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Chromosome conditions

Chromosome conditions are linked to chromosomal aneuploidy. A chromosomal aneuploidy can be too many or too few chromosome copies in a chromosomal pair. Vision can screen for aneuploidy-linked chromosomal conditions such as Turner’s syndrome (Monsomy X/XO), as well as trisomy, where there are 3 copies in a chromosomal pair instead of the usual 2. Vision is able to screen for trisomy at any chromosomal location, screening for conditions such as Down’s Syndrome (trisomy 21) and Edwards’ syndrome (trisomy 18).

Trisomy 1

Pregnancies with trisomy 1 will usually miscarry spontaneously. There are no reports of full trisomy 1 in a livebirth. In mosaic trisomy 1 (where only some of the cells have this trisomy), the chance of the pregnancy progressing increases slightly, and there is a chance of progressing to term. However, children born with mosaic trisomy 1 are expected to have a wide range of medical complications as well as physical and developmental sequelae, which may not always be detected by ultrasound. Confined placental mosaicism is not frequently reported for trisomy 1. The prevalence of trisomy 1 is unknown.

Trisomy 2

Pregnancies with trisomy 2 will usually miscarry spontaneously. In mosaic trisomy 2 (where only some of the cells have this trisomy), the chance of the pregnancy progressing increases slightly, and there is a chance of progressing to term, however serious medical problems are associated in cases of livebirths with full or mosaic trisomy 2. There is variable clinical presentation of this trisomy, which is believed to be because of confined placental mosaicism. Common features of trisomy 2 include congenital abnormalities, growth delay, motor delay, and at ultrasound intrauterine growth restriction may be observed. There are multiple cases of this condition reported from invasive diagnostic testing methods, however the exact prevalence of this condition is unknown.

Trisomy 3

Pregnancies with trisomy 3 will usually miscarry spontaneously, however full trisomy 3 is rare and often due to confined placental mosaicism. Confined placental mosaicism is thought to cause the variable clinical presentation of this condition. In mosaic trisomy 3 (where only some of the cells have this trisomy), the chance of the pregnancy progressing increases slightly, and there is a chance of progressing to term, however serious medical conditions are expected for children born with this condition (full form or mosaic form), including congenital heart defects, reduced life expectancy, intellectual disability, dimorphism and a short stature. This is a very rare condition however the exact prevalence of this condition is unknown.

Trisomy 4

Pregnancies with trisomy 4 will usually miscarry spontaneously. In mosaic trisomy 4 (where only some of the cells have this trisomy), the chance of the pregnancy progressing increases slightly, and there is a chance of progressing to term, however serious medical problems are associated in cases of livebirths with full or mosaic trisomy 4. Common features of trisomy 4 include birth defects and dysmorphism. The degree of mosaicism in the foetus or confined placental mosaicism can contribute to the variability in the prognosis of this condition. This is a very rare condition however the exact prevalence of this condition is unknown.

Trisomy 5

Pregnancies with trisomy 5 will usually miscarry spontaneously. In mosaic trisomy 5 (where only some of the cells have this trisomy), the chance of the pregnancy progressing increases slightly, and there is a chance of progressing to term, however serious medical problems are associated in cases of livebirths with full or mosaic trisomy 5. Common features of trisomy 5 include birth defects and intellectual disability. The degree of mosaicism in the foetus or confined placental mosaicism can contribute to the variability in the prognosis of this condition. This is a rare condition however the exact prevalence of this condition is unknown.

Trisomy 6

Pregnancies with trisomy 6 will usually miscarry spontaneously. In mosaic trisomy 6 (where only some of the cells have this trisomy), the chance of the pregnancy progressing increases slightly, and there is a chance of progressing to term, however serious medical problems are associated in cases of livebirths with full or mosaic trisomy 6. Common features of trisomy 6 include congenital heart defects, malformations of the hands/feet and minor facial dysmorphism. In cases of mosaic trisomy 6, common features include growth anomalies, reduced lifespan, birth defects and intellectual disability. The degree of mosaicism in the foetus or confined placental mosaicism can contribute to the variability in the prognosis of this condition. This is a very rare condition however the exact prevalence of this condition is unknown.

Trisomy 7

Pregnancies with trisomy 7 will usually miscarry spontaneously. There are no reports of full trisomy 7 in a livebirth. In mosaic trisomy 7 (where only some of the cells have this trisomy), the chance of the pregnancy progressing increases slightly, and there is a chance of progressing to term, however serious medical problems are associated in cases of livebirths with mosaic trisomy 7. In cases of mosaic trisomy 7, common features include facial dysmorphism, skin pigmentary disorders, renal malformations, growth retardation and body asymmetry. The degree of mosaicism in the foetus or confined placental mosaicism can contribute to the variability in the prognosis of this condition. This is a very rare condition however the exact prevalence of this condition is unknown.

Trisomy 8

Pregnancies with trisomy 8 will usually miscarry spontaneously. Full trisomy 8 is usually lethal early in pregnancy, however generally life expectancy is normal for individuals with mosaic trisomy 8. In mosaic trisomy 8 (where only some of the cells have this trisomy), the chance of the pregnancy progressing increases slightly, and there is a chance of progressing to term, however serious medical problems are associated in cases of livebirths with mosaic trisomy 8. Common features of mosaic trisomy 8 include cardiac and renal system anomalies (as well as other organ system anomalies), dysmorphism, variable growth restriction and intellectual disability. The degree of mosaicism in the foetus or confined placental mosaicism can contribute to the variability in the prognosis of this condition. This condition is estimated to be present in 1 in 25,000 – 1 in 50,000 live births. Constitutional trisomy 8 mosaicism occurs in approximately 0.1% of recognised pregnancies.

Trisomy 9

This rare and severe abnormality causes spontaneous miscarriage in most pregnancies in which it occurs, few surviving past the first trimester. Babies born with mosaic trisomy 9, where only some of the cells have trisomy also demonstrate malformation, as well as mental deficiency.

Trisomy 10

Pregnancies with trisomy 10 will usually miscarry spontaneously. In mosaic trisomy 10 (where only some of the cells have this trisomy), the chance of the pregnancy progressing increases slightly, and there is a chance of progressing to term, however a common feature of mosaic trisomy 10 is neonatal or early infancy death. Other serious medical problems are associated in cases of livebirths with mosaic trisomy 10, including organ system anomalies and dysmorphism. The degree of mosaicism in the foetus or confined placental mosaicism can contribute to the variability in the prognosis of this condition. This is a rare condition however the exact prevalence of this condition is unknown.

Trisomy 11

There have been no reported live births with trisomy 11 and presumably this condition leads to early pregnancy loss. Mosaic trisomy 11 has been reported prenatally, however almost all reported live births with this condition have a normal prenatal and postnatal outcome, with no evidence of trisomy 1 postnatally. This is an extremely rare condition however the exact prevalence of this condition is unknown.

Trisomy 12

Pregnancies with trisomy 12 will usually miscarry spontaneously. There are no reports of full trisomy 12 in a livebirth. In mosaic trisomy 12 (where only some of the cells have this trisomy), the chance of the pregnancy progressing increases slightly, and there is a chance of progressing to term, however serious medical problems are associated in cases of livebirths with mosaic trisomy 12. In cases of mosaic trisomy 12, common features include dysmorphism, intellectual disability and organ system anomalies. Mosaic trisomy 12 can also lead to foetal or neonatal death. Approximately 50% of prenatally diagnosed cases of trisomy 12 represent true foetal mosaicism. The degree of mosaicism in the foetus or confined placental mosaicism can contribute to the variability in the prognosis of this condition. This is a rare condition however the exact prevalence of this condition is unknown.

Trisomy 13

Patau’s syndrome is a genetic condition that affects around 1 in 5000 births. Babies afflicted with this condition will experience severe physical and psychological difficulties. Unfortunately, due to the extreme nature of this condition many babies diagnosed with Patau’s syndrome will be lost during pregnancy.

Trisomy 14

Pregnancies with trisomy 14 will usually miscarry spontaneously. There are no reports of full trisomy 14 in livebirths and very few reports of viable pregnancies with trisomy 14 into the late 1st or 2nd trimester. In mosaic trisomy 14 (where only some of the cells have this trisomy), the chance of the pregnancy progressing increases slightly, and there is a chance of progressing to term, however serious medical problems are associated in cases of livebirths with mosaic trisomy 14. In cases of mosaic trisomy 14, common features include organ system anomalies, dysmorphism, intellectual disability and growth restriction. The degree of mosaicism in the foetus or confined placental mosaicism can contribute to the variability in the prognosis of this condition. This is a rare condition however the exact prevalence of this condition is unknown.

Trisomy 15

Pregnancies with trisomy 15 will usually miscarry spontaneously. In mosaic trisomy 15 (where only some of the cells have this trisomy), the chance of the pregnancy progressing increases slightly, and there is a chance of progressing to term, however serious medical problems are associated in cases of livebirths with full or mosaic trisomy 15. Trisomy 15 has been associated with reports of multiple congenital anomalies and neonatal death. Other common features of trisomy 15 include intellectual disability (this can sometimes be mild), growth restriction and birth defects. The degree of mosaicism in the foetus or confined placental mosaicism can contribute to the variability in the prognosis of this condition. This is a rare condition however the exact prevalence of this condition is unknown.

Trisomy 16

Trisomy 16 is the most common chromosomal trisomy for autosomes and occurs in approximately 1% of all pregnancies. In the majority of cases of full trisomy 16 (where the trisomy occurs in all of the body’s cells), this aneuploidy results in spontaneous miscarriage during the first trimester and has been shown to account for 12% of chromosomally abnormal miscarriages.

Trisomy 17

Pregnancies with trisomy 17 will usually miscarry spontaneously. There have been no reported live births with trisomy 17 and presumably this condition leads to early pregnancy loss. In mosaic trisomy 17 (where only some of the cells have this trisomy), the chance of the pregnancy progressing increases slightly, and there is a chance of progressing to term, however serious medical problems are associated in cases of livebirths with mosaic trisomy 17. Common features of this condition include organ system anomalies, intellectual disability and growth restriction. . The degree of mosaicism in the foetus or confined placental mosaicism can contribute to the variability in the prognosis of this condition. This is a rare condition however the exact prevalence of this condition is unknown.

Trisomy 18

Edwards’ syndrome is a serious genetic condition affecting 1 in 6,000 live births and can lead to miscarriages or stillborn births. Babies that are affected by this condition are often slow to develop and will experience severe medical problems. Sadly, if carried to full term, there is a low chance that the baby will survive longer than a year.

Trisomy 19

Full trisomy 19 has not been reported in a livebirth and presumably this condition leads to early pregnancy loss. There has been a single reported case of amniocentesis presenting a prenatal diagnosis of mosaic trisomy 19, however this case resulted in a normal live birth, so it is likely that this diagnosis was due to confined placental mosaicism and therefore the mosaic trisomy 19 was not present in the foetus. This is an extremely rare condition however the exact prevalence of this condition is unknown.

Trisomy 20

Pregnancies with trisomy 20 will usually miscarry spontaneously. In mosaic trisomy 20 (where only some of the cells have this trisomy), the chance of the pregnancy progressing increases slightly, and there is a chance of progressing to term, however serious medical problems are associated in cases of livebirths with mosaic trisomy 20. Cases of full trisomy 20 are rarely reported in live births and are associated with anomalies that involve the central nervous system and heart. Features commonly associated with mosaic trisomy 20 include intellectual disability, cardiac and renal anomalies (as well as other organ system anomalies), growth restriction and dysmorphism. The degree of mosaicism in the foetus or confined placental mosaicism can contribute to the variability in the prognosis of this condition. This is a rare condition and the exact prevalence of this condition is unknown, however 1 in 5,000 amniocentesis samples detect mosaic trisomy 20.

Trisomy 21

Down’s syndrome affects 1 in 1,000 babies and is a genetic disorder which can cause specific learning difficulties and physical differences. Every child diagnosed with the condition will have slightly different characteristics and difficulties, however, all will be affected to some degree by psychological/physical differences.

Trisomy 22

Pregnancies with trisomy 22 will usually miscarry spontaneously. In mosaic trisomy 22 (where only some of the cells have this trisomy), the chance of the pregnancy progressing increases slightly, and there is a chance of progressing to term, however serious medical problems are associated in cases of livebirths with full or mosaic trisomy 22. Full trisomy 22 usually results in a poor prognosis, often fatal, and is therefore rarely reported in live births. Commonly, features associated with this condition include organ system anomalies, dysmorphia and intrauterine growth restriction. The degree of mosaicism in the foetus or confined placental mosaicism can contribute to the variability in the prognosis of this condition. In cases of liveborns with mosaic trisomy 22, most do not survive past the first few months. There is a >60% risk of an abnormal outcome for cases where mosaic trisomy 22 has been detected by amniocentesis. Full trisomy 22 is rare and not entirely known, however it may be around 1 in 30,000 to 1 in 50,000 live births.

Microdeletion syndromes

Small parts of chromosomal DNA can be lost during the cell division and replication process, this is known as a microdeletion. Microdeletions are randomly occurring and therefore there may not be any family history of microdeletion.

The Vision test can screen for the below microdeletion syndromes:

DiGeorge syndrome

Incidence:1 in 4,000

Symptoms Include: Learning problems, congenital heart defects, palatal abnormalities

1p36 deletion syndrome

Incidence:1 in 4,000 to 1 in 10,000

Symptoms Include: Characteristic craniofacial features, intellectual disability, seizures, brain and heart defects

Angelman syndrome

Incidence: 1 in 12,000

Symptoms Include: Intellectual disability, speech impairment, seizures

Prader-Willi syndrome

Incidence: 1 in 10,000 to 1 in 25,000

Symptoms Include: Hypotonia, morbid obesity, delayed motor and language skills, intellectual disability, hypogonadism

Cri du Chat syndrome

Incidence: 1 in 20,000 to 1 in 50,000

Symptoms Include: Intellectual disability, speech delay, cat-like cry

Wolf-Hirschhorn syndrome

Incidence: 1 in 50,000

Symptoms Include: Growth deficiency, hypotonia, craniofacial features, intellectual disability, heart and brain abnormalities

Jacobsen syndrome

Incidence: 1 in 100,000 (estimate)

Symptoms Include: Bleeding disorder (Paris-Trousseau syndrome), heart defects, distinctive facial features (e.g. macrocephaly, trigonocephaly, small lower jaw and small low set ears), learning difficulties, delayed development of motor skills, cognitive impairment, impaired communication skills

Langer-Giedion syndrome

Incidence: Less than 1 in 100,000

Symptoms Include: Short stature, thin upper lip, small and abnormal number of teeth, sparse scalp hair, malformed bones and joints, intellectual disability, osteochondromas, broad nose

Smith-Magenis syndrome

Incidence: 1 in 15,000 to 1 in 25,000

Symptoms Include: Delayed language skills, delayed speech, intellectual disability, sleep disturbances, behavioural problems, scoliosis, dental abnormalities, distinctive facial features, vision problems, reduced sensitivity to pain/temperature, ear abnormalities

Negative test results

If the results are negative, this indicates that the baby is not displaying any of the genetic abnormalities screened for, and therefore later diagnosis of these conditions is unlikely.

Positive test results

If the results return a positive, this indicates that your baby may have one of the conditions that Vision identifies. The nature of the positive result will be identified on the report.

Genetic counselling service

Genetic counselling is available to all Vision clients. Contact us about this service and we will put you in touch with someone who is trained to talk you through your result, whatever the outcome.