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Alpha thalassemia demonstrates problems with alpha globin chain production. One to four loci that code for the alpha chain may be deleted from chromosome 16. The greater the number of loci deleted or inactivated, the greater the severity of the anemia which develops. Many different mutations exist that result from partial deletions of alpha genes. This unit of study deals only with the forms of alpha thalassemia that have entire loci deleted.

Beta thalassemia demonstrates problems with beta globin chain production. One or two loci that code for the beta chain may be deleted from chromosome 11. The greater the number of loci deleted or inactivated, the greater the severity of the anemia which develops. Many different mutations exist that result from partial deletions of beta genes. This unit of study deals only with the forms of beta thalassemia that have entire loci deleted. Deletions of additional globin genes coded for on chromosome 11 can result in such combinations as delta-beta thalassemia.

Beta thalassemia major, B0/B0 (two gene mutations, deletions or combination) results in very few to no beta chains being produced.Hemoglobin A levels are at or near 0%.(drawing modified from Harmening, 1999)

Because of the two separation processes, more information and separated solutes can be gained from a sample. The use of two-dimensional electrophoresis is specialized and most applications are in research fields. It is used to study families of proteins in the field of proteomics and protein content in different types of cells. It is also used extensively in genetics to study differences in diseases, gene mutations, and bacterial DNA. In an effort to find ways to detect malignancies earlier, two-dimensional electrophoresis is used to study tumor cells.

The reason to chose a particular molecular method can be influenced by disease detection, monitoring or therapy in certain patient populations. Molecular methodologies can be used to identify alterations or variations or changes in DNA sequencing that can cause disease. Sequence alterations that are known to cause disease are termed mutations. These changes or mutations can be applied to areas of the clinical lab such as infectious disease, paternity, genetic testing, and pharmacogenetics. Some of the more common alterations are:Deletion: a missing nucleotide or other portion of DNA sequence Insertion: an extra DNA nucleotide or other portion of DNA sequence Missense: a nucleotide or sequence substitution that codes for a different amino acidNonsense: a nucleotide substitution that ends in early termination of the protein manufacturing process; usually due to a stop codon.The most common alteration is a single base change or single nucleotide polymorphism (SNP)

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.

A hemochromatosis gene, HFE, was identified in 1996. Mutations in the HFE gene are found in the majority of patients diagnosed with hereditary hemochromatosis (HH). The locus for the gene is on the long arm of chromosome 6 where it codes for a membrane protein, HFE. The exact mechanism of the role of HFE protein in iron metabolism is incompletely understood. It is thought that HFE, along with a second protein, beta-2 microglobin, interacts with transferrin receptors (TfR) on cell membranes. This interaction supresses the affinity of transferrin for TfR, thus lowering the uptake of transferrin--and its attached iron--into the cell. Transferrin receptors have been found on the surface of a variety of cells, with the greatest concentration on cell membranes of intestinal cells, hepatocytes, and RBC precursors. In addition to HFE, HH is also associated with mutations in other genes involved in iron homeostasis, including hemojuvelin (HJV), TfR, hepcidin, and ferroportin. Hepcidin production is reduced in HH due to all of these genetic causes, with a resulting increase in iron absorption. Mutations in HFE are the most common cause of HH.

Several mutations of the HFE gene have been described. In the C282Y mutation, a base substitution leads to a change in the amino acid in position 282 from cysteine (C) to tyrosine (Y). The loss of the sulfhydryl-containing amino acid disrupts the tertiary structure of HFE so that it no longer binds to beta-2 microglobulin. Beta-2 microglobulin appears to act along with other proteins to chaperone the newly synthesized HFE out of the Golgi apparatus and to the cell surface where it can then bind to TfR. In the C282Y mutation, HFE remains in the Golgi, never making it to the cell surface. The result is that transferrin binding to TfR is enhanced and excessive amounts of iron enter the cells of the small intestine, liver, and other tissues. A second mutation, H63D, causes a histidine (H) residue in position 63 to be replaced by aspartic acid (D). The mechanism by which this mutation leads to increased iron uptake is less well understood when compared to the C282Y mutation. Unlike the C282Y mutation, the H63D mutation does not seem to affect the binding of beta-2 microglobulin and intracellular movement, since detectable concentrations of the mutated protein are found on cell membranes. Some researchers speculate that the H63D mutation affects the binding of proteins involved in iron regulation and uptake at the cell surface.A third mutation, S65C, leads to a serine-to-cysteine substitution in its associated protein. This mutation has been been found in some compound heterozygotes for C282Y or H63D, but is rarely associated with iron overload in HH.Additional mutations of HFE have been identified, but their clinical significance is unclear. Most laboratories performing molecular assays test for only the C282Y, H63D, and S65C mutations.

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.

The C282Y mutation is common in the Caucasian population, especially in people of northern European descent. Approximately 10% of Caucasian Americans are heterozygous carriers of a single C282Y mutation.(8) A greater percentage are carriers of the H63D mutation, but this mutation is much less clinically significant. Hereditary hemochromatosis appears to be most prevalent among people in the Northern British Isles--Scotland, Ireland and Great Britain--who are of Celtic descent. Persons of Celtic descent in the United States, Australia, and France also have a relatively high incidence of HH. The prevalence of HFE mutations in African Americans and Hispanic Americans is low.

Genes in addition to HFE have been linked to hereditary hemochromatosis (HH). They include the hepcidin, hemojuvelin, transferrin receptor, and ferroportin genes. Mutations of some are linked with dominantly inherited HH, juvenile HH, and African iron overload. Unlike HH due to HFE mutations, these clinical disorders are rarely observed in the US population.(9)

Hereditary hemochromatosis (HH) is frequently discovered only during management of associated illness or routine health evaluations. It has been estimated that only a small percentage of all affected persons are actually diagnosed. Individuals with HH may be symptomatic for several years prior to diagnosis and may have consulted multiple health care providers.Under-diagnosis of HH is thought to occur due to:• Lack of specificity of early signs and symptoms• Asymptomatic status of some patients until damage to organs and tissues has occurred• Confusion with liver disease due to other causes• Insufficient awareness and knowledge of HHEarly identification of persons with HH is essential to prevent serious and irreversible complications associated with severe iron overload. A classic triad of skin hyperpigmentation (bronzing), type 2 diabetes, and hepatic cirrhosis has long been recognized as evidence of advanced iron overload. However, persons with HH may present with a much wider variety of signs and symptoms, particularly if they are seen before significant iron accumulation has occurred. Age of presentation and disease severity are highly variable. A diagnosis of HH is based on laboratory evidence of iron overload, genetic mutations associated with HH, and presence of clinical signs and symptoms consistent with HH.(10)

The diagnosis of hereditary hemochromatosis (HH) is made through a combination of laboratory tests and medical evaluation of a patient's signs and symptoms. Iron overload is identified by tests that evaluate iron metabolism, while molecular assays are needed to document mutations in the HFE gene or others such as hepcidin, hemojuvelin, or transferrin receptor. Individuals with documented iron overload who exhibit signs and symptoms consistent with HH and who possess HFE or other mutations are considered to have HH. Other causes of secondary iron overload may need to be ruled out.An example of a testing algorithm is shown.

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.

DNA tests for HFE mutations associated with hereditary hemochromatosis (HH) are available in some clinical laboratories and reference laboratories. Testing for the presence of the C282Y is essential, although most labs also test for H63D and S65C mutations. Molecular testing is most appropriate for confirmatory testing of symptomatic individuals with altered iron studies (increased TS and SF), in pre-symptomatic individuals (increased TS, normal SF and liver function tests), and in family members of individuals diagnosed with HH. The use of genetic tests alone for routine screening of asymptomatic persons is not recommended for several reasons. A positive test indicating the presence of HFE mutations does not guarantee that an individual will develop clinically significant iron overload or predict severity of symptoms. A negative result (no HFE mutations present) does not rule out a diagnosis of iron overload because of genetic heterogeneity. Compared to biochemical analyses for iron, molecular assays are expensive. Finally, molecular testing may result in the diagnosis of a genetic disease, thus opening up the possibility for discrimination in health insurance coverage. Using molecular methods, DNA is extracted from leukocytes in whole blood samples or from buccal cells and analyzed for specific HFE mutations using polymerase chain reaction (PCR) with melt curve analysis. Currently there are no FDA-cleared products for HFE testing, and testing laboratories are using "home brew" reagents. This situation is expected to change as manufacturers submit products for FDA approval.

Measuring the amount of iron deposited in the liver is considered definitive for iron overload. This may be done by liver biopsy, computed tomography (CT), or magnetic resonance imaging (MRI). Demonstrating iron in parenchymal liver cells helps determine disease severity. Liver sections obtained by biopsy are stained with Perls Prussian blue which stains iron present in parenchymal cells. A photomicrograph of this reaction is shown.Although liver biopsy may not be necessary for diagnosing hereditary hemochromatosis (HH), it offers the advantage of detecting liver fibrosis if present. Molecular tests for mutations associated with HH are considered the gold standard of current HH testing. Liver biopsy is not needed for diagnosing all patients suspected of having HH, but may be ordered in some cases.

Genetic mutations in HIV are well known and are very likely, considering the presence of two RNA molecules per virus. Either or both RNA molecules can mutate. These mutations potentially lead to drug resistance or encourage the virus to evade the body's immune response. Mutations have created three major groups of HIV - M, N, and O. M is found in 99% of all the HIV cases in the world. N and O are primarily found in West African countries. N, though, infects only a very small number of individuals. The M group has subgroups lettered A to J. Subgroup B predominates in North America.

Specialists in cytogenetics detect chromosome abnormalities and genetic disorders. Cytogenetics counseling may only be performed by an individual licenses in the cytogenetics specialty at the director level. Specialists in molecular genetics analyze DNA and RNA to find disease-related genotypes, mutations, and phenotypes in order to detect or predict disease and identify carriers. Specialists in histocompatibility test to determine tissue compatibility, prevent infections, and investigate and post-transplant problems. Techniques include blood typing, HLA typing, HLA antibody screening, disease markers, flow cytometry, crossmatching, HLA antibody identification, lymphocyte immunophenotyping, immunosuppressive drug assays, allogenic, isogeneic and autologous bone marrow processing and storage, mixed lymphocyte culture, stem cell culture, cell mediated assays, and assays for the presence of cytokines. Specialists in andrology and embryology examine gametes and embryos, including production, morphology, number, and motility, to address issues of fertility and infertility.

In addition to protein availability, other factors may affect drug absorption and distribution in the body as a whole or at specific sites within the body. The following table highlights some of these other factors. Factor Discussion Regional blood flow Reduced area blood flow can be seen in diabetics and enhanced blood flow can be seen in tumors. Lipid solubility of the drug The more lipophilic a drug is, the more likely it will enter the central nervous system. The integrity of the GI tract In a diseased gut, an orally-administered drug may not be absorbed as expected. Age Drug kinetics and dispositions change throughout life. In general, metabolism of drugs is reduced in the elderly. Genetics Mutations or deletions in drug metabolizing enzymes can greatly affect a drug's disposition.

The following is a list of enzymes for which known mutations have been associated with clinical effects. Enzymes Substrates (Drugs) Acetylaldehyde dehydrogenase Alcohol Acetylcholinesterase Succinylcholine Alcohol dehydrogenase Alcohol Dihydropyrimidine dehydrogenase Fluorouracil CYP2C9 Warfarin, phenytoin, losartan CYP2C19 Diazepam, omeprazole (Prilosec) CYP2D6 Many antidepressants, opioids, antiarrhythmics Glucose-6-phosphate dehydrogenase Aspirin, quinidine N-acetyltransferase Procainamide, isoniazid Thioprine methyltransferase 6-mercaptopurine UDP-glucuronosyl transferase Acetaminophen, tolbutamide, irinotecan

Variables other than mutations also affect CYP450 enzymes. Many drugs are able to induce CYP450 enzymes, and CYP450s can be inhibited by a variety of substances. For example, CYP2D6 can be inhibited by the common medications cimetidine (Tagamet) and fluoxetine (Prozac). Since many patients are on multiple medications and since dietary and environmental factors can change, CYP450 expression levels cannot be solely predicted based on their genotype. Some CYP450 inducers and inhibitors are listed in the table on the following page.

Hemoblobin H disease follows deletions of 3 of the 4 alpha globulin chains. Beta chains, unable to bind with insufficient numbers of alpha chains, form beta chain tetramers, or HbH.These beta chain tetramers appear as numerous dot size inclusions in erythrocyte cytoplasm, best seen in supravital brilliant cresyl blue stains (lower photograph).The most common molecular defect in alpha thalassemia is DELETION, not MUTATION; whereas, in beta thalassemia, the molecular defect is MUTATION.Leptocytes, as illustrated in the upper photograph,(lepto, derived from a Greek word meaning thin, fine, or slight), are characteristic of HbH disease. They have thinner cell membranes than the cells we recognize as target cells. They stain more lightly than normal erythrocytes and their centers are almost colorless.Subtle changes perhaps, but worth keeping in mind

Chediak-Higashi syndrome is a rare autosomal recessive disorder. It results from a mutation of the gene LYST which encodes a protein with multiple phosphorylation sites. This defect causes a cellular abnormality involving the fusion of cytoplasmic granules. Early in neutrophil maturation normal azurophilic granules form, but they fuse together to form megagranules. Later during the myelocyte stage, normal specific granules form. The mature neutrophils contain both normal specific granules and abnormal azurophilic granules. These large abnormal granules can be seen in the cytoplasm of neutrophils, eosinophils, basophils, monocytes and lymphocytes. These abnormal granules are able to kill bacteria in neutrophils and monocytes; however, the process is much less effective than in normal cells in part, because these neutrophils have impaired locomotion. For these reasons, individuals with Chediak-Higashi have recurrent infections. An accelerated lymphoma-like phase occurs, with lymphadenopathy, hepatosplenomegaly, and pancytopenia. Death often occurs at an early age.