About Dyskeratosis Congenita (DKC)

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Zinsser Cole Engman Syndrome & Dyskeratosis Congenita (DKC)

Dyskeratosis congenita (DKC), also called Zinsser-Cole-Engman syndrome, 570 is a rare progressive congenital disorder with a highly variable phenotype. The entity was classically defined by the triad of abnormal skin pigmentation, nail dystrophy, and leukoplakia of the oral mucosa, but these components do not always occur.

DKC is characterized by short telomeres. Some of the manifestations resemble premature aging (similar to progeria). The disease initially mainly affects the skin, but a major consequence is progressive bone marrow failure which occurs in over 80%, causing early mortality.

Zinsser-Cole-Engmann syndrome also called Dyskeratosis Congenita (DKC) is a rare genodermatosis first described by Zinsser in 1906. Mutations in DKC1 gene is responsible for DKC. It is usually inherited as an X-linked recessive trait, resulting in a striking male predilection. It is characterized by a triad of reticular skin pigmentation, nail dystrophy and mucosal leukoplakia.

Complications include predisposition to malignancy and bone marrow failure. Here, we report a case of DKC in a 9-year-old boy with classic triad of signs. Special investigations like endoscopy, barium swallow and bone-marrow aspiration study confirmed the diagnosis. There is no effective treatment for DKC. Some preventive measures can be adopted and the only long term cure for the haematological abnormalities is allogenic haemopoietic stem cell transplantation.

A 24-year-old Japanese man presented with dyskeratosis congenita (DC, Zinsser-Cole-Engman syndrome) complicated by non-cirrhotic portal hypertension, signet ring carcinoma of the rectum and Pneumocystis carinii pneumonia. At the age of 9 years, he was diagnosed as having DC on the basis of typical clinical manifestations including atrophic lingual papillae, hyperpigmentation of the skin, thrombocytopenia, and ophthalmological abnormalities.

A few years later pancytopenia and splenomegaly developed. At 24 years, signet ring carcinoma of the rectum was detected but could not be resected because of the severity of the pancytopenia. Death was due to respiratory failure from P. carinii pneumonia.

At autopsy the case illustrated several unique findings for DC, including non-cirrhotic portal hypertension, atrophy of frontal lobe and markedly slender folia of the cerebellum and superimposed infections with herpes zoster virus and P. carinii. Striking lymphocyte depletion and atrophy of lymphoid parenchyma in lymph nodes, tonsils, spleen, gastrointestinal tract, or thymus were seen histologically.

The morphological picture supports the suggestion that there is a defect in the cell-mediated immune system in patients with DC, although immunoglobulin levels in the blood are normal. The cell-immune deficiency is a major factor in the poor prognosis.

It is possible that the main title of the report Dyskeratosis Congenita is not the name you expected. Please check the synonyms listing to find the alternate name(s) and disorder subdivision(s) covered by this report.

Discussion

Zinsser-Cole-Engman syndrome commonly called as Dyskeratosis Congenita (DKC) is a rare hereditary disease, which was first described by Zinsser in 1906. Later Engman (1926) and Cole et al., (1930) reported other cases in detail and hence it is known as Zinsser-Cole-Engman syndrome. It is a rare genodermatosis that is usually inherited as an X-linked recessive trait, resulting in a striking male predilection.

Its onset is reported in individuals ranging from 5 to 50 years of age. Prevalence is estimated to be one in one million. Mutations in DKC 1 gene at Xq28 has been determined to cause the X-linked form of DKC. The mutated gene appears to disrupt the normal maintenance of telomerase, an enzyme that is critical in determining normal cellular longevity. It is characterized by a triad of nail dystrophy, reticulated hyper pigmentation of skin and mucosal leukoplakia. The syndrome often proves fatal due to progressive bone marrow failure or malignant change within areas of mucosal leukoplakia.

In general, the abnormalities are not neonatal in manifestation, but develop progressively at a variable rate. The primary defect has not been identified and none of the proposed theories is able to account for all of observed features. The basic defect in DKC may be at the level of cell division.

The abnormality in one of the enzymatic steps essential to normal cell division, for example DNA polymerase II whose activity correlates positively with the rate of tissue regeneration, can lead to hypo-proliferation or impaired regeneration of the skin, nails, bone marrow, and neurons in DKC . Study of the haematological involvements showed the bone marrow failure to result from a defect of stem cells rather than suppression by any circulating factor.

Clinical manifestations of DKC often appear during childhood. Pedodontists should be aware of this disorder for many reasons: orofacial symptoms may be the first signs of the disorder and clinicians will have the opportunity to make the diagnosis. The patient should be referred for genetic counselling, as other family members may be affected.

Dyskeratosis congenita is a rare genetic form of bone marrow failure, the inability of the marrow to produce sufficient blood cells. Dyskeratosis is Latin and means the irreversible degeneration of skin tissue, and congenita means inborn. First described in the medical literature in 1906, dyskeratosis congenita was originally thought to be a skin disease that also affects the nails and the mouth.

Only later in the sixties was it realized that patients with these skin changes almost always develop bone marrow failure. Thus, for the last 40 years or so, the bone marrow failure syndrome dyskeratosis congenita was diagnosed when patients presented with the triad of abnormal skin, malformation (dystrophy) of the nails, and white, thickened patches on the mucous membranes of the mouth (oral leukoplakia).

The skin changes may be present before the development of bone marrow failure. Bone marrow failure is usually diagnosed by the low number of circulating blood cells including red blood cells, white blood cells, and platelets.  Additional findings in patients with dyskeratosis congenita may include short stature, eye and tooth abnormalities, thin and early graying of the hair, lung (pulmonary) disease, liver disease, gut abnormalities, bone thinning (osteoporosis), infertility, learning difficulties, and delays in reaching developmental milestones. An increased incidence of leukemia and cancer has also been documented.

Today, in addition to examining the skin, nails, and mouth for these classical changes, we also use other tests to diagnose dyskeratosis congenita including testing for the genetic abnormality responsible for the development of the disease. Using these more sensitive tests, we are beginning to realize, that only a minority of patients with the genetic abnormality actually develop the full clinical picture of dyskeratosis congenita as outlined above.

We find that there are many more individuals with the genetic abnormality (mutation) who have only a mild form of the disease. Often these individuals may only show one or two of the clinical features and these only become obvious, late in life. Some never develop the classic skin abnormalities that coined the name of the disease. Whether the disease in these patients in the absence of skin manifestations should also be labeled with dyskeratosis congenita is controversial and often these individuals are referred to as having atypical dyskeratosis congenita.

There are even individuals carrying the mutation who will never develop disease, however their children or grandchildren might. These individuals are often referred to as silent mutation carriers. This new knowledge is important for physicians and patients because much of what has previously been published about this disease may actually not apply anymore for all individuals newly diagnosed with dyskeratosis congenita.

In addition to the many more mild manifestations of this disease we also realize that there are some rare but very severe forms of dyskeratosis congenita. These were previously known as the Hoyeraal-Hreidarsson syndrome and the Revesz syndrome but today we know that they have the same underlying abnormality and are caused at least in part by mutations in the same genes responsible for dyskeratosis congenita. These severe forms manifest early in life and are associated with additional clinical features that are usually not present in other forms of dyskeratosis congenita (see also below).

In the majority of cases dyskeratosis congenita is inherited. The pattern of inheritance may be X-linked (Zinsser-Cole-Engleman syndrome), autosomal dominant (dyskeratosis congenita, Scoggins type) or autosomal recessive. However, in a large proportion of patients dyskeratosis congenita occurs sporadically, meaning that the parents do not show disease. In some patients with sporadic DC the genetic abnormality may have newly arisen (de novo mutation) and therefore is not present in either parent.

Synonyms

  • DKC
  • DC
  • dysfunctional telomere maintenance
  • dyskeratosis congenita syndrome
  • short telomere disease

Diagnosis

The clinical findings were suggestive of Dyskeratosis Congenita (DKC) should be differentiated from other conditions that cause skin pigmentation such as Fanconi’s anemia and Graft versus host disease. However, in Fanconis anemia, pigmentation of skin is more uniform and other than bone marrow failure, eye, renal and limb anomalies will also be present.

In graft versus host disease similar skin pigmentation and nail features may be occasionally seen but these changes manifest after the transplantation of bone marrow. Skin lesions in Bloom’s, Kindler’s and Rothmund-Thomson syndromes may be similar to that seen in DKC, but are more sun sensitive and also differ in associated features.

Characteristics

DKC can be characterized by cutaneous pigmentation, premature graying, dystrophy of the nails, leukoplakia of the oral mucosa, continuous lacrimation due to atresia of the lacrimal ducts, often thrombocytopenia, anemia, testicular atrophy in the male carriers, and predisposition to cancer. Many of these symptoms are characteristic of geriatrics, and those carrying the more serious forms of the disease often have significantly shortened lifespans.

Clinical features

Age:

The mucocutaneous features of DKC typically develop between ages 5 and 15 years. The median age of onset of the peripheral cytopenia is 10 years.

Sex:

The male-to-female ratio is approximately 3:1.

Physical:

The triad of reticulated hyperpigmentation of the skin, nail dystrophy, and leukoplakia characterizes DKC. The syndrome is clinically heterogeneous; in addition to the diagnostic mucocutaneous features and bone marrow failure, affected individuals can have a variety of other clinical features.

Cutaneous findings:

The primary finding is abnormal skin pigmentation, with tan-to-gray hyperpigmented or hypopigmented macules and patches in a mottled or reticulated pattern. Reticulated pigmentation occurs in approximately 90% of patients. Poikilodermatous changes with atrophy and telangiectasia are common.

The cutaneous presentation may clinically and histologically resemble graft versus host disease. The typical distribution involves the sun-exposed areas, including the upper trunk, neck, and face. Other cutaneous findings may include alopecia of the scalp, eyebrows, and eyelashes; premature graying of the hair; hyperhidrosis; hyperkeratosis of the palms and soles; and adermatoglyphia (loss of dermal ridges on fingers and toes).

Nail findings:

Nail dystrophy is seen in approximately 90% of patients, with fingernail involvement often preceding toenail involvement. Progressive nail dystrophy begins with ridging and longitudinal splitting. Progressive atrophy, thinning, pterygium, and distortion eventuate in small, rudimentary, or absent nails.

Mucosal findings:

Mucosal leukoplakia occurs in approximately 80% of patients and typically involves the buccal mucosa, tongue, and oropharynx. The leukoplakia may become verrucous, and ulceration may occur. Patients also may have an increased prevalence and severity of periodontal disease.

Other mucosal sites may be involved (e.g., esophagus, urethral meatus, glans penis, lacrimal duct, conjunctiva, vagina, anus). Constriction and stenosis can occur at these sites, with subsequent development of dysphagia, dysuria, phimosis, and epiphora.

Bone marrow failure:

Approximately 90% have peripheral cytopenia of one or more lineages. In some cases, this is the initial presentation, with a median age of onset of 10 years. Bone marrow failure is a major cause of death, with approximately 70% of deaths related to bleeding and opportunistic infections as a result of bone marrow failure.

Pulmonary complications:

Approximately 20% of individuals with DKC develop pulmonary complications, including pulmonary fibrosis and abnormalities of pulmonary vasculature. The recommendation is that DKC patients avoid taking drugs with pulmonary toxicity (e.g., busulfan) and that they have their lungs shielded from radiation during bone marrow transplant(BMT).

Increased risk of malignancy:

Patients have an increased prevalence of malignant mucosal neoplasms, particularly squamous cell carcinoma of the mouth, nasopharynx, esophagus, rectum, vagina, or cervix. These often occur within sites of leukoplakia. The prevalence of squamous cell carcinoma of the skin is also increased. Other malignancies reported include Hodgkin lymphoma, adenocarcinoma of the gastrointestinal tract, and bronchial and laryngeal carcinoma. Malignancy tends to develop in the third decade of life.

Neurologic system findings:

Patients may have learning difficulties and mental retardation.

Ophthalmic system findings:

DKC reportedly is associated with conjunctivitis, blepharitides, and pterygium. Lacrimal duct stenosis resulting in epiphora (i.e., excessive tearing) occurs in approximately 80% of patients.

Skeletal system findings:

Patients may have mandibular hypoplasia, osteoporosis, avascular necrosis, and scoliosis.

Gastrointestinal system findings:

These may include esophageal webs, hepatosplenomegaly, enteropathy, and cirrhosis.

Genitourinary system findings:

Hypospastic testes, hypospadias, and ureteral stenosis are reported.

Female carriers:

Female carriers of DKC may have subtle clinical features. One study showed that 3 of 20 female carriers had clinical features that included a single dystrophic nail, a patch of hypopigmentation, or mild leukoplakia.

Clinical Characteristics

Ocular Features: 

The conjunctiva and eyelids are prominently involved as part of the generalized mucocutaneous disease.  Keratinization of the lid margins, absent lacrimal puncta, trichiasis, cicatrizing conjunctivitis, entropion, ectropion, blepharitis, sparse eyelashes, and symblephara are important features.  The cornea is also involved with keratinization of the epithelial surface and vascularization.  The nasolacrimal duct is sometimes blocked.  At least one patient has been reported to have an exudative retinopathy.

Systemic Features: 

Dyskeratosis congenita consists of a heterogeneous (genetic and clinical) group of inherited bone marrow failure and premature aging syndromes with the common feature of shortened telomeres.  There is considerable variability in the clinical features.  Prominent manifestations include nail dysplasia, oral leukoplakia, abnormal dentition, and reticulated skin pigmentation. Some patients have cognitive impairments.  Liver failure, testicular atrophy, pulmonary fibrosis, aplastic anemia, and osteoporosis along with features of aging such as premature grey hair and loss are typical.  There is an increased risk of malignancies, especially acute myelogenous leukemia.  Bone marrow failure is the major cause of early death.

Conclusion

Dyskeratosis Congenita (DKC) is a severe multisystem disorder associated with premature mortality usually due to Bone Marrow (BM) failure/immuno-deficiency. Dentist should be able to recognize this fatal condition in its early stages and advice appropriate haematologic investigations. Dentists may be the first to see and diagnose DKC and have an important role in monitoring the oral malignant changes in the mucosa.

Genetics

Of the components of the telomerase RNA component (TERC), one of key importance is the box H/ACA domain. This H/ACA domain is responsible for maturation and stability of TERC and therefore of telomerase as a whole. The mammalian H/ACA ribonucleoprotein contains four protein subunits: dyskerin, Gar1, Nop10, and Nhp2. Mutations in Nop10, Nhp2  and dyskerin have all been shown to lead to DKC-like symptoms.

X-linked

The best characterized form of dyskeratosis congenita is a result of one or more mutations in the long arm of the X chromosome in the gene DKC1. This results in the X-linked recessive form of the disease wherein the major protein affected is dyskerin. Of the five mutations described by Heiss and colleagues in Nature Genetics, four were single nucleotide polymorphisms all resulting in the change of highly conserved amino acids.

One case was an in-frame deletion resulting in the loss of a leucine residue, also conserved in mammals. In three of the cases, the specific amino acids affected (phenylalanine, proline, glycine) are found in the same locus in humans as they are in yeast (S. Cerevisiae) and the brown rat (R. Norvegicus).

This establishes the sequence conservation and importance of dyskerin within the eukaryotes. The relevant nature of dyskerin throughout most species is to catalyze the post-transcriptional pseudouridylation of specific uridines found in non-coding RNAs, such as ribosomal RNA (rRNA). Cbf5, the yeast analog of human dyskerin, is indeed known to be associated with the processing and maturation of rRNA.

In humans this role can be attributed to dyskerin. Thus, the X-linked form of this disease may result in specific issues related to dysfunctional rRNA and perhaps a graver phenotype. Within the vertebrates, as opposed to single celled eukaryotes, dyskerin is a key component of the telomerase RNA component (TERC) in the form of the H/ACA motif. This X-linked variety, like the Nop10 and Nhp2 mutations, demonstrates shortened telomeres as a result of lower TERC concentrations.

Autosomal dominant

3 genes: TERC, TERT, TINF2 The evidence supporting the importance of the H/ACA domain in human telomerase is abundant. At least one study has shown that these mutations affect telomerase activity by negatively affecting pre-RNP assembly and maturation of human telomerase RNA.

Nonetheless, mutations which directly affect the telomerase RNA components would presumably exist and should also cause premature aging or DKC-like symptoms. Indeed, three families with mutations in the human TERC gene have been studied with intriguing results.

 In two of these families, two family-specific single nucleotide polymorphisms were present while in the other there persisted a large-scale deletion (821 base pairs of DNA) on chromosome 3 which includes 74 bases coding for a section of the H/ACA domain.

These three different mutations result in a mild form of dyskeratosis congenita which uniquely follows an autosomal dominant pattern of inheritance. Premature graying, early dental loss, predisposition to skin cancer, as well as shortening of telomere length continue to be characteristic of this disease.

Autosomal Recessive

6 genes: The true phenotype of DKC individuals may depend upon which protein has incurred a mutation. One documented autosomal recessive mutation in a family that carries DKC has been found in Nop10. Specifically, the mutation is a change of base from cytosine to thymine in a highly conserved region of the Nop10 sequence. This mutation, on chromosome 15, results in an amino acid change from arginine to tryptophan.

Homozygous recessive individuals show the symptoms of dyskeratosis congenita in full. As compared to age-matched normal individuals, those suffering from DKC have telomeres of a much shorter length. Furthermore, heterozygotes, those who have one normal allele and one coding for the disease, also show relatively shortened telomeres. The cause of this was determined to be a reduction in TERC levels in those with the Nop10 mutation. With TERC levels down, telomere maintenance, especially in development, would be presumed to suffer accordingly. This would lead to the telomere shortening described.

Nhp2 mutations are similar in characterization to Nop10. These mutations are also autosomal recessive with three specific single-nucleotide polymorphisms being recognized which result in dyskeratosis congenita. Also like Nop10, individuals with these Nhp2 mutations have a reduction in the amount of telomerase RNA component (TERC) present in the cell. Again it can be presumed that a reduction in TERC results in aberrant telomere maintenance and thus shortened telomeres. Those homozygous recessive for mutations in Nhp2 do show shorter telomeres when compared with age-matched normal individuals.

Predisposition to Cancer

Susceptibility to cancer seems counterintuitive because in many known cancers reactivation of telomerase is actually a required step for malignancy to evolve (see telomere). In a disease where telomerase is affected, it does not seem to follow that cancer would be a complication to result.

The authors note the paradoxical nature of cancer predisposition in individuals who seem to lack one of the required components for cancer to form. It is thought that without functional telomerase, chromosomes will likely be attached together at their ends through the non-homologous end joining pathway. If this proves to be a common enough occurrence, malignancy even without telomerase present is possible.

Summary

A 24-year-old Japanese man presented with dyskeratosis congenita (DC, Zinsser-Cole-Engman syndrome) complicated by non-cirrhotic portal hypertension, signet ring carcinoma of the rectum andPneumocystis carinii pneumonia. At the age of 9 years, he was diagnosed as having DC on the basis of typical clinical manifestations including atrophic lingual papillae, hyperpigmentation of the skin, thrombocytopenia, and ophthalmological abnormalities.

A few years later pancytopenia and splenomegaly developed. At 24 years, signet ring carcinoma of the rectum was detected but could not be resected because of the severity of the pancytopenia. Death was due to respiratory failure fromP. carinii pneumonia.

At autopsy the case illustrated several unique findings for DC, including non-cirrhotic portal hypertension, atrophy of frontal lobe and markedly slender folia of the cerebellum and superimposed infections with herpes zoster virus andP. carinii.

Striking lymphocyte depletion and atrophy of lymphoid parenchyma in lymph nodes, tonsils, spleen, gastrointestinal tract, or thymus were seen histologically. The morphological picture supports the suggestion that there is a defect in the cell-mediated immune system in patients with DC, although immunoglobulin levels in the blood are normal. The cell-immune deficiency is a major factor in the poor prognosis.

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