Congenital central hypoventilation syndrome (CCHS or Ondine's curse; OMIM 209880) is a life-threatening disorder involving an impaired ventilatory response to hypercarbia and hypoxemia. This core phenotype is associated with lower-penetrance anomalies of the autonomic nervous system (ANS) including Hirschsprung disease and tumors of neural-crest derivatives such as ganglioneuromas and neuroblastomas. In mice, the development of ANS reflex circuits is dependent on the paired-like homeobox gene Phox2b. Thus, we regarded its human ortholog, PHOX2B, as a candidate gene in CCHS. We found heterozygous de novo mutations in PHOX2B in 18 of 29 individuals with CCHS. Most mutations consisted of 5–9 alanine expansions within a 20-residue polyalanine tract probably resulting from non-homologous recombination. We show that PHOX2B is expressed in both the central and the peripheral ANS during human embryonic development. Our data support an essential role of PHOX2B in the normal patterning of the autonomous ventilation system and, more generally, of the ANS in humans.

Form and Function: The Planar Cell Polarity (PCP) signaling pathway governs cell movements that drive axis elongation and neural tube closure in vertebrate embryos, and certain vertebrate PCP proteins have also been implicated in ciliogenesis. Likewise, the septin cytoskeleton controls diverse cell behaviors, such as cytokinesis and cell migration, but little is known about how septin functions are regulated in vivo. Kim et al. (p. 1337 , published online 29 July; see the Perspective by Barral ) found that control of septins by the PCP effector protein, Fritz, was a crucial control point for morphogenesis and ciliogenesis. During neural tube closure, Fritz-mediated septin localization maintained cell shape but not cell polarity. In ciliated epithelial cells, Fritz was required for assembly of the septin rings at the base of cilia, which are needed for normal ciliogenesis and signaling.

Nicholas Katsanis and colleagues show that biallelic mutations in TTC21B, encoding the retrograde intraflagellar transport protein IFT139, are associated with diverse ciliopathy phenotypes in humans. They further show that pathogenic alleles of TTC21B are present in as many as 5% of ciliopathy cases, supporting an oligogenic model of disease. Ciliary dysfunction leads to a broad range of overlapping phenotypes, collectively termed ciliopathies. This grouping is underscored by genetic overlap, where causal genes can also contribute modifier alleles to clinically distinct disorders. Here we show that mutations in TTC21B, which encodes the retrograde intraflagellar transport protein IFT139, cause both isolated nephronophthisis and syndromic Jeune asphyxiating thoracic dystrophy. Moreover, although resequencing of TTC21B in a large, clinically diverse ciliopathy cohort and matched controls showed a similar frequency of rare changes, in vivo and in vitro evaluations showed a significant enrichment of pathogenic alleles in cases (P < 0.003), suggesting that TTC21B contributes pathogenic alleles to ∼5% of ciliopathy cases. Our data illustrate how genetic lesions can be both causally associated with diverse ciliopathies and interact in trans with other disease-causing genes and highlight how saturated resequencing followed by functional analysis of all variants informs the genetic architecture of inherited disorders.