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Sensorineural Hearing Loss
Published in R James A England, Eamon Shamil, Rajeev Mathew, Manohar Bance, Pavol Surda, Jemy Jose, Omar Hilmi, Adam J Donne, Scott-Brown's Essential Otorhinolaryngology, 2022
Linnea Cheung, David M. Baguley, Andrew McCombe
Non-syndromic SNHL accounts for approximately 70% of genetic SNHL cases. The remaining 30% are recognised as being part of a syndrome. The inheritance pattern can be autosomal dominant, recessive, X-linked, or mitochondrial. A genetic HL may be recognised when it is observed that several generations of family members have been affected. However, de novo mutation or, a reduced penetrance inheritance pattern, may cause a singleton case. Linkage analysis combined with whole genome/exome sequence analysis enables the identification of novel genes and pathways causing inherited SNHL. To date more than 60 loci for genes causing HL have been mapped, but only just over half of the specific genes have been identified.
Genetic Counseling in Assisted Reproductive Technology
Published in Carlos Simón, Carmen Rubio, Handbook of Genetic Diagnostic Technologies in Reproductive Medicine, 2022
Autosomal dominant inheritance is when mutation in one allele of an autosomal gene is sufficient to cause disease. An affected individual typically has one non-functional allele and one functional allele. Either allele can be passed on to subsequent generations, resulting in a 50% recurrence risk for each offspring. Dominant conditions can sometimes be seen in a family, passed down from generation to generation and shared among siblings. Sometimes, dominant conditions are caused by a de novo gene change, when an individual can be the first in the family to be affected.
Basic genetics and patterns of inheritance
Published in Hung N. Winn, Frank A. Chervenak, Roberto Romero, Clinical Maternal-Fetal Medicine Online, 2021
Genetic counseling is an important part of the practice of medical genetics. The field of genetics is unique in that a diagnosis of a genetic disorder in an individual has an impact on his or her entire family. Multiple family members and their present or future offspring may be at risk for the genetic disorder as well. Genetic counseling involves the explanation of the manifestations of the disorder, the natural history and treatment, the inheritance pattern, the risks of recurrence, and the methods of prenatal and postnatal diagnosis. The genetic counselor also helps the family make the best possible adjustment to the disorder and the risks of recurrence. This often involves referral to a support organization through which the family can make contact with other affected individuals. The vast majority of genetic counselors and clinical geneticists seek to provide nondirective counseling, whereby information about the disorder and the recurrence risk is given in an unbiased and neutral way, and the family makes decisions about reproductive options in accordance with their own beliefs and values.
Laboratory testing for mitochondrial diseases: biomarkers for diagnosis and follow-up
Published in Critical Reviews in Clinical Laboratory Sciences, 2023
Abraham J. Paredes-Fuentes, Clara Oliva, Roser Urreizti, Delia Yubero, Rafael Artuch
The mitochondrial metabolism is probably the most intricate within cellular metabolism. The double genetic origin that controls oxidative phosphorylation (OXPHOS), in which proteins are codified by either nuclear or mitochondrial genomes (mitochondria are the only organelles with such double genetic regulation), and the fundamental pathways that occur in mitochondria partially explain this complexity [1,2]. All clinical presentations, ages of disease onset and inheritance types (e.g. maternal, X-linked, dominant, recessive, or sporadic) are possible in mitochondrial diseases (MDs), which are a group of rare genetic disorders that impair different mitochondrial biological functions [2,3]. When mutations are detected in nuclear genes (nDNA), they follow Mendelian inheritance and exhibit dominant, recessive or X-linked patterns. However, when mutations are localized in mitochondrial DNA (mtDNA), maternal inheritance, or sporadic mutations occur along with other genetic features such as heteroplasmy, mitotic segregation, or random distributions of mutated mtDNA among cells. Thus, the pathophysiological mechanisms of MDs are heterogeneous, and the diagnostic and treatment monitoring aspects present challenges to health professionals and researchers working in this field [3–5]. This group includes clinical laboratory professionals, because the lack of specificity and sensitivity of the currently available biomarkers used in clinical laboratories for both diagnostic and patient follow-up purposes is generally recognized [6–8].
Congenital stationary night blindness in a patient with mild learning disability due to a compound heterozygous microdeletion of 15q13 and a missense mutation in TRPM1
Published in Ophthalmic Genetics, 2021
M. Delle Fave, M. Cordonnier, l. Vallee, C. Condroyer, C. Zeitz, I. Balikova
We also found that the patient is a heterozygous carrier of a deletion on chromosome 15. Heterozygous microdeletion 15q13 leads to variable degree of mental retardation, autism spectrum disorder, epilepsy and hypotonia (18). The deletion has variable clinical expressivity. Our patient presents with mild developmental delay, no other neurological problems and no facial dysmorphism. The deletion was also present in the normal mother. Hassfurther et al. reported the inheritance of 15q13 deletions from normal parents to be up to 81% (18). The same group hypothesizes that the maternal inheritance enhances the clinical phenotype in the patients. Homozygous deletions of the 15q13 locus have also been reported (19) The two affected siblings had abnormal electroretinography with negative scotopic and atypical photopic responses probably indicative for cCSNB.
Duchenne muscular dystrophy: an overview to the cardiologist
Published in Expert Review of Cardiovascular Therapy, 2020
Fabio de Souza, Caroline Bittar Braune, Ana Paula Cassetta Dos Santos Nucera
Duchenne muscular dystrophy (DMD), described more than 150 years ago, is the most common form of muscular dystrophy in children, affecting approximately one in 3,500/5,000 liveborn boys [1,2]. It takes part in a large group of pathologies called dystrophinopathies, which are caused by genetic changes in the gene that codes for dystrophin, a protein that plays a structural role in the cytoskeleton of muscle cells by connecting intracellular structures with the extracellular matrix [3]. Mutations related to the dystrophin gene occur in the short arm of the X chromosome (Xp21.1), which represents the largest known gene, composed of 79 exons [4,5]. Mutations causing a shift in the open reading frame result in the absence of dystrophin, leading to the DMD phenotype. With a X-linked recessive inheritance pattern, a mother with this mutation has a 50% chance of transmitting it to her male children. Although most DMD mutations are inherited, spontaneous mutations can occur in up to 30% of cases [6].