Original Investigation

Human Genetics

, Volume 121, Issue 2, pp 179-185

A case of true hermaphroditism reveals an unusual mechanism of twinning

  • Vivienne L. SouterAffiliated withDepartment of Obstetrics and Gynecology, Banner Good Samaritan Medical Center Email author 
  • , Melissa A. ParisiAffiliated withDepartment of Pediatrics, Childrens Hospital and Regional Medical Center, University of Washington
  • , Dale R. NyholtAffiliated withGenetic Epidemiology Laboratory, Queensland Institute of Medical Research
  • , Raj P. KapurAffiliated withDepartment of Laboratories, Seattle Childrens Hospital and Regional Medical Center
  • , Anjali K. HendersAffiliated withGenetic Epidemiology Laboratory, Queensland Institute of Medical Research
  • , Kent E. OpheimAffiliated withDepartment of Laboratories, Seattle Childrens Hospital and Regional Medical Center
  • , Daniel F. GuntherAffiliated withDepartment of Pediatrics, Childrens Hospital and Regional Medical Center, University of Washington
  • , Michael E. MitchellAffiliated withDepartment of Urology, Seattle Childrens Hospital and Regional Medical Center
  • , Ian A. GlassAffiliated withDepartment of Pediatrics, Childrens Hospital and Regional Medical Center, University of Washington
    • , Grant W. MontgomeryAffiliated withGenetic Epidemiology Laboratory, Queensland Institute of Medical Research

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Abstract

Traditionally twins are classified as dizygous or fraternal and monozygous or identical (Hall Twinning, 362, 2003 and 735–743). We report a rare case of 46,XX/46,XY twins: Twin A presented with ambiguous genitalia and Twin B was a phenotypically normal male. These twins demonstrate a third, previously unreported mechanism for twinning. The twins underwent initial investigation with 17-hydroxyprogesterone and testosterone levels, pelvic ultrasound and diagnostic laparoscopy. Cytogenetic analysis was performed on peripheral blood cells and skin fibroblasts. Histological examination and Fluorescence in situ hybridization studies on touch imprints were performed on gonadal biopsies. DNA analysis using more than 6,000 DNA markers was performed on skin fibroblast samples from the twins and on peripheral blood samples from both parents. Twin A was determined to be a true hermaphrodite and Twin B an apparently normal male. Both twins had a 46,XX/46,XY chromosome complement in peripheral lymphocytes, skin fibroblasts, and gonadal biopsies. The proportion of XX to XY cells varied between the twins and the tissues evaluated. Most significantly the twins shared 100% of maternal alleles and approximately 50% of paternal alleles in DNA analysis of skin fibroblasts. The twins are chimeric and share a single genetic contribution from their mother but have two genetic contributions from their father thus supporting the existence of a third, previously unreported type of twinning.