STRs database » PHOX2B locus

Overview of repeats

Polyalanine repeat expansions in exon 3 of PHOX2B have been shown to be the main cause of the central hypoventilation syndrome (CCHS) and pathogenic alleles range from 24-33 alanine repeats, whereas the usual normal length of the allele is 20 repeats (Sivan et al. (2019)).

In an international registry analysis of 148 surveys, Vandemore et al. (2026) reported multisystem autonomic symptoms in genetically confirmed CCHS. Participants in the more severe PHOX2B variant group reported more symptoms in six of the seven organ systems assessed. Repetto et al. (2009) described later-onset hypoventilation with a 20/24 genotype and variably affected or asymptomatic relatives carrying the same allele, demonstrating reduced penetrance at 24 repeats.

→ View STRipy's population-wide repeat data for PHOX2B locus