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Homocystinuria
Published in Charles Theisler, Adjuvant Medical Care, 2023
Homocystinuria is an inherited disorder that prevents the full breakdown of methionine and the proper use of its breakdown product, homocysteine. This leads to an abnormal and harmful buildup of homocysteine in the blood and urine and may also cause low levels of cysteine. The disorder is characterized by myopia, dislocation of the lens in the eye, an increased risk of abnormal blood clots, brittle bones, Marfan-like features, and sometimes problems with development and learning. One type of homocystinuria results in poor metabolism of folate (vitamin B9) which also leads to excess homocysteine levels. Nutritional causes of hyperhomocysteinemia are vitamin B6 or B12 deficiency and, less often, folate deficiency.1 These disorders can cause intellectual disability, seizures, problems with movement, and megaloblastic anemia. Homocystinuria usually does not show symptoms in a newborn baby. A goal of treatment is to decrease elevated homocysteine blood levels. In general, there are three possible therapeutic approaches to homocystinuria: (1) restriction of substrate (low methionine diet), (2) replacement of missing products (e.g., cystine), and (3) supplementation with coenzymes (pyridoxine, betaine anhydrous).1 Nutritional causes should be handled appropriately or ruled out.
Hyperkinetic Movement Disorders
Published in Philip B. Gorelick, Fernando D. Testai, Graeme J. Hankey, Joanna M. Wardlaw, Hankey's Clinical Neurology, 2020
Morales-Briceno Hugo, Victor S.C. Fung, Annu Aggarwal, Philip Thompson
Amino acidurias (AA): Glutaric aciduria, methylmalonic aciduria.Homocystinuria.Propionic academia.
Paper 4
Published in Amanda Rabone, Benedict Thomson, Nicky Dineen, Vincent Helyar, Aidan Shaw, The Final FRCR, 2020
Amanda Rabone, Benedict Thomson, Nicky Dineen, Vincent Helyar, Aidan Shaw
All of the options provided are possible causes of pectus excavatum. The imaging features described are consistent with underlying diagnosis of Marfan syndrome, which is a connective tissue disorder. Skeletal features in this condition include posterior vertebral body scalloping due to dural ectasia, scoliosis, spondylolisthesis, acetabular protrusion and arachnodactyly. Cardiac complications in this condition include aortic root dilatation, mitral valve regurgitation and aortic dissection. Cardiac disease is the cause of death in 90% of patients. Homocystinuria is rare. Patients can have Marfanoid features, and mortality in these patients is also mostly due to cardiovascular complications. Screening for this condition is performed in the neonate with the heel-prick test. Patients often have developmental delay.
High levels of blood glutamic acid and ornithine in children with intellectual disability
Published in International Journal of Developmental Disabilities, 2022
Muhammad Wasim, Haq Nawaz Khan, Hina Ayesha, Abdul Tawab, Fazal e Habib, Muhammad Rafique Asi, Mazhar Iqbal, Fazli Rabbi Awan
Cystathionine Beta Synthase (CBS) deficiency is involved in classical homocystinuria disorder, which is the second most prevalent disorder among aminoacidopathies in different populations (Mazaheri et al.2017), reflecting homocystinuria is probably the prevalent disorder in Pakistani population instead of PKU. Homocystinuria (HCU) is an autosomal recessive disorder which is caused by Cystathionine Beta Synthase (CBS: encoded by CBS) deficiency. If the patients are not treated early, they suffer with various pathologies including excessive height, long limbs, tall stature, thrombosis, osteoporosis, mental retardation, ectopia lentis, delayed developmental milestones etc., (Poloni et al. 2018, Li et al.2018), and if diagnosis are delayed then significant long-term morbidity occurs or even death is caused (Huemer et al.2015).
Cystathionine β-synthase Deficiency Impairs Vision in the Fruit Fly, Drosophila melanogaster
Published in Current Eye Research, 2021
Marycruz Flores-Flores, Leonardo Moreno-García, Felipe Castro-Martínez, Marcos Nahmad
Classic homocystinuria is a metabolic disease mainly caused by inherited deficiency of Cystathionine-β-synthase (CBS), a vitamin B6-dependent enzyme that catalyzes the flux of sulfur from methionine to cysteine in the transsulfuration pathway.1 In humans, genetic variants causing low CBS expression lead to the accumulation of toxic levels of homocysteine and methionine in urine and plasma, affecting skeletal, visual, the central nervous system,2,3 and also poses an independent risk factor for thrombosis and vascular disease.4,5 One of the most common clinical manifestations of homocystinuria is severe myopia followed by ectopia lentis that affects about 90% of patients with a CBS deficiency.6,7 Despite the high prevalence of eye-related abnormalities caused by this disease, the molecular mechanisms that relate CBS deficiency to vision problems are poorly understood. Murine models of genetic deficiency of cbs have been used as a model of homocystinuria,8,9 including visual manifestations. For instance, studies using cbs-mutant mice have reported alterations of retinal vasculature,10 retinal ganglion cell death,11,12 and visual function.13 However, the widespread use of this experimental model is challenging due to a large degree of neonatal lethality.9
The evolving role of genetics in ophthalmology
Published in Ophthalmic Genetics, 2021
Natario L. Couser, Brian P. Brooks, Arlene V. Drack, Suma P. Shankar
It is not uncommon for the initial referral clinical diagnosis to be found incorrect or incomplete upon pursuing additional specialized testing and/or genetic testing to obtain the molecular genetic diagnosis; see examples of this in Figure 2. Establishing an accurate diagnosis allows for optimal medical management and often life-changing care, for example, initiating medical therapy following accurate diagnosis of homocystinuria in individuals presenting with ectopia lentis (8). Previous reports have found that consultations to an ocular genetics service revealed 30%-50% of patients were carrying an incorrect or incomplete diagnosis or had been given inaccurate information regarding their eye disease (9,10). A recent survey of practice patterns among American Association for Pediatric Ophthalmology and Strabismus (AAPOS) members revealed that over 90% of respondents reported caring for at least one patient per week with a suspected genetic disorder affecting the eye. However, there were significant knowledge gaps in areas such as genetic testing – 11.7–34.1% reporting baseline understanding depending on testing modality with 48% reporting no understanding in any modality. Additionally, only 42% reported that they can identify and refer genetic patients for clinical trials (11). Furthermore, most respondents expressed a desire for further education within this area (11). It is likely this assessment reflects concerns by ophthalmologists in similar ways across most traditional subspecialties, thus, reinforcing the need for experts in this area.