Table 5. [PHOX2B GCN Expansion Technical Considerations]. - GeneReviews®

Technical Issue	Comment [Reference]
Sequence of repeat	The polyalanine repeat comprises any 1 of 4 codon combinations — GCA, GCT, GCC, or GCG – & is referred to as GCN.
Methods to detect expanded allele	Sanger sequencing
Repeat interruptions	None reported. See Sequence of repeat Comment (above) for variability in codon sequence.
Somatic instability	Not reported
Germline instability	Repeat stability during parent-to-child transmission, incl instances of parental mosaicism for the expansion, has been consistently observed [Weese-Mayer et al 2003, Trochet et al 2005, Weese-Mayer et al 2005, Antic et al 2006].

From: Congenital Central Hypoventilation Syndrome

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