Dyskeratosis congenita

What it is, symptoms and effects

From: MedlinePlus Genetics, National Library of Medicine

Dyskeratosis congenita is a disorder that can affect many parts of the body. There are three features that are characteristic of this disorder: fingernails and toenails that grow poorly or are abnormally shaped (nail dystrophy); changes in skin coloring (pigmentation), especially on the neck and chest, in a pattern often described as "lacy"; and white patches inside the mouth (oral leukoplakia).

People with dyskeratosis congenita have an increased risk of developing several life-threatening conditions. They are especially vulnerable to disorders that impair bone marrow function. These disorders disrupt the ability of the bone marrow to produce new blood cells. Affected individuals may develop aplastic anemia, also known as bone marrow failure, which occurs when the bone marrow does not produce enough new blood cells. They are also at higher than average risk for myelodysplastic syndrome, a condition in which immature blood cells fail to develop normally; this condition may progress to a form of blood cancer called leukemia. People with dyskeratosis congenita are also at increased risk of developing leukemia even if they never develop myelodysplastic syndrome. In addition, they have a higher than average risk of developing other cancers, especially cancers of the head, neck, anus, or genitals.

People with dyskeratosis congenita may also develop pulmonary fibrosis, a condition that causes scar tissue (fibrosis) to build up in the lungs, decreasing the transport of oxygen into the bloodstream. Additional signs and symptoms that occur in some people with dyskeratosis congenita include eye abnormalities such as narrow tear ducts that may become blocked, preventing drainage of tears and leading to eyelid irritation; dental problems; hair loss or prematurely grey hair; low bone mineral density (osteoporosis); degeneration (avascular necrosis) of the hip and shoulder joints; or liver disease. Some affected males may have narrowing (stenosis) of the urethra, which is the tube that carries urine out of the body from the bladder. Urethral stenosis may lead to difficult or painful urination and urinary tract infections.

The severity of dyskeratosis congenita varies widely among affected individuals. The least severely affected individuals have only a few mild physical features of the disorder and normal bone marrow function. More severely affected individuals have many of the characteristic physical features and experience bone marrow failure, cancer, or pulmonary fibrosis by early adulthood.

While most people with dyskeratosis congenita have normal intelligence and development of motor skills such as standing and walking, developmental delay may occur in some severely affected individuals. In one severe form of the disorder called Hoyeraal Hreidaarsson syndrome, affected individuals have an unusually small and underdeveloped cerebellum, which is the part of the brain that coordinates movement. Another severe variant called Revesz syndrome involves abnormalities in the light-sensitive tissue at the back of the eye (retina) in addition to the other symptoms of dyskeratosis congenita.

Causes and biological mechanisms

From: MedlinePlus Genetics, National Library of Medicine

In about half of people with dyskeratosis congenita, the disorder is caused by mutations in the TERT, TERC, DKC1, or TINF2 gene. These genes provide instructions for making proteins that help maintain structures known as telomeres, which are found at the ends of chromosomes. In a small number of individuals with dyskeratosis congenita, mutations in other genes involved with telomere maintenance have been identified. Other affected individuals have no mutations in any of the genes currently associated with dyskeratosis congenita. In these cases, the cause of the disorder is unknown, but other unidentified genes related to telomere maintenance are likely involved.

Telomeres help protect chromosomes from abnormally sticking together or breaking down (degrading). In most cells, telomeres become progressively shorter as the cell divides. After a certain number of cell divisions, the telomeres become so short that they trigger the cell to stop dividing or to self-destruct (undergo apoptosis).

Telomeres are maintained by two important protein complexes called telomerase and shelterin. Telomerase helps maintain normal telomere length by adding small repeated segments of DNA to the ends of chromosomes each time the cell divides. The main components of telomerase, called hTR and hTERT, are produced from the TERC and TERT genes, respectively. The hTR component is an RNA molecule, a chemical cousin of DNA. It provides a template for creating the repeated sequence of DNA that telomerase adds to the ends of chromosomes. The function of the hTERT component is to add the new DNA segment to chromosome ends. The DKC1 gene provides instructions for making another protein that is important in telomerase function. This protein, called dyskerin, attaches (binds) to hTR and helps stabilize the telomerase complex.

The shelterin complex helps protect telomeres from the cell's DNA repair process. Without the protection of shelterin, the repair mechanism would sense the chromosome ends as abnormal breaks in the DNA sequence and either attempt to join the ends together or initiate apoptosis. The TINF2 gene provides instructions for making a protein that is part of the shelterin complex.

TERT, TERC, DKC1, or TINF2 gene mutations result in dysfunction of the telomerase or shelterin complexes, leading to impaired maintenance of telomeres and reduced telomere length. Cells that divide rapidly are especially vulnerable to the effects of shortened telomeres. As a result, people with dyskeratosis congenita may experience a variety of problems affecting quickly dividing cells in the body such as cells of the nail beds, hair follicles, skin, lining of the mouth (oral mucosa), and bone marrow.

Breakage and instability of chromosomes resulting from inadequate telomere maintenance may lead to genetic changes that allow cells to divide in an uncontrolled way, resulting in the development of cancer in people with dyskeratosis congenita.

Inheritance and family implications

From: MedlinePlus Genetics, National Library of Medicine

Dyskeratosis congenita can have different inheritance patterns.

When dyskeratosis congenita is caused by DKC1 gene mutations, it is inherited in an X-linked recessive pattern. The DKC1 gene is located on the X chromosome, which is one of the two sex chromosomes. In males (who have only one X chromosome), one altered copy of the gene in each cell is sufficient to cause the condition. In females (who have two X chromosomes), a mutation would have to occur in both copies of the gene to cause the disorder. Because it is unlikely that females will have two altered copies of this gene, males are affected by X-linked recessive disorders much more frequently than females. A characteristic of X-linked inheritance is that fathers cannot pass X-linked traits to their sons.

When dyskeratosis congenita is caused by mutations in other genes, it can be inherited in an autosomal dominant or autosomal recessive pattern. Autosomal dominant means one copy of the altered gene in each cell is sufficient to cause the disorder. Autosomal recessive means both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition.

How common is it?

From: MedlinePlus Genetics, National Library of Medicine

The exact prevalence of dyskeratosis congenita is unknown. It is estimated to occur in approximately 1 in 1 million people.

Reported clinical features and what the terms mean

The following findings are associated with this condition in Orphanet. They are not a checklist for diagnosing yourself, and they do not all occur in every affected person. Some are examination, imaging or laboratory findings that cannot be recognised at home.

The frequency labels describe how often a finding was reported among people with the condition in the source. They do not give the chance that a person with that symptom has the condition. Definitions below reproduce HPO terminology; they explain the term, not the likely severity in an individual.

Abnormal blistering of the skin · Very frequent (99-80%)

The presence of one or more bullae on the skin, defined as fluid-filled blisters more than 5 mm in diameter with thin walls.

Abnormal fingernail morphology · Very frequent (99-80%)

An abnormality of the fingernails.

Abnormality of neutrophils · Very frequent (99-80%)

A neutrophil abnormality.

Anemia · Very frequent (99-80%)

A reduction in erythrocytes volume or hemoglobin concentration.

Hypermelanotic macule · Very frequent (99-80%)

A hyperpigmented circumscribed area of change in normal skin color without elevation or depression of any size.

Macule · Very frequent (99-80%)

A flat, distinct, discolored area of skin less than 1 cm wide that does not involve any change in the thickness or texture of the skin.

Nail dystrophy · Very frequent (99-80%)

Onychodystrophy (nail dystrophy) refers to nail changes apart from changes of the color (nail dyschromia) and involves partial or complete disruption of the various keratinous layers of the nail plate.

Oral leukoplakia · Very frequent (99-80%)

A thickened white patch on the oral mucosa that cannot be rubbed off.

Other findings in the same source

From: Orphanet

Additional reported features include Thrombocytopenia (Very frequent (99-80%)); Abnormal morphology of female internal genitalia (Frequent (79-30%)); Abnormality of coagulation (Frequent (79-30%)); Abnormality of the dentition (Frequent (79-30%)); Abnormality of the pharynx (Frequent (79-30%)); Anorectal anomaly (Frequent (79-30%)); Aplastic/hypoplastic toenail (Frequent (79-30%)); Bone marrow hypocellularity (Frequent (79-30%)); Carious teeth (Frequent (79-30%)); Cellular immunodeficiency (Frequent (79-30%)). This is a selected summary, not a complete description of the condition.

Which doctor should you see?

The suggested department for discussing Dyskeratosis congenita is Haematology, with a haematologist as the relevant type of clinician. General physician / Family Medicine; paediatrician for children. Referral depends on symptoms.

Additional services that may be relevant, depending on the findings, include: Clinical Genetics.

This is an editorial referral starting point. The appropriate clinic depends on the person’s age, symptoms, previous diagnosis and local services. The first clinician can decide whether another specialty or a team is needed; a department label does not confirm the diagnosis.

How to prepare for an assessment

Bring a short timeline of the main symptoms: when they first appeared, whether they are constant or episodic, what seems to change them, and how they affect daily activities. Include previous reports, discharge summaries, current medicines and supplements, allergies, and any relevant family history. A dated record is more useful than trying to match every feature in an online article.

Ask the clinician what is already established and what remains uncertain. If a test is suggested, ask what question it answers, what its limitations are and how the result would change the next step. The information here is not an instruction to arrange every possible test. In children, bring growth, developmental and school information if it is relevant to the concern.

• Which blood-cell, marrow, bleeding or clotting finding matters most?
• Does the diagnosis need confirmation or a more precise subtype?
• Which symptoms or laboratory changes should trigger earlier review?

Treatment discussions and follow-up

The material gathered for this draft does not provide a complete condition-specific treatment pathway for Dyskeratosis congenita. That gap does not mean that treatment is unavailable. A clinician needs to establish the diagnosis and review current guidance before recommending medicines, procedures, rehabilitation or other support.

Before leaving the appointment, clarify the next review date, who will communicate results, and whom to contact if the situation changes. Discuss difficulties with sleep, work, school, mobility, eating or emotional wellbeing when these are relevant. Practical support may require coordination between the treating clinician and other services.

When to seek emergency help

Severe breathing difficulty, collapse, new stroke-like symptoms, a seizure that is prolonged or repeated without recovery, uncontrolled major bleeding, or an immediate risk of self-harm require emergency help. In India, call 112 or reach the nearest emergency department. This is a general, non-exhaustive warning list; it is not a condition-specific triage tool.