Down syndrome and Turner syndrome are both caused by a change in the number of chromosomes, but in opposite directions: one adds genetic material, and the other is missing some. Down syndrome can affect anyone, while Turner syndrome happens only in girls and women.1Special Strong. Turner Syndrome, Down Syndrome & Maternal Age The bigger difference shows up in daily life. Down syndrome usually brings intellectual disability, while most girls with Turner syndrome have normal intelligence and face mainly physical and hormonal challenges.2PubMed. Congenital cardiovascular disease in Turner syndrome
What Goes Wrong With the Chromosomes
Chromosomes are the packages of genes inside each cell. Most people have 46 of them, arranged in 23 pairs, including two sex chromosomes (XX or XY). Down syndrome happens when there are three copies of chromosome 21 instead of two.3PubMed Central. Understanding etiology of chromosome 21 nondisjunction from gene × environment models The extra copy arises because chromosomes fail to separate properly when an egg or sperm is made.4PubMed Central. Understanding etiology of chromosome 21 nondisjunction from gene × environment models In the overwhelming majority of cases, the error happens while the egg is forming, not the sperm.5PubMed Central. Understanding etiology of chromosome 21 nondisjunction from gene × environment models
Turner syndrome is caused by the total or partial loss of the second sex chromosome, which leaves one working X.6PubMed Central. Chromosomal Abnormalities of Interest in Turner Syndrome: An Update Only about 40% have the simple form with 45 chromosomes and a single X.7PubMed Central. Chromosomal Abnormalities of Interest in Turner Syndrome: An Update The rest have other changes, such as a missing piece of one X, a ring-shaped X, or a mix of cells.8PubMed Central. Chromosomal Abnormalities of Interest in Turner Syndrome: An Update A “mosaic” girl has some cells with two X chromosomes and some with one, which can make her features milder. In 75–90% of people with a single X, the X that remains came from the mother.9PubMed. Parental Origin of the Retained X Chromosome in Monosomy X Miscarriages and Ongoing Pregnancies
A chromosome test, called a karyotype, counts and pictures the chromosomes from a blood or tissue sample. For Down syndrome the report usually reads 47,XX,+21 or 47,XY,+21, meaning one extra chromosome 21. The classic Turner form reads 45,X, meaning only one sex chromosome. If a report lists two cell lines separated by a slash, that means mosaicism, and it’s worth asking the doctor what it means for your child.
Neither condition is caused by anything the parents did. Both result from random errors in cell division, not from diet, activity, or anything done during pregnancy. Most cases are not inherited from a parent who has the condition. Knowing the exact type of change helps genetic counselors explain any risk in a future pregnancy.
Who Gets Each Condition and Whether Maternal Age Matters
Turner syndrome occurs only in girls and women, roughly 1 in every 2,000 to 2,500–3,000 live female births.10PubMed Central. Understanding etiology of chromosome 21 nondisjunction from gene × environment models11PubMed Central. Chromosomal Abnormalities of Interest in Turner Syndrome: An Update That’s because a baby needs at least one X chromosome to survive, and having no second sex chromosome results in a female body. Many pregnancies with a single X end in early miscarriage, so the girls who are born represent the survivors.12PubMed. Parental Origin of the Retained X Chromosome in Monosomy X Miscarriages and Ongoing Pregnancies
A mother’s age matters a great deal for Down syndrome. The link with older mothers is tied to errors in the egg, not in sperm.13PubMed Central. Maternal age and risk for trisomy 21 assessed by the origin of chromosome nondisjunction: a report from the Atlanta and National Down Syndrome Projects Mothers of babies with Down syndrome were 8.5 to 15 times more likely to be 40 or older rather than 20 to 24, depending on the type of egg error.14PubMed Central. Maternal age and risk for trisomy 21 assessed by the origin of chromosome nondisjunction: a report from the Atlanta and National Down Syndrome Projects Turner syndrome does not show this rise with maternal age.15Special Strong. Turner Syndrome, Down Syndrome & Maternal Age
A higher risk with age does not mean most babies of older mothers have Down syndrome. In fact, many babies with Down syndrome are born to younger mothers, simply because younger women have more babies overall. This is one reason doctors offer screening to everyone, not only older women.
How Each Condition Looks and Shows Up in a Child
The signs of Down syndrome are usually present at birth and become clearer as the baby grows.16Centers for Disease Control and Prevention. Down Syndrome They include a flattened face and nose bridge, eyes that slant upward, small ears, and a tongue that tends to stick out.17Centers for Disease Control and Prevention. Down Syndrome Many babies also have low muscle tone, small hands with a single crease across the palm, and a deep gap between the first and second toes.18Eunice Kennedy Shriver National Institute of Child Health and Human Development. What are the symptoms of Down syndrome? Some have small white spots on the colored part of the eye.19Eunice Kennedy Shriver National Institute of Child Health and Human Development. What are the symptoms of Down syndrome?
Turner syndrome is often subtler. Its most common feature is short height, which becomes noticeable by about age 5.20MedlinePlus Genetics. Turner syndrome Some babies are born with puffy, swollen hands and feet and a short neck with extra skin folds.21NICHD. Turner Syndrome Other signs can include a low hairline at the back of the neck, low-set ears, and soft nails that turn upward.22NICHD. Turner Syndrome Still, only about 30% have features like a webbed neck or swelling, so many girls have few obvious signs.23MedlinePlus Genetics. Turner syndrome Some are diagnosed only when they’re much shorter than classmates or when puberty doesn’t start.
The two conditions overlap a little. Both can include a short neck with extra skin, which is why they are sometimes confused at birth. Upward-slanting eyes and a flattened face point toward Down syndrome, not Turner. Only a chromosome test can confirm either one.
Learning and Intelligence
In Turner syndrome, intelligence is usually normal.24PubMed. Congenital cardiovascular disease in Turner syndrome The profile is uneven, though. Girls often have strong verbal skills and weaker spatial, math, and planning skills.25PubMed. Executive Functions in Children and Adolescents with Turner Syndrome: A Systematic Review and Meta-Analysis In one group of adult women, 77% had a clear gap between verbal and nonverbal test scores.26PubMed. Cognitive profile in adult women with turner syndrome: IQ split and associations with ADHD and ASD Reading social situations can also be harder for some girls.27PubMed. Executive Functions in Children and Adolescents with Turner Syndrome: A Systematic Review and Meta-Analysis
School support differs accordingly. Children with Down syndrome often benefit from early intervention, speech therapy, and individualized education plans. Girls with Turner syndrome may do well in reading but need targeted math help. Their spatial difficulty can also affect tasks like reading maps, judging distances, or learning to drive. A neuropsychological assessment can pinpoint which help is needed. Later in life, nearly everyone with Down syndrome has Alzheimer’s-type brain changes by age 40.28PubMed Central. Understanding etiology of chromosome 21 nondisjunction from gene × environment models29PubMed. Down syndrome and Alzheimer’s disease: insights into biomarkers, clinical symptoms, and pathology About 70% are diagnosed with dementia by around age 54, with a lifetime risk of about 95%.30PubMed. Down syndrome and Alzheimer’s disease: insights into biomarkers, clinical symptoms, and pathology
For adults with Down syndrome, family members are often the first to notice changes in daily skills or personality. New forgetfulness in the forties or fifties should be checked by a doctor. Thyroid problems can mimic dementia, so they need to be ruled out.
Heart Problems in Each Condition
About 48% of babies with Down syndrome are born with a heart defect, compared with 0.7% of all babies.31PubMed Central. Down syndrome and associated atrioventricular septal defects in a nationwide Norwegian cohort: Prevalence, time trends, and outcomes The most common is a hole in the center of the heart affecting both upper and lower chambers.32PubMed Central. Down syndrome and associated atrioventricular septal defects in a nationwide Norwegian cohort: Prevalence, time trends, and outcomes This and holes between the lower chambers make up about three quarters of the heart defects seen in Down syndrome.33PubMed Central. Cardiovascular Complications of Down Syndrome: Scoping Review and Expert Consensus
In Turner syndrome, about one third to one half of girls are born with a heart defect.34MedlinePlus Genetics. Turner syndrome These involve the main artery and its valve. The most common is an aortic valve with two flaps instead of three, found in about 39% in one scan study.35PubMed. Cardiovascular anomalies in Turner syndrome: spectrum, prevalence, and cardiac MRI findings in a pediatric and young adult population A narrowing of the aorta, called coarctation, appeared in about 16%.36PubMed. Cardiovascular anomalies in Turner syndrome: spectrum, prevalence, and cardiac MRI findings in a pediatric and young adult population Widening of the aorta develops in 15–30% of people with Turner syndrome.37European Journal of Pediatrics. Serious Aortic Complications in a Patient with Turner Syndrome This can lead to aortic dissection, a tear in the aorta wall, which caused 8 deaths among 20 women who had one in a 17-year follow-up.38Endocrine Abstracts. Mortality in young women with turner syndrome is mainly due to aortic dissection – a 25-year follow-up in sweden
Babies with Down syndrome are usually given a heart ultrasound (echocardiogram) soon after birth, and many of the heart holes are repaired with surgery in the first months. Girls with Turner syndrome need heart imaging at diagnosis, often including an MRI to see the aorta clearly.
Sudden severe chest, back, or belly pain, sometimes described as tearing, needs emergency care, and women with Turner syndrome should tell emergency staff about their diagnosis. Keeping blood pressure under control helps protect the aorta, and regular scans let doctors act before a tear happens.
Puberty, Fertility and Having Children
Most women with Turner syndrome have underdeveloped ovaries because egg cells are lost before birth.39PubMed Central. Ovarian dysfunction in women with Turner syndrome As a result, about 70–80% don’t start puberty on their own and 90% never get a period without treatment.40PubMed Central. Fertility Preservation in Females with Turner Syndrome: A Comprehensive Review and Practical Guidelines They are at very high risk of primary ovarian insufficiency, meaning ovaries that stop working early, and of infertility.41PubMed Central. Fertility Preservation in Females with Turner Syndrome: A Comprehensive Review and Practical Guidelines Some girls, especially with the mosaic form, still have a few eggs in childhood.42PubMed Central. Fertility Preservation in Females with Turner Syndrome: A Comprehensive Review and Practical Guidelines After a first period, freezing eggs may be offered to girls with mosaic Turner syndrome.43PubMed Central. Reproductive health in Turner’s syndrome: from puberty to pregnancy
Down syndrome affects fertility less completely. It is linked to sperm production problems in men and early menopause in women.44PubMed Central. Down syndrome and infertility: what support should we provide? Even so, men with Down syndrome have fathered children in a few confirmed cases,45PubMed. Causes of infertility in men with Down syndrome and women with Down syndrome can become pregnant.
For women with Turner syndrome, pregnancy using a donor egg is possible because the uterus can carry a baby after hormone treatment. It is high risk because of the strain on the heart and aorta, so a heart check and a team of specialists are needed before and during pregnancy.
The timing of questions matters. For Turner syndrome, ask early in childhood whether any eggs remain, since that window can close. For Down syndrome, families should discuss puberty, sexual health, and contraception as the child grows. Genetic counseling explains the chance of passing a condition on.
How Reliable Prenatal Screening Is for Each
A prenatal blood screen, often called NIPT or cell-free DNA screening, looks at bits of DNA from the placenta in the mother’s blood. When it flags Down syndrome, the result is correct about 91% of the time in higher-risk pregnancies and 82% in lower-risk ones.46PubMed Central. Turner syndrome: New insights from prenatal genomics and transcriptomics When it flags a missing X chromosome, it is correct only about 26% of the time.47PubMed Central. Turner syndrome: New insights from prenatal genomics and transcriptomics Any positive screen should be confirmed with a diagnostic test like amniocentesis or CVS before decisions are made.
The screen struggles with Turner syndrome because it reads DNA from the placenta, which doesn’t always match the baby. Mosaic changes in the placenta, or in the mother herself, can mimic a missing X. Ultrasound signs, like neck swelling, can add information but don’t confirm anything.
After a positive screen, ask for a meeting with a genetic counselor to explain the result. Amniocentesis tests the fluid around the baby, while CVS tests placenta tissue. Some families instead wait for a test after birth, which is also an option to discuss.
Treatment and Ongoing Checkups
Turner syndrome care centers on hormones. Growth hormone treatment adds about 7 cm to adult height.48PubMed Central. Height outcome of the recombinant human growth hormone treatment in Turner syndrome: a meta-analysis Growth hormone works best when started early, once growth begins to fall behind, and it is usually given as daily injections at home. Estrogen treatment usually begins around age 11 to 12 to start puberty.49PubMed. Estrogen Replacement in Turner Syndrome: Literature Review and Practical Considerations Low starting doses increased over 2 to 3 years preserve remaining growth.50PubMed. Estrogen Replacement in Turner Syndrome: Literature Review and Practical Considerations Starting estrogen too early or at a high dose can shorten the growth window. Estrogen also supports bone strength and growth of the uterus.51PubMed. Estrogen Replacement in Turner Syndrome: Literature Review and Practical Considerations
Down syndrome care includes regular thyroid testing. Thyroid blood tests are recommended at birth, at 6 and 12 months, and then every year.52PubMed Central. Autoimmune Thyroid Disease in Patients with Down Syndrome—Review If thyroid antibodies are found, testing moves to every 6 months.53PubMed Central. Autoimmune Thyroid Disease in Patients with Down Syndrome—Review
Each child usually sees a different team. Girls with Turner syndrome typically see an endocrinologist, a cardiologist, and a kidney specialist. Children with Down syndrome often see a cardiologist, speech and physical therapists, and hearing and eye specialists. A pediatrician coordinates care and tracks the recommended screenings.
Life Expectancy and Adult Life
The average life expectancy for someone with Down syndrome is now nearly 60 years and rising.54Nationwide Children’s Hospital. Down Syndrome Life Expectancy Is Higher, But Not For Everyone It has been much lower for minority groups than for white people in the United States.55Nationwide Children’s Hospital. Down Syndrome Life Expectancy Is Higher, But Not For Everyone Women with Turner syndrome lose about 10 to 12.5 years of life expectancy on average.56PubMed Central. Mortality ratios, life expectancy, and causes of death in patients with Turner’s syndrome Heart and blood vessel disease is the main cause of early death in adults with Turner syndrome,57PubMed. Congenital cardiovascular disease in Turner syndrome and deaths from it were about 9 times more common than in other women.58Endocrine Abstracts. Mortality in young women with turner syndrome is mainly due to aortic dissection – a 25-year follow-up in sweden