified methods reviewed in this article permit the molecular diagnosis of the disease and carrier stage of large numbers of samples within 1 week.     

From the clinic to the research laboratory. The role of the clinician in molecular genetic studies

BACKGROUND: The first physician to examine a patient with a genetic disorder or birth defect is usually a specialist in a field other than genetics. The presentation of certain categories of patients of particular interest to molecular genetics research may be distinct. The recognition of these patients by clinicians is fundamental to the study of genetic disorders at the DNA level. OBSERVATIONS: Neurofibromatosis type 1 is a paradigm for how the study of a single genetic disease and its multiple molecular features has been facilitated by the use of various categories of patients. Other examples of interest to dermatologists, surgeons, and other specialists are discussed to demonstrate how the identification of key patients was instrumental in studies of gene localization and subsequent cloning, gene clusters or contiguous gene deletion syndromes, or mutation phenomena such as imprinting, uniparental disomy, and gonadal mosaicism. The molecular researcher has limited access to surgical specimens, and the donation of skin, tumor, and other tissues may lead to increased knowledge of new mutations in somatic mosaicism, or loss of heterozygosity of tumor suppression genes in cancer. CONCLUSIONS: Guidelines are suggested to alert the physician to each of these categories of individuals with unusual presentation, as well as to recognize that the study of families with rare disorders may enable scientists to locate the responsible genes. The teamwork of clinician and molecular researcher is essential for the advancement of our understanding of DNA mechanisms in genetic disease. The ethics involved in referral of patients to molecular genetic research studies are discussed.     

Phagocytic and metabolic activities of macrophages from mummichog naturally exposed to pulp mill effluents in the Miramichi River

The large ethnic differences in prevalence of coronary artery disease between China and Europe may relate to both genetic and environmental differences. To assess possible genetic factors we have therefore studied the frequencies of disease-related variants of genes involved in lipid transport in 69 hypertriglyceridemic Chinese subjects and 74 healthy Chinese controls. The loci studied include lipoprotein lipase (Asp9Asn, Asn291Ser, Ser447Ter, and Thr361Thr); apolipoprotein A1 (restriction sites at MspI, XmnI, and PstI); and apolipoprotein (apo) CIII (G3175C). All these variants have been shown in previous literature publications to relate to either dyslipidemia and/or premature coronary heart disease in Caucasians. Two disease-related genetic variants in Europeans (Asp9Asn and Asn291Ser) were not found in the Chinese sample. The apo CIII G3175C variant was found more frequently in the upper tertile distributions for apolipoprotein CIII, apolipoprotein E, and plasma triglyceride/HDL ratios (P < 0.05). The rare allele of the apo AI MspI restriction site polymorphic variant was also found more frequently in the upper tertiles for apo CIII, apo E, and plasma triglyceride/HDL ratios (P < 0.04). Eleven of the most lipaemic Chinese subjects (with fasting plasma triglycerides >700 mg/dl) were analyzed for DNA sequence variation. One novel mutation was observed C1338A (which is a silent mutation at Thr361) and two others that are also found in European subjects (Ala261Thr and Ser447Ter). We conclude that genetic differences between Chinese and Europeans may have an effect on the prevalence of coronary artery risk factors involved in lipid transport, and further extended study is warranted.     

Prediction of the helix/strand content of globular proteins based on their primary sequences

Population screening for hemochromatosis done by using the transferrin saturation test has been advocated by experts to permit the initiation of therapeutic phlebotomy before the onset of clinical disease. The discovery of a gene associated with hemochromatosis has made DNA testing another option for screening and diagnosis. In this paper, U.S. Preventive Services Task Force criteria are used to evaluate the evidence for the usefulness of population screening done by using iron measures or genetic testing. Published clinical research offers little evidence to suggest that population screening for hemochromatosis done by using genetic testing improves clinical outcomes. Although one recently discovered mutation, C282Y, accounts for 60% to 92% of cases of the disease in series of patients with hemochromatosis, uncertainties remain about the clinical penetrance of various genotypes; the accuracy of genetic testing; and the ethical, legal, and social effects of genetic testing. Before population screening for hemochromatosis done by using transferrin saturation testing can be recommended, laboratory standardization needs to be addressed and questions about risk for clinical disease in asymptomatic persons with mutations or early biochemical expression of disease require resolution. Evidence from case series suggests that hemochromatosis may be associated with liver cancer, other liver disease, diabetes, bradyarrhythmias, and arthritis. In all studies but one, however, estimation of the magnitude and significance of this risk is limited by lack of adequate comparison groups. The need for population data to answer questions about penetrance among asymptomatic persons should not impede efforts to increase the detection and treatment of hemochromatosis in persons found to have elevated iron measures a family history of hemochromatosis, or consistent early signs and symptoms of the disease.     

Neuromuscular disorders in childhood

The understanding of the molecular genetics of inherited neuromuscular disorders has unfolded rapidly in recent years. Identification of the genetic defects involved has enhanced diagnosis, prognosis, carrier detection, and prenatal diagnosis and has provided a basis for rational treatment strategies. This review provides an update on the most common neuromuscular disorders that present in childhood, eg, spinal muscular atrophy, muscular dystrophies, and myotonic disorders, and includes information on molecular genetics, pathogenesis, natural history, and experimental therapeutic strategies.     

Measurement error does not explain the persistence of a body mass index association with endometrial cancer after adjustment for endogenous hormones

Genome projects are providing vast amounts of sequence data. This raw material makes possible a completely new era of experimental approaches. Among these, DNA array technology, which allows one to assay thousands of unique nucleic acid samples simultaneously, will be important in genomic research, and the results of this research are likely to affect virtually every field of biology. DNA array technology is still in its infancy, but many have demonstrated its power by using it for such diverse applications as global monitoring of gene expression, mutation detection, and genetic mapping.     

Factor V Leiden and other coagulation factor mutations affecting thrombotic risk

Five genetic defects have been established as risk factors for venous thrombosis. Three are protein C, protein S, and antithrombin deficiencies, defects in the anticoagulant pathways of blood coagulation. Together they can be found in approximately 15% of families with inherited thrombophilia. Their laboratory diagnosis is hampered by the large genetic heterogeneity of these defects. The other two genetic risk factors, resistance to activated protein C associated with the factor V Leiden mutation and increased prothrombin associated with the prothrombin 20210 A allele, are much more prevalent and together can be found in 63% of the thrombophilia families. Because both defects are caused by a single mutation, DNA analysis is the basis of their laboratory diagnosis.     

Forward and reverse genetic approaches to behavior in the mouse

Modern molecular genetic and genomic approaches are revolutionizing the study of behavior in the mouse. "Reverse genetics" (from gene to phenotype) with targeted gene transfer provides a powerful tool to dissect behavior and has been used successfully to study the effects of null mutations in genes implicated in the regulation of long-term potentiation and spatial learning in mice. In addition, "forward genetics" (from phenotype to gene) with high-efficiency mutagenesis in the mouse can uncover unknown genes and has been used to isolate a behavioral mutant of the circadian system. With the recent availability of high-density genetic maps and physical mapping resources, positional cloning of virtually any mutation is now feasible in the mouse. Together, these approaches permit a molecular analysis of both known and previously unknown genes regulating behavior.     

Familial adenomatous polyposis coli in the Czech population. I. Detection of an additional 3 mutations out of a total of 7 in exon 15 of the APC gene

BACKGROUND: Familial adenomatous polyposis (FAP) is an autosomal dominant inherited disease characterized by multiple adenomatous polyps in the colon which progress to carcinoma. FAP is caused by germ-line mutation of the tumor-suppressor adenomatous polyposis coli (APC) gene, the structure and coding sequence of which have been known from 1991. The diagnosis of FAP has classically been based on the detection of multiple colorectal adenomas, often after carcinoma development. Presymptomatic genetic testing for the presence of an allele carrying the FAP mutation is now possible using a variety of techniques. METHODS AND RESULTS: The present paper is the first part of an analysis of 37 different Czech families with 83 members affected by FAP. Our goal is to identify the mutation characteristic for each family for early diagnosis of FAP. We screened clinically manifest representatives of nine families for mutations in exon 15 of the APC gene. First, we searched for the mutation hot spots (codons 1061 and 1309, respectively) and later for the entire exon 15. Denatured gradient gel electrophoresis (DGGE) of amplified regions ov exon 15 has been used to identify DNA sequence variations followed by sequencing verification. In seven patients, seven different mutations in exon 15 of APC gene, four deletion mutants (5-base deletions in codons 1061 and 1309, 1-base deletion in codons 759 and 7-base deletion combined with a 2-base insertion in codon 712), one insertion mutation (1-base/A/insertion in codon 1554) and two point mutations (C to T and C to A substitutions in codons 737 and 935, respectively, in both cases leading to formation of stop codons) have been found. CONCLUSIONS: From seven different mutations found, 4 mutations have been previously described (mutations in codons 935, 1061, 1309 and 1554), 3 mutations in the APC gene are described here for the first time, namely the mutations in codons 712, 759 and 767.     

Two Japanese siblings with Bloom syndrome gene mutation and B-cell lymphoma

Bloom syndrome (BS) is a rare autosomal recessive genetic disorder characterized by lupus-like erythematous telangiectasia of the face, sun sensitivity, infertility and stunted growth. Upper respiratory tract and gastrointestinal infections are commonly associated with the decreased immunoglobulin levels found in BS patients. Chromosomal abnormalities are hallmarks of the disorder, and high frequencies of sister chromatid exchanges and quadriradial configurations in lymphocytes and fibroblasts are virtually diagnostic. Recently, the causative gene for BS (BLM) has been identified. We encountered and defined a family with a nonsense mutation in BLM. The brother and sister were homozygous for the mutation and both developed B-cell malignant lymphoma in their twenties. These findings indicate the importance of prenatal diagnosis and the detection of BS carriers based on molecular genetic analysis.     

Genetics in the OR--implications for perioperative nursing practice

New developments in deoxyribonucleic acid (DNA) technology are increasing understanding of the role of genetics in health and disease. This kind of health information requires that perioperative nurses develop new skills and roles that will enhance the quality of genetic health care they provide to patients, particularly with regard to managing genetic information. Perioperative nurses expand their scope of practice to incorporate a genetic focus into health assessment, patient education, and patient support as they assimilate new genetic information into their daily lives. Perioperative nurses familiar with genetic counseling services--and how and when to refer patients for such services--will ensure that all patients have access to the most current and appropriate genetic information with which to make informed health choices.     

The power of linkage detection by the transmission/disequilibrium tests

Despite growing interest in the use of transmission/disequilibrium test (TDT)-type analysis in association studies, there has been surprisingly scant attention paid to the issues as to what factors affect the power of the TDT for linkage detection. We demonstrate in this paper that the power is a function of several genetic parameters including the recombination fraction, penetrance, the age of mutant disease allele, marker allele frequency, recurrent mutation rates at marker and/or disease locus, and initial linkage disequilibrium. In general, TDT has greater power to detect linkage for a 'recessive'-type model than for a 'dominant'-type model. Its power also is higher when there is greater differential in marker allele frequency between disease and normal chromosomes. And since the presence of marker mutation and/or recurrent mutation at the disease locus, or the age of disease mutation, or the initial incomplete linkage disequilibrium, all hasten the process to reach linkage equilibrium, all of them can affect the power of TDT to detect linkage. The effect of marker mutation rate or the mutation rate at the disease locus can be minimal if mutation rates are low. The results on the impact of recombination fraction and of age of mutation on the power of TDT in linkage detection seem to be disheartening for gene mappers of complex diseases: for a disease with small genetic influence, a vastly large sample size is needed to detect the linkage, if the marker is not very close to the disease locus. This is particularly true if the disease is 'old'.     

Relationship between parental trinucleotide GCT repeat length and severity of myotonic dystrophy in offspring

OBJECTIVE: To assess the relationship between the GCT repeat number in the myotonic dystrophy gene and the clinical phenotype and examine its predictive utility in prenatal testing. DESIGN: DNA from patients was examined for the length of the myotonic dystrophy GCT repeat region, using both Southern blot analysis and polymerase chain reaction. The results were compared with the clinical onset of disease, as well as with pregnancy outcomes. SETTING: Patient samples were referred to the Kleberg DNA Diagnostic Laboratory at the Baylor College of Medicine for DNA analysis by geneticists and genetic counselors (84%), neurologists (10%), and obstetricians and other specialists (6%). Clinical features including onset of disease and family pedigrees were determined by the referring centers. PATIENTS: A total of 241 patient samples from 118 families referred from primarily genetic or neurological centers for genetic linkage analysis or mutation analysis for myotonic dystrophy. This included 44 families referred for prenatal diagnosis. MAIN OUTCOME MEASURES: A relationship between myotonic dystrophy disease onset and length of the GCT repeat allele, parental origin of the disease allele, and results of prenatal diagnosis predictions of disease status were measured. RESULTS: There is a relationship between increasing repeat length and earlier clinical onset of disease. Essentially all (> 99%) myotonic mutations causing myotonic dystrophy are accounted for by GCT repeat amplification. Congenital myotonic dystrophy occurs with as few as 730 GCT repeats but only with alleles of maternal origin. Maternal GCT repeats were found as low as 75 (asymptomatic) that were amplified to result in a child with congenital myotonic dystrophy. Application of DNA diagnosis to 32 pregnancies provided an accurate method for identification of at-risk fetuses and allele enlargement. CONCLUSIONS: The GCT repeat in myotonic dystrophy is highly mutable. The triplet repeat amplification is highly specific for mutations involving the myotonin protein kinase gene accounting for myotonic dystrophy. The quantitation of triplet repeats can be more sensitive than physical, ophthalmologic, and electromyography examinations since the mutation can be detected in patients without evidence of myotonic dystrophy clinical findings. The length of the triplet expansion is influenced by the sex of the transmitting parent and is related to the clinical onset of disease features. Prenatal measurement of the GCT triplet repeat has utility for families with myotonic dystrophy risk since mutant and normal repeats are distinguishable and the length of mutant repeat alleles is associated with clinical severity. Thus, GCT triplet measurement provides a highly accurate means of detecting the myotonic dystrophy mutation in patients and offers a new reproductive option for families at risk for myotonic dystrophy.     

Detecting fetal abnormalities

Three per cent of infants suffer from birth defects, (mostly genetic) including single gene diseases, such as cystic fibrosis or thalassaemia; chromosomal aneuploidies such as Down syndrome; or multifactorial conditions such as spina bifida and congenital heart defects. Perhaps the most important reason for focusing attention on genetics in 1997 is that the field has changed dramatically due to advances in technology and in our understanding of the human genome. New opportunities for prevention combined with more effective treatment, represent the new standard of care that the community has the right to expect for genetic disease. This article looks at antenatal diagnosis early in pregnancy and reviews what progress is to be expected in this field during the coming decade.     

Importance of long-range interactions in (alpha/beta)8 barrel fold

There is widespread interest in documenting the amount and geographic distribution of genetic variation in the human species. This information is desired by the biomedical community, who want a densely packed map of SNP (single nucleotide polymorphism) sites to be used to identify genes associated with disease by linkage disequilibrium between sets of adjacent markers and the occurence of disease in populations, and to characterize disease-related variation among populations. Anthropologists use genetic variation to reconstruct our species' history, and to understand the role of culture and geography in the global distribution of human variation. The requirements for these two perspectives seem to be converging on a need for an accessible, representative DNA bank and statistical database of human variation. However, both fields have been using conceptual models that are oversimplified, and this may lead to unrealistic expectations of the questions that can be answered from genetic data.     

The role of genetic factors in the pathogenesis of thyroid neoplasms

This paper summarizes the current knowledge on the role of genetic factors in the development of thyroid neoplasms. The introduction of the methods and concepts of molecular genetics (as, e.g. recombinant DNA technology) have elucidated etiopathogenesis of the majority of thyroid tumours and, in the future, can make the diagnosis easier. Mutations of genes involved in the control of cellular growth and/or differentiation (ras, c-myc, RET, met) affect the development of thyroid neoplasms. Loss of heterozygosity (LOH) may suggest the presence of tumor suppressor genes and has been reported in thyroid follicular carcinomas. Activation of tyrosine kinase, whether by specific oncogene amplification or by rearrangement, appears to be highly specific for the transformation of thyroid follicular cells into papillary tumours. Cytogenetic studies have shown frequent clonal abnormalities in thyroid follicular adenomas and carcinomas.     

Independent segregation of von Hippel-Lindau disease and cerebral cavernomas

A probable diagnosis of von Hippel-Lindau disease was made in a two generation family in which the proband had a phaeochromocytoma, renal cysts, and multiple cerebral cavernomas. His sister had multiple similar cerebral vascular lesions and his father died from renal carcinoma aged 42. Although the family did not satisfy the conventional diagnostic criteria for von Hippel-Lindau disease, an underlying germline mutation in the von Hippel-Lindau disease tumour suppressor gene was identified in the proband. Molecular genetic analysis not only confirmed the putative diagnosis of the disease in the proband but also showed that the cerebral vascular lesions segregated independently from the von Hippel-Lindau disease mutation. This report exemplifies how molecular genetic investigations can enhance the diagnosis and management of families with suspected von Hippel-Lindau disease, particularly when the manifestations, as in this family, are not typical.     

Mutation scanning methods for the analysis of parasite genes

Molecular variation is widespread in parasite populations, and its analysis has important implications for studying aspects relating to the function and organisation of genes, and the taxonomy, phylogeny and population genetics of parasites. This article reviews some PCR-based mutation scanning techniques that have advantages over currently used DNA methods for the analysis of genetic variation in parasites. The review is technical and describes briefly the principles of relevant techniques, examines some of their advantages and disadvantages and gives several examples for possible applications.     

Scoring systems for predicting prognoses of the patients with AML treated according to the Japan Adult Leukemia Study Group (JALSG) protocols

Population genetics is almost eighty years old, but benefited only very recently from the advantages of direct DNA analysis. Nevertheless, much knowledge had already accumulated and was completely confirmed by the study of DNA markers. Major benefits of the latter came with microsatellites. It allowed to discover an error made with classical markers but even more seriously with RFLPs, because of the practically involuntary sampling of individuals almost exclusively of European origin for the detection of polymorphisms. Among other evolutionary application of microsatellites, the most attractive is their very recent use for dating population separations during the recent migration out of Africa of modern humans. They confirm the theory that this expansion was quite recent. Single nucleotide substitutions are the major material of evolution, and so far markers of this kind were rare. A new method, DHPLC, is excellent for their detection and testing. In humans it has been applied almost exclusively to the Y chromosome, and in a year it has given a completely new picture of Y chromosome genetics. Some applications of statistical methods to genetic geography of classical markers and ADN markers will show the power of the geographical approach, and therefore the need of a wide collection of population samples, as will be made possible by the HGDP (Human Genome Diversity Project).