Strong evidence for a novel schizophrenia risk locus on chromosome 1p31.1 in homogeneous pedigrees from Tamil Nadu, India.
OBJECTIVE
The study of ethnically homogeneous populations may help to identify schizophrenia risk loci. The authors conducted a genomewide linkage scan for schizophrenia in an Indian population.


METHODS
Participants were 441 individuals (262 affected probands and siblings) who were recruited primarily from one ethnically homogeneous group, the Tamil Brahmin caste, although individuals from other geographically proximal castes also participated. Genotyping of 124 affected sibling pair pedigrees was performed with 402 short tandem repeat polymorphisms. Linkage analyses were conducted using nonparametric exponential LOD (logarithm of the odds ratio for linkage) scores and parametric heterogeneity LOD scores. Parametric heterogeneity scores were calculated using simple dominant and recessive models, correcting for multiple statistics. The data were examined for evidence of consanguinity. Genomewide significance levels were determined using 10,000 gene dropping simulations.


RESULTS
These findings revealed genomewide significant linkage to chromosome 1p31.1, through the use of both exponential and heterogeneity LOD scores, incorporating correction for multiple statistics and mild consanguinity. The estimated sibling recurrence risk associated with this putative locus was 1.95. Analysis for heterogeneity LOD scores also detected suggestive linkage to chromosomes 13q22.1 and 16q12.2. Using 117 tag single nucleotide polymorphisms (SNPs), family-based association analyses of phosphodiesterase 4B (PDE4B), the closest schizophrenia candidate gene, detected no convincing evidence of association, suggesting that the chromosome 1 peak represents a novel risk locus.


CONCLUSIONS
This is the first study-to the authors' knowledge-to report significant linkage of schizophrenia to chromosome 1p31.1. Further investigation of this chromosome region in diverse populations is warranted to identify underlying sequence variants.
Holliday
Elizabeth G
EG
correspondence and reprint requests to Prof. Mowry; bryan_mowry@qcmhr.uq.edu.au.
Nyholt
Dale R
DR
Tirupati
Srinivasan
S
John
Sujit
S
Ramachandran
Padmavati
P
Ramamurti
Mangala
M
Ramadoss
Ayankaran Jothi
AJ
Jeyagurunathan
Anitha
A
Kottiswaran
Sowndari
S
Smith
Heather J
HJ
Filippich
Cheryl
C
Nertney
Deborah A
DA
Nancarrow
Derek J
DJ
Hayward
Nicholas K
NK
Watkins
W Scott
WS
Jorde
Lynn B
LB
Thara
Rangaswamy
R
Mowry
Bryan J
BJ
D000328:Adult; D000483:Alleles; D002874:Chromosome Mapping; D002878:Chromosomes, Human, Pair 1 / Q000235:genetics*; D003241:Consanguinity; D054703:Cyclic Nucleotide Phosphodiesterases, Type 4 / Q000235:genetics; D005260:Female; D005838:Genotype; D006801:Humans; D007194:India; D008126:Lod Score; D008297:Male; D018895:Microsatellite Repeats / Q000235:genetics; D008875:Middle Aged; D020641:Polymorphism, Single Nucleotide / Q000235:genetics; D012559:Schizophrenia / Q000175:diagnosis / Q000208:ethnology / Q000235:genetics*
D054703:Cyclic Nucleotide Phosphodiesterases, Type 4; C517360:PDE4B protein, human