Turner syndrome

Turner syndrome can be defined as loss or abnormality of the second X chromosome in at least one cell line in a phenotypic female. In the majority of affected girls, the normal X chromosome is maternal in origin.

Obvious physical stigmata such as neck webbing affect only approximately 20% of girls with Turner syndrome¹ . Many girls with Turner syndrome experience few problems other than short stature and ovarian failure² . Short stature or a poor growth rate can be the first manifestation of Turner syndrome³ .

Turner syndrome should be considered in any girl with short stature or primary amenorrhoea. Almost all affected women are infertile, but some are able to conceive with assisted reproduction⁴ .

Turner syndrome is associated with an increased risk of congenital heart defects, congenital lymphoedema, renal malformations, hearing loss (conductive or sensorineural), osteoporosis, obesity, diabetes and an atherogenic lipid profile. Intelligence is usually normal but there may be problems with nonverbal, social and psychomotor skills.

Epidemiology²

• Turner syndrome is estimated to occur in 25 to 210 per 100,000 women, according to cytogenetic studies. According to a study from 1999 to 2004, the incidence in 119,158 births was 1/1,180 or 0.85%⁵ .

• It has been estimated that 1-2% of all conceptuses are affected, of whom only 1% will survive to term.

• Complete 45,X monosomy accounts for 40-60% of the karyotypes. Most of the remaining karyotypes show a mosaic pattern - eg, 45,X/46,XX, 45,X/46,XiXq, 45,X/46,XY, 45,X/46,XrX.

NB: advanced maternal age is not a risk factor for Turner syndrome.

Clinical features^{2 6}

Clinical features by age include:

• Newborn infants: may be recognised because they are often borderline small for dates, have lymphoedema of the hands and feet and excessive skin at the nape of the neck, and cardiac abnormalities (eg, coarctation of aorta, pulmonary stenosis, aortic stenosis, bicuspid aortic valve).

• Infancy: length usually close to and parallel to the 3rd centile, feeding difficulties with poor weight gain, poor sleeping pattern.

• Preschool: short stature (height velocity usually low or normal), high activity levels, behavioural difficulties with exaggerated fearfulness, recurrent middle ear infections (otitis media with effusion, conductive hearing loss), sensorineural deafness.

• Older children: height gradually falls away from the 3rd centile, gonadal dysgenesis, middle ear disease, obesity, specific learning difficulties, social vulnerability (social problems, immaturity, less social activity), foot problems (eg, toenail involution, cellulitis), renal anomalies.

• Adolescence: impaired pubertal growth spurt (even with oestrogen induction), ovarian failure (absent/incomplete puberty), obesity, hypertension, increased prevalence of immune disorders (eg, autoimmune thyroiditis, coeliac disease, inflammatory bowel disease), specific learning difficulties, social vulnerability, foot problems.

• Adulthood: infertility, obesity, hypertension, aortic dilatation/dissection, autoimmune thyroiditis, osteoporosis, visuospatial difficulties, sensorineural deafness.

Dysmorphic features

• Eyes - epicanthic folds, oblique palpebral fissures, ptosis, squint, nystagmus, cataracts, amblyopia, and hypermetropia.

• Ears - low-set, posteriorly rotated ears, prominent upturned lobules. Deafness may develop secondary to chronic otitis media; sensorineural hearing impairment.

• Mouth - micrognathia, high palate and mandible abnormalities can result in crowding of teeth and malocclusion.

• Neck - short, webbed; low hairline.

• Chest - broad chest, pectus excavatum, inverted, hypoplastic, widely-spaced nipples.

• Joints - cubitus valgus, congenital hip dislocation.

• Hands - short 4th/5th metacarpals, short fingers, forearm and carpal developmental abnormalities; nail hypoplasia, hyperconvex nails, nail-fold oedema.

• Skin lymphoedema - hands, feet, neck (pterygium coli), pigmented naevi, telangiectasias, vitiligo, keloid, seborrhoeic dermatitis; increased body hair with alopecia. There is a risk of keloid formation with surgery.

Cardiovascular problems

• Coarctation of the aorta.

• Bicuspid aortic valve; aortic stenosis.

• Aortic aneurysms.

• Mitral valve prolapse.

• Ectopia cordis.

• Hypoplastic left heart.

• Pulmonary stenosis.

• Vascular malformations (including generalised vascular dysplasia, intestinal telangiectasias, haemangiomas, venous ectasias, lymphangiectasia, cystic hygroma and multiple renal arteries).

• Conduction defects, including prolonged QT interval.

Genitourinary anomalies

• Double collecting system.

• Absent kidney.

• Malrotation.

• Horseshoe kidneys.

• Silent hydronephrosis.

Gonadal dysgenesis/failure

• Many have fibrotic ovarian streaks at the time of birth. Removal of bilateral streak gonads prior to starting school is recommended in 45,XO/46,XY mosaics.

• Approximately 30% of girls with Turner syndrome have some spontaneous pubertal development.

Associated diseases⁶

There is an increased incidence of autoimmune disorders, particularly autoimmune thyroid disease (both Hashimoto's thyroiditis and Graves' disease), coeliac disease, inflammatory bowel disease, alopecia areata and type 1 diabetes mellitus.

Investigations⁵

• Chromosome analysis: required for diagnosis. A male phenotype excludes the diagnosis, regardless of karyotype. A buccal smear for Barr bodies is now obsolete. Investigation for the presence of Y chromosomal material (using a Y-centromeric probe): patients with 45,X/46,XY mosaicism may have mixed gonadal dysgenesis and are at a high risk for gonadoblastoma.

• Gonadotrophins: LH and FSH may be elevated in untreated patients aged younger than 4 years. Gonadotrophins are later suppressed to normal or near-normal levels, and then increase to menopausal levels after the age of 10 years. LH and FSH levels should be measured before initiating oestrogen replacement therapy.

• TFTs, thyroid antibodies.

• Haemoglobin A1c or fasting glucose level to screen for diabetes mellitus.

• Renal: renal function tests, electrolytes, urine cultures and ultrasound scan of the renal tract.

• ECG, echocardiography, MRI examination of the heart and aorta.

• Bone age: usually normal before adolescence but is then delayed because of oestrogen deficiency. Bone age should be performed before starting growth hormone or oestrogen therapy. Growth hormone is contra-indicated if the epiphyses are fused.

• Bone density in adulthood: osteoporosis is common.

• Virilisation: the presence of virilisation should prompt a thorough search for Y chromosome material and for gonadal, adrenal or midline tumours.

• Hearing tests.

Prenatal diagnosis

Initial screening is by ultrasound⁷ . Turner syndrome can be diagnosed by amniocentesis or chorionic villous sampling which allows karyotyping of the fetus. Errors can occur, so a complete karyotype analysis needs to be performed after birth to verify those results.

Differential diagnosis

• Other causes of short stature and delayed puberty.

• Noonan's syndrome is associated with some of the clinical features of Turner syndrome.

Management⁸

Turner syndrome is obviously a lifelong condition and, although the majority of patients are healthy, they are susceptible to a number of chronic conditions. For this reason, multidisciplinary follow-up is required as an exercise in screening and prevention, as well as treatment where necessary² . Cardiac defects are likely to be the most significant associated health problems⁹ . The need for long-term surveillance and awareness of associated conditions should be promoted. Regular renal ultrasound, and screening for impaired glucose tolerance and hypertension are recommended.

Problems of most concern to patients may vary with age but the main four concerns revolve around growth, puberty, fertility and general health. Shared care should include:

• Paediatrics and paediatric endocrinology: particular attention should be given to:

  • Growth.

  • Pubertal development.

  • Thyroid function.

  • Screening for coeliac disease .

  • Prevention of osteoporosis.

• Ophthalmology: screening for amblyopia and other associated eye disorders is recommended.

• Ear, nose and throat: screening for deafness and secretory otitis media is appropriate.

• Dentist: problems with crowding of teeth and malocclusion should be addressed. Antibiotic prophylaxis to prevent subacute bacterial endocarditis is now less likely to be necessary (see the separate Prevention of Infective Endocarditis article).

• Orthopaedics: regular review is usually unnecessary.

• Cardiology: all patients should have regular periodic cardiological evaluation including echocardiography in infants and children and MRI in older girls and women.

• Urology: about 30% of patients have renal anomalies. There is an increased risk of Wilms' tumour. Annual renal function tests and electrolytes, and urine culture are recommended.

• Genetic counselling: it should be emphasised that Turner syndrome is not inherited.

• Psychological support: generally, psychological health is good but educational and social assessments and support may help integration and general well-being¹⁰ . There is some evidence for lower-than-average levels of neuroticism and a tendency to be more extrovert¹¹ . There are also studies that show increased levels of hyperactivity and inattention¹² . Therefore, regular psychosocial assessment and support, support for families and appropriate support at school are very important¹³ .

Growth and puberty^{5 14}

Whilst there are no global consensus guidelines on the management of Turner syndrome, those produced after the 2016 Cincinnati International Turner Syndrome meeting have endorsement from a wide number of authorities, several from Europe. They recommend:

• Growth hormone (GH) treatment from 4-6 years of age, and before 12-13 years if the child already has evidence of growth failure (eg, below 50th percentile height velocity observed over six months in the absence of other treatable cause of poor growth), the child is already short, or has a strong likelihood of short stature (eg, short parents and short predicted adult height or already pubertal at the time of diagnosis).

• A GH dose of 45-50 µg/kg/day or 1.3-1.5 mg/m²/day (4.0–4.5 IU/m²/day) in most instances, increasing to 68 µg/kg/day (2.0 mg/m²/day) if adult height potential is substantially compromised.

• Monitoring growth-promoting treatment by measurement of height at least every 4-6 months during the first year of treatment and at least every six months subsequently.

• Monitoring insulin-growth factor (IGF-I) at least annually. If an IGF-I value is measured above +3 SDS, a GH dose decrease is justified. For an IGF-I value between +2 SDS and +3 SDS, clinical judgment should be used to determine further GH dose selection.

• Concomitant treatment with oxandrolone (an androgen) from the age of 10 years or older at 0.03 mg/kg/day maintained below 0.05 mg/kg/day, if the diagnosis (and therefore GH treatment initiation) is delayed, and/or adult height outcome is likely to be unsatisfactory with the standard GH dose alone. NB: the British National Formulary for Children recommends a dose range of 0.625-2.5mg daily¹⁵ .

• Avoiding adding very low-dose estrogen supplementation routinely in the prepubertal years to further promote growth.

• Commencing adding oestrogen replacement between 11 and 12 years of age increasing to adult dosing over 2-3 years.

• Adding progesterone once breakthrough bleeding occurs, or after two years of oestrogen treatment. This aids pubertal development and prevention of osteoporosis.

• Fertility may be achieved with oocyte donation, and gamete or embryo transplantation.

Prognosis⁸

• Patients are usually shorter than average (even with growth hormone therapy) and almost all are infertile (although assisted fertility may be successful).

• The mortality rate is three times greater than the general population due to complications from cardiovascular disease such as coronary heart disease and stroke. Congenital aortic aneurysm, pneumonia, diabetes, epilepsy, liver disease, and kidney disease are also responsible for an increase in mortality.