{{Rsnum
|rsid=4148740
|Gene=ABCB1
|Chromosome=7
|position=87522787
|Orientation=minus
|GMAF=0.1299
|Assembly=GRCh38
|GenomeBuild=38.1
|dbSNPBuild=141
|geno1=(C;C)
|geno2=(C;T)
|geno3=(T;T)
|Gene_s=ABCB1
}}{{ population diversity
| geno1=(C;C)
| geno2=(C;T)
| geno3=(T;T)
| CEU | 1.8 | 17.9 | 80.4
| HCB | 0.0 | 4.8 | 95.2
| JPT | 2.4 | 9.5 | 88.1
| YRI | 3.9 | 17.6 | 78.4
| ASW | 0.0 | 0.0 | 0.0
| CHB | 0.0 | 4.8 | 95.2
| CHD | 0.0 | 0.0 | 0.0
| GIH | 0.0 | 0.0 | 0.0
| LWK | 0.0 | 0.0 | 0.0
| MEX | 0.0 | 0.0 | 0.0
| MKK | 0.0 | 0.0 | 0.0
| TSI | 0.0 | 0.0 | 0.0
| HapMapRevision=28
}}[[rs4148740]] is a SNP in the [[ABCB1]] gene (also known as the MDR1 gene), which encodes a protein that transports certain molecules across the blood-brain barrier. SNPs in [[ABCB1]] may thus influence the intracerebral concentrations of certain drugs and thus their efficacy or potential for adverse side effects. [[rs4148740]] is one of 9 SNPs found within a tight linkage block (r<sup>2</sup> >= 0.8 ) such that the minor allele at any one of them predicts (with ~80%+ accuracy) that the other SNPs will also be the minor allele. The list of the 9 SNPs is shown below.

When treated for [[depression]] with substrates of the protein encoded by [[ABCB1]], carriers of one or two minor alleles at these [[ABCB1]] SNPs have been reported to respond better than non-carriers. The [[antidepressant]] drugs that are known to be substrates include [[citalopram]], [[paroxetine]], [[amitriptyline]], and [[venlafaxine]]. The relative odds of better response for [[rs4148740]](T) carriers is 7.72 (CI: 2.8-21.3, p=0.000065) based on a study of ~400 primarily Caucasian patients.{{doi|10.1016/j.neuron.2007.11.017}}

The 9 SNPs in the linkage block identified are {{doi|10.1016/j.neuron.2007.11.017}}:
* [[rs2235067]]
* [[rs4148740]]
* [[rs2032583]]
* [[rs4148739]]
* [[rs11983225]]
* [[rs2235040]]
* [[rs12720067]]
* [[rs7787082]]
* [[rs10248420]]

{{PharmGKB
|RSID=rs4148740
|Name_s=
|Gene_s=ABCB1
|Feature=
|Evidence=PubMed ID:18215618
|Annotation=This variant is associated with differences in clinical efficacy of antidepressants, most likely by influencing their access to the brain.
|Drugs=amitriptyline; citalopram; paroxetine; venlafaxine
|Drug Classes=
|Diseases=Depression
|Curation Level=Curated
|PharmGKB Accession ID=PA161615693
}}

{{PMID Auto
|PMID=15197162
|Title=Identifying candidate causal variants responsible for altered activity of the ABCB1 multidrug resistance gene.
|OA=1
}}

{{GET Evidence
|impact=pharmacogenetic
|qualified_impact=Insufficiently evaluated pharmacogenetic
|inheritance=unknown
|quality_scores=Array
|dbsnp_id=rs4148740
|overall_frequency_n=19
|overall_frequency_d=128
|overall_frequency=0.148438
|n_genomes=14
|n_genomes_annotated=0
|n_haplomes=17
|n_articles=1
|n_articles_annotated=0
|in_pharmgkb=Y
|autoscore=2
|webscore=N
|n_web_uneval=10
}}

{{on chip | 23andMe v3}}
{{on chip | 23andMe v4}}
{{on chip | HumanOmni1Quad}}