Published online before print
March 13, 2001, 10.1101/gr.GR-1610R
Vol. 11, Issue 4, 531-539, April 2001
Identification and Functional Analysis of Mutations in the Hypocretin (Orexin) Genes of Narcoleptic Canines
Marcel
Hungs,1,3
Jun
Fan,2,3
Ling
Lin,1
Xiaoyan
Lin,1
Richard A.
Maki,2 and
Emmanuel
Mignot1,4
1 Stanford Center for Narcolepsy, Stanford University
Medical Center, Department of Psychiatry and Behavioral Sciences, Palo
Alto, California 94304-5485, USA; 2 Neurocrine Biosciences,
San Diego, California 92121, USA
Narcolepsy is a sleep disorder affecting animals and humans. Exon
skipping mutations of the Hypocretin/Orexin-receptor-2
(Hcrtr2) gene were identified as the cause of narcolepsy in
Dobermans and Labradors. Preprohypocretin (Hcrt) knockout mice
have symptoms similar to human and canine narcolepsy. In this study, 11 sporadic cases of canine narcolepsy and two additional multiplex
families were investigated for possible Hcrt and
Hcrtr2 mutations. Sporadic cases have been shown to have more
variable disease onset, increased disease severity, and undetectable
Hypocretin-1 levels in cerebrospinal fluid. The canine Hcrt
locus was isolated and characterized for this project. Only one novel
mutation was identified in these two loci. This alteration results in a
single amino acid substitution (E54K) in the N-terminal region of the
Hcrtr2 receptor and autosomal recessive transmission in a Dachshund
family. Functional analysis of previously-described exon-skipping
mutations and of the E54K substitution were also performed using
HEK-293 cell lines transfected with wild-type and mutated constructs.
Results indicate a truncated Hcrtr2 protein, an absence of proper
membrane localization, and undetectable binding and signal transduction
for exon-skipping mutated constructs. In contrast, the E54K abnormality
was associated with proper membrane localization, loss of ligand
binding, and dramatically diminished calcium mobilization on activation
of the receptor. These results are consistent with a loss of function for all three mutations. The absence of mutation in sporadic cases also
indicates genetic heterogeneity in canine narcolepsy, as reported
previously in humans.
3
These authors contributed equally to this work.
4
Corresponding author.
11:531-539 ©2001 by Cold Spring Harbor Laboratory Press ISSN 1088-9051/01 $5.00

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