Dyskeratosis congenita (dkc) is a rare genetic disorder characterized by abnormal fingernails and skin pigmentation, the formation of white patches on the tongue and cheek, and progressive failure of the bone marrow. an autosomal dominant form of dkc results from mutations in the gene that encodes the rna component of telomerase. tom vulliamy and his colleagues examined 15 families with autosomal dominant dkc (t. vulliamy et al., 2004, nature genetics 36: 447–449). they observed that the median age of onset of dkc in parents was 37 years, whereas the median age of onset in the children of affected parents was 14.5 years. thus, dkc in these families arose at progressively younger ages in successive generations, a phenomenon known as anticipation. the researchers measured telomere length of members of these families; the measurements are given in the adjoining table. telomere length normally shortens with age, and so telomere length was adjusted for age. note that the age-adjusted telomere length of all members of these families is negative, indicating that their telomeres are shorter than normal. for age-adjusted telomere length, the more negative the number, the shorter the telomere. how does telomere length of the parents compare with telomere length of the children? explain wiry the telomeres of people with dkc are shorter than normal explain why dkc arises at an earlier ago in subsequent generations

Comparison of the lentgth of telomeres

In children, as well as the next generation of this family, the size of the telomeres will decrease proportionally to the succession of generations (due to the anticipation of the disease). Therefore telomere lengths at parents are greater than those of their children, hence the earlier onset of the disease.

Why telomeres are shorter than normal ?

Individuals with the disease have defective telomerase, and are therefore unable to synthesize telomeres. They will therefore have abnormally short telomeres and will be unable to restore a normal size of their telomeres due to insufficient telomerase activity; in this hypothesis, the shorter the telomere of the chromosomes inherited from the parent carrying the mutation, the sooner the symptoms of the disease will be declared.

Why DCK arises earlier ago in subsequent generations ?

With the succession of generations, the spermatozoa of the sick parents will not only transmit the mutation that will cause the congenital dyskeratosis, but in addition, their own telomeres are shortened. and since the cell is deficient in telomerase, the telomeres will shorten further, hence the decrease in the length of the telomeres and the evolution of the disease with the generations (anticipation).

the oxygenated blood then leaves the lungs through pulmonary veins, which return it to the left heart, completing the pulmonary cycle. this blood then enters the left atrium, which pumps it through the mitral valve into the left ventricle. from the left ventricle, the blood passes through the aortic valve to the aorta.

deoxygenated blood leaves through the right ventricle through the pulmonary artery. from the right atrium, the blood is pumped through the tricuspid valve (or right atrioventricular valve), into the right ventricle.