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Genetic counselling in Mendelian disorders
Published in Angus Clarke, Alex Murray, Julian Sampson, Harper's Practical Genetic Counselling, 2019
An autosomal dominant disorder or trait can be defined either by the observed pattern of transmission between generations in families or as one that is largely or completely expressed in the heterozygote. The homozygous state is either unknown or excessively rare in dominantly inherited disorders, but when it does occur it is usually much more severe than the normal heterozygous form (e.g. familial hypercholesterolaemia) or lethal (e.g. achondroplasia). In Huntington's disease, however, the homozygote appears to be little different from the heterozygote, so this is one of the few cases known to fit both definitions.
Disorders of keratinization and other genodermatoses
Published in Ronald Marks, Richard Motley, Common Skin Diseases, 2019
The condition is inherited as an autosomal dominant disorder, but the biochemical basis is unclear. It has been estimated that the gene occurs with a frequency of 1 in 500. Histologically, the only abnormality detectable is a much diminished granular cell layer (Fig. 18.5).
Pre-existing conditions and the individual mandate 1
Published in Phelps Charles E, Parente Stephen T, The Economics of US Health Care Policy, 2017
Phelps Charles E, Parente Stephen T
When genetically-related diseases actually emerge, pre-existing condition exclusions may make many of them uninsurable. Some of these are known because of strong familial links. One form of such genetic diseases can be passed from either parent that carries the gene—an autosomal dominant disorder. Humans receive two copies of each gene—one from the mother and one from the father. With autosomal dominant diseases, if either parent carries the genetic code for the disease, each child has a 50% chance of becoming afflicted with the disorder. (The odds go up to three out of four if both parents carry the disorder.) These diseases include a variety of neurologic disorders, some cancers (breast and colon most notably), some cardiac diseases and some skeletal disorders. Geneticists estimate that seven persons per 1000 are affected by an autosomal dominant disorder. Some common autosomal dominant disorders (and their risks of occurrence) include:
Personal Utility and Early Intervention in Alzheimer’s Disease
Published in AJOB Neuroscience, 2021
Ana M. Tyler, Jennifer S. Yokoyama, Jalayne J. Arias
These factors informed the model for genetic testing in HD, which might provide a relevant example. Like the current state of AD, there are no evidence-based disease-modifying therapies for HD. HD, however, only presents as an autosomal dominant disorder. AD, on the other hand, has rare familial forms inherited in an autosomal dominant fashion, but the most common form is late-onset and non-familial. Non-familial AD risk is multifactorial and, although genetic risk variant APOE e4 increases AD risk 2–10-fold, there are no genetic determinants of late-onset AD. Prenatal testing is an option for would-be parents concerned about HD; in considering prenatal predictive tools for familial AD only, the authors’ concerns with respect to pregnancy termination are valid. However, there is a very clear difference in risk assessment via biomarkers for late-onset, non-familial disease versus inherited autosomal dominant disease genetic screening, the nuances of which are not elucidated by McKeown et al.
Double decentred lenses in an eye: a therapeutic dilemma in Marfan syndrome
Published in Clinical and Experimental Optometry, 2020
Wei‐shan Tsai, Yuan‐chieh Lee, Fang‐ling Chang, Ming‐shan He
Marfan syndrome occurs in one in 5,000 children. It is an autosomal dominant disorder that mainly affects the connective tissue. It is caused by the mutation of the fibrillin‐1 gene (FBN1) and subsequently results in elastic fibre malformation.1991 Ectopia lentis was found to be the most common ocular complication, which significantly affects vision.2017 The abnormal fibrillin‐related loose zonules in Marfan syndrome allow the crystalline lens to become more spherical and to decentre relative to the visual axis. Typically, the most common refractive error in Marfan syndrome is high myopia resulting from microspherophakia and longer axial length. The patient in this case received bilateral anterior chamber intraocular lens implantation at another clinic to correct her high myopia. Nevertheless, an anterior chamber intraocular lens implantation in a patient with Marfan syndrome may have a higher risk of intraocular lens decentring due to the unusually deep and large anterior chamber anatomy. Diplopia occurred when the light was bisected simultaneously by the subluxated natural lens and the decentred anterior chamber intraocular lens. Thus, a phenomenon of ‘double decentred lenses in an eye’ was observed in our patient. Therefore anterior chamber intraocular lens implantation alone without removal of the subluxated natural lens may not be sufficient to treat patients with Marfan syndrome.
The utility of whole exome sequencing in diagnosing neurological disorders in adults from a highly consanguineous population
Published in Journal of Neurogenetics, 2019
Weiyi Mu, Nicoline Schiess, Jennifer L. Orthmann-Murphy, Ayman W. El-Hattab
The genetic etiology of adult neurological disorders is complex, and as demonstrated from our data, may include de novo variants causing an autosomal dominant disorder, as well as the expected high rate of autosomal recessive disorders owing to the increased consanguinity rate. Limitations of our data include the limited cohort and phenotypic heterogeneity of cases. Further reports of clinical genetic testing in neurological disorders will improve estimates of WES detection rates, further our understanding of the phenotypic variance in non-European populations and contribute to our knowledge of founder mutations in recessive conditions by identification of novel and rare pathogenic variants.