Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (1155 page)

   Fetal sexing for history of X-linked disorders

   Limitations

   
FISH

   Targeted test that assesses only specific region on chromosome; does not ensure that entire chromosome is normal and does not assess every chromosome.

   Mosaicism may also confound results.

   
Chromosome analysis

   Analysis cannot detect aberrations smaller than 5–10 megabases; requires cell culture to obtain actively dividing metaphase cells.

   Mosaicism, the presence of two cell lines, may be difficult to interpret, because chromosome anomalies can arise in vitro during specimen culture.

GENOMIC MICROARRAY ANALYSIS—ARRAY COMPARATIVE GENOMIC HYBRIDIZATION (aCGH)
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   Definition

   This technology uses probes covering the entire genome and can detect chromosome abnormalities up to 10 times smaller than those detectable by conventional chromosome analysis.

   Use

   Detection of chromosome abnormalities (copy number changes; e.g., deletion, duplication) up to 10 times smaller than can be detected by conventional chromosome analysis

   Detection of abnormalities that may be causal for developmental delay, autism, and congenital anomalies. Some laboratories are offering aCGH for prenatal diagnosis.