Registers for the prevention of genetic disease.
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Genetic diseases are important to family doctors. I have analysed my role as a Dutch general practitioner in caring for patients with such disorders and describe this with some examples.
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The current status of our knowledge of genetic diseases is reviewed. The incidence of monogenic, multifactorial and chromosomal disorders, according to the literature to date, is given, and the possibilities of mass screening programmes are discussed. The prospects for antenatal diagnosis of genetic diseases are reviewed, with emphasis on the indications for amniocentesis and the safety of the procedure. Finally, speculations are made regarding the possible effects of medical and social practices on the frequency of genetic disorders in future generations.
Many dominant genetic disorders result from protein-altering mutations, acting primarily through dominant-negative (DN), gain-of-function (GOF), and loss-of-function (LOF) mechanisms. Deciphering the mechanisms by which dominant diseases exert their effects is often experimentally challenging and resource intensive, but is essential for developing appropriate therapeutic approaches. Diseases that arise via a LOF mechanism are more amenable to be treated by conventional gene therapy, whereas DN and GOF mechanisms may require gene editing or targeting by small molecules. Moreover, pathogenic missense mutations that act via DN and GOF mechanisms are more difficult to identify than those that act via LOF using nearly all currently available variant effect predictors. Here, we introduce a tripartite statistical model made up of support vector machine binary classifiers trained to predict whether human protein coding genes are likely to be associated with DN, GOF, or LOF molecular disease mechanisms. We test the utility of the predictions by examining biologically and clinically meaningful properties known to be associated with the mechanisms. Our results strongly support that the models are able to generalise on unseen data and offer insight into the functional attributes of proteins associated with different mechanisms. We hope that our predictions will serve as a springboard for researchers studying novel variants and those of uncertain clinical significance, guiding variant interpretation strategies and experimental characterisation. Predictions for the human UniProt reference proteome are available at https://osf.io/z4dcp/.
Epigenetic regulation may underlie asymmetric allelic expression of many genes during development and disease pathogenesis. Allele-specific epigenetic modification could provide an efficient therapy for dominant genetic diseases due to heterozygous mutations. We developed an allele-specific epigenetic editing method ("Epi-Allele") for silencing pathogenic alleles and found surprisingly elevated expression of the non-targeted alleles, leaving total gene expression unchanged. Genome-wide screening revealed that such compensated allelic expression represents a common phenomenon, suggesting that the Epi-Allele approach could avoid the haploinsufficiency induced by current allele-specific silencing therapies. This notion was validated by allele-specific epigenetic remodeling of Myh6 and MYH7 genes in ameliorating cardiac phenotypes in a hypertrophic cardiomyopathy (HCM) mouse model and HCM patient iPSC-derived cardiomyocytes, respectively. Thus, Epi-Allele offers an allele-specific haploinsufficiency-free therapeutic approach for treating dominant genetic diseases.
To meet the challenge of unravelling the molecular pathology of the ever expanding number of known genetic diseases in man, new efficient investigative techniques have to be designed. A procedure is presented for detection of protein defects in genetic diseases on the basis of structural rather than functional alterations. The technique is based on double labeling of normal and diseased fibroblast proteins followed by extensive fractionation and analysis. The rationale, advantages, and limitations of the procedure are discussed and the technical aspects of its use explained.
In order to adequately assess the genetic risks to man of an altered mutation rate, it is necessary to know the naturally occurring frequency of mutation-maintained genetic ill-health and the burden that such defects impose. The relevant data that are available are largely inadequate to determine the incidence of genetic disease that is maintained by mutation, and measures of various aspects of the social and personal burdens due to hereditary ill-health are almost wholly lacking. It is suggested that the creation of individual and family histories, using large scale automatic record linkage and existing files of vital and ill-health records, may be a useful approach to these kinds of problems. Using such linked individual health histories, new data are presented that relate to measures of the burden due to childhood dominant and recessive diseases and congenital malformations.
The high incidence of some genetic diseases in certain ethnic groups is important in planning of medical genetic programs. Simple interaction models predict that at least some lethal recessive alleles will have "hitchhiked" to increased frequencies because of linkage to genes whose alleles have been favored by selection for other reasons in certain populations. In the absence of linkage or epistasis with a gene favored by selection, heterozygote advantage for a recessive lethal may produce the same phenomenon. In the hitchhiking model (linkage), the increase in the gene frequency is temporary, but the length of time that the increased gene frequency is at least double the base frequency may be quite long. Changes in gene frequency for the unlinked epistatic model result in a new equilibrium with a possibly higher gene frequency. The most likely chromosomal regions in which hitchhiked lethal recessives would be found are in the vicinity of genes whose allelic frequencies vary substantially among human racial groups (e.g., Gm, Rh, Duffy, lactose tolerance, or HL-A). There will be a hitchhiking effect if recombination distance is less than the selective advantage. The closer the linkage of two loci, the easier hitchhiking effects will be to detect. Hitchhiking is suggested by nonrandom association of the recessive disease and one of the selected markers, as in the case of Gm and cystic fibrosis. However, there is so far insufficient evidence of linkage between them. More pedigree information is necessary than is now available.
PURPOSE: To systematically evaluate the diagnostic yield and clinical utility of genome sequencing (GS) and exome sequencing (ES; genome-wide sequencing [GWS]) in pediatric patients with rare and undiagnosed genetic diseases. METHODS: We conducted a meta-analysis of studies published between 2011 and 2023. To address study heterogeneity, comparative analyses included within-cohort studies using random-effects models. RESULTS: We identified 108 studies including 24,631 probands with diverse clinical indications. The pooled diagnostic yield among within-cohort studies (N = 13) for GWS was 34.2% (95% CI: 27.6-41.5; I2: 86%) vs 18.1% (95% CI: 13.1-24.6; I2: 89%) for non-GWS, with 2.4-times odds of diagnosis (95% CI: 1.40-4.04; P < .05). The pooled diagnostic yield among within-cohort studies (N = 3) for GS was 30.6% (95% CI: 18.6-45.9; I2: 79%) vs 23.2% (95% CI: 18.5-28.7; I2: 58%) for ES, with 1.7-times the odds of diagnosis (95% CI: 0.94-2.92; P = .13). In first-line testing, the diagnostic yield tended to be higher for GS than for ES across clinical subgroups. The pooled clinical utility among patients with a positive diagnosis was 58.7% (95% CI: 47.3-69.2; I2: 81%) for GS and 54.5% (95% CI: 40.7-67.6; I2: 87%) for ES. CONCLUSION: GS appears to have a higher diagnostic yield than ES, with similar clinical utility per positive diagnosis.
The use of electron microscopy as a further method of diagnosis of disease in cultured skin fibroblasts and cultured amniotic fluid fibroblasts is presented. It was demonstrated that Tay-Sachs disease, Fabry's disease, and metachromatic leukodystrophy had distinctive abnormalities in both cultured skin fibroblasts and cultured amniotic fluid fibroblasts. It was shown that control of culturing conditions made it possible to distinguish normal cell lines from certain cell lines carrying known genetic diseases.
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PURPOSE: The effect of Mendelian disorders on pregnancy and neonatal outcomes is poorly understood because of their rarity and the challenge of compiling complete prenatal and postnatal records. METHODS: Using electronic health records from a single academic center, we developed a retrospective cohort of maternal-infant dyads. Cases were mothers with molecularly confirmed Mendelian disorders paired with live-born infants; controls had no documented genetic disease. Outcomes were evaluated overall, by organ system, and by individual disorder. RESULTS: The cohort included 58,912 dyads, 241 with genetic diagnoses and 58,671 controls. Although overall outcomes were generally favorable, mothers with genetic disorders had higher rates of cesarean delivery and neonatal intensive care unit admission, earlier gestational age, and lower Apgar scores. Neonatal risks were greatest among neurological and cardiovascular disorders. Known associations were replicated, including increased neonatal intensive care unit admission in 22q11.2 deletion syndrome, cesarean delivery in Turner syndrome, and gestational diabetes in cystic fibrosis. We also provided descriptive electronic-health-record-based case reports and case series for 35 disorders previously lacking published pregnancy outcome data. CONCLUSION: This study identifies elevated perinatal risks in specific Mendelian disease groups and demonstrates how electronic-health-record-linked data can support prenatal counseling, risk stratification, and individualized care for individuals with genetic disorders.
A study of 1223 amniocenteses carried out during 1020 pregnancies in 990 women showed that 2nd-trimester amniocentesis at about 16 weeks' gestation is a safe, accurate and reliable procedure for the diagnosis of certain classes of genetic disease when it is monitored by ultrasound, performed by a trained obstetrician and carried out in a major health sciences centre. The percentage of fetal losses (4.7%) and neonatal deaths (0.5%) during the study was not greater than in control samples for women 35 years of age and older. The best results were obtained when needles of gauge 20 or 21 were used. The use of needles of gauge 19 or larger and more than two insertions during a single amniocentesis were associated with a significantly greater frequency of fetal loss than a second or even a third amniocentesis during the same pregnancy. For 39 fetuses (3.8%) a diagnosis of a genetic abnormality was made and 23 male fetuses were found to be potentially hemizygous for an X-linked gene. There were 51 therapeutic abortions as a result of the diagnosis. Sixty-six tests (5.4%) gave an inconclusive result and seven (0.6%) gave an erroneous diagnosis; five of the latter (two false-positives and three false-negatives) resulted from the alpha1-fetoprotein test for neural-tube defects and in two cases the sex was incorrectly determined. The frequency of all chromosome abnormalities was 1:20 when the mother's age was 40 years or more and 1:60 when the mother's age was between 35 and 39 years. When a mother had previously had a child with a chromosome abnormality the risk of recurrence of such an abnormality was 1:100 when the age of the mother was 35 years or more.
Methodology is described to enrich for heterokaryons after mammalian cell fusion. A heterogeneous cell mixture can be separated on a Sta-Put apparatus into fractions of uniform size cells by sedimentation through a 1% bovine serum albumin-5% Ficoll gradient. Unfused RAG and LM/TK- cells, differing by 10% in diameter, have been sorted by size; following fusion, larger and faster sedimenting cells were shown to be hybrids. This methodology can be utilized in genetic complementation studies of human genetic diseases where selection procedures for proliferating hybrids do not exist. When fibroblasts from individuals with Tay-Sachs disease [deficient in hexosaminidase A (HEX A-)] and Sandhoff-Jatzkewitz disease (HEX A- and HEX B-) are fused, HEX A is generated, demonstrating complementation of two different mutations. After Sta-Put fractionation, the HEX A complementation product was associated with the faster sedimenting multinuclear cells and not with the mononuclear parental cells. This methodology will facilitate detection of genetic differences in fibroblasts from related inherited disorders.
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