Partial trisomy 21 (PT21) is a type of trisomy 21 where only a part of chromosome 21 is present in three copies. Individuals with PT21 may exhibit a smaller number of Down's syndrome (DS) characteristics. The existence of PT21 is helpful in identifying the gene loci responsible for the Down's syndrome phenotypes.
Partial trisomy 21 is a rare clinical entity. It is characterized by the presence of only a part of chromosome 21 as an extra copy. Usually, through non-disjunction during meiosis or mitosis, there are three complete copies of chromosome 21. In the case of mosaicism, some of the cells of the body express the trisomy. PT21 has been used in Down's syndrome research, to try and locate the genes responsible for the typical Down's syndrome phenotype, with the discovery of regions such as the Down syndrome critical region (DSCR) . PT21 shows a heterogeneous expression of phenotypes, as well as genetic variation.
Studies have shown that several genes on chromosome 21 are able to code for abnormalities expressed, such as cognitive impairment  . Furthermore, it has been shown that the DSCR region is not solely responsible for the phenotypes observed, but may have an input in their expression  .
Typically, children with PT21 exhibit fewer features of DS or none at all. Some cases only experience mental impairment .
DS is the most frequently reported birth defect, with the incidence increasing with maternal age . The typical features of the condition include intellectual impairment, hypotonia during the neonatal period, flat profile, flattening of the nasal bridge and occiput, epicanthal folds, upward slanted eyes, microcephaly, macroglossia with lack of a central fissure, and small ears. Brushfield spots may be observed in the iris.
In addition, children with DS may have a single palmar crease, short hands and fingers, clinodactyly, sandal gap deformity, and plantar furrow. Growth delay, short stature, decreased intelligence quotient (IQ) may be detected during development, as well as traits of depression, autism, and attention deficit hyperactivity disorder may be seen.
Systemic effects of DS include a higher incidence of duodenal atresia, duodenal stenosis, intestinal obstruction, leukemia, Hirschsprung's disease, Alzheimer's disease, and congenital heart diseases such as ventricular septal defect and atrioventricular canal defect.
Entire Body System
Although trisomy 21 is not sufficient to cause CHD, three copies of at least part of chromosome 21 (Hsa21) increases the risk for CHD. [ncbi.nlm.nih.gov]
Partial Trisomy 21 in a Patient without the Down Syndrome Phenotype. A. Umrigar 1, T. J. Chen 2, F. [ashg.org]
Partial trisomy 21 (PT21) is a type of trisomy 21 where only a part of chromosome 21 is present in three copies. Individuals with PT21 may exhibit a smaller number of Down's syndrome (DS) characteristics. [symptoma.com]
Multiple Congenital Anomalies
Abstract A patient with a double partial trisomy 20 and 21 with mild mental retardation and multiple congenital anomalies is presented. [ncbi.nlm.nih.gov]
Bilateral sandal gaps, right inguinal hernia and bilateral hydrocele of testis have also been found. The complete description of dysmorphic features observed in our patient is shown in Tables 1 and 2. [omicsonline.org]
Jaw & Teeth
Face, Head & Neck
They presented only a few common features, such as: large fontanels, ear abnormalities and mental retardation, which we have also seen in our patient. These symptoms seem to be nonspecific and not relating to any particular chromosomal localisation. [omicsonline.org]
The proband postnatally displayed by dysmorphic features of a round flat face with prominent cheeks and high forehead, upward slanting palpebral fissures, epicanthic folds, hypertelorism, a short nose, a broad and depressed nasal bridge, anteverted nares [ncbi.nlm.nih.gov]
lips, retrognathia and high arched palate, along with a short neck. [omicsonline.org]
Prenatal diagnosis of Down's syndrome, and hence some cases of partial trisomy 21, can be achieved through amniocentesis or chorionic villus sampling . Abnormal features can be distinguished in a fetus, through ultrasound, usually between 14 and 24 weeks gestation . These include flattened nasal bridge, thickened nuchal fold and dilated ventricles. The prenatal screening is extremely effective in detecting DS .
Prenatal biochemical markers include abnormally high levels of alpha-fetoprotein, inhibin, estriol, and beta HCG (human chorionic gonadotropin), which are tested in the first and second trimesters. Fetal DNA present in maternal blood can also be tested for trisomy 21 and PT21 in noninvasive prenatal screening (NIPS).
After birth, features of DS may be present, and additional chromosome or karyotype analysis will reveal PT21 . A correlation of the clinical characteristics of DS is needed in order to make a clinical diagnosis.
The material is in no way intended to replace professional medical care by a qualified specialist and should not be used as a basis for diagnosis or treatment. [orpha.net]
New treatment prospects The application of novel molecular techniques on one of the genes in this presumed critical region is starting to open up interesting prospects for treatment of the syndrome at the gene level. [bbvaopenmind.com]
Adolescents or teens with developmental delays live in community-based group homes at our treatment center that provide a normal living environment and increase chances for success. [ascentchs.com]
[…] wide array of specialties-including neurology, cardiology, hematology, nephrology, genetics, endocrinology, oncology, dermatology, and psychiatry-revealing the underlying molecular mechanisms of disease, as well as novel routes to the unprecedented treatments [books.google.com]
Many physicians quote 5-10% survival but the research from which this information is obtained seldom includes any information about the treatment provided to children. [internationaltrisomyalliance.com]
PROGNOSIS life expectancy, formerly poor, has greatly increased, due to antibiotherapy and surgery. prognosis can be impaired by: 1 - the extreme susceptibility to infections. 2 - malformations, cardiac malformations in particular. 3 - acute leukemia [atlasgeneticsoncology.org]
[…] has 3 copies of chromosome 21 in some, but not every cell of the body Please find comprehensive information on Down Syndrome regarding definition, distribution, risk factors, causes, signs & symptoms, diagnosis, complications, treatment, prevention, prognosis [dovemed.com]
Prognosis Median life expectancy is now above the age of 55 years. The documents contained in this web site are presented for information purposes only. [orpha.net]
[…] cataracts Seizures (5-10%) Correlation between age and prevalence Peaks at infancy and 4th-5th decade of life Short stature (average at 3rd percentile) Obesity Wide gap between first and second toes Hypotonia Clinodactyly of the 5th fingers Natural History/Prognosis [en.wikibooks.org]
We called in a clergyperson for one case who candidly said he’d end the pregnancy, so bleak was the prognosis. [blogs.plos.org]
nondisjunction in meiosis; craniofacial, ocular and cerebral malformations, limb and cardiovascular anomalies, defects of heart, diaphragm and kidneys Edwards Syndrome-most die within a year; etiology: nondisjunction in meiosis; low birth weight, multiple [quizlet.com]
Etiology In 95% of the cases, trisomy 21 is free'': the extra chromosome is due to an accidental non-disjunction during meiosis. 2-3% of those cases are in a mosaic state. [orpha.net]
Jump to navigation Jump to search Down Syndrome - Trisomy 21 Genetics [ edit ] 3 possible etiologies: Full trisomy 21 (95% of the cases) Due to nondisjunction during meiosis Usually maternal nondisjunction (90-95% of these cases) 75% of maternal nondisjunction [en.wikibooks.org]
Down syndrome was described in 1861 by Seguin in 1866 by Langdon-Down who specify the clinical features of this syndrome and in 1959, Lejeune specifies the chromosomal etiology. [doctortipster.com]
In Etiology and Pathogenesis of Down Syndrome, Wiley-Liss, 1995, p 43-55. Hernandez D and Fisher EMC. Down syndrome genetics: unravelling a multifactorial disorder. Hum. mol. Genet., 5: 1411-1416, 1996. Shapiro, BL. [ds-health.com]
EPIDEMIOLOGY (a question on epidemiology would also include recurrence risks according to the karyotypic findings: see paragraph on the karyotype). 1,5 /1 000 births. Sex ratio: 3 males/2 females. Increased median maternal age (34 years). [atlasgeneticsoncology.org]
Epidemiology Incidence Down's syndrome is one of the most common genetic disorders, affecting 1 in 650-1,000 [ 5 ]. The underlying genetic defect is trisomy 21 in 94% of cases. [patient.info]
Atlantoaxial instability in individuals with Down Syndrome: epidemiologic, radiographic, and clinical studies. Pediatrics. 1987. 80:555-560. Juj H, Emery H. The arthropathy of Down syndrome: an underdiagnosed and under-recognized condition. [emedicine.medscape.com]
Within the framework of clinical internal medicine, they will gain critical knowledge of the many powerful molecular biology-based developments now so rapidly enhancing our understanding of the pathophysiology of disease, improving the feasibility and [books.google.com]
Antonarakis SE, Lyle R, Dermitzakis ET, Reymond A, Deutsch S (2004) Chromosome 21 and down syndrome: from genomics to pathophysiology. Nat Rev Genet 5: 725-738. [omicsonline.org]
These are made up of a protein called tau that builds up inside of neurons in the brain and prevents them from functioning properly. [theconversation.com]
[…] individual has 3 copies of chromosome 21 in some, but not every cell of the body Please find comprehensive information on Down Syndrome regarding definition, distribution, risk factors, causes, signs & symptoms, diagnosis, complications, treatment, prevention [dovemed.com]
If Your Baby Has Trisomy 22 If you have been told that a baby you miscarried had trisomy 22, rest assured that the miscarriage was not your fault and there was nothing you could have done to prevent it. [verywell.com]
Accounting for nearly 20% of all infant deaths, birth defects are the leading cause of infant mortality, according to the Centers for Disease Control And Prevention. Three of the most common newborn aneuplodies are trisomies 13, 18, and 21. [blog.geneticslab.emory.edu]
The exact cause and prevention of Down syndrome are currently unknown. Our program has been tracking Down Syndrome among live births in select counties since 2005 and are gradually expanding statewide. [health.state.mn.us]
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