diff --git a/scripts/importer/data_importer/raw_data_importer.py b/scripts/importer/data_importer/raw_data_importer.py
index 54becd36b..ec754f597 100644
--- a/scripts/importer/data_importer/raw_data_importer.py
+++ b/scripts/importer/data_importer/raw_data_importer.py
@@ -298,29 +298,43 @@ def _parse_manta(self):  # pylint: disable=too-many-locals,too-many-branches,too
                                                       finished=True)
         self.log_insertion(counter, "breakend", start)
 
-    def _add_variants_to_db(self, batch: list, genes: list, transcripts: list,  # pylint: disable=too-many-arguments
-                            ref_genes: dict, ref_transcripts: dict):
-        """Add variants to db."""
+    def _estimate_variant_lastid(self):  # pylint: disable=no-self-use
+        """
+        Return the id of the variant with the highest id.
+
+        Returns 0 if table is empty.
+
+        Returns:
+            int: id of the variant with highest id or 0
+
+        """
+        try:
+            return (db.Variant.select(db.Variant.id)
+                    .order_by(db.Variant.id.desc())
+                    .limit(1)
+                    .get().id)
+        except db.Variant.DoesNotExist:
+            return 0
+
+    def _add_variants_to_db(self, batch: list, genes: list, transcripts: list, references: dict):
+        """
+        Add variants to db.
+
+        Args:
+            batch (list): variant data (dict)
+            genes (list): genes for the variants
+            transcripts(list): transcripts for the variants
+            references (dict): reference genes and transcripts
+        """
         if not self.settings.beacon_only:
-            # estimate variant dbid start
-            try:
-                curr_id = (db.Variant.select(db.Variant.id)
-                           .order_by(db.Variant.id.desc())
-                           .limit(1)
-                           .get().id)
-            except db.Variant.DoesNotExist:
-                # assumes next id will be 1 if table is empty
-                curr_id = 0
+            curr_id = self._estimate_variant_lastid()
 
         db.Variant.insert_many(batch).execute()
 
         # check if the variant dbid estimate is correct, otherwise must check manually
         if not self.settings.beacon_only:
-            last_id = (db.Variant.select(db.Variant.id)
-                       .order_by(db.Variant.id.desc())
-                       .limit(1)
-                       .get().id)
-            if last_id-curr_id == len(batch):
+            last_id = self._estimate_variant_lastid()
+            if last_id and last_id-curr_id == len(batch):
                 indexes = list(range(curr_id+1, last_id+1))
             else:
                 logging.warning("Bad match between ids - slow check")
@@ -329,8 +343,8 @@ def _add_variants_to_db(self, batch: list, genes: list, transcripts: list,  # py
                     indexes.append(db.Variant.select(db.Variant.id)
                                    .where(db.Variant.variant_id == entry['variant_id'])
                                    .get().id)
-            self._add_variant_genes(indexes, genes, ref_genes)
-            self._add_variant_transcripts(indexes, transcripts, ref_transcripts)
+            self._add_variant_genes(indexes, genes, references['genes'])
+            self._add_variant_transcripts(indexes, transcripts, references['transcripts'])
 
     def _get_genes_transcripts(self):
         """
@@ -368,7 +382,7 @@ def _insert_variants(self):  # pylint: disable=too-many-locals,too-many-branches
         vep_field_names = None
         with db.database.atomic():
             for filename in self.settings.variant_file:  # pylint: disable=too-many-nested-blocks
-                ref_genes, ref_transcripts = self._get_genes_transcripts()
+                references = dict(zip(('genes', 'transcripts'), self._get_genes_transcripts()))
                 for line in self._open(filename, binary=False):
                     line = line.strip()
 
@@ -480,8 +494,7 @@ def _insert_variants(self):  # pylint: disable=too-many-locals,too-many-branches
                             self._add_variants_to_db(batch,
                                                      genes,
                                                      transcripts,
-                                                     ref_genes,
-                                                     ref_transcripts)
+                                                     references)
                         genes = []
                         transcripts = []
                         batch = []
@@ -495,8 +508,7 @@ def _insert_variants(self):  # pylint: disable=too-many-locals,too-many-branches
                 self._add_variants_to_db(batch,
                                          genes,
                                          transcripts,
-                                         ref_genes,
-                                         ref_transcripts)
+                                         references)
 
         if self.settings.set_vcf_sampleset_size and samples:
             self.sampleset.sample_size = samples