diff --git a/transcriptomics_data_service/routers/normalization.py b/transcriptomics_data_service/routers/normalization.py
index a507208..d845ce7 100644
--- a/transcriptomics_data_service/routers/normalization.py
+++ b/transcriptomics_data_service/routers/normalization.py
@@ -5,7 +5,7 @@
 from transcriptomics_data_service.db import DatabaseDependency
 from transcriptomics_data_service.models import GeneExpression
 from transcriptomics_data_service.scripts.normalize import (
-    read_counts2tpm,
+    tpm_normalization,
     tmm_normalization,
     getmm_normalization,
 )
@@ -36,35 +36,38 @@ async def normalize(
     """
     Normalize gene expressions using the specified method for a given experiment_result_id.
     """
-    # method validation
-    if method not in VALID_METHODS:
+    # Method validation
+    if method.lower() not in VALID_METHODS:
         raise HTTPException(
             status_code=status.HTTP_400_BAD_REQUEST, detail=f"Unsupported normalization method: {method}"
         )
 
-    # load gene lengths
-    if method in [NORM_TPM, NORM_GETMM]:
+    # Load gene lengths if required
+    if method.lower() in [NORM_TPM, NORM_GETMM]:
         if gene_lengths_file is None:
             raise HTTPException(
                 status_code=status.HTTP_400_BAD_REQUEST,
                 detail=f"Gene lengths file is required for {method.upper()} normalization.",
             )
         gene_lengths = await _load_gene_lengths(gene_lengths_file)
+    else:
+        gene_lengths = None
 
+    # Fetch raw counts from the database
     raw_counts_df = await _fetch_raw_counts(db, experiment_result_id)
 
-    # normalization
-    if method == NORM_TPM:
+    # Perform normalization
+    if method.lower() == NORM_TPM:
         raw_counts_df, gene_lengths_series = _align_gene_lengths(raw_counts_df, gene_lengths)
-        normalized_df = read_counts2tpm(raw_counts_df, gene_lengths_series)
-    elif method == NORM_TMM:
+        normalized_df = tpm_normalization(raw_counts_df, gene_lengths_series)
+    elif method.lower() == NORM_TMM:
         normalized_df = tmm_normalization(raw_counts_df)
-    elif method == NORM_GETMM:
+    elif method.lower() == NORM_GETMM:
         raw_counts_df, gene_lengths_series = _align_gene_lengths(raw_counts_df, gene_lengths)
         normalized_df = getmm_normalization(raw_counts_df, gene_lengths_series)
 
-    #  database update using normalized values
-    await _update_normalized_values(db, normalized_df, experiment_result_id, method=method)
+    # Update database with normalized values
+    await _update_normalized_values(db, normalized_df, experiment_result_id, method=method.lower())
 
     return {"message": f"{method.upper()} normalization completed successfully"}
 
@@ -74,8 +77,13 @@ async def _load_gene_lengths(gene_lengths_file: UploadFile) -> pd.Series:
     Load gene lengths from the uploaded file.
     """
     content = await gene_lengths_file.read()
-    gene_lengths_df = pd.read_csv(StringIO(content.decode("utf-8")), index_col="GeneID")
-    gene_lengths_series = gene_lengths_df["GeneLength"]
+    gene_lengths_df = pd.read_csv(StringIO(content.decode("utf-8")), index_col=0)
+    if gene_lengths_df.shape[1] != 1:
+        raise HTTPException(
+            status_code=status.HTTP_400_BAD_REQUEST,
+            detail="Gene lengths file should contain exactly one column of gene lengths.",
+        )
+    gene_lengths_series = gene_lengths_df.iloc[:, 0]
     gene_lengths_series = gene_lengths_series.apply(pd.to_numeric, errors="raise")
     return gene_lengths_series
 
@@ -85,7 +93,9 @@ async def _fetch_raw_counts(db, experiment_result_id: str) -> pd.DataFrame:
     Fetch raw counts from the database for the given experiment_result_id.
     Returns a DataFrame with genes as rows and samples as columns.
     """
-    expressions = await db.fetch_gene_expressions_by_experiment_id(experiment_result_id)
+    expressions, _ = await db.fetch_gene_expressions(
+        experiments=[experiment_result_id], method="raw", paginate=False
+    )
     if not expressions:
         raise HTTPException(status_code=status.HTTP_404_NOT_FOUND, detail="Experiment result not found.")
 
@@ -116,10 +126,12 @@ def _align_gene_lengths(raw_counts_df: pd.DataFrame, gene_lengths: pd.Series):
 
 async def _update_normalized_values(db, normalized_df: pd.DataFrame, experiment_result_id: str, method: str):
     """
-    Update the normalized values in the database
+    Update the normalized values in the database.
     """
     # Fetch existing expressions to get raw_count values
-    existing_expressions = await db.fetch_gene_expressions_by_experiment_id(experiment_result_id)
+    existing_expressions, _ = await db.fetch_gene_expressions(
+        experiments=[experiment_result_id], method="raw", paginate=False
+    )
     raw_count_dict = {(expr.gene_code, expr.sample_id): expr.raw_count for expr in existing_expressions}
 
     normalized_df = normalized_df.reset_index().melt(
@@ -138,6 +150,7 @@ async def _update_normalized_values(db, normalized_df: pd.DataFrame, experiment_
                 detail=f"Raw count not found for gene {gene_code}, sample {sample_id}",
             )
 
+        # Create a GeneExpression object with the normalized value
         gene_expression = GeneExpression(
             gene_code=gene_code,
             sample_id=sample_id,