A cll-year-old man fell into type II respiratory failure after catching a c
old, and became dependent on a respirator, Chest radiography showed no abno
rmalities and the hyperventilation test showed improved arterial blood gas
findings. His sleep study showed marked nocturnal desaturation due to hypop
nea and apnea with a decrease of thoracic and abdominal movement during sle
ep, Therefore, we diagnosed hint as primary alveolar hypoventilation syndro
me (PAH), Seven years previously, his 2-year elder sister had suffered from
similar respiratory failure during her second pregnancy and had been diagn
osed as PAH, While myopathy was suspected in both cases, attenuation of mus
cle strength was slight and it appeared not to be the main cause of alveola
r hypoventilation, Since medication was not effective in each case, they un
derwent non-invasive positive pressure ventilation (NIPPV). While sustained
mild hypercapnia remained during the daytime, it improved their respirator
y failure, To our knowledge, this is the first study of familial adult onse
t PAH.