Turner syndrome
Also known as: 45,X, monosomy X
Medically reviewed by Hormone Journal Editorial Team · Last reviewed 2026-05-22
Turner syndrome is a chromosomal condition affecting roughly 1 in 2,000 female births in which one X chromosome is missing or structurally abnormal, causing short stature, ovarian failure, and lifelong cardiovascular risk.
What it is
Turner syndrome is a chromosomal condition affecting approximately 1 in 2,000 to 2,500 female births, in which one of the two X chromosomes is either completely absent or structurally abnormal. Also called monosomy X or 45,X (its classic karyotype designation), it is one of the most common chromosomal conditions overall and the only monosomy compatible with survival to adulthood. The two most consistent features are short stature and primary ovarian insufficiency (POI) — the failure of the ovaries to develop and produce estrogen. Without hormone replacement, estrogen deficiency leads to absent puberty, severe bone loss, and elevated cardiovascular risk. Structural heart defects and aortic abnormalities occur in 30–50% of affected individuals and require lifelong monitoring independent of hormonal status. In Canada, diagnosis and ongoing care typically involve endocrinology, cardiology, and gynaecology teams at academic health centres; transition from paediatric to adult care is a recognized gap that Canadian clinical groups have highlighted.
Causes and mechanism
Turner syndrome arises from a random chromosomal error — most often meiotic nondisjunction or loss of a sex chromosome early in embryonic development. It does not follow a traditional inheritance pattern and does not run in families the way single-gene disorders do. There is no consistent association with advanced maternal age, which distinguishes it from trisomy conditions such as Down syndrome.
Three main karyotype subtypes account for nearly all cases:
| Karyotype | Frequency | Key features |
|---|---|---|
| 45,X (monosomy X) | ~45% of cases | Classic phenotype; complete absence of second X |
| Mosaic (45,X / 46,XX or other) | ~30–40% of cases | Mixed cell lines; features often milder; some residual ovarian function possible |
| Structural X abnormality (isochromosome Xq, ring X, deletions) | ~15–25% of cases | Phenotype depends on which X-chromosome region is affected |
Because roughly 30–40% of cases are mosaic, the clinical picture varies considerably from person to person. Women with mosaic Turner syndrome may have near-normal puberty and only subtle physical features, which is one reason diagnosis is sometimes delayed until adulthood.
Symptoms and diagnosis
Features differ by karyotype and life stage.
Prenatal and newborn period: lymphoedema of the hands and feet, webbed or wide neck (pterygium colli), low posterior hairline, widely spaced nipples, and cardiac defects — particularly coarctation of the aorta — may be apparent at birth or detected on prenatal ultrasound or non-invasive prenatal testing (NIPT).
Childhood: short stature is the most consistent finding across all karyotypes. Without growth hormone therapy, adult height typically falls between 143 and 145 cm. Recurrent middle ear infections, hearing loss, and difficulties with spatial and mathematical reasoning are also common.
Adolescence: most girls do not enter puberty spontaneously because the ovaries have failed. Absent or very incomplete puberty and primary amenorrhoea (no menstrual periods by age 15) are frequent presenting complaints that prompt karyotype testing.
Adulthood: infertility affects the vast majority of women. Ongoing risks include aortic dilation and dissection, hypertension, metabolic syndrome, type 2 diabetes, Hashimoto's thyroiditis (autoimmune hypothyroidism), and coeliac disease.
Diagnostic workup typically includes:
- Karyotype — the definitive test, performed on a blood sample
- Prenatal diagnosis — via CVS, amniocentesis, or NIPT
- Hormone panel — elevated FSH and LH with low or absent estradiol confirms POI
- Cardiac imaging — echocardiogram and cardiac MRI to assess for bicuspid aortic valve, coarctation, and aortic dimensions
- Renal ultrasound — structural kidney abnormalities are present in approximately 30% of cases
- Bone density scan — to quantify the skeletal impact of estrogen deficiency
- Thyroid function and antibodies — to screen for autoimmune thyroid disease, which affects roughly 30–47% of women with Turner syndrome
Treatment options
Management is multidisciplinary and spans the entire lifespan.
Growth hormone therapy: recombinant human growth hormone is recommended from approximately age 4–6 years. When started early, it can add roughly 5–8 cm to final adult height. In Canada, growth hormone for Turner syndrome is covered under most provincial drug benefit programs when prescribed through a paediatric endocrinologist, though coverage criteria vary by province.
Estrogen replacement therapy (ERT): the cornerstone of hormonal management. Estrogen is initiated at around age 11–12 to induce puberty and develop secondary sexual characteristics. Combined estrogen-progesterone therapy is added later to protect the uterus and provide regular withdrawal bleeds. ERT should continue until at least the average age of natural menopause (approximately 51 years) to protect bone density, cardiovascular health, cognitive function, and quality of life. The doses used are physiological — replacing what a healthy ovary would produce — not supraphysiological.
Fertility: the large majority of women with Turner syndrome cannot conceive naturally. Oocyte donation with IVF is the primary pathway to pregnancy. Pregnancy in Turner syndrome carries significant cardiovascular risks, particularly aortic dissection, and must be planned and managed in a specialist centre with pre-conception cardiac imaging. Women with mosaic Turner syndrome who retain some ovarian function may be candidates for fertility preservation (egg or embryo freezing) before ovarian reserve is exhausted.
Cardiovascular surveillance: regular echocardiogram and cardiac MRI to monitor aortic root dimensions; active blood pressure management, as hypertension is common and amplifies aortic risk.
Other ongoing care: annual thyroid function testing; hearing assessments; psychological support for identity, self-esteem, and fertility-related concerns; and structured transition planning from paediatric to adult care.
When to see a clinician in Canada
Seek evaluation if a girl has short stature significantly below family-expected height, a webbed or wide neck at birth, lymphoedema of the hands or feet at birth, or absent puberty or primary amenorrhoea by age 14–15. These features warrant a karyotype referral through a paediatrician or paediatric endocrinologist.
Women with a confirmed diagnosis should be followed by a multidisciplinary team — typically including endocrinology, cardiology, gynaecology, and reproductive medicine where relevant. Canadian academic centres in Toronto, Montreal, Vancouver, and Calgary have established Turner syndrome clinics or multidisciplinary programs. For adults managing hormone replacement between specialist visits, Canadian telehealth platforms (Felix, Maple, Cleo, Phoenix, and others) can support prescription continuity, but specialist oversight for cardiac surveillance and bone health should not be replaced by virtual-only care.
All women with Turner syndrome require lifelong cardiovascular monitoring. Aortic dissection can occur without warning and is a leading cause of premature death in the condition.
Limitations and open questions
Research is still emerging on several aspects of Turner syndrome management. The optimal timing and formulation of estrogen replacement — particularly whether transdermal estrogen more closely mimics normal ovarian physiology than oral estrogen during puberty induction — remains an active area of study, and guidelines from the Endocrine Society and European Society for Paediatric Endocrinology do not yet fully agree. The long-term cardiovascular benefit of specific antihypertensive agents in Turner syndrome has not been established in large randomized trials. Fertility preservation in girls with Turner syndrome before ovarian reserve is lost is technically feasible but remains experimental, and success rates are not yet well characterized. Health Canada has not issued Turner syndrome-specific clinical guidelines; Canadian practitioners generally follow international consensus statements adapted to local care contexts. The psychological burden of delayed diagnosis — particularly in women identified only in adulthood — is under-studied in Canadian populations.
FAQs
Can women with Turner syndrome have children?
The large majority of women with Turner syndrome cannot conceive naturally because the ovaries fail to develop and produce eggs. Pregnancy is possible using donor eggs with IVF, and live birth rates with donor oocytes are comparable to those in other women using donor eggs. However, pregnancy in Turner syndrome carries significant cardiovascular risks — particularly aortic dissection — so pre-conception cardiac imaging and management in a specialist centre are essential. A small proportion of women with mosaic Turner syndrome retain some ovarian function and may conceive naturally or with fertility support.
Is Turner syndrome diagnosed at birth?
It can be, particularly when obvious physical features such as lymphoedema, webbed neck, or a cardiac defect are present. Prenatal diagnosis is increasingly made through NIPT or amniocentesis. However, many women are not diagnosed until adolescence, when absent puberty or primary amenorrhoea prompts investigation — and some are identified only in adulthood during workup for infertility. Earlier diagnosis matters because growth hormone therapy adds the most height (roughly 5–8 cm) when started before age 6.
Does estrogen replacement in Turner syndrome increase cancer risk?
Current evidence does not show an increased cancer risk from appropriately dosed estrogen replacement in Turner syndrome. The therapy replaces hormones the body cannot produce — doses are physiological, matching what a healthy ovary would make, not supraphysiological. By contrast, the risks of not replacing estrogen are well documented: severe osteoporosis, cardiovascular disease, and adverse cognitive effects. Women with Turner syndrome should discuss their individual risk profile with their endocrinologist or gynaecologist.
What is the most serious long-term health risk in Turner syndrome beyond infertility?
The most serious long-term risk is cardiovascular disease, specifically aortic complications. Approximately 30–50% of women with Turner syndrome have a bicuspid aortic valve and/or coarctation of the aorta, and the aortic root tends to be wider and stiffer than average. This creates a risk of aortic dissection — a potentially fatal tearing of the aortic wall — which is the leading cause of premature death in the condition. Regular cardiac imaging (echocardiogram and cardiac MRI) and blood pressure control are lifelong necessities, not optional follow-up.
Is growth hormone therapy for Turner syndrome covered in Canada?
In most Canadian provinces, recombinant human growth hormone for Turner syndrome is covered under provincial drug benefit programs when prescribed by a paediatric endocrinologist and when the child meets defined eligibility criteria (typically confirmed karyotype and documented growth failure). Coverage details vary by province — for example, Ontario's Exceptional Access Program and BC's PharmaCare each have their own criteria and renewal requirements. Families should confirm coverage through their provincial drug plan and the prescribing specialist before starting therapy.
Sources
- Turner Syndrome — StatPearls (NCBI Bookshelf)
- Turner syndrome: Symptoms and causes — Mayo Clinic
- A basic understanding of Turner syndrome: Incidence, complications and treatment — PMC
- Clinical Practice Guidelines for the Care of Girls and Women with Turner Syndrome — Endocrine Society
- Turner Syndrome Genotype and Phenotype and Their Effect on Presenting Features and Timing of Diagnosis — PMC