Phenotypic Information and Courses from MediaLab, Inc.
These are the MediaLab courses that cover Phenotypic and links to relevant pages within the course.
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| Enterococcus faecium ID As a high percentage of Enterococcus faecium strains carry the Van A gene and are highly resistant to vancomycin. Species identifications are performed in some laboratories where MIC susceptibility testing may not be available.Methods for the phenotypic separation of E. faecium from E. faecalis are limited.Illustrated in this photograph are positive reactions for acid production from arabinose and melibiose (yellow color), characteristic of E. faecium. E. faecalis are negative for these reactions.A few preformed substrates such as beta galactosidase (E. faecium positive, E. faecalis negative) also serve to separate these two species, accomplished by certain commercial systems that include these substrates.E. faecium is not motile, an additional characteristic helpful to separate vancomycin-resistant Enterococcus species from E. cassiloflavus and E. gallinarum, both of which are motile, and carry the low level resistant gene VAN-c. | View Page |
| General Overview of Testing Tests for evaluating iron metabolism are generally used as initial or screening tests for hereditary hemochromatosis (HH) as they will detect the phenotypic expression of HH. These tests include serum iron (SI), transferrin (Tf) or total iron binding capacity (TIBC), serum ferritin (SF), and unsaturated iron binding capacity (UIBC).The serum ferritin assay is also used to assess the effectiveness of HH treatment.Molecular (DNA) analyses for HFE mutations are considered to be confirmatory tests for HH which may be ordered reflexively in patients with elevated iron results. Laboratories should establish their own reference intervals for assays of iron metabolism. In general, reference intervals vary by sex and by method used for the assays discussed in the following section. Typical reference intervals are included in the following sections for instructive purposes only and should not be used for evaluating actual patient data.The results of laboratory tests assessing iron metabolism should be interpreted with caution because a number of pre-analytical and physiologic factors can affect the results. Repeating elevated test results on fasting specimens is often advisable. | View Page |
| Epidemiology of HFE Mutations The prevalence of common HFE mutations among persons with hereditary hemochromatosis (HH) has been reported in numerous studies conducted in the US, France, Australia, and other countries. Homozygous C282Y mutation (C282Y/C282Y) is present in 82% to 90% of Caucasian patients diagnosed with iron overload due to HH.(7) This suggests a strong link between the genotype and the phenotypic presentation of clinical iron overload. Much lower percentages of persons diagnosed with HH do not have two C282Y mutations. A small percentage of persons diagnosed with HH are compound heterozygotes for C282Y and H63D (C282Y/H63D), are homozygous for H63D (H63D/H63D), heterozygous for C282Y (C282Y/wild type) or for H63D (H63D/wild type), or carry S65C or other HFE mutations.It may be that symptomatic heterozygotes are actually HFE-compound heterozygotes with additional unidentified mutations modifying the expression of the more severe known mutation. It is quite possible that more mutations of HFE and elucidation of other gene mutations modifying HFE will be discovered in the future enabling scientists to better explain the phenotypic heterogeneity of this disorder.In the US, the C282Y mutation is most prevalent in the non-Hispanic white population. It is much less common among Hispanics and African Americans. | View Page |
| Incomplete Penetrance For reasons as yet unknown, not all individuals who are homozygous for the C282Y mutation display phenotypic features of HH, and persons with H63D polymorphisms rarely develop iron overload. The penetrance (percentage of individuals with a specific genotype who express the associated phenotype) of HFE mutations is generally considered to be low. Results of a recent meta analysis by the US Preventive Services Task Force conclude that 38% to 50% of all C282Y homozygotes develop some evidence of iron overload, but that only 10% to 33% develop clinical disease due to HH. (8) In other words, some individuals may have elevated iron test results such as transferrin saturation, but do not demonstrate significant organ damage. Estimates of penetrance in some studies have found it to be even lower. Penetrance of HFE mutations is currently a controversial subject among experts, and the significance of finding HFE mutations in a given individual is often unclear. The probability that a given individual with HFE mutations will develop clinical disease from iron overload cannot be determined at this time. | View Page |
| Screening Controversies The subject of screening for hereditary hemochromatosis (HH) is controversial and is currently being debated in the medical literature. Using laboratory tests to screen the asymptomatic general population is currently not recommended due to issues of testing costs, low genetic penetrance, and the possible risk of discrimination. Targeted case finding in select high risk populations such as men of Northern European ancestry may be a better approach to screening. (12)Molecular-based (DNA) assays required for confirmation of HH are costly when used for general population screening. Because recent studies have shown that a high percentage of persons with C282Y mutations do not develop iron overload or HH-related clinical conditions, screening for these mutations may falsely label an individual with a disease diagnosis. At the present time, it is impossible to determine which homozygotes or heterozygotes for HFE mutations will eventually develop iron overload. Furthermore, there is potential risk of discrimination in obtaining health insurance for persons identified as having genetic disorders.In contrast, some experts do advocate for screening the general population. Mutations associated with HH are very common in Caucasians in the US. Individuals who know they carry mutations associated with HH may benefit from periodic testing for iron overload. Finally, laboratory tests that assess iron status are relatively inexpensive, widely available, and offer one approach to screening for phenotypic expression of HH. Screening first-degree family members of a person with documented HH is generally considered to be worthwhile. Early detection of HH in relatives with common mutations may permit treatment before the development of substantial iron overload and related disease due to organ damage. | View Page |
| Match the names of each of the species of yeast listed with its associated phenotypic property that is helpful in establishing a species identification. | View Page |
| The ability of Candida albicans to alternate between two phenotypes, which may be related to the virulence of this species, is called: | View Page |
| Each of the following is considered to be a virulence factor in Cryptococcus neoformans except: | View Page |
| The nuclear appendage at the tip of the arrow is a normal finding in females but not in males. | View Page |