Dyskeratosis congenita

Every chromosome ends in a repeating stretch of DNA that works like the plastic tip on a shoelace. It is not a gene — it is a buffer, and a little of it is lost each time a cell divides. When it gets critically short, the cell stops dividing. That is a telomere.

An enzyme called telomerase rebuilds the buffer in the cells that need to keep dividing, including blood stem cells. Dyskeratosis congenita is what happens when telomerase, or the proteins that guard the telomere, do not work properly.

One fact explains most of the disease: the tissues that renew constantly run out of buffer first. Bone marrow, the lining of the lungs, the lining of the gut, skin. It reads as accelerated wear rather than as one broken system.

The name now sits inside a wider family called telomere biology disorders, and the classic three signs — ridged, thinning nails; lacy net-like pigmentation on the chest and neck; white patches inside the mouth that will not scrape off — are frequently absent. Many people never develop them, and may present in middle age with only one problem, such as lung scarring or an empty marrow.

What actually settles the diagnosis is telomere length, measured in white blood cells, rather than skin. Even that has limits in adults, where a result above the lowest percentile does not by itself clear someone.

It is caused by inherited faults in the genes that build, recruit or protect telomerase and the telomere. Around nineteen genes are known, and roughly 35% of cases still have no identified genetic cause — which is why telomere length testing matters alongside gene sequencing.

Three different inheritance patterns occur within the same disease family — X-linked, dominant and recessive — which is why family patterns can look inconsistent from the outside.

There is an unusual feature worth understanding, called anticipation: in some families the disorder appears earlier and more severely in each successive generation. The mechanism is that a child can inherit not just the faulty gene but the already-shortened telomeres — a shorter starting buffer, so the clock runs out sooner. It is reported rather than guaranteed, and mainly in dominant families.

This is a germline genetic condition. Nothing a parent did or failed to do causes it, and it cannot be passed between people.

The marrow stops producing enough blood cells. Roughly half of people develop some degree of marrow failure by age 40, and it can be the first sign at any age.

There is a raised risk of blood cancers — myelodysplastic neoplasms, which can progress to acute myeloid leukemia — with a median age at onset in the early thirties in the reported cohorts.

Solid tumours, chiefly squamous cell carcinoma of the head, neck and tongue, occur far more often than in the general population and at a much younger age, with a median around 38 across all cancers.

Then the part that a transplant does not reach. Pulmonary fibrosis — progressive scarring that stiffens the lungs and makes oxygen transfer harder — is reported in up to a fifth of people and may be commoner than appreciated. It is progressive, and it can be lethal independently of the marrow. Liver disease is increasingly recognised as a serious complication too.

There is no treatment that repairs the underlying telomere problem. What exists is supportive care, marrow-directed treatment, and — for organs that fail — replacement.

Surveillance runs for life: marrow monitoring, cancer checks especially of the mouth, lung function and liver function. Because data on radiation effects in this condition are limited, guidance is to minimise therapeutic radiation where possible.

Androgens such as oxymetholone or danazol push the marrow to produce more cells, and most people show some response. The costs are liver toxicity and masculinising changes, which are a particular problem for girls and women. People with this condition may be more sensitive to androgens than people with Fanconi anemia, so doses are adjusted downward — and combining androgens with G-CSF has been associated with rupture of the spleen and is avoided.

The best-known trial of danazol is smaller than its reputation suggests: 27 people enrolled with a mix of telomere diseases, stopped early, and only 12 evaluable for the main outcome. Its telomere-lengthening finding has since been contested by a study that found no difference in telomere loss between treated and untreated patients.

A transplant is the only curative treatment for severe marrow failure or leukemia. Note where that sentence stops — for the marrow failure or the leukemia, not for the disorder.

Conditioning has to be reduced here, and for a different reason than in Fanconi anemia: the mucosa, blood vessels, lungs and liver are already fragile, and chemotherapy makes that worse. One published radiation-free reduced-intensity regimen in seven children saw all of them engraft.

The route to a diagnosis is often long and indirect, because the classic signs are so often absent. Some people are diagnosed in infancy with a severe form. Others reach it in their thirties or later, after an unexplained marrow failure, or lung scarring, or a mouth cancer that looks wrong for their age and history.

Once made, the diagnosis reaches through a family. Relatives are tested — and the results can be unwelcome in a specific way, because someone can be found to have the condition while feeling entirely well.

For those with marrow failure, the treatment decisions are hard and made against a background of organs that are already fragile. Androgens buy time at a real cost. A transplant is a major undertaking in a body less able to absorb it.

And the part that is hardest to sit with: successfully treating the blood does not stop the lungs. Someone can come through a transplant well and still be watching lung function tests for years afterward. Surveillance for the mouth, the liver and the lungs continues regardless.

A donation can replace a failing blood system — the marrow failure, the MDS, the leukemia. It does not treat the lungs, the liver, the eyes or the gut. The reduced-intensity conditioning study says so in as many words: a transplant does not alter the other features of the disease, including pulmonary fibrosis and liver scarring.

That is the honest boundary, and it is the reason we will not describe a donor as a cure for this condition.

The family constraint here is as strict as in Fanconi anemia and for a related reason. A brother or sister can be a perfect tissue match, feel completely well, and still be unsuitable — because they carry the same telomere problem and it has not shown itself yet. Related donors must be proven unaffected by genetic or telomere length testing before being used.

What goes wrong when an affected relative is used is documented: graft failure, accelerated telomere shortening, and graft-versus-host disease.

So tissue typing alone is not enough in a family with a telomere biology disorder. Some people end up needing an unrelated donor from a registry even though they have siblings who match — and that is a specific, unglamorous reason for the registry to be deep.