Phenylthiocarbamide taste sensitivity in chronic peptic ulcer

The genetics of phenylthiocarbamide perception

The ability to taste the bitter compound phenylthiocarbamide (PTC) and related chemicals is bimodal, and all human populations tested to date contain some people who can and some people who cannot taste PTC. Why this trait has been maintained in the population is uncertain but this polymorphism may influence food selection, nutritional status or thyroid metabolism. The gene product that gives rise to this phenotype is unknown, and its characterization would provide insight into the mechanism of bitter taste perception. Although this trait is often considered a simple Mendelian trait, i.e. one gene two alleles, a recent linkage study found a major locus on chromosome 5p15 and evidence for an additional locus on chromosome 7. The development of methods to identify these genes will provide a good stepping-stone between single-gene disorders and polygenic traits.

Variation in taste of topical lignocaine anaesthesia for gastroscopy

AIM

To study the distribution and determinants of taste variation for lignocaiine spray (Xylocaine; Astra Pharmaceuticals, King's Langley, UK).

METHODS

Sixty-nine patients (male:female 49:20, mean age 48.5 years) attending for open access upper gastrointestinal endoscopy were studied. Taste perceived after applying 4 doses (40 mg) of lignocaine spray to the oro-pharynx was recorded prior to endoscopy.

RESULTS

37/69 (54%, 95% CI: 41-66%) perceived the taste of the lignocaine spray as bitter. whilst 24/69 (35%, 95% CI: 24-47%) and 6/69 (9%, 95% CI: 3-18%) perceived the taste as either fruity/sweet or tasteless. The variation in taste did not correlate with either demographic features or H. pylori inflection, but duodenal ulceration was slightly more common amongst bitter tasters.

CONCLUSION

The taste of lignocaine is not uniform, but the basis of this variability is uncertain.

Epidemiology and genetics of peptic ulcer

At the turn of the century, duodenal ulcer rose from rarity to affect 10% of males in their life time, subsequently declining in some countries such as UK, levelling off in others such as Germany, and continuing to increase in still others such as Hong Kong. The annual incidence per 1000 population varies from about 1 in Japan to 1.5 in Norway, 1.8 in USA and 2.7 in Scotland, and the frequency also varies within many individual countries, such as Australia, China and India, and among races such as a higher prevalence among whites than blacks in USA and among Chinese than Javanese in Indonesia. Ulcer frequency is higher in winter months, and this appears universal, being true in cold as well as in warm countries. Most places report a rise of ulcer rates among the elderly in recent decades. The male to female ratio also varies geographically, for example from 1:1 in USA to 18:1 in India, and with time such as moving from 2:1 to 1:1 in the last two decades in USA, and the duodenal ulcer to gastric ulcer ratio varies widely from place to place, for example from 0.8 in Japan to 19:1 in Africa and 32:1 in India. Placebo healing rates also differ geographically, ranging from 5% in Philippines to 78% in Mexico. These epidemiological data can only be explained by the presence of multiple aetiological factors, including analgesics, society stress, cigarette smoking, Helicobacter pylori, dietary factors, and genetic factors. Three lines of evidence support a genetic role: family studies, twin studies and blood group studies. Family aggregation occurs more commonly in patients with early-onset (< 30 yr) of symptoms. Blood group O prevalence is more associated with late-onset of symptoms. Other genetic markers include nonsecretor status, HLA antigens, phenylthiocarbamide taste sensitivity, and alpha-1-antitrypsin. Genetic syndromes such as MEN I also support a genetic role and give insight into pathogenetic mechanisms. The best physiological marker is still hyperpepsinogenemia I, which is transmitted by autosomal dominance, despite recent report of lower serum pepsinogen 1 after healing of Helicobacter pylori associated gastritis.