Werner syndrome (WS) is a rare autosomal recessive disorder characterized by systemic accelerated aging. It is caused by pathogenic variants of the WRN gene that encodes a nuclear helicase. In this report, we describe 4 newly identified WS cases among those referred to the Japanese Werner Consortium, Chiba University, Japan. All 4 cases were compound heterozygotes of the Japanese founder mutation, c.3139-1G>C, and a novel null pathogenic variant, c.1587G>A, c.2448+1G>A, or c.3233+1G>T, or an amino acid substitution variant, c.1720G>A, p.Gly574Arg. These 3 null pathogenic variants were not previously described. The p. Gly574Arg was previously reported in a European patient, and the identification of the second p. Gly574Arg case, with classical WS features, further confirmed the pathogenic nature of this variant. For the case with c.3233+1G>T, we determined the phase of 2 disease-causing mutations and demonstrated that they are on different chromosomes. This assay would be particularly important for those cases with ambiguous clinical diagnosis.