A Therapeutic Fast for Lymphoma Resulting in Wernicke Encephalopathy.

BACKGROUND: Wernicke encephalopathy is an acute neurological emergency caused by thiamine (vitamin B1) deficiency. The syndrome is associated with a significant morbidity and mortality, and prompt recognition and treatment of the syndrome in the emergency department (ED) is essential to improving patient outcomes. Numerous factors and clinical settings have been identified that predispose a patient to thiamine deficiency and subsequent Wernicke encephalopathy. CASE REPORT: We present the rare case of a 42-year-old man with a recent diagnosis of non-Hodgkin lymphoma who opted against chemotherapy in favor of a 60-day therapeutic water-only fast. On day 53 of his fast, the patient arrived to our ED in a coma and respiratory failure. Moments after the administration of thiamine, the patient's mental status and respiratory status improved significantly. Prior to admission and transport to the medical intensive care unit, the patient was awake, alert, and following basic commands. He was ultimately diagnosed with Wernicke encephalopathy. WHY SHOULD AN EMERGENCY PHYSICIAN BE AWARE OF THIS?: With the increasing incidence of patients choosing alternative medical therapies to treat a variety of diseases, numerous electrolyte, metabolic, and nutritional disorders are becoming increasingly more common in the ED setting. In some cases, patients may choose a therapeutic fast in an effort to combat a malignancy; the danger being that patients with cancers such as lymphoma are already at risk for thiamine deficiency as a result of the increased thiamine consumption associated with rapid cellular turnover. Wernicke encephalopathy is a life-threatening neurological emergency, and the emergency physician must be aware of the numerous predisposing factors to the condition, as early identification and treatment improves patient outcomes.

Yeast telomerase is capable of limited repeat addition processivity.

Telomerase is a ribonucleoprotein reverse transcriptase responsible for the maintenance of one strand of telomere terminal repeats. Telomerase-mediated sequence addition is dictated by a short 'template' region of the RNA component. Despite the short template segment, telomerases from many organisms have been shown to mediate the synthesis of long extension products. This synthesis presumably depends on two types of translocation events: simultaneous translocation of the RNA-DNA duplex relative to the active site after each nucleotide incorporation (type I or nucleotide addition processivity), and translocation of the RNA relative to the DNA product after each round of repeat synthesis (type II or repeat addition processivity). In contrast, telomerases from yeasts have been shown to synthesize mostly short products, implying a defect in one or both types of translocation. In this report, we analyzed the processivity of yeast telomerase in vitro, and identified two position-specific elongation barriers within the 5' region of the RNA template that can account for the synthesis of incomplete first round products. These barriers respond differently to variations in nucleotide concentration, primer sequence and mutations in the catalytic protein subunit, consistent with their having distinct mechanistic bases. In addition, by using optimal primers and high concentrations of dGTP, we were able to detect significant type II translocation by the yeast enzyme. Thus, the difference between the elongation property of yeast and other telomerases appears to be quantitative rather than qualitative. Our results suggest that yeast may be a useful system for investigating the physiologic significance of repeat addition processivity.

Telomerase can act as a template- and RNA-independent terminal transferase.

Telomerase is a special reverse transcriptase that extends one strand of the telomere repeat by using a template embedded in an RNA subunit. Like other polymerases, telomerase is believed to use a pair of divalent metal ions (coordinated by a triad of aspartic acid residues) for catalyzing nucleotide addition. Here we show that, in the presence of manganese, both yeast and human telomerase can switch to a template- and RNA-independent mode of DNA synthesis, acting in effect as a terminal transferase. Even as a terminal transferase, yeast telomerase retains a species-dependent preference for GT-rich, telomere-like DNA on the 5' end of the substrate. The terminal transferase activity of telomerase may account for some of the hitherto unexplained effects of telomerase overexpression on cell physiology.

Conserved N-terminal motifs of telomerase reverse transcriptase required for ribonucleoprotein assembly in vivo.

Telomerase is a ribonucleoprotein (RNP) reverse transcriptase responsible for the maintenance of one strand of the telomere terminal repeats. The key protein subunit of the telomerase complex, known as TERT, possesses reverse transcriptase (RT)-like motifs that directly mediate nucleotide addition. The RT motifs are located in the C-terminal region of the polypeptide. Sequence alignments also revealed the existence of four conserved motifs (named GQ, CP, QFP, and T) in the N-terminal region of TERT. The GQ motif of yeast TERT has been demonstrated previously to be essential for telomerase catalysis and may participate in RNP formation. In this report, we show that substitution of conserved residues in the CP, QFP, and T motifs of yeast TERT also impairs both telomere maintenance and telomerase activity, thus confirming the validity of the sequence alignment. The extent of telomere shortening correlates with the extent of reduction in the level of telomerase activity, TERT protein, and TERT-associated TLC1 RNA. Overexpression of the mutant proteins does not result in telomere shortening, implying that assembly rather than catalytic function was affected. This notion was further supported by comparing the efficiency of RNP formation in the wild type and the overexpression strains. Taken together, our results show that three of the four N-terminal motifs are required for efficient telomerase RNP formation in vivo but not for the enzymatic function of telomerase. We also show that the majority of telomerase-associated TLC1 RNA has a more upstream 3' end than previously reported, consistent with additional processing events during RNP maturation.