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Down syndrome results from the presence of an extra copy of chromosome 21 meaning that these patients have three copies of this chromosome (trisomy 21). Down syndrome is the leading cause of intellectual disability and is the most common genetic alteration in humans. Prevalence is estimated at 1 in 750-800 births. The average life expectancy is over 50 years.
The risk of having a child affected by this syndrome increases with maternal age, especially after 35 years of age.
Most frequent clinical findings in patients with Down syndrome:
Additional information
Ds-int.org – Down Syndrome International
Edwards syndrome (trisomy 18) is a genetic disorder produced by the presence of an extra chromosome 18. It is the second most common autosomal trisomy after Down syndrome.
The prevalence is estimated at 1 in 6,000 births. Life expectancy is limited: mortality is around 60% in the first week of life and reaches 94-95% between the first and second year of life. Babies with Edwards may have a number of serious medical problems for which they require specialized care.
Similar to Down syndrome, Edwards syndrome is more frequent in mothers with advanced age: after 35 years the incidence progressively increases from 1/2,500 live births at age 36 years to 1/500 at age 43 years.
Most frequent clinical findings in patients with Edwards syndrome:
Additional information
Internationaltrisomyalliance.com – International Trisomy 13/18 Alliance
Orpha.net – The portal for rare diseases and orphan drugs
Patau syndrome (Trisomy 13) is a genetic disorder caused by the presence of an extra chromosome 13. It is the least common but the most serious of the viable chromosomal trisomies.
The prevalence is estimated at 1 in 12,000 births.
Life expectancy is limited, with an average 2.5 day survival rate. Ninety percent of infants die before they reach their first year. Many of the fetuses affected by the syndrome die before they are born (spontaneously miscarry). Babies with Patau syndrome suffer from multiple serious malformations resulting in profound physical and mental damage which causes the high mortality rate.
Most frequent clinical findings in patients with Patau syndrome:
Additional information
Internationaltrisomyalliance.com – International Trisomy 13/18 Alliance
Orpha.net – The portal for rare diseases and orphan drugs
Turner syndrome is associated with the total or partial absence (complete or partial monosomy) of chromosome X. Even though patients with Turner syndrome only have one normal X chromosome, all of them are women.
The prevalence is between 1/2000 to 1/5000 live female births. Around 1% of all conceptions present with monosomy X. Of these, the majority end in spontaneous abortion, generally during the first week of pregnancy. There is a reduced life expectancy.
Most frequent clinical findings in patients with Turner syndrome – 45,X0)
The majority of women with Turner syndrome have normal intelligence.
Additional information
Tsint.org – Turner Syndrome International
Orpha.net – The portal for rare diseases and orphan drugs
Klinefelter syndrome only occurs in males and results from the presence of an extra chromosome X.
The prevalence is estimated at 1 in 500-1000 male births. Life expectancy is normal.
Most frequent clinical findings in patients with Klinefelter syndrome – 47,XXY
Additional information
Aaksis.org – American Association for Klinefelter Syndrome Information and Support (AAKSIS)
Orpha.net – The portal for rare diseases and orphan drugs
Patau syndrome (Trisomy 13) is a genetic disorder caused by the presence of an extra chromosome 13. It is the least common but the most serious of the viable chromosomal trisomies.
The prevalence is estimated at 1 in 12,000 births.
Life expectancy is limited, with an average 2.5 day survival rate. Ninety percent of infants die before they reach their first year. Many of the fetuses affected by the syndrome die before they are born (spontaneously miscarry). Babies with Patau syndrome suffer from multiple serious malformations resulting in profound physical and mental damage which causes the high mortality rate.
Most frequent clinical findings in patients with Patau syndrome:
Additional information
Internationaltrisomyalliance.com – International Trisomy 13/18 Alliance
Orpha.net – The portal for rare diseases and orphan drugs
Trisomy of chromosome X, also known as triple X syndrome, is the most common female trisomy and has a variable phenotype caused by the presence of an extra chromosome X.
The prevalence is estimated at 1 in 1000 female births. Life expectancy is normal.
Most frequent clinical findings in patients with 47, XXX syndrome:
Triple X syndrome does not normally present with unusual physical characteristics or medical problems, although women with this condition are often taller than average.
However, there are exceptional cases in which various symptoms have been reported such as:
Additional information
Orpha.net – The portal for rare diseases and orphan drugs