What Is Christ Siemens Touraine Syndrome (CST)?

Christ-Siemens-Touraine Syndrome (CST) is a rare condition affecting small numbers of the population. Whilst its causes are well-defined, less talked about are its clinical signs and implications on individuals’ health. As such, this article will provide a comprehensive oversight of all aspects of this rare disorder. 

Defining christ siemens touraine syndrome (CST) 

Christ-Siemens-Touraine Syndrome (CST), otherwise known as ‘Hypohidrotic Ectodermal Dysplasia’ (HED), is an extremely rare genetic condition. To understand what this disorder entails, we need to understand what exactly ‘Hypohidrotic Ectodermal Dysplasia’ means. With ‘hypo’ referring to something that is in quantities less than ‘normal’ and with ‘hidrotic’ referring to the sweat produced by humans, this aspect of the disorder refers specifically to defects in the sweat glands.

Next, we consider what is meant by ‘Ectodermal Dysplasia.’ Following the successful fertilization of a human egg, an ‘embryo’ begins its development within the womb. In turn, this embryo consists of what are known as the three ‘germ layers’: the endoderm, mesoderm, and ectoderm.¹  Consider each germ layer to be similar to a ‘production line’ programmed to generate specific products. In this case, these products are all of the tissues, bones, and organs in the body. Looking specifically at the ectoderm, this is responsible for the formation of the skin, external glands (i.e. sweat glands), hair, nails, and other internal glands.¹ 

With an understanding now of what the ‘ectodermal’ component refers to, what does this mean when considered in the context of ‘dysplasia’? Simply referring to the abnormal development and functioning of cells, we can now see that ‘ectodermal dysplasia’ refers to the abnormal development of cells from the ‘ectoderm layer’. You may now be wondering, ‘So what are the implications of this?’. Having examined the definitions, we can now see that this disease simply refers to defects in tissues such as hair, tooth, nail and sweat glands.² 

What are the causes of christ siemens touraine syndrome (CST)?

Christ-Siemens-Touraine Syndrome (CST), also known as Hypohidrotic Ectodermal Dysplasia, arises from genetic abnormalities within the embryo, notably linked to 'X-linked recessive inheritance'.1 To clarify, this inheritance pattern involves the X and Y chromosomes that determine an individual's sex. In individuals assigned male at birth (AMAB), the 'X' chromosome comes from the mother and the 'Y' chromosome from the father (XY). Those assigned females at birth (AFAB) inherit an 'X' from both parents. The 'recessive' aspect means a characteristic is visible only when inherited from both parents (XX).²

Given CST's connection to the 'X' chromosome, AMAB individuals, having just one 'X,' always exhibit CST characteristics if inherited.¹ Conversely, it is exceedingly rare in AFAB individuals as they require defective 'X' chromosomes from both parents.²

Genetically established, CST's core issue pertains to 'signalling'.¹ This issue has a two-fold impact: first, non-defective genes signal components of the embryo, specifically the ectoderm, guiding normal development. In CST, these signals are disrupted and altered. Second, these disrupted signals program the ectoderm to develop abnormally, resulting in various defects.²

CST's manifestations encompass abnormalities in sweat glands, skin, teeth, and hair.¹ The ectodermal dysplasia disrupts these vital developmental processes, often leading to distinct clinical features.²

In summary, CST's genetic basis is rooted in 'X-linked recessive inheritance,' impacting signalling pathways critical for embryonic development, ultimately causing the syndrome's characteristic abnormalities.^1,2

Clinical features of christ siemens touraine syndrome (CST)

Primary features of CST

The following symptoms are those most commonly found in patients with CST: 

Hypohidrosis (reduced ability to sweat) and associated symptoms:

• The diminished functioning of the sweat glands caused by CST may result in patients developing hyperthermia (overheating) with minimal physical effort.
• Intolerance to hot water and hot environments.²
• Dry skin due to the absence of moisture from sweat.

Hypotrichosis (sparse or absent hair) and its presentations: 

• Sparse and sometimes lighter-coloured hair around the scalp area.⁴
• Thin eyebrows and eyelashes²
• In some patients, there may be evidence of a retracted hairline towards the scalp⁴
• In people AMAB, they may notice thin beard hair⁴
• Thin hair around the armpit and pubic areas.⁴

Hypodontia (missing or abnormally developed teeth) and its presentations:

• A history of slow or delayed tooth development.²
• Missing teeth. An absence of more than six teeth is known as oligodontia. This is mostly localized to the frontal regions of the mouth²
• Abnormally developed teeth. The teeth affected are often the ones located towards the front of the mouth and are often described as smaller in size and ‘conical’ in shape.⁴ 
• Widely spaced teeth.³

Additional symptoms and variations in CST

There are also some less frequent but equally as important symptoms that patients with CST can experience. These include: 

Nail abnormalities: 

• In some rare cases, some patients present with abnormally developed nails²

Facial abnormalities: 

• Many patients are reported to have what is known as a ‘saddle nose’.’² This means that the top aspect of their nose appears abnormally flattened.
• A bulging forehead, known as ‘frontal bossing’² 
• Excessive wrinkling of the area around the eyes.⁴ 
• ‘Sunken’ appearance of cheeks⁴
• Thick, prominent, and full lips⁴

Skin changes: 

• Smooth, shiny skin with some wrinkles in areas of the body.⁴
• Scaling of the skin.²

Early signs of CST in children

The below symptoms are a list of those reported to have been observed in children with CST. Such signs include: 

• A higher number of chest infections, often pneumonia, due to reduced mucus production.⁴ Due to this, children may experience issues with feeding, which subsequently impacts their growth and development. 
• Recurrent fevers⁴
• Slowed or absent development of teeth⁵
• Slower-than-normal development of speech and language skills. This has been attributed to the abnormal development of teeth associated with CST⁵

How is christ siemens touraine syndrome (CST) diagnosed? 

The clinical diagnosis

Diagnosing CST is challenging due to its variable characteristics. Patients typically seek medical attention for issues like abnormal tooth development. Clinicians gather a detailed patient history through specific questions, akin to assembling puzzle pieces, to build a diagnostic picture. High suspicion of CST prompts inquiries about oral/dental history, overheating, and warm environment intolerance. Healthcare professionals then conduct an examination to identify CST features, forming the basis of a clinical diagnosis. When considering the characteristics and history of the patient, a diagnosis of CST is dependent on the presence of fevers and their frequency, sparse hair growth, absence of teeth, and abnormal tooth shapes.² 

With regards to children, those born with CST are often diagnosed within the first two years of life due to them suffering from recurrent fevers which require medical attention.⁵

Genetic testing and its basis for diagnosis 

If the clinical diagnosis is strongly suggestive of CST, genetic testing can be offered. This essentially allows us to analyze patients’ genetic data to detect if the defective genes involved in CST are present. The process of genetic testing involves the following: 

• A sample of DNA is first taken. This can be taken in the form of blood samples, saliva samples or swabs of the inner cheek. 
• The genetic mutations commonly associated with CST are those found in genes (units of DNA that determine certain characteristics) called the EDA, EDAR and EDARADD genes.⁴ Special laboratory techniques are used to read and analyze DNA to look for defects in these genes. 
• Once this analysis is complete, it is then compared to normal copies of these genes to detect any mutations (changes) in the genes.
• If CST-related mutations are detected, then the diagnosis of CST is confirmed. If not, then other tests are conducted to look for other causes of the patient’s problems.

How is christ siemens touraine syndrome (CST) managed and treated? 

As CST is irreversible, management is mostly aimed at managing symptoms in those affected by the disorder. The following symptomatic-focused approaches can be adopted: 

1. Strategies to address heat intolerance and overheating
   1. It is recommended that cooler environments be maintained to manage this issue.⁴ Most report good responses to measures such as wet clothes, air conditioning and wet bands to control their temperature.⁴ However, it has been noted that these issues with temperature control ease as the patient ages. This is due to some developing the ability to sweat during their teenage years.⁴
2. Dental and oral interventions
   1. It is highly recommended that children with CST receive early cosmetic intervention with the addition of artificial teeth as they age. This will not only assist with speech development but will also be psychologically beneficial to the child due to them being able to resemble their peers.²
   2. The use of artificial teeth also supports the sufficient growth of facial and oral features so that children may further resemble their peers.⁴
3. Hair and skin management
   1. Skin Management:
      1. Moisturisation of the skin is good practice in those with CST due to the dryness often experienced.
      2. Those with CST may be more sun-sensitive, so they should wear sunscreen to protect their skin.
      3. Patients should remain well hydrated due to their inability to sweat. 
      4. Avoid the use of harsh fragrances and irritating creams to avoid skin irritation.
   2. Hair Management:
      1. Frequent shampoo and conditioning with mild agents is recommended. Patients should use a soft comb or brush to avoid damaging fragile hair.
      2. Some patients may use wigs or supplements to improve their self-confidence in their appearance. 
      3. Patients should also make use of good scalp care to prevent issues with the scalp. 

The Importance of a multi-disciplinary approach

Multi-disciplinary refers to the involvement of more than one medical team in the treatment of a condition. As CST affects numerous structures in the body, a wide array of teams are involved in the care. This can include involvement from numerous dental teams focusing on artificial teeth, cosmetic approaches and tooth health and medical teams focusing on skincare and ear, nose and throat care. Critical to the management of CST is also the involvement of a psychologist and/or a speech therapist. Most commonly used in a patient's younger years, the use of a speech therapist is essential to developing their proper language development whilst ensuring greater confidence and self-esteem. The role of a psychologist is essential in enabling the patient to develop strategies to cope with the challenges of CST whilst working through the mental toll that the condition can have. 

Summary

Christ-Siemens-Touraine Syndrome (CST), or HED, is a genetic condition affecting the skin, teeth, sweat glands, and hair development. Common symptoms include reduced sweating, sparse hair, and abnormal teeth. Skin, nail, and facial issues may also occur. Children may experience recurrent fevers, feeding difficulties, and delayed growth and speech development. A clinical diagnosis is confirmed through DNA analysis. Treatment focuses on supportive care: cooling aids and hydration for sweat deficiencies, dental care for abnormal teeth, and appropriate skin care and hair care. Psychological support is crucial to addressing self-esteem and confidence issues, involving speech therapists and psychologists, especially in younger patients.