Genomic Analisys of Notch Mutations in a Case of Alagille Syndrome with Acute Lymphoblastic Leukemia

Alagille syndrome (ALGS), or arteriohepatic dysplasia, is a congenital multisystem disease due to Notch signalling pathway mutations, most commonly affecting JAGGED-1 (ALGS type 1), and more rarely NOTCH-2 (ALGS type 2), leading to hepatic, lung, renal and ocular dysfunction (chronic cholestasis, peripheral pulmonary artery stenosis, dysplastic kidneys pigmentary retinopathy), and skeletal abnormalies (minor vertebral segmentation, characteristic facies, posterior embryotoxon/anterior segment defects). ALGS is an autosomal dominant disease, but it is characterized also by variable penetrance and clinical expression and somatic/germline mosaicism.

A 20-year-old man with ALGS was admitted to the University Hospital of Verona because of pancytopenia. Following analyses led to the diagnosis of Philadelphia chromosome/bcr-abl-negative, CD10-positive, B-lineage acute lymphoblastic leukemia (common B-ALL).

In order to identify the genetic components involved in this complex phenotype, we sequenced the exome of a bone marrow sample collected from the patient. By genome interpretation with Knome pipeline applied to the reference genome UCSC hg19, we found missense variants both in NOTCH-2 (E38K) and JAGGED-1 (P871R) genes that are mainly involved in the syndrome, although their effect on protein function was predicted not to be deleterious. However, we detected putative damaging mutations in genes such as PAX5 (R38H) and NOTCH-1 (K1821N), which might be strongly related to the observed disease. In fact, PAX5 is a member of PAX protein family of transcription factors implicated into regulation of early development that binds NOTCH-2 and likely altering its functionality. On the other hand, NOTCH-1 is involved in cell growth and proliferation and thus the predicted alteration of function of the corresponding protein may have an important role in neoplastic transformation.