diff --git a/cellbase-core/src/main/java/org/opencb/cellbase/core/variant/annotation/VariationDataReader.java b/cellbase-core/src/main/java/org/opencb/cellbase/core/variant/annotation/VariationDataReader.java
index <HASH>..<HASH> 100644
--- a/cellbase-core/src/main/java/org/opencb/cellbase/core/variant/annotation/VariationDataReader.java
+++ b/cellbase-core/src/main/java/org/opencb/cellbase/core/variant/annotation/VariationDataReader.java
@@ -24,7 +24,7 @@ public class VariationDataReader implements DataReader<Variant> {
     private Iterator<Variant> iterator;
     private final Logger logger = LoggerFactory.getLogger(this.getClass());
     private int nReadVariants = 0;
-    private static final String VARIANT_STRING_PATTERN = "[ACGTN]*";
+    private static final String VARIANT_STRING_PATTERN = "[ACGT]*";
 
     public VariationDataReader(VariantDBAdaptor dbAdaptor, Query query, QueryOptions options) {
         this.dbAdaptor = dbAdaptor;
feature/annotatevariation: fix at VariationDataReader; Ns are no longer allowed in the ref/alt alleles