Question: What is (are) Trisomy 18 ?
Answer: Trisomy 18 is a chromosome disorder characterized by having 3 copies of chromosome 18 instead of the usual 2 copies. Signs and symptoms include severe intellectual disability; low birth weight; a small, abnormally shaped head; a small jaw and mouth; clenched fists with overlapping fingers; congenital heart defects; and various abnormalities of other organs. Trisomy 18 is a life-threatening condition; many affected people die before birth or within the first month of life. Some children have survived to their teenage years, but with serious medical and developmental problems. Most cases are not inherited and occur sporadically (by chance).
Source: GARD

Question: What are the symptoms of Trisomy 18 ?
Answer: What are the signs and symptoms of Trisomy 18? The Human Phenotype Ontology provides the following list of signs and symptoms for Trisomy 18. If the information is available, the table below includes how often the symptom is seen in people with this condition. You can use the MedlinePlus Medical Dictionary to look up the definitions for these medical terms. Signs and Symptoms Approximate number of patients (when available) Abnormality of chromosome segregation 90% Atria septal defect 90% Broad forehead 90% Camptodactyly of finger 90% Cognitive impairment 90% Cryptorchidism 90% Decreased body weight 90% Deviation of finger 90% Dolichocephaly 90% High forehead 90% Hypertelorism 90% Hypertonia 90% Intrauterine growth retardation 90% Low-set, posteriorly rotated ears 90% Muscular hypotonia 90% Narrow face 90% Narrow mouth 90% Omphalocele 90% Pointed helix 90% Prominent occiput 90% Short nose 90% Short stature 90% Triangular face 90% Underdeveloped supraorbital ridges 90% Ventricular septal defect 90% Abnormality of female internal genitalia 50% Abnormality of the fontanelles or cranial sutures 50% Abnormality of the hip bone 50% Abnormality of the toenails 50% Abnormality of the upper urinary tract 50% Blepharophimosis 50% Choanal atresia 50% Cleft palate 50% Congenital diaphragmatic hernia 50% Delayed skeletal maturation 50% Epicanthus 50% Microcephaly 50% Non-midline cleft lip 50% Oligohydramnios 50% Single transverse palmar crease 50% Urogenital fistula 50% Webbed neck 50% Abnormality of retinal pigmentation 7.5% Abnormality of the ribs 7.5% Anencephaly 7.5% Aplasia/Hypoplasia affecting the eye 7.5% Aplasia/Hypoplasia of the corpus callosum 7.5% Arnold-Chiari malformation 7.5% Cataract 7.5% Cyclopia 7.5% Glaucoma 7.5% Holoprosencephaly 7.5% Iris coloboma 7.5% Microcornea 7.5% Postaxial hand polydactyly 7.5% Spina bifida 7.5% The Human Phenotype Ontology (HPO) has collected information on how often a sign or symptom occurs in a condition. Much of this information comes from Orphanet, a European rare disease database. The frequency of a sign or symptom is usually listed as a rough estimate of the percentage of patients who have that feature. The frequency may also be listed as a fraction. The first number of the fraction is how many people had the symptom, and the second number is the total number of people who were examined in one study. For example, a frequency of 25/25 means that in a study of 25 people all patients were found to have that symptom. Because these frequencies are based on a specific study, the fractions may be different if another group of patients are examined. Sometimes, no information on frequency is available. In these cases, the sign or symptom may be rare or common.
Source: GARD

Question: What causes Trisomy 18 ?
Answer: What causes Trisomy 18? In most cases, trisomy 18 is caused by having 3 copies of chromosome 18 in each cell in the body, instead of the usual 2 copies. The extra genetic material from the 3rd copy of the chromosome disrupts development, causing the characteristic signs and symptoms of the condition. About 5% of people with trisomy 18 have 'mosaic trisomy 18' (when there is an extra copy of the chromosome in only some of the body's cells). The severity of mosaic trisomy 18 depends on the number and locations of cells with the extra copy. Very rarely, an extra piece of chromosome 18 is attached to another chromosome; this is called translocation trisomy 18, or partial trisomy 18. If only part of the long (q) arm of chromosome 18 is present in 3 copies, the features may be less severe than in people with full trisomy 18.
Source: GARD

Question: Is Trisomy 18 inherited ?
Answer: Is trisomy 18 inherited? Most cases of trisomy 18 are not inherited and occur randomly due to errors in the formation of eggs or sperm. If an egg or sperm gains an extra copy of chromosome 18 during cell division and contributes to a pregnancy, the embryo will have an extra chromosome 18 (trisomy) in each cell of the body. Mosaic trisomy 18 (when some body cells have trisomy 18 and some have a normal chromosome make-up), is also typically not inherited. Mosaic trisomy 18 is also due to an error in cell division, but the error occurs early in embryonic development. About 5% of affected people have a mosaic form of trisomy 18. Partial trisomy 18 (when only part of chromosome 18 is present in 3 copies) can be inherited. An unaffected parent can carry a rearrangement of genetic material between chromosome 18 and another chromosome. This rearrangement is called a balanced translocation because there is no extra or missing genetic material. However, a person with a balanced translocation has an increased risk with each pregnancy to have a child with trisomy 18.
Source: GARD