Congenital Central Hypoventilation Syndrome due to PHOX2b gene defects: inheritance from asymptomatic parents

Congenital Central Hypoventilation Syndrome (CCHS, Ondine's curse) is a rare syndrome of dysfunction of the autonomic nervous system characterized by a decreased response to hypercarbia requiring mechanical ventilation in most cases. CCHS is an autosomal-dominant disease associated with tumors of neural crest origin, segmental aganglionosis of the colon, and diffuse autonomic dysregulation symptoms. Most cases of CCHS are caused by de novo heterozygous in-frame expansions within in the PHOX2b gene.

Here we report two families in which a PHOX2b defect was inherited from an asymptomatic parent. In family 1 an asymptomatic mother carried a mild mutation (15 bp expansion within the polyalanine repeat) also found in her daughter who was symptomatic immediately after birth but did not require mechanical ventilation. In family 2, two newborn infants with respiratory failure due to insufficient respiratory drive requiring mechanical ventilation were born to asymptomatic parents. A 39 pb expansion within the PHOX2b polyalanine repeat was found in one patient in whom DNA was available, but not in blood leukocytes from any parent. Microsatellite analyses confirmed the identity of the parents, such that a germline mosaicism has to be deduced.

Carriers of mild PHOX2b mutations causing disease in their offspring may be asymptomatic; Modifier genes determining the clinical course may exist. Germline mosaicism may lead to CCHS in children from unaffected parents. Genetic counseling should include these variations.