BACKGROUND: The deficiency of Rh proteins on red blood cells (RBCs) from individuals of the Rhnull amorph type are the result of homozygosity for a silent RHCE in cis with a deleted RHD. A novel mutation in RHce was identified in two Caucasian Brazilian girls with the amorph type of Rh null who were born to parents who were first cousins. STUDY DESIGN AND METHODS: RBCs from the Rhnull sisters and from family members were analyzed by serology and flow cytometry with specific antibodies. Genomic DNA and transcripts were tested by polymerase chain reaction and sequence analysis. RESULTS: Rhnull RBCs were nonreactive with anti-Rh and anti-LW. Molecular analyses showed a deletion of RHD and of one nucleotide (960/963; GGGG→GGG) in exon 7 of the RHce. This deletion introduced a frameshift after Gly321, a new C-terminal sequence, and a premature stop codon, resulting in a shorter predicted protein with 357 amino acids. CONCLUSION: The detection of a unique RHce transcript indicated that the two sisters were homozygous, whereas the other family members were heterozygous for the mutation. A novel mutation resulting in the amorph Rhnull with loss of Rh antigen expression is described.451117961798Huang, C.H., Liu, P.Z., Cheng, J.G., Molecular biology and genetics of the Rh blood group system (2000) Semin Hematol, 37, pp. 150-65Huang, C.H., Chen, Y., Reid, M.E., Seidl, C., Rhnull disease. the amorph type results from a novel double mutation in RhCe gene on D-negative background (1998) Blood, 92, pp. 664-71Cherif-Zahar, B., Matassi, G., Raynal, V., Molecular defects of the RHCE gene in Rh-deficient individuals of the amorph type (1998) Blood, 92, pp. 639-46Yamazaki, M.K., Okuda, H., Omi, T., Molecular genetic analysis of the Japanese amorph Rhnull phenotype (2000) Transfusion, 40, pp. 617-8Mallinson, G., Anstee, D.J., Avent, N.D., Murine monoclonal antibody MB-2D10 recognizes Rh-related glycoproteins in human red cell membrane (1990) Transfusion, 30, pp. 222-5Flegel, W.A., Wagner, F.F., RHD epitope density profiles of RHD variant red cells analysed by flow cytometry (1996) Transfus Clin Biol, 3, pp. 429-31Castilho, L., Rios, M., Bianco, C., DNA-based typing of blood groups for the management of multiply-transfused sickle cell disease patients (2002) Transfusion, 42, pp. 232-8