Although any disorder for which the genetic basis and responsible genetic variant(s) are known can be diagnosed prenatally by DNA analysis, more than 100 metabolic disorders can also be diagnosed by biochemical analysis of chorionic villus tissue or cultured amniotic fluid cells. A few rare conditions can even be identified directly by assaying a substance in amniotic fluid. Most metabolic disorders are rare in the general population but have a high recurrence risk since most are autosomal recessive conditions. Because each condition is rare, the experience of the laboratory performing the prenatal diagnostic testing is important and it should be done at specialized centers. Whenever possible, a biochemical assay on directly sampled chorionic villus tissue (as opposed to cultures) is preferred to avoid misinterpretation of results due to the expansion in culture of contaminating maternal cells. Access to a cultured cell line from an affected individual in the family is highly advisable so that the laboratory can confirm its ability to detect the biochemical abnormality in the proband before the assay is attempted in CVS or amniotic fluid cells from the pregnancy at risk. Many metabolic disorders cannot be diagnosed prenatally by enzyme assays because the enzyme is not expressed in amniocytes or chorionic villi or a reliable biochemical assay is not available. For these, DNA sequencing should be performed.

Biochemical tests have one advantage over DNA: they can detect abnormalities caused by any mutant allele that has a significant effect on the protein function. This is particularly significant for disorders with a high degree of allelic heterogeneity, genes in which pathogenic variants occur in regions that are not routinely sequenced, or by a high proportion of new mutations. In addition, biochemical testing may be the only option for prenatal diagnosis if the causative mutations in the family are unknown.

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مواضيع ذات صلة

Laboratory Diagnosis of Urinary Tract Infections

Identification of Mycoplasma Infections

Laboratory Diagnosis of Infections of the Eyes

Laboratory Diagnosis of Central Nervous System Infections

Diagnosis and Differential Diagnosis of Paroxysmal Nocturnal Hemoglobinuria

Differential Diagnosis of Pancytopenia

Diagnosis of Aplastic anemia

Diagnosis of Upper Respiratory Tract Infections

tuberculosis testing (TB testing, Interferon gamma release assay [IGRA, T-Spot.TB], QuantiFERON-TB Gold [QFT, QFT-G, TB Gold test, TB blood test], Nucleic acid amplification for TB [NAAT], TB antibody)

thyrotropin-releasing hormone stimulation test (TRH stimulation test, Thyrotropin-releasing factor stimulation test [TRF stimulation test])

Laboratory Diagnosis of Lower Respiratory Tract Infections: Specimen Processing

Laboratory Diagnosis of Lower Respiratory Tract Infections: Specimen Collection and Transport