Stage IV is a large tumor involving intracranial or infratemporal regions, an extensive neck disease, and/or any distant metastasis. Risk factors
Nasopharyngeal carcinoma, classified as a squamous cell cancer, has not been linked to excessive use of tobacco. However, there are certain risk factors that can predispose an individual to NPC if exposed to them. These risk factors include: having Chinese, or Asian, ancestry, exposure to Epstein- Barr virus (EBV), unknown factors that result in rare familial clusters, and heavy alcohol consumption. EBV
Epstein- Barr virus infects and persists in more than 90% of world population. Transmission of this virus occurs through saliva and is more commonly seen in developing countries where there are living areas are more packed together and less hygienic. Replication of this virus can occur in the oropharyngeal epithelial tissue and nasopharyngeal tissue. EBV primarily targets B lymphocytes. Patients diagnosed with NPC were found to show elevated levels of the antibodies against the EBV antigen than in individuals not diagnosed with NPC. Smoking
Individuals that are exposed to cigarette smoking have an increased risk of developing NPC by 2- to 6-fold. Approximately two-thirds of patients with type 1 NPC was attributed to smoking in the United States. However the declining rates of smoking in the US can be associated with less prevalence of type 1 NPC. In southern China and North Africa, it has been suggested that high smoking rates come from wood fires in the country rather than cigarette smoking. Treatment
NPC can be treated by surgery, by chemotherapy, or by radiotherapy.
Dihydropteridine reductase deficiency (DHPRD) is a genetic disorder affecting the tetrahydrobiopterin (BH4) synthesis pathway, inherited in the autosomal recessive pattern. It is one of the six known disorders causing tetrahydrobiopterin deficiency, and occurs in patients with mutations of the QDPR gene. The disease presents with such symptoms as elevated levels of phenylalanine (hyperphenylalaninemia), microcephaly, hypotonus, mental retardation and epileptic seizures. Diagnostics
Besides the traditional analysis of symptoms and investigation of phenylalanine concentrations, patients suspected for DHPRD undergo the assessment of enzymatic activity using the dried blood spot method - this permits to distinguish DHPR deficiency from the other forms of BH4 deficiency. Treatment
Patients are prescribed a phenylalanine-reduced diet, with regular monitoring of phenylalanine levels in the blood. Besides the diet, a patient may be prescribed sapropterin, a synthetic analogue of tetrahydrobiopterin. In order to restore dopamine levels in the central nervous system, patients are given L-dopa in conjunction with an inhibitor of aromatic amino acid decarboxylase that acts outside the nervous system, so as to promote the transformation of L-dopa into dopamine inside the central nervous system, and thus to improve the efficiency of the treatment. Since the insufficient levels of BH4 inhibit the transformation of tryptophan into 5-hydroxytryptophan in a reaction in which BH4 serves as a cofactor of the enzyme tryptophane hydroxylase 2, patients suffer from a lack of serotonin in their CNS. In order to correct this deficiency, they are given 5-hydroxytryptophan. In patients with DHPR deficiency, a pronounced lack of 5-methyltetrahydrofolate (5-MTHF) is observed in the central nervous system.