Introduction

What is Turner Syndrome? 

Turner syndrome (TS) is a chromosomal abnormality affecting solely people assigned female at birth (AFAB). It occurs when one of the X chromosomes is partially or completely missing, and can lead to a myriad of physiological symptoms.^1,2 It is also referred to as congenital ovarian hypoplasia syndrome, which translates to incomplete genetic development affecting the female reproductive system and, thus fertility.² 

While some individuals with Turner Syndrome have a complete absence of one X chromosome, others present with a more complex genetic picture. This variation in genetic presentation leads to different subtypes of the condition.^1.2,3

Approximately 45% of TS patients miss one of their X chromosomes completely. Clinicians can refer to this TS subcategory as Monosomy 45,X, or 45,XO referring to the absence of a whole chromosomal copy.^2,3 

The rest of TS cases include patients who possess two X chromosomes with one having structural abnormalities such as missing parts or abnormal genetic components. This subtype is also referred to as 45, X with mosaicism given the chimeric appearance of the X chromosome we can observe in these cases.^1,2 

Prevalence in children

Turner syndrome is the most common sex chromosome-linked disorder in people AFAB, affecting 1 in 2500 AFAB births, and interestingly having the highest incidence rate in China.^1,2

The condition is not inherited in most cases but is caused by an error during cell division called nondisjunction that occurs while the embryo forms. Therefore, even though the genetic abnormality is already present prenatally and could be tested for, parents are usually unaware of the condition until birth, or even longer. In some milder cases, the condition can stay undetected until adulthood.^1,3

The Importance of early detection

Undetected cases prove to be a serious problem, given the array of clinical symptoms the condition is associated with, including ovarian dysgenesis, malfunctioning of the endocrine glands, cognitive deficits, type 2 diabetes, and cardiovascular issues, as well as short stature, webbed neck and low hairline.^1,2,3 The mortality rate of TS patients is known to be three times higher than that of healthy individuals.

Diagnosis can occur prenatally, sometimes after picking up signs of lymphoedema or cardiac defects on the ultrasound examination and then performing chorionic villus sampling to evaluate the cause of these symptoms.³ Some countries recommend foetuses suspected of TS to be electively aborted early on in the pregnancy.² However, for full diagnosis confirmation is required after birth in the form of a full karyotype analysis of the newborn’s chromosomes, usually accompanied by genetic testing in cases with mosaicism.^1,2

Early detection is crucial, as it allows us to closely monitor and evaluate clinical symptoms in patients during their childhood and adolescence.^2,3 However, unfortunately, the mean age at diagnosis is currently 15 years.³

Symptoms associated with Turner Syndrome

Growth and development

Growth abnormalities are the most visible and one of the earliest detectable signs of Turner Syndrome. There is a sharp decline in growth between birth and two years of age, which will then turn into a smaller, gradual decline for the rest of childhood.⁵

The characteristics of short stature and delayed physical development can have significant impacts on both health and quality of life. Developmental symptoms are caused as the X chromosome contains genes crucial for growth and sexual maturation. 

Skeletal development is also heavily affected, with numerous possible symptoms affecting bone structure and composition.^1,4,5 Developmental symptoms in TS include:

• Short stature (average 20 cm smaller than healthy individuals)
• Delay or absence of puberty
• Broad chest with widely spaced nipples
• Webbed neck
• Low hairline 
• Ptosis (eyelid drooping over the eye)
• Abnormal growth of fingers 
• Abnormal joint development (elbows, knees - most significant physical impact on life quality)
• Scoliosis
• Osteoporosis (bone fragility)
• Increased chance of skeletal damage or fractures^1,5,6
  

Reproductive system

Given the X chromosome-linked nature of this condition, reproductive abnormalities are a hallmark feature of Turner Syndrome. The delay or underdevelopment of the ovaries that stems from the faulty genetic code can lead to a range of issues with sexual development, from the delayed onset of puberty to premature ovarian failure, and also impacts fertility and hormonal regulation of the patients.^1,2,3,5,6 These symptoms can include:

• Ovarian dysgenesis (otherwise known as underdevelopment)
• Infertility 
• Delayed, incomplete, or absent puberty
• Lack of or infrequent menstrual periods
• Sex hormonal imbalance (especially depleted oestrogen)^1,3,6

Cardiovascular system

Cardiovascular abnormalities represent one of the most serious complications of Turner Syndrome and are present in approximately 41% of patients.² These heart and blood vessel issues are the main contributors to the elevated mortality rate of TS patients, thus early detection and appropriate management of these symptoms are crucial.³ 

Cardiovascular symptoms associated with Turner Syndrome can include:

• Heart defects (aortic valve malfunction due to the deformation of the bicuspid aortic valve, or the narrowing of the aorta) 
• Aortic rupture
• Dilated aortic root
• High blood pressure^1,2,3
  

Kidney and the urinary tract 

Renal and urinary tract issues are common symptoms among Turner syndrome patients, with some studies finding them affecting approximately 40-50% of their patient cohort.^1,3,7

• Horse-shoe kidney
• Kidney malrotation or positional abnormalities
• Obstruction to the ureteropelvic junction (the area where the urine transporter tubes known as ureters stem from the kidney)
• Swollen kidneys due to urine buildup (hydronephrosis)
• Pyelonephritis (a urinary tract infection that reaches the kidneys)^3,7

Endocrine system

Turner Syndrome significantly affects endocrine signalling, leading to various hormonal imbalances. The arising hormonal issues are central to the clinical manifestations of the syndrome, such as growth and sexual maturation, and require continuous management throughout the patient’s life. Hormonal imbalances in TS can include:^1,3

• Growth hormone deficiency
• Oestrogen deficiency
• Thyroid dysfunction
• Glucose intolerance (which can lead to Type I Diabetes)
• Tendency for weight gain³

Autoimmune diseases

Partially due to the effect of the genetic abnormalities on immune system regulation, which is partially due to the arising hormonal imbalance, TS patients are highly susceptible to certain autoimmune diseases. The prevalence of these autoimmune conditions increases with age, and can include:³

• Coeliac Disease (associated with gluten sensitivity)
• Hashimoto’s Thyroiditis 
• Type 1 Diabetes
• Inflammatory bowel disease
• Alopecia (hair loss due to the immune system attacking hair follicles)
• Chronic inflammation of joints (rheumatoid arthritis)
• Psoriasis (dry, flaky patches on skin)^1,2,3
  

Brain development and cognition

While Turner Syndrome is primarily known for its physical manifestations, it can also significantly affect cognitive function and development. Thankfully, these cognitive abnormalities are within a mild to moderate range and usually do not affect the overall intelligence of the patients (Intellectual disability is only present in 10%).³

It, however, can present challenges with certain tasks associated with specific cognitive domains.^1,3,8 Recognising these difficulties early is essential for implementing therapeutic and support strategies to help TS patients reach their full potential.⁸ Cognitive symptoms associated with TS include:

• Learning disabilities 
• Impaired attention
• Hearing loss
• Poor visuospatial memory
• Below-average motor skills
• Impaired social cognition (including facial recognition and body image issues, also linked to the delay of puberty)^3,8

Managing the symptoms of Turner Syndrome 

The management of Turner Syndrome in children involves a multidisciplinary approach that is tailored to the needs of each patient individually. For instance, growth hormone therapy can be initiated early to address short stature by increasing height by a few inches. 

Oestrogen replacement therapy can be administered from age 10-12 to induce puberty and improve bone health. Cardiovascular issues should also be monitored and intervened if necessary, for instance, by administering vasodilators to prevent high blood pressure or aortic dissection through the dilation of blood vessels. 

Regular screenings for associated conditions such as hypothyroidism, celiac disease and osteoporosis are essential, with the application of appropriate therapeutic approaches if needed.

Educational, psychological and emotional support are also vital parts of management, as they help address the cognitive and social challenges associated with the condition. Fulfilling this comprehensive care can significantly improve the quality of life and the long-term health outcomes for patients with Turner Syndrome, also decreasing their mortality rate.

Summary

Turner Syndrome (TS) is a chromosomal disorder affecting people AFAB, characterised by complete, or partial loss of one of the X chromosomes. It occurs in 1:2500 female births, typically caused by a random genetic error while the cells are proliferating during embryo formation. The syndrome manifests in various symptoms, affecting numerous physiological systems across the body:

1. Growth and development: Short stature, delayed puberty, and skeletal abnormalities
2. Reproductive system: Ovarian dysgenesis, infertility, and hormonal imbalances
3. Cardiovascular system: Heart defects, high blood pressure and increased risk of aortic rupture
4. Renal system: Kidney malformations and urinary tract issues
5. Endocrine system: Hormonal imbalances that affect growth, sexual maturation and metabolism
6. Immune system: Increased susceptibility to most autoimmune diseases
7. Cognitive function: Mild to moderate effects on specific cognitive domains

Early detection is crucial for the management of TS, as it allows for timely interventions including growth hormone therapy, oestrogen replacement, and cardiovascular monitoring. A multifaceted management approach including regular screenings, medical treatments, and psychosocial support can significantly improve the quality of life and long-term health outcomes of Turner Syndrome patients.