Normal

None

None

7.35–7.45

3.5–5.0

12–18

None

Respiratory acidosis

Pco2 ↑ (co2 retention)

↑ Hco3–

↓

↑

N

Dyspnea, polypnea, respiratory outflow obstruction, ↑ anterior-posterior chest diameter, rales, wheezes. In severe cases, stupor, disorientation, coma.

Respiratory alkalosis

Pco2 ↓ (co2 depletion)

↓ Hco3–

↑

↓

N or ↓

Anxiety, occasional complaint of breathlessness, frequent sighing, lungs usually clear to examination, positive Chvostek and Trousseau signs.

Metabolic acidosis

Hco3− depletion

↓ Pco2

↓

↑ or ↓

N or ↑

Weakness, air hunger, Kussmaul respiration, dry skin and mucous membranes, poor skin turgor. In severe cases, coma, hypotension, death.

Metabolic alkalosis

Hco3−

↑ Pco2

↑

↓

N

Weakness, positive Chvostek and Trousseau signs, hyporeflexia.

Microcytic, hypochromic

<80

<32

Iron deficiency

Hypochromic red cells, elliptocytes, low reticulocyte count, low serum ferritin, low serum and bone marrow iron, high TIBC, high serum/plasma soluble transferrin receptor (sTfR).

Mucositis, brittle nails, bleeding (eg, positive fecal occult blood), esophageal webs, pica.

Variable, but usually <32

Thalassemias

Abnormal red cell morphology, normal to high RBC count, elevated reticulocyte count, normal serum iron parameters, abnormal hemoglobin electrophoresis, high hemoglobin A2 in β-thalassemia minor.

Asian, African, or Mediterranean descent. Splenomegaly, growth failure, bony deformities.

<32

Chronic lead poisoning

Basophilic stippling of RBCs, elevated blood lead and free erythrocyte protoporphyrin levels.

Peripheral neuropathy (eg, wrist drop), abdominal pain, learning disorders (in children), headache, history of exposure to lead.

Variable, but usually < 32

Sideroblastic anemia

High serum iron, high transferrin saturation, erythroid hyperplasia with ring sideroblasts in bone marrow.

Dimorphic red cell population with hypochromic red cells on blood smear.

Normocytic, normochromic

80–100

32–36

Acute blood loss

Fecal occult blood test positive if GI bleeding is the underlying cause. High reticulocyte count, thromobocytosis (variable)

Recent blood loss.

32–36

Hemolysis

Haptoglobin low or absent, high reticulocyte count, high indirect bilirubin, high serum LDH, spherocytes, schistocytes, or “bite” cells on smear.

Hemoglobinuria, splenomegaly.

32–36

Chronic disease1

Low serum iron, TIBC low or low normal, normal sTfR, normal or high ferritin, low reticulocyte count, normal or high bone marrow iron stores with rare or no sideroblasts.

Depends on cause, typically chronic inflammatory conditions.

Macrocytic, normochromic

>1012

32–36

Vitamin B12 deficiency

Hypersegmented PMNs, macro-ovalocytes, neutropenia and/or thrombocytopenia, low serum vitamin B12 levels, high serum/urine MMA, achlorhydria and high serum gastrin, and high serum LDH.

Peripheral neuropathy, glossitis, anorexia and diarrhea.

32–36

Folate deficiency

Hypersegmented PMNs, macro-ovalocytes, neutropenia and/or thrombocytopenia, low serum and red cell folate levels, high homocysteine level.

Alcoholism, tropical sprue, malnutrition, antifolate agents (eg, trimethoprim- sulfamethoxasole, methotrexate, others).

32–36

Liver disease

Decreased platelets; MCV usually <120 fL; normal serum vitamin B12 and folate levels.

Signs of liver disease, alcohol abuse.

Usually 32–36

Myelodysplastic syndrome

MCV usually <120 fL, low reticulocyte count, may have neutropenia and/or thrombocytopenia, pseudo-Pelgeroid neutrophils, unilineage or multilineage dysplasia in the marrow.

Chronic anemia with or without pancytopenia.

32–36 or >36

Reticulocytosis

Marked (>15%) reticulocytosis.

Variable, including acute hemorrhage or hemolysis.

Normal

80–100

50–175

250–460

16–55

50–300

<35

Absent

Present

Iron deficiency anemia

↓

<30

↑

<16

<451

↑

Absent

Absent

Anemia of chronic disease

N or ↓

↓

N or ↓

N or ↓

N or ↑

↑

Absent

Present

Thalassemia minor

↓

N

N

N

N

N

Usually present

Present

Normal

<3.5

Transparent, clear

<200

<25%

Neg

Equal to serum glucose

Non- inflammatory (Group I)

Often >3.5

Transparent, yellow

<2000

<25%

Neg

Equal to serum glucose

Degenerative joint disease, trauma, avascular necrosis, osteochondritis dissecans, osteochondromatosis, neuropathic arthropathy, subsiding or early inflammation, hypertrophic osteoarthropathy, pigmented villonodular synovitis.

Inflammatory (Group II)

Often >3.5

Translucent to opaque, yellow to opalescent

2000–75,000 (occasionally >75,000 but rarely >100,000)

≥50%

>25, but lower than serum glucose

Rheumatoid arthritis, acute crystal-induced synovitis (gout, pseudogout), reactive arthritis, ankylosing spondylitis, psoriatic arthritis, sarcoidosis, arthritis accompanying ulcerative colitis and Crohn disease, rheumatic fever, systemic lupus erythematosus, scleroderma; tuberculous, viral, or mycotic infections.

Crystals are diagnostic of gout or pseudogout: gout crystals (urate) are needle-shaped and show negative birefringence; pseudogout crystals (calcium pyrophosphate) are more rectangular and show positive birefringence when red compensator filter is used with polarized light microscopy.

Phagocytic inclusions in PMNs suggest rheumatoid arthritis (RA cells).

Purulent (Group III)

Often >3.5

Opaque, yellow to green

>100,000

≥75%

Usually positive (gonococci seen in only about 25% of cases)

<25, much lower than serum glucose

Mostly pyogenic bacterial infections (eg, Staphylococcus aureus, Neisseria gonorrhoeae).

WBC count and % PMN lower with infections caused by organisms of low virulence (eg, N. gonorrhoeae) or if antibiotic therapy already started.

Hemorrhagic (Group IV)

Often >3.5

Cloudy, pink to red

Usually >2000; many RBCs.

<30%

Neg

Equal to serum glucose

Trauma with or without fracture, hemophilia or other hemorrhagic diathesis, neuropathic arthropathy, pigmented villonodular synovitis, synovioma, hemangioma and other benign neoplasms.

Fat globules strongly suggest intra-articular fracture

Normal

Clear

<3.0

Equal to plasma glucose

<250

Few or none

Neg

Neg

HIGH SAAG

Cirrhosis

Clear

<3.0

≥1.1

N

<250, MN

Few

Neg

Neg

Occasionally turbid, rarely bloody.

Congestive heart failure

Clear

<2.5

≥1.1

N

<250, MN

Few

Neg

Neg

LOW SAAG

Nephrotic syndrome

Clear

<2.5

<1.1

N

<250, MN

Few

Neg

Neg

Bacterial peritonitis

Cloudy

>3.0

<1.1

<50 with perforated viscus

>500, PMN

Few

Pos

Neg

Blood cultures frequently positive.

Tuberculous peritonitis

Clear

>3.0

<1.1

<60

>500, MN

Few, occasionally many

Stain Pos in 25%; culture Pos in 65%

Neg

Occasionally chylous. Peritoneal biopsy positive in 65%.

Malignancy

Clear or bloody

>3.0

<1.1

<60

>500, MN, PMN

Many

Neg

Pos in 60–90%

Occasionally chylous. Peritoneal biopsy diagnostic.

Pancreatitis

Clear or bloody

>2.5

<1.1

N

>500, MN, PMN

Many

Neg

Neg

Occasionally chylous. Fluid amylase >1000 IU/L, sometimes >10,000 IU/L.

Fluid amylase > serum amylase.

OTHER

Chylous ascites

Turbid

Varies, often >2.5

N

Few

Few

Neg

Neg

Fluid TG > 400 mg/dL (turbid).

Fluid TG > serum TG.

Pseudomyxoma peritonei

Gelatinous

<2.5

N

<250

Few

Neg

Occ Pos

Rheumatoid arthritis

30–60

0–5

70

0

0–5

0–2

0

0

0

0

Systemic lupus erythematosus

95–100

60

20

10–25

15–20

5–20

0

0

0

0–1

Sjögren syndrome

95

0

75

0

65

65

0

0

0

0

Diffuse scleroderma

80–95

0

30

0

0

0

33

1

0

0

Limited scleroderma (CREST syndrome)

80–95

0

30

0

0

0

20

50

0

0

Polymyositis/dermatomyositis

80–95

0

33

0

0

0

0

0

20–30

0

Polyangiitis with granulomatosis

0–15

0

50

0

0

0

0

0

0

93–961

Idiopathic thrombocytopenic purpura (ITP), drug effect, bone marrow suppression

↓

N

N

N

Platelet antibodies, bone marrow examination.

Disseminated intravascular coagulation (DIC)

↓

↑

↑

↑

Fibrinogen (functional), D-dimers.

Platelet function defect, salicylates, or uremia

N

N

N

N

Bleeding time or PFA-100 CT, platelet aggregation, blood urea nitrogen, creatinine.

von Willebrand disease

N

N

↑ or N

N

Bleeding time or PFA-100 CT, factor VIII assay, vWF antigen and activity, vWF multimer analysis.

Factor VII deficiency or inhibitor

N

↑

N

N

Factor VII assay (normal plasma should correct PT if no inhibitor is present).

Factor V, X, II, I deficiencies as in liver disease or with anticoagulants

N

↑

↑

N or ↑

Liver function tests.

Factor VIII (hemophilia), IX, or XI deficiencies or inhibitor

N

N

↑

N

Inhibitor screen (mixing study), individual factor assays, Bethesda assay.

Factor XIII deficiency

N

N

N

N

5M urea solubility test (screen test), factor XIII assay.

Increase in fibrinolytic activity

N

N

N

N

Euglobulin clot lysis time (screening test), α2-antiplasmin, plasminogen activator inhibitor-1 (PAI-1), renal function test (eg, eGFR)

Normal

Clear, colorless

70–200

0

≤5 MN, 0 PMN

45–85

15–45

Neg

Neg

Bacterial meningitis

Cloudy

↑↑↑↑

0

200–20,000, mostly PMN

<45

>50

Gram stain Pos

Pos

Tuberculous meningitis

N or cloudy

↑↑↑

0

100–1000, mostly MN

<45

>50

AFB stain Pos

±

PMN predominance may be seen early in course.

Fungal meningitis

N or cloudy

N or ↑

0

100–1000, mostly MN

<45

>50

±

Counterimmunoelectrophoresis or latex agglutination may be diagnostic. CSF and serum cryptococcal antigen positive in cryptococcal meningitis.

Viral (aseptic) meningitis

N

N or ↑

0

100–1000, mostly MN

45–85

N or ↑

Neg

Neg

RBC count may be elevated in herpes simplex encephalitis. Glucose may be decreased in herpes simplex or mumps infections. Viral cultures may be helpful.

Parasitic meningitis

N or cloudy

N or ↑

0

100–1000, mostly MN, E

<45

N or ↑

Amebae may be seen on wet smear

±

Carcinomatous meningitis

N or cloudy

N or ↑

0

N or 100–1000, mostly MN

<45

N or ↑

Cytology Pos

Neg

Cerebral lupus erythematosus

N

N or ↑

0

N or ↑, mostly MN

N

N or ↑

Neg

Neg

Subarachnoid hemorrhage

Pink-red, supernatant yellow

↑

↑ crenated or fresh

N or 100–1000, mostly PMN

N or ↓

N or ↑

Neg

Neg

Blood in all tubes equally. Pleocytosis and low glucose sometimes seen several days after subarachnoid hemorrhage, reflecting chemical meningitis caused by subarachnoid blood.

“Traumatic” tap

Bloody, supernatant clear

N

↑↑↑ fresh

↑

N

↑

Neg

Neg

Most blood in tube #1; least blood in tube #4.

Spirochetal, early, acute syphilitic meningitis

Clear to turbid

↑

0

25–2000, mostly MN

15–75

>50

Neg

Neg

PMN may predominate early. Positive serum RPR or VDRL. CSF VDRL insensitive. If clinical suspicion is high, institute treatment despite negative CSF VDRL.

Late CNS syphilis

Clear

Usually N

0

N or ↑

N

N or ↑

Neg

Neg

CSF VDRL insensitive.

“Neighborhood” meningeal reaction

Clear or turbid, often xanthochromic

Variable, usually N

Variable

↑

N

N or ↑

Neg

Usually Neg

May occur in mastoiditis, brain abscess, sinusitis, septic thrombophlebitis, brain tumor, intrathecal drug therapy.

Hepatic encephalopathy

N

N

0

≤5

N

N

Neg

Neg

CSF glutamine >15 mg/dL.

Uremia

N

Usually ↑

0

N or ↑

N or ↑

N or ↑

Neg

Neg

Diabetic coma

N

Low

0

N or ↑

↑

N

Neg

Neg

Ascites

None

Slight

Moderate to severe

Encephalopathy

None

Slight to moderate

Moderate to severe

Bilirubin, mg/dL (mcmol/L)

<2.0

(<34.2)

2–3

(34.2–51.3)

>3.0

(>51.3)

Albumin, g/dL (g/L)

>3.5

(>35)

2.8–3.5

(28–35)

<2.8

(<28)

Prothrombin time (seconds increased)

1–3

4–6

>6.0

Total Numerical Score and Corresponding Child Class

Breast cancer BRCA1 and BRCA2 mutations

Blood

Lavender

Mutations in two genes, BRCA1 and BRCA2, are the major cause of familial early-onset breast cancer. A mutation in either gene confers an increased risk of breast and ovarian cancer. Although many mutations have been reported in BRCA1 and BRCA2, three mutations found in Ashkenazi Jews have carrier frequencies high enough to warrant a preliminary screen before comprehensive and expensive testing such as DNA sequencing.

This assay detects the 185 del AG and 5382 ins C mutations in BRCA1 and the 6174 del T mutation in BRCA2. These three mutations have a combined carrier frequency of approximately 1.7% in the Ashkenazi Jewish population.

Euhus DM. New insights into the prevention and treatment of familial breast cancer. J Surg Oncol 2011;103:294. [PubMed: 21337561]

Surbone A. Social and ethical implications of BRCA testing. Ann Oncol 2011;22(Suppl 1):i60. [PubMed: 21285154]

Cystic fibrosis mutation

PCR + reverse dot blot

Blood

Lavender

Cystic fibrosis is caused by a mutation in the cystic fibrosis transmembrane regulator gene (CFTR). Over 800 mutations have been found, with the most common being ΔF508, present in 70% of cases. Approximately 90% persons with cystic fibrosis carry at least one ΔF508 mutation. Another mutation, G551D, accounts for 5% of CFTR mutations and identifies a select subgroup of patients for treatment with an agent that targets the specific mutant protein.

Test specificity approaches 100%, so a positive result should be considered diagnostic of a cystic fibrosis mutation. Because of the wide range of mutations, an assay for the Δ F508 mutation alone is 68% sensitive. Screening for 64 mutations provides a sensitivity of 70–95% in all US ethnic groups except Asians, and >81% when the US population is considered as a whole. The test can distinguish between heterozygous carriers and homozygous patients.

Cystic fibrosis is the most common inherited disease in North American Caucasians, affecting 1 in 2500 births. Caucasians have a carrier frequency of 1 in 25. The disease is autosomal recessive. Carrier screening might be offered to individuals and couples in high-risk groups (eg, Ashkenazi Jews, central or northern Europeans, one partner with cystic fibrosis, and individuals with a family history of cystic fibrosis) who seek preconception counseling, infertility care, or prenatal care.

Accurso FJ et al. Effect of VX-770 in persons with cystic fibrosis and the G551D-CFTR mutation. N Engl J Med 2010;363:1991. [PubMed: 21083385]

Lommatzsch ST et al. Genetics of cystic fibrosis. Semin Respir Crit Care Med 2009;30:531. [PubMed: 19760540]

Duchenne muscular dystrophy (DMD)

PCR, sequencing

Blood (lavender)

DMD is a rare, X-linked disease. It occurs as a result of mutations (mainly deletions) in the dystrophin gene at locus Xp21.2. Mutations lead to an absence of or defect in dystrophin, causing progressive muscle degeneration and loss of independent ambulation by the age of 13–16 years.

The multiplex PCR-based genetic testing may not detect all mutations, and dystrophin gene sequencing may be necessary.

Testing for a DMD mutation is necessary for confirming the diagnosis even if muscle biopsy demonstrates the absence of dystrophin protein expression.

Bushby K et al. Diagnosis and management of Duchenne muscular dystrophy. Part 1: diagnosis, and pharmacological and psychological management. Lancet Neurol 2010;9:77. [PubMed: 19945913]

Familial adenomatous polyposis (FAP)

PCR, Sequencing

Lavender

Familial adenomatous polyposis is an autosomal dominant condition, which predisposes the mutation carrier to colorectal cancer in early adulthood. The condition is characterized by hundreds to thousands of adenomatous polyps in the colon that usually develop in the second to third decade of life. A milder condition, termed Attenuated FAP (AFAP), lacks the classical features of FAP, with patients having fewer polyps and an older age of onset.

FAP has been linked to germline mutations of the APC gene.

A PCR-based assay is used to amplify all exons of the APC gene, and direct sequence analysis of PCR products corresponding to the entire APC coding region is performed.

The testing is used only to confirm clinical diagnosis of FAP and AFAP and to identify affected but asymptomatic family members in FAP/AFAP families in which a familial mutation has been identified.

Numerous germline mutations have been located between codons 156 and 2011 of the APC gene. Mutations spanning the region between codons 543 and 1309 are strongly associated with congenital hypertrophy of retinal pigment epithelium. Mutations between codons 1310 and 2011 are associated with increased risk of desmoid tumors. Mutations at codon 1309 are associated with early development of colorectal cancer. Mutations between codons 976 and 1067 are associated with increased risk of duodenal adenomas. The cumulative frequency of extracolonic manifestations is highest for mutations between codons 976 and 1067.

Jasperson KW et al. Hereditary and familial colon cancer. Gastroenterology 2010;138:2044. [PubMed: 20420945]

Pineda M et al. Detection of genetic alterations in hereditary colorectal cancer screening. Mutat Res 2010;693:19. [PubMed: 19931546]

Fragile X syndrome

PCR, Southern blot

Blood, cultured amniocytes

Lavender

Fragile X syndrome results from a mutation in the familial mental retardation-1 gene (FMRI), located at Xq27.3. Fully symptomatic patients have abnormal methylation of the gene (which blocks transcription) during oogenesis. The gene contains a variable number of repeating CGG sequences and, as the number of sequences increases, the probability of abnormal methylation increases. The number of copies increases with subsequent generations so that women who are unaffected carriers may have offspring who are affected.

Normal patients have 6–52 CGG repeat sequences. Patients with 52–200 repeat sequences are asymptomatic carriers (premutation). Patients with more than 200 repeat sequences (full mutation) are very likely to have abnormal methylation and to be symptomatic.

Fragile X syndrome is the most common cause of inherited mental retardation, occurring in 1 in 1000–1500 men and 1 in 2000–2500 women. Full mutations can show variable penetration in females, but most such women will be at least mildly retarded.

Chonchaiya W et al. Fragile X: a family of disorders. Adv Pediatr 2009;56:165. [PubMed: 19968948]

Hill MK et al. A systematic review of population screening for fragile X syndrome. Genet Med 2010;12:396. [PubMed: 20548240]

Hemochromatosis, hereditary

Blood

Lavender

Hereditary hemochromatosis is an autosomal recessive disorder of iron metabolism that varies in clinical severity. Three HFE gene mutations (C282Y, H63D, and S65C) have been described in most patients with hemochromatosis.

Mutations in genes encoding other iron regulation proteins (hepcidin, ferroportin, hemojuvelin, transferrin receptor 2) account for rare cases of hereditary hemochromatosis.

Homozygosity for the C282Y mutation is responsible for up to 90% of hemochromatosis patients. The estimated penetrance is 80% for men and 35% for women over 40. Compound heterozygosity (C282Y/H63D or C282Y/S65C) may cause hemochromatosis, but the penetrance is very low. Homozygous H63D genotypes (H63D/H63D) rarely show symptoms of hemochromatosis. Heterozygotes for C282Y (C282Y/WT), H63D (H63D/WT), or S65C (S65C/WT) are not significantly associated with hemochromatosis.

Pietrangelo A. Hereditary hemochromatosis: pathogenesis, diagnosis, and treatment. Gastroenterology 2010;139:393. [PubMed: 20542038]

Van Bokhoven MA et al. Diagnosis and management of hereditary haemochromatosis. BMJ 2011;342:c7251. [PubMed: 21248018]

Hemophilia A

Southern blot

Blood, cultured amniocytes

Lavender

Approximately half of severe hemophilia A cases are caused by a recurrent mutation, ie, an inversion mutations within intron 22 of the factor VIII gene. Methods are available for rapid detection of the intron 22 inversions.

Test specificity approaches 100%, so a positive result should be considered diagnostic of a hemophilia A inversion mutation. Because of a variety of mutations, however, test sensitivity for hemophilia A is only about 50%.

Hemophilia A is one of the most common X-linked diseases in humans, affecting 1 in 5000 men.

De Brasi CD et al. Molecular characteristics of the intron 22 homologs of the coagulation factor VIII gene: an update. J thromb Haemost 2008;6:1822. [PubMed: 19647227]

Shetty S et al. Challenges of multiple mutations in individual patients with haemophilia. Eur J Haematol 2011;86:185. [PubMed: 21175850]

Hereditary nonpolyposis colorectal cancer

PCR, sequencing

Blood (EDTA) and tumor tissue block

Hereditary nonpolyposis colorectal cancer (HNPCC) (also called Lynch syndrome) accounts for 3–4% of all colorectal cancers. It is caused by inactivation of DNA mismatch repair genes (eg, MLH1, MSH2, MSH6), resulting in accumulation of spontaneous mutations in short repetitive DNA sequences termed microsatellites.

Initial screening includes microsatellite instability (MSI) and immunohistochemistry (IHC) analysis. If MSI is scored as high (MSI-H) and IHC demonstrates the absence of one of the three mismatch repair protein in tumor tissue, then direct sequencing of MLH1, MSH2, or MSH6 is performed to identify the mutation(s).

Testing is used to confirm clinical diagnosis in those with colorectal cancer who meet Amsterdam and/or Bethesda criteria for diagnosis of HNPCC. Once the familial mutation is identified, testing at-risk family members for the specific mutation can be performed.

Jasperson KW et al. Hereditary and familial colon cancer. Gastroenterology 2010;138:2044. [PubMed: 20420945]

Pineda M et al. Detection of genetic alterations in hereditary colorectal cancer screening. Mutat Res 2010;693:19. [PubMed: 19931546]

Huntington disease

PCR + Southern blot

Blood, cultured amniocytes, or buccal cells

Lavender

Huntington disease is an inherited neurodegenerative disorder associated with an autosomal dominant mutation on chromosome 4. The disease is highly penetrant, but symptoms (disordered movements, cognitive decline, and emotional disturbance) are often not expressed until middle age. The mutation results in the expansion of a CAG trinucleotide repeat sequence within the gene that encodes Huntington protein.

Normal patients have fewer than 34 CAG repeats, whereas patients with disease usually have more than 37 repeats and may have 80 or more. Occasional affected patients can be seen with “high normal” (32–34) numbers of repeats. Tests showing 34–37 repeats are indeterminate.

Huntington disease testing involves ethical dilemmas. Counseling is recommended before testing.

Ross CA et al. Huntington’s disease: from molecular pathogenesis to clinical treatment. Lancet Neurol 2011;10:83. [PubMed: 21163446]

Roze E et al. Huntington’s disease. Adv Exp Med Biol 2010;685:45. [PubMed: 20687494]

Kennedy disease/spinal and bulbar muscular atrophy (KD/SBMA)

PCR, Southern blot, sequencing

Lavender

The disease is a degenerative neuromuscular disorder. Familial and sporadic cases are caused by expansion of a CAG trinucleotide tandem repeat in exon 1 of the androgen receptor gene on chromosome Xq11-12.

Normal individuals have up to 30 CAG repeats; patients with KD/SBMA have ≥ 40 CAG repeats (sensitivity >99%).

Finsterer J. Perspective of Kennedy’s disease. J Neurol Sci 2010;298:1. [PubMed: 20846673]

Myotonic dystrophy (MD)

PCR, Southern blot, sequencing

Lavender

The disease is caused by expansions of microsatellite repeats. The most common mutation associated with DM1 is expansion of the trinucleotide repeat CTG in the DMPK gene, and for DM2, the expansion of the CCTG repeat in the ZNF9 gene.

Affected individuals have 50 to several thousands repeats.

Radvansky J et al. The expanding world of myotonic dystrophies: how can they be detected? Genet Test Mol Biomarkers 2010;14:733. [PubMed: 20939737]

Turner C et al. The myotonic dystrophies: diagnosis and management. J Neurol Neurosurg Psychiatry 2010;81:358-67. [PubMed: 20176601]

Neurofibromatosis (NF): von Recklinghausen disease (NF1) and bilateral acoustic NF (NF2)

PCR, Southern blot

Lavender

NF1 is one of the most common genetic disorders of humans (1 in 3500). The NF1 gene is located at chromosome region 17q11.2 and codes for the neurofibromin protein. Mutations in the merlin gene are responsible for NF2, which is characterized by bilateral schwannomas.

The mutations tested by the DNA analysis are laboratory-dependent. Clinical correlation is important.

Ferner RE. The neurofibromatosis. Pract Neurol 2010;10:82. [20308235]

Lu-Emerson C et al. The neurofibromatosis. Part 1: NF1. Rev Neurol Dis 2009;6:E47. [PubMed: 19587630]

Lu-Emerson C et al. The neurofibromatosis. Part 2: NF2 and schwannomatosis. Rev Neurol Dis 2009;6:E81. [PubMed: 19898272]

Niemann-Pick disease

PCR, sequencing

Lavender

The disease is rare autosomal recessive lysosomal storage disorder. Three mutations (c.911T>C, c.996delC, c.1493G>T) in the acid sphingomyelinase (SMPD1) gene account for >94% of cases of type A disease that results in severe neurologic impairment in infancy and childhood. For type C disease, mutational analysis (NPC1 or NPC2/HE1 gene) is also available.

The combination of DNA and biochemical (sphingomyelinase activity) analyses improves the detection rate of the disease.

Rosenbaum AI et al. Niemann-Pick type C disease: molecular mechanisms and potential therapeutic approaches. J Neurochem 2011;116:789. [PubMed: 20807315]

Schuchman EH. The pathogenesis and treatment of acid sphingomyelinase-deficienct Niemann-Pick disease. Int J Clin Pharmacol Ther 2009;47(Suppl 1):S48. [PubMed: 20040312]

Phenylketonuria (PKU)

PCR, sequencing, Southern blot

Lavender

The severity of the disease correlates with extent of mutations of the phenylalanine hydroxylase (PAH) gene. Little or no enzyme activity results in the classic PKU.

Phenylalanine hydroxylase activity determines the type of replacement therapy.

More than 400 point mutations in the PAH gene have been reported, and thus direct sequencing the entire coding regions of the gene may be necessary.

Blau N et al. Phenylketonuria. Lancet 2010;376:1417. [PubMed: 20971365]

Prader-Willi syndrome (PWS), Angelman syndrome (AS)

FISH, chromosomal analysis

Blood

Green

Prader-Willi syndrome and Angelman syndrome are clinically different diseases related at the molecular level. They are caused by loss of function mutations in two chromosomal regions located close to each other on chromosome 15. An interstitial deletion of 15q11-13 is found in about 70% of patients with PWS or AS. PWS results when the deletion affects the paternal chromosome, and AS occurs when it affects the maternal chromosome. A DNA probe from the affected region is used to determine the origin of the deletion by Southern blot analysis. In about 33% of patients with PWS and 20–30% with AS, no deletion can be found. Instead, uniparental disomy (UPD) may be found resulting in either two maternal or two paternal copies of chromosome 15. In 1–2% of patients with PWS and 20% of patients with AS, neither a deletion nor UPD can be found.

This test detects both the deletion and the UPD defects in PWS and AS.

Buiting K. Prader-Willi syndrome and Angelman syndrome. Am J Med Genet C Semin Med Genet 2010;154C:365. [PubMed: 20803659]

Tay-Sachs disease

PCR, Sequencing

Lavender

Tay-Sachs disease is an autosomal recessive disease caused by a deficiency of β-hexosaminidase A. Mutations in the α-subunit of hexosaminidase A are responsible for the enzyme deficiency. More than 75 mutations of the α-subunit gene have been described.

The mutations tested by the DNA analysis are laboratory-dependent. The combination of DNA and biochemical analyses improves the detection rate of the disease.

Norton ME. Genetic screening and counseling. Curr Opin Obstet Gynecol 2008;20:157. [PubMed: 18388816]

α-Thalassemia

PCR + Southern blot

Blood, cultured amniocytes, chorionic villi

Lavender

A deletion mutation in the α-globin gene region of chromosome 16 due to unequal crossing-over events can lead to defective synthesis of the α-globin chain of hemoglobin. Normally, there are two copies of the α-globin gene on each chromosome 16, and the severity of disease increases with the number of defective genes.

This assay is highly specific (approaches 100%). Sensitivity, however, can vary because detection of different mutations may require the use of different probes. α-Thalassemia due to point mutations may not be detected.

Patients with one deleted gene are usually normal or very slightly anemic; patients with two deletions usually have hypochromic microcytic anemia; patients with three deletions have elevated hemoglobin H and moderately severe hemolytic anemia (Hb H disease); patients with four deletions generally die in utero with hydrops fetalis.

The most clinically significant situations arise when both parents are carriers for a deletion that encompasses both α-globin genes (cis deletion), as seen mostly in Southeast Asian and Filipino populations. Each offspring of such carriers has a 25% risk of hydrops fetalis.

Less deleterious effects arise from chromosomes of Mediterranean and black ancestries. These chromosomes usually carry one α-globin gene deletion per chromosome. Offspring of carriers of a two α-globin gene deletion and single α-gene deletion are at risk for Hb H disease.

Higgs DR et al. The molecular basis of alpha thalassemia: a model for understanding human molecular genetics. Hematol Oncol Clin North Am 2010;24:1033. [PubMed: 21075279]

Lal A et al. Heterogeneity of hemoglobin H disease in childhood. N Engl J Med 2011;364:710. [PubMed: 21345100]

β-Thalassemia

PCR + reverse dot blot

Blood, chorionic villi, cultured amniocytes

Lavender

β-Thalassemia results from a mutation in the gene encoding the β-globin subunit of hemoglobin A (which is composed of a pair of α chains and a pair of β chains). A relative excess of α-globin chains precipitates within red blood cells, causing hemolysis and anemia. Over 300 different mutations have been described; testing usually covers a panel of the more common mutations. The test can distinguish between heterozygous and homozygous individuals.

Test specificity approaches 100%, so a positive result should be considered diagnostic of a thalassemia mutation. Because of the large number of mutations, sensitivity can be poor. A panel with the 43 most common mutations has a sensitivity that approaches 95%.

β-Thalassemia is very common; about 3% of the world’s population are carriers. The incidence is increased in persons of Mediterranean, African, and Asian descent. The mutations may vary from population to population, and different testing panels may be needed for patients of different ethnicities.

Cousens NE et al. Carrier screening for beta-thalassemia: a review of international practice. Eur J Hum Genet 2010;18:1077. [PubMed: 20571509]

Galanello R et al. Beta-thalassemia. Orphanet J Rare Dis 2010;5:11. [PubMed: 20492708]

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