Prolonged exposure to thiopurines (eg, mercaptopurine [MP]) is essential for curative therapy in acute lymphoblastic leukemia (ALL), but is also associated with frequent dose-limiting hematopoietic toxicities, which is partly explained by inherited genetic polymorphisms in drug metabolizing enzymes (eg, ). Recently, our group and others identified germ line genetic variants in as another major cause of thiopurine-related myelosuppression, particularly in Asian and Hispanic people. In this article, we describe 3 novel coding variants (p.R34T, p.K35E, and p.G17_V18del) in 5 children with ALL enrolled in frontline protocols in Singapore, Taiwan, and at St. Jude Children's Research Hospital. Patients carrying these variants experienced significant toxicity and reduced tolerance to MP across treatment protocols. Functionally, all 3 variants led to partial to complete loss of NUDT15 nucleotide diphosphatase activity and negatively influenced protein stability. In particular, the p.G17_V18del variant protein showed extremely low thermostability and was completely void of catalytic activity, thus likely to confer a high risk of thiopurine intolerance. This in-frame deletion was only seen in African and European patients, and is the first risk variant identified in non-Asian, non-Hispanic populations. In conclusion, we discovered 3 novel loss-of-function variants in associated with MP toxicity, enabling more comprehensive pharmacogenetics-based thiopurine dose adjustments across diverse populations.

In this study, we demonstrate that an E3-ubiquitin ligase associated with human X-linked intellectual disability, CUL4B, plays a crucial role in post-meiotic sperm development. Initially, Cul4bΔ/Y male mice were found to be sterile and exhibited a progressive loss in germ cells, thereby leading to oligoasthenospermia. Adult Cul4b mutant epididymides also contained very low numbers of mature spermatozoa, and these spermatazoa exhibited pronounced morphological abnormalities. In post-meiotic spermatids, CUL4B was dynamically expressed and mitosis of spermatogonia and meiosis of spermatocytes both appeared unaffected. However, the spermatids exhibited significantly higher levels of apoptosis during spermiogenesis, particularly during the acrosome phase through the cap phase. Comparative proteomic analyses identified a large-scale shift between wild-type and Cul4b mutant testes during early post-meiotic sperm development. Ultrastructural pathology studies further detected aberrant acrosomes in spermatids and nuclear morphology. The protein levels of both canonical and non-canonical histones were also affected in an early spermatid stage in the absence of Cul4b. Thus, X-linked CUL4B appears to play a critical role in acrosomal formation, nuclear condensation, and in regulating histone dynamics during haploid male germ cell differentiation in relation to male fertility in mice. Thus, it is possible that CUL4B-selective substrates are required for post-meiotic sperm morphogenesis.

Mercaptopurine intolerance is an adverse effect of mercaptopurine administration in pediatric acute lymphoblastic leukemia. Recently, NUDT15 variants were identified as a major determinant of mercaptopurine intolerance. Two NUDT15 variants, c.36_37insGGAGTC and c.415C > T, are located on exons 1 and 3, respectively. Patients with heterozygous c.36_37insGGAGTC and c.415C > T can be either compound heterozygous with two variants on different alleles or heterozygous with both variants on the same allele. Because patients with biallelic NUDT15 variants are extremely sensitive to mercaptopurine, clinical identification of NUDT15 diplotype would be advantageous. A cohort of 37 patients with c.36_37insGGAGTC and c.415C > T NUDT15 variants were selected for haplotyping by targeted sequencing. NUDT15 complementary DNA was amplified and sequenced by 300-bp paired-end sequencing on Illumina MiSeq. Of the 37 patients carrying NUDT15 variants, 35 had heterozygous NUDT15 *1/*2 variants and two had compound heterozygous NUDT1 5*3/*6 and NUDT15 *2/*7 variants. These two patients with compound heterozygous variants could only tolerate low doses of mercaptopurine, similar to patients with homozygous NUDT15 variants. Targeted sequencing of NUDT15 cDNA can be used to determine NUDT15 diplotype and identify patients with compound heterozygous NUDT15 variants .

T-cell acute lymphoblastic leukemia (T-ALL) is caused by the accumulation of multiple genetic alterations. To determine the frequency of common genetic mutations and possible prognostic markers in childhood T-ALL, we performed targeted sequencing of 67 genes across 64 cases treated according to Taiwan Pediatric Oncology Group protocols between January 2002 and December 2015. Together, 302 variants were identified in 60 genes including 233 single nucleotide variants and 69 indels. Sixty-four samples had a median number of six genetic lesions each (range 1–17). Thirteen genes had mutation frequencies > 10%, and 5 were > 20%, with the highest being NOTCH1 (70.31%). Protocadherins FAT1 (32.81%) and FAT3 (17.19%), and the ubiquitin ligase component FBXW7 (28.13%) had higher mutation frequencies than previously reported. Other mutation frequencies (PHF6, DNM2, DNMT3A, CNOT3, and WT1) were within previously reported ranges. Three epigenetic-related genes (KMT2D, DNMT3A, and EZH2) were mutated in our cohort. JAK-STAT signaling pathway genes had mutation frequencies of 3–13% and were observed in 23 cases (35.94%). Changes to genes in the ErbB signaling pathway were detected in 20 cases (31.25%). Patients with NOTCH1/FBXW7 mutations and RAS/PTEN germline exhibited better 5-year overall survival rates.

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