Most isolated GHD is sporadic; thus, genetic screening of all cases for gene mutations is not feasible at present. However, new molecular techniques may soon make more widespread surveying possible. Evaluations for inherited GHAD should be considered in any family with a history of consanguinity or a second case of GHAD.
Initial observations of GH-1 deletions in patients were made using Southern blot analyses (64). PCR techniques provide an easier screening tool as they make it possible to amplify specific sequences from complex genomic samples directly. Vnencak-Jones et al. in 1990 described a technique where PCR amplification, followed by digestion with the restriction enzymes Bgll, Haell, and Smal, and then visualization of DNA fragments, could identify individuals with a variety of GH-1 gene deletions (147). This technique is useful for screening, but Southern blot analysis is still necessary in order to obtain the size of the deletion.
PCR-based single-strand conformational polymorphism (SSCP) analysis uses differential electrophoretic mobility to identify subtle conformational differences in single-stranded DNA (148). These differences can be evident even from a change as small as a point mutation resulting in a single base substitution. This technique also allows for monitoring of cosegregation by restriction-length polymorphism (RFLP) analysis.
Dideoxy fingerprinting (ddF) improves SSCP analysis, bringing its accuracy for detecting single base changes to nearly 100% (149). It also allows for amplification of large segments and subsequent screening of smaller regions. Reverse transcription PCR (RT-PCR) allows analysis of mutant mRNA transcripts to determine the effects of the genetic mutations in specific tissues (150). In the future, it is probable that these newer molecular diagnostic techniques will prove useful both in the prenatal and postnatal diagnosis of GHAD (151).
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