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.
Drug interactions
Drug interactions are extensive, and are as follows:
Azathioprine and 6-mercaptopurine: Azathioprine is metabolised to 6-mercaptopurine which in turn is inactivated by the action of xanthine oxidase - the target of allopurinol. Giving allopurinol with either of these drugs at their normal dose will lead to overdose of either drug;  only one-quarter of the usual dose of 6-mercaptopurine or azathioprine should be given;
Didanosine: plasma didanosine Cmax and AUC values were approximately doubled with concomitant allopurinol treatment; it should not be co-administered with allopurinol and if it must be, the dose of should be reduced and the person should be closely monitored.Allopurinol may also increase the activity or half-life of the following drugs, in order of seriousness and certainty of the interaction:
Ciclosporin
Coumarin anticoagulants, such as warfarin (reported rarely, but is serious when it occurs)
Vidarabine
Chlorpropamide
Phenytoin
Theophylline
Cyclophosphamide, doxorubicin, bleomycin, procarbazine, mechlorethamineCo-administration of the following drugs may make allopurinol less active or decrease its half-life:
Salicylates and medicines that increase the secretion of uric acid
furosemide (see more on diuretics below)Co-administration of the following drugs may cause hypersensitivity or skin rash:
Ampicillin and amoxicillin
Diuretics, in particular thiazides, especially in renal impairment
Angiotensin-converting-enzyme inhibitors (ACE inhibitors)

Pharmacology
A common misconception is that allopurinol is metabolized by its target, xanthine oxidase, but this action is principally carried out by aldehyde oxidase. The active metabolite of allopurinol is oxipurinol, which is also an inhibitor of xanthine oxidase. Allopurinol is almost completely metabolized to oxipurinol within two hours of oral administration, whereas oxipurinol is slowly excreted by the kidneys over 18–30 hours.