Overview

Turner syndrome is a rare disorder that causes people assigned female at birth (AFAB) hypergonadotropic hypogonadism, infertility, small stature, endocrine and metabolic abnormalities, higher risk of autoimmune disease, and other medical diseases, including cardiovascular disease.¹ Three independent clinicians, Seresevskij, Ullrich, and Turner, originally described the disorder with a full or partially missing X chromosome approximately 100 years ago.² 

When compared to the general population, women with Turner Syndrome have mortality rates that are three times higher, with cardiovascular disease being the leading cause of death. Understanding that aortic dissection (AoD) and aortic rupture are largely lethal consequences that affect young adult women with Turner Syndrome, is essential for prompt identification of the signs and symptoms of these conditions.⁵

This article aims to uncover Turner syndrome with a focus on the associated heart conditions. 

Turner syndrome

Turner's syndrome affects approximately 1 in 2500 to 1 in 3000 live-born children assigned female at birth (AFAB). Approximately 50% have monosomy X (45, X), while 5-10% have isochromosome duplication of one X's long arm (46, X, i(Xq)). The majority of the remaining individuals exhibit mosaicism for 45, X and one or more other cell lineages. 

Turner Syndrome can be diagnosed at various stages of life, from prenatal through adulthood. Prenatal (before birth) diagnosis has become more common with the advent of non-invasive prenatal testing (NIPT) and chorionic villus sampling (CVS). 

Postnatal (after birth) diagnosis often occurs during infancy or childhood due to the presentation of characteristic features such as short stature, lymphoedema, or congenital heart defects. Some women are diagnosed later in life when they present with primary amenorrhea or infertility issues.³ 

Turner syndrome and heart conditions

When compared to the general population, persons with Turner Syndrome experience higher rates of early morbidity and death, which are primarily caused by cardiovascular disorders.⁴ 

Aortic coarctation, thoracic aortic aneurysm, and the bicuspid aortic valve (BAV) are examples of congenital cardiac abnormalities that affect up to 50% of people and primarily affect the left side of the heart. 

The bicuspid aortic valve, present in about 30% of TS patients, involves the aortic valve having only two leaflets instead of three. This can lead to valve dysfunction, including stenosis and regurgitation, potentially requiring surgical intervention. 

Coarctation of the aorta, a narrowing of the aorta typically located near the ductus arteriosus, occurs in approximately 10-15% of TS cases. This condition leads to increased cardiac workload and hypertension, necessitating surgical correction in severe cases. 

Aortic root dilation is another critical concern, with TS patients at a higher risk for aortic aneurysm and dissection. Regular cardiovascular monitoring and early intervention are essential for managing these risks.

Pathophysiology of Turner syndrome 

The pathophysiology of Turner syndrome involves the impact of this chromosomal abnormality on multiple organ systems due to the haploinsufficiency of genes located on the X chromosome.⁶

Genetic and cellular impacts

1. Chromosomal abnormalities
   • The most common karyotype in Turner Syndrome is 45, X, where one X chromosome is completely missing. However, other variations include mosaicism (45, X/46, XX or 45, X/46, XY) and structural abnormalities like isochromosomes, deletions, or ring chromosomes
   • The loss of the second X chromosome results in the absence or dysfunction of numerous genes crucial for normal development and physiological function
2. Gene dosage effect
   • Females have two X chromosomes, with one undergoing random inactivation in each cell to balance gene expression. In Turner Syndrome, the absence of one X chromosome leads to a deficit in the dosage of X-linked genes, which disrupts normal development and function
   • Critical genes impacted include those involved in growth, skeletal development, and ovarian function^7,8

Specific gene impacts

1. SHOX Gene
   • The SHOX (short stature homeobox) gene, located on the pseudoautosomal regions (PAR1) of the X and Y chromosomes, is essential for skeletal development
   • In Turner syndrome, the absence of a second functional SHOX gene results in short stature and skeletal anomalies, such as short stature, short fourth metacarpals, and Madelung deformity^9,10
2. Ovarian development and hormonal imbalance
   • During foetal development, primordial germ cells in individuals with Turner syndrome degenerate prematurely, leading to streak gonads and ovarian dysgenesis
   • This results in primary ovarian insufficiency, characterised by low oestrogen levels, delayed puberty, primary amenorrhea, and infertility. The hormonal imbalance further contributes to the lack of secondary sexual characteristics and increased risk of osteoporosis due to reduced bone mineral density¹¹

Cardiovascular and renal abnormalities

1.  Cardiovascular abnormalities
   • Turner syndrome is associated with a high prevalence of congenital heart defects, including bicuspid aortic valve (BAV), coarctation of the aorta (CoA), and aortic root dilation
   • BAV, present in about 30% of TS patients, can lead to valve dysfunction, stenosis, or regurgitation, potentially requiring surgical intervention
   • CoA, a narrowing of the aorta, occurs in 10-15% of cases, leading to increased cardiac workload and hypertension
   • Aortic root dilation increases the risk for aortic aneurysm and dissection, necessitating regular cardiovascular monitoring^12,13
2. Renal abnormalities
   • Renal malformations, such as horseshoe kidney and duplicated collecting systems, are observed in about one-third of individuals with TS
   • These anomalies complicate cardiovascular management and contribute to hypertension¹⁴

Metabolic and endocrine dysregulation

1. Metabolic abnormalities
   • Insulin resistance and an increased risk of type 2 diabetes mellitus are notable features of Turner Syndrome. These metabolic disturbances are partly due to hormonal imbalances and genetic predispositions inherent in TS¹⁵
2. Endocrine disorders
   • Hypothyroidism, often due to autoimmune thyroiditis, is common in TS, further complicating the metabolic profile¹⁶

Cognitive and behavioural aspects

• While individuals with Turner syndrome typically have normal intellectual abilities, they may experience subtle cognitive deficits
• These challenges often involve spatial reasoning, executive function, and social cognition, likely due to the absence of certain X-linked gene products involved in neural development and function^17,18,19

Turner syndrome and cardiovascular implications

Cardiovascular abnormalities in Turner syndrome include congenital defects such as bicuspid aortic valve (BAV), coarctation of the aorta (CoA), and aortic root dilation. These anomalies significantly contribute to the morbidity and mortality associated with TS. BAV, found in about 30% of Turner Syndrome patients, can lead to valve dysfunction, stenosis, and regurgitation. CoA, present in 10-15% of cases, results in increased cardiac workload and hypertension. Aortic root dilation is particularly concerning due to the elevated risk of aortic aneurysm and dissection, conditions that necessitate regular monitoring and potentially life-saving interventions. 

For BAV and CoA, surgical intervention may be necessary to correct the defects and alleviate symptoms. In cases of aortic root dilation, careful monitoring through regular imaging studies is essential to detect and manage potential aneurysms. 

The life expectancy of individuals with Turner Syndrome is slightly reduced compared to the general population, primarily due to cardiovascular complications. Regular monitoring and proactive management of heart conditions can mitigate some of these risks. Morbidity in TS is largely related to the associated comorbidities, which necessitate a comprehensive and multidisciplinary approach to care.

While Turner syndrome itself cannot be prevented due to its genetic nature, early detection and proactive management of associated conditions can significantly improve outcomes. 

Prenatal screening and genetic counselling play vital roles in the early diagnosis of TS. Postnatally, regular follow-ups with a multidisciplinary team, including endocrinologists, cardiologists, and psychologists, ensure comprehensive care. 

Pharmacological treatment, including beta-blockers and angiotensin-converting enzyme (ACE) inhibitors, may be used to control blood pressure and reduce the risk of aortic complications. Hormone replacement therapy (HRT) is another cornerstone of Turner Syndrome management, addressing the hormonal deficiencies resulting from ovarian dysgenesis. HRT helps in the development of secondary sexual characteristics, the maintenance of bone density, and the reduction of cardiovascular risk factors. Growth hormone therapy is also commonly used to address short stature associated with Turner Syndrome.

Research into the molecular mechanisms underlying TS continues to offer hope for future therapeutic advancements. Understanding the specific gene deficiencies and their impact on development and physiology may lead to targeted therapies that address the root causes of the various TS manifestations.

Summary

Turner Syndrome is a complex genetic disorder with significant implications for cardiovascular health. The primary feature of Turner Syndrome is the partial or complete absence of one X chromosome, leading to the haploinsufficiency of several critical genes. This genetic imbalance manifests in various physical and medical anomalies, with cardiovascular abnormalities being among the most serious and life-threatening complications. 

Understanding the relationship between Turner Syndrome and heart conditions is crucial for improving patient outcomes through timely diagnosis, effective treatment strategies, and comprehensive management.

The management of cardiovascular conditions in TS requires a multidisciplinary approach. Early and accurate diagnosis through echocardiography and other imaging techniques is vital.