A trisomy is a term for a genetic condition in which there are three chromosomes instead of the usual pair.
Trisomy 21, more commonly known as Down syndrome, is a condition caused by an extra copy of chromosome 21. Unfortunately, miscarriage occurs in about 30% of pregnancies with Down syndrome. Children born with Down syndrome will need additional medical care, depending on their specific health problems. Most children with Down syndrome have intellectual disabilities that range from mild to moderate. Early intervention has proven to be essential in enabling individuals with Down syndrome to lead healthy and productive lives. For more information or support, please see our resources page.
Trisomy 18, or Edwards syndrome, occurs when the baby has three copies of chromosome 18 instead of two. Unfortunately, pregnancies with Edwards syndrome are at high risk of miscarriage, and most babies born with it die within the first few weeks of life. Less than 10% live beyond one year. Infants with Edwards syndrome have severe intellectual and congenital disabilities typically involving the heart, brain, and kidneys, and external abnormalities such as cleft lip/palate, small head, club feet, underdeveloped digits, and small jaw.
Trisomy 13, or Patau syndrome, occurs when the baby has three copies of chromosome 13 instead of two. Unfortunately, pregnancies with Patau syndrome are at high risk for miscarriage or stillbirth, and most babies born with it will not survive beyond the first weeks of life. Babies with Patau syndrome may have heart defects, brain or spinal cord problems, extra fingers and/or toes, cleft lip, and/or cleft palate, and weak muscle tone. Many babies also have congenital disabilities of other organs
Trisomy of chromosome 22 is mostly lethal and is a common cause of spontaneous abortions in the first trimester of pregnancy. Such pregnancies rarely continue into the second trimester and ever more unlikely into the third. If the child is born, it only survives for a couple of days.
Trisomy of chromosome 16 is the most common trisomy that causes spontaneous abortion. The birth of a live baby with a trisomy of chromosome 16 is not possible.
Trisomy of chromosome 9 is lethal; the majority of the affected die before or soon after birth.
Deletion syndromes are defined as a group of clinically recognisable disorders characterised by a small deletion of a chromosomal segment. The size and the position of the deletion determine which clinical features are manifested and how severe they are.
The mental retardation syndrome in patients causes severe mental disorders and both body and facial anomalies. Under the typical facial features, there is a wider spacing between the eyes, the epicanthus (the eye branch that covers the upper part of the eye), a small triangle shaped nose, ﬂattened face and microcephaly. Most patients also have genital anomalies and severe anaemia.
Angelman syndrome is a consequence of the deletion of a part of the maternal chromosome 15. It is characterized by severe forms of developmental abnormalities (incapability of verbal speech), motion disorder and balance problems, specific behaviour (abnormal amount of constant joy) and reduced sex hormone secretion. Most aﬀected people have a very low IQ, problems with normal behaviour and excessive eating. Common clinical signs include microcephaly, seizures, pigmentary skin changes (hypopigmentation), small palms/feet, small genitals in males and low growth. In infants, low muscle tone, feeding difficulties and developmental issues are detected. The incidence of the syndrome is about 1 to 20,000 newborns.
Clinical signs of the syndrome refer mainly to eye disorders, such as foggy vision, underdevelopment or absence of the iris, distortion of the eye membranes and the appearance of various defects in the outer (anterior) area of the eye.
The syndrome is recognized primarily on the basis of a significantly modified face, including the lower foreskin of the scalp, elevated eyebrows, single eyebrow, curled nose, reduced lower jaw growth (maxillary prognathism), the enlarged middle part of the upper lips and narrow lips. The main clinical features are also premorphological and postnatal developmental delays, mental disorders and abnormal growth of the upper limbs.
Characteristics of Cowden’s syndrome are benign lesions in common tissue (skin, mucous membrane, chest and thyroid), on the face (near the mouth and in them) and on the limbs.
Patients with this syndrome are characterized by high, monotone crying, microcephaly, round face, wider spacing between the eyes (hypertellosis), epicanthus, inborn unusual smallness of the upper or lower jaw (micrognathia), low muscular tone, small ears, growth disorder, development problems and learning difficulties. The probability of developing all of the described disorders is 1 to 20,000 to 1 per 50,000 births. The most common sign of the syndrome in newborns is a high-sounding crying and screaming, but without other typical signs, it can indicate the presence of deletion 5p15.3.
The consequences of Dandy-Walker syndrome are small-brain disorders (underdevelopment) and cystic enlargement of some parts of the brain, specifically the fourth ventricle. People with this syndrome often have delayed development of their motor skills, low muscle tonus and low muscular strength. In addition, they may also have problems with muscle coordination movements (ataxia). Half of the patients also have mental disorders and hydrocephalus (excessive brain liquid formation).
DiGeorge syndrome 2 is a consequence of the deletion of a small part of the chromosome 10 (10p14). It is characterized by several clinical problems, such as cardiac congestion, decreased parathyroid function, deformed facial features and lack of T cells that are important for the eﬀective immune system. People with this syndrome are also characterized by typical facial features, slow development and low growth, eating disorders and learning difficulties. The severity of the syndrome-related problems varies greatly between individual cases.
Common clinical features of type 2B distal arthrogryposis include clenched fist, overlapping fingers, camptodactyly, ulnar deviation, and positional foot deformities from birth. Patients with this syndrome are also known by nasolabial folds, down-slanting palpebral fissures, and small mouth.
The most distinctive feature of Duchenne muscular dystrophy is a progressive proximal muscular dystrophy with characteristic pseudohypertrophy of the calves. The bulbar (extraocular) muscles are spared but the myocardium is aﬀected. There is a massive elevation of creatine kinase levels in the blood, myopathic changes by electromyography, and myofiber degeneration with fibrosis and fatty infiltration on muscle biopsy. The onset of Duchenne muscular dystrophy usually occurs before 3 years of age, the victim is chair-ridden by the age of 12 and usually dies in their teen years. Becker muscular dystrophy often occurs in the 20s and 30s and has a high survival rate to a relatively advanced age.
People with Dyggve-Melchior-Clausen syndrome are mentally deprived, having excessively ﬂattened vertebrae over the entire spine. Due to the absence of certain spine bones, a person feels constant pressure on the spinal cord (spinal cord compression).
Ectrodactyly type 3 causes disorders such as fusion of a large number of the toes and fingers, split palms and feet, and the absence and/or incomplete development of diﬀerent bones of the hand, fingers, foot and toes. In certain cases, deficiencies in brain development, mental disorders and orofacial clefting also occur.
Split-hand/split-foot malformation (SHFM) is a limb malformation involving the structural abnormalities of the limbs, which include deformation of palms and feet, which can also cause finger jointing, aplasia and/or hypoplasia of the phalanges, metacarpals, and metatarsals. In certain cases deficiencies in brain development, mental disorders and orofacial clefting also occur.
Feingold syndrome is an autoimmune dominant disorder, characterized by various forms of microcephaly, hand and feet deformation, congenital absence of the esophagus and duodenum and learning and mental disorders. Hand and foot abnormalities may include hypoplastic thumbs, clinodactyly of the second and fifth finger, syndactyly (characteristically between second and third and fourth and fifth toe), and shortened or absent middle phalanges. In the minority of patients, cardiac and renal anomalies, vertebral anomalies and deafness could also occur.
Holoprosencephaly type 1 is characterized by orbital hypotelorism (reduced distance between two organs), absence of a nose and an elongated tissue between both eyes without a function. One form of the disease is called cebocephalia, where a person has a nose with one nostril, while for another, etmocephalia, a distinct split lip, underdevelopment of a nasal bone and hypotelorism (reduced distance between the nose and the eyes) can occur.
Holoprosencephaly type 4 is characterized by severe facial and brain anomalies. The degree of disability depends on the degree of brain injury. Severe forms of the syndrome are often fatal.
Type 6 holoprozencephaly is characterized by deformation of the brain and face.
Jacobsen syndrome is a consequence of microdeletion on the terminal part of the chromosome 11. It occurs once every 100,000 births. The features of Jacobsen syndrome are growth disorders, psychomotor disabilities, triangular head formation, occasional tingling, epicanthus (skin fold of the upper eyelid that covers the upper part of the eye), increased distance between the eyes, a broad nasal bridge, a short nose with raised nostrils, carp-shaped upper lip, convex position of one jaw compared to the other, small ears, irreversible deformation of certain fingers, deformation of the toe incision and isoimmune thrombocytopenia (autoimmune response to red blood cells).
People with Langer-Giedione syndrome are mentally disabled and have face anomalies involving large, protruding ears, round nasal tip, enlarged upper lip, and sparse scalp hair. Other clinical features include anomalies of the blades, multiple exostoses (abnormal formations on a bone) and excess skin. There may also be blood in the uterus and ﬂuid retention in the vaginal opening.
Leukodystrophy is accompanied by an epileptic seizure in infants, severe psychomotor disabilities, growth and developmental disorders, microcephaly, microphallus, structural brain disorders and facial anomalies (e.g., round nasal tip, forehead deformity, and eyelid). Patients with leukodystrophy die during childhood.
X-linked lymphoproliferative syndrome is a very complex syndrome, which is a severe or fatal form of mononucleosis. Clinical features include acquired hypogammaglobulinemia (low levels of antibodies in the blood), haemopoietic lymphochystocytosis (an excessive amount of activated immune cells) or malignant lymphoma. Aplastic anaemia can occur due to the syndrome (bone marrow failure) and disorders in the production of red and white blood cells.
The syndrome is an autosomal dominantly inherited disorder that causes partial or total hearing loss, structural damage to the inner, middle and outer ears and the formation of cysts on the glands. Renal anomalies (inadequate kidney size or even absence of them) are common.
Mental retardation caused by X-linked growth hormone deficiency is reﬂected as a wider spacing between the eyes, the epicanthus (an eye patch covering the upper part of the eye), a single eyebrow, delayed pubertal development, nerve damage, a mental disability, a broad nasal bridge, a high arched oral skeleton, diﬀerent facial anomalies (big lips and tongue, teeth deformation, large head, deformed nose etc.). In the aﬀected subjects, thyroid function disorders (lack of thyroid hormones) and reduced elimination of one or more hormones produced by the pituitary gland occur. Lack of the hormone can lead to dwarfism in children and premature ageing in adults.
Microphthalmia with linear skin defects is the dominant disorder associated with the chromosome X with fatal outcome in a male fetus. Microphthalmia is also called “small eye syndrome”, where the eye has not developed properly in the uterus. One-sided or bilaterally small, poorly developed eyeball, linear skin damage on the face and neck are present. Aplastic skin will heal with age to form hyperpigmented areas.
Orofaciodigital syndrome is the X-linked chromosome dominant disorder that leads to death in males. It appears as a deformation of the face, an oral cavity (a thinned mouth bone, anomalies of the teeth and the absence of incisors) and fingers. In 40 % of the cases the central nervous system would be aﬀected. Although clinical signs are very similar to other forms of orofaciodigital syndrome, this form can be accurately determined by X-linked dominant inheritance and polycystic kidney disease. Panhypopituitarism, X-linked: Due to the syndrome, there is reduced excretion of one or more hormones produced by the pituitary gland, which can lead to dwarfism in children and premature ageing in adults. Disorders of onadotropin secretion have an eﬀect on the reproductive functions.
The syndrome is characterized by normal facial features. Clinical signs of a mild form of mental retardation are reduced cognitive abilities, behavioural disorders, attention deficit, hyperactivity, and sometimes autism. Most people with the syndrome have shorter stature.
Congenital diaphragmatic hernia is a set of congenital defects in the structure of the diaphragm, which are often associated with lethal pulmonary hypoplasia (a decrease in the lung tissue, leading to a decrease in the lung volume) and pulmonary hypertension (high blood pressure in the pulmonary system). The incidence of congenital disease in neonates is from 1 per 2,500 to 1 per 4,000 births, with a mortality rate of 30-60 %. There are several types of diseases: Bochdalek's hernia, Morgagniev hernia, central hernia and diaphragmatic hernia. In 70-90 % the affected person has Bochdalek's hernia, which most often happens on the left side. Pathological consequences of the hernia refer to the abdominal contents entering the chest cavity. Due to the effects of hernia, the disease leads to death in newborns.
The characteristics of the syndrome are abnormal development of the anterior segment of the eye, which can lead to blindness (in approximately 50 % of the aﬀected individuals), absence/underdevelopment of the eye muscle, teeth fragility, hydrocephalus, skeletal anomalies and disorders in the development of periumbilical skin. In certain patients, insufficient development of brain vessels can occur.
The characteristics of the Saethre-Chotzing syndrome include presence of low-set frontal hairline, an irregular eyelid (ptosis), abnormal ear length, an enlarged parietal foramina (an opening in the cranial skull), a skin formation between fingers, an enlarged thumb, deformation of the fingers and increased pressure in the brain.
The main characteristics of the disease are deafness and infertility. In addition, the aﬀected person is also mentally challenged, has short stature and various physical anomalies (small ears, high nose bridge, small area between the nose and the lips, occasional swelling of the palms and feet, thin eyelashes, head and nasal anomalies, high-arched palate, short fingers and a single eyebrow).
The sindrome is characterized by lower fetal activity, obesity, muscular hypotonia, mental retardation, short stature, hypogonadotropic hypogonadism and small hands and feet.
The clinical features of the syndrome are high-arched palate, head anomalies, the formation of benign tumours in early childhood, and hemangiomas (abnormal spread of the vascular system that can lead to bleeding). Arteriovenous malformation can lead to leg amputation. Brain haemorrhage can lead to epileptic seizures. Aﬀected persons have increased birth weight and length, but the growth rate decreases at the age of 6 or 7. Delayed motor development with incoordination, delayed speech development, and mild mental disability is present. Anomalies of the ribs and drooling are also common.
Main characteristics of this syndrome are severe form of mental disability, short stature, split or high-arched palate, rare and thin hair, various ear anomalies and lipodystrophy (inability to produce fats), inguinal hernia (abnormalities of the abdominal structures), epileptic seizures and feeding problems. Most likely, these problems are a consequence of a missing SATB2 gene that is located in this area.
The syndrome is primarily recognized on the basis of a significantly modified face, which includes a lower foreskin of the scalp, raised eyebrows, a single eyebrow, tight nose, reduced growth of the lower jaw (maxillary prognathism), an enlarged middle part of the upper lip and narrow lips. The main clinical features are a prefrontal and postnatal developmental delay, mental disabilities and abnormal growth of the upper limbs.
The clinical features of the 8p23.1 deletion are congenital heart disease, congenital diaphragmatic hernia, developmental delay and typical behavioural disorders – hyperactivity and impulsiveness.
The deletion is accompanied by facial asymmetry, pronounced nose, narrow upper lip, low birth weight, short stature, fifth fnger clinodactyl and male cryptorchidism (absence of one or both testes). People with the 10q deletion have diﬀerent forms of learning difficulties and developmental delay.
The main features of the syndrome are psychomotor delay, mental disorder, problems with eye contact, disturbed growth, microcephaly, plagioccephaly, poor head control, triangular facial features, unusual smallness of the upper or lower jaw, an enlarged area between the upper lip and nose, short/broad nose, ﬂattened nose root, small and deformed ears, triangular eyebrows, epichantal folds, deep-set eyes, short palpebral fissures widely-spaced eyes, optic atrophy that can lead to cortical blindness, small mouth and high-arched palate. People with deletion have heart problems such as heart ventricular barrier disorders and congenital holes in the heart compartments. This deletion is also characterized by the absence of one or both testes, hypertonia (increased muscular activity or increased muscular tension), inability to walk, minimal or lack of speech, seizures, spasticity, hyperrelaxis, abnormal myelinization in childhood and inadequate development of brain corpus.
The 17q21.31deletion syndrome is accompanied by intellectual disabilities, low muscular tone, high and wide forehead, inclined eyes directed upward, epicanthus (eye pectoris covering the upper part of the eye), round tip of the nose, large and low ears, anomalies of the eyelid (ptosis) and long fingers. Patients often have neurological disorders leading to epileptic seizures, cardiac problems (cardiac atrioventricular septal disorders), urologic anomalies (cryptorchidism - absence of one or both testes, hypospadias, vesicoureteric reﬂux, duplex kidney, renal scarring and hydronephrosishypospadia – the external urethra is not at the top of the penis head but lower) and genital disorders. The clinical features of the syndrome are teeth anomalies, periodic dislocation of the elbows, excessive joint mobility, scoliosis, loss of hearing, slender lower limbs, split lip or palate. Delayed psychomotor development is also present in patients with this syndrome.
The main clinical features of the deletion are mental disabilities, growth disturbances, head and face anomalies (round face, enlarged oral cavity), abnormal ears and anomalies of the limbs, sexual organs, brain, eyes, heart and teeth.
The characteristics of this deletion are highly variable and are recognized by mental disorders, short stature, low muscular tone, hearing disorders, feet deformation, pointed toes and enlarged mouth.
The duplication is accompanied by speech defects, congenital heart disease, developmental delay, pronounced or enlarged forehead and raised eyebrows.
The syndrome is characterized by congenital deafness due to an underdeveloped inner ear. In addition, the duplication causes underdevelopment of the external part of the ears, and very small teeth are also a common feature.
The duplication syndrome 17q21.31 refers to short stature, microcephaly, finger anomalies, hirsutism (excessive body hair), atopic dermatitis, digestive problems, facial anomalies (small mouth, ears anomalies, small nose etc.) and anomalies of the toes. People with this duplication are mentally challenged, have difficulties in social integration, poor motor skills and behavioural problems (aggression, hyperactivity, obsessive disorders, communication disorders).
The Cat-eye Syndrome is accompanied by colobomata (distortion of the eye membranes), wider spacing between the eyes (eye hyperelorism), preauricular tags, slant to the eyes, depressed lower eyelids, and micrognathia, inborn unusual smallness of the upper or lower jaw, deformation of the rectum and a single umbilical artery, which can lead to inadequate development of the fetus. Patients also have cardiac and renal anomalies and mental disabilities. The syndrome is also characterized by VACTERL disorders that aﬀect many body systems that develop from the embryonic mesoderm.
The deletion of p36 on the chromosome 1 causes severe mental disability. Symptoms of the syndrome include microcephaly, brachycephalia, and dwarfism, which can occur during pregnancy or immediately after birth. The characteristic facial features include an inverted eye, ﬂat nasal bridge, asymmetric ears and a pointed chin. The main clinical features include developmental delay (100 %), hypotonia (100 %), epileptic seizures (up to 72 %), cardiac defect (40 %), including cardiomyopathy (about 23 %) and split lip or palate (20-40 %). Mild high frequency sensorineural hearing loss is also very common in Microdeletion 1p36.
Common clinical features of the microlocation 1q41-q42 include a significant developmental delay and distinct facial dysmorphism such as deep-seated eyes, broad nasal tip, depressed nasal bridge. In some cases features such as microcephaly, cleft palate, clubfeet, seizures, and short stature are present. The 10q22.3-q23.31 microdeletion Syndrome: Symptoms of the syndrome are short stature, delayed puberty, deformed facial features and an atrioventricular septal defect.
The microdeletion 12q14 leads to a mild form of mental disability, early developmental disorders, and osteopoicilosis (excessive bone density leading to bone pain). Patients are characterized by short stature.
The microdeletion is accompanied by anomalies of the face, which include a ﬂattened face, down-slanting palpebral fissures and anomaly of the eyes. Small ears and mental disability are also typical for this microdeletion.
This microduplication syndrome is accompanied by developmental delay, autistic and/or repetitive behaviour, dysmorphic features, microcephaly, hyperactivity, echolalia and possibility of seizures. Other clinical signs relating to body anomalies are a wider gap between the eyes (hypertelorism), cerebral anomalies, short stature, tapering fingers, wide and large nose bridge, strabismus (crossed eyes) and anomalies of the fingers.
Clinical signs of this microdeletion are independent of gender and duplication size. Typical clinical signs are various forms of seizures. Aﬀected persons are shy and stubborn and their behaviour is similar to that of a person with autistic disorder.
For patients with this syndrome absence of one or both eyes, a brachycephaly (shorter skull), retrognathia (deformation of a lower jaw), small ears, anomalies of the fingers, underdevelopment of the external genitalia and a hypophlastic kidney are known. Patients have brain disorders such as small cerebellum and the absence of specific brain structures.
The most common clinical features that occur in more than 50 % of the patients are developmental and psychomotor disorders, a triangular shape of the head, ﬂat midface, short palpebral fissures, highly arched eyebrows, low-set ears, short ﬂat nose with anteverted nostrils, thin upper lip, long philtrum, high palate, micrognathia, short neck, enlarged internipple distance, tapering fingers, ﬂat feet, and hypotonia. Patients have problems with speech, but it can improve over the years.
The androgen insensitivity syndrome is an X-linked recessive disorder, where external female genitalia develop in males (absence of the uterus, vagina and other genital organs around the uterus). Development of female breasts in male patients (gynecomastia) and development of testes in the abdominal cavity or groin occur. Although men have a normal sex chromosome karyotype (XY), they have hypospadia (a congenital defect in which the urethra does not develop on the penis tip) and micropenitis.
The overgrowth syndrome is characterized by renal anomalies (45 %), including horseshoe kidney and renal agenesis (one or both fetal kidneys fail to develop). Hydronephrosis (an inadequate function of the kidneys), vesico-ureteric reﬂux (inadequate direction of urine travel), polycystic kidney and right renal pelvic duplication are also common. People with the syndrome can also be mentally challenged, have developmental delay and are born with tall stature.
Patients with Smith-Magenis syndrome have a ﬂat and square face. They are often overweight, short and have small feet and hands. Newborns could have a weak muscle tone, developmental delay, behavioural disorders (especially sleep disturbances and self-injurious behaviours) and sometimes food-searching behaviours. All individuals with Smith-Magenis syndrome have mild to severe learning disabilities with no diﬀerences overall between verbal and performance skills, but with a particular profile of cognitive strengths and weaknesses. Adults with Smith-Magenis syndrome were more dependent on carers than might be expected from their general level of intellectual functioning.
The syndrome is characterized by typical deformation of the head and skeleton. Head deformations include sparse scalp hair, a bulbous tip of the nose, long ﬂat philtrum (upper lip), thin upper vermilion border and protruding ears. Skeletal abnormalities include cone-shaped epiphyses at the phalanges, hip malformations and short stature.
The Van der Woude syndrome is caused by the mutation in a single gene with equal distribution between the sexes. The clinical symptoms vary but may include lower lip pits with cleft lip and cleft palate.
The Wilms tumour 1 is one of the most common tumours that occur in childhood (1 per 10,000 children) and represents 8 % of all cancers in children. It is believed to result from malignant transformation of abnormally persistent renal stem cells which retain embryonic diﬀerentiation potential.
Each cell in our body contains 46 chromosomes arranged into 23 pairs. One of them is known as the sex chromosome pair because it determines our sex. The abnormalities occur when sex chromosomes are missing, added, or altered.
Klinefelter syndrome is a genetic condition that only affects males. It is caused by an extra X chromosome, which results in small testes, not capable of producing enough male hormone testosterone before birth and during puberty. This lack of testosterone prevents the full development of normal male sexual characteristics, leading to reduced facial and pubic hair, and even the growth of breast tissue. The lack of testosterone is also responsible for other symptoms such as infertility.
The Turner syndrome is caused by the completely or partially missing X sex chromosome in females. Females with Turner syndrome often have a wide range of symptoms and some distinctive characteristics. Two that occur in almost all cases of Turner syndrome are shorter than average and underdeveloped ovaries (female reproductive organs), resulting in a lack of monthly periods and infertility.
Triple X syndrome, also called trisomy X, is characterised by the presence of an additional X chromosome in each of the female’s cells. The symptoms and physical features associated with trisomy X vary greatly from one person to another. Some females may have no symptoms (asymptomatic) or very mild symptoms and may go undiagnosed. Other women may have a wide variety of different abnormalities. Triple X syndrome is associated with an increased risk of learning disabilities and delayed development of speech and language skills. Delayed development of motor skills (such as sitting and walking), weak muscle tone (hypotonia), and behavioural and emotional difficulties are also possible, but these characteristics vary widely among affected girls and women. Seizures or kidney abnormalities occur in about 10 percent of affected females.
XYY, sometimes called Jacob syndrome, affects only males and is caused by the presence of an extra Y chromosome. Affected individuals are usually very tall. Many experience severe acne during adolescence. Additional symptoms may include learning disabilities and behavioural problems such as impulsivity.
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