lepsy:  This subtype is caused by exon 21 DNA (cytosine-5)-methyltransferase-1 mu-
tations and is characterized by late-onset (age 30–40 years) narcolepsy (with low or
intermediate CSF hypocretin-1 levels), deafness, cerebellar ataxia, and eventually de-
mentia. 
347.00 (G47.419) Autosomal dominant narcolepsy, obesity, and type 2 diabetes:
Narcolepsy, obesity, and type 2 diabetes and low CSF hypocretin-1 levels have been
described in rare cases and are associated with a mutation in the myelin oligodendro-
cyte glycoprotein gene.
347.10 (G47.429) Narcolepsy secondary to a nother medical condition:  This sub-
type is for narcolepsy that develops secondary to medical conditions that cause infec-
tious (e.g., Whipple’s disease, sarcoidosis), traumatic, or tumoral destruction of
hypocretin neurons.
Coding note  (for ICD-9-CM code 347.10 only): Code first the underlying medical con-
dition (e.g., 040.2 Whipple’s disease; 347.10 narcolepsy secondary to Whipple’s dis-
ease).
Specify current severity:
Mild:  Infrequent cataplexy (less than once per week), need for naps only once or twice
per day, and less disturbed nocturnal sleep.
Moderate: Cataplexy once daily or every few days, disturbed nocturnal sleep, and
need for multiple naps daily.
Severe:  Drug-resistant cataplexy with multiple attacks daily, nearly constant sleepi-