A Rare Variant of Turner Syndrome With Isodicentric X Chromosome Resulting in Trisomy: A Case Report

Introduction: Turner syndrome is a genetic disorder caused by the loss of an X-chromosome affecting approximately 1 in every 2,500 females. A constitutional karyotype of 45, X accounts for nearly 50% of patients, while mosaicism and other chromosomal structural abnormalities such as deletions, duplications, ring, isodicentric chromosomes, inversions and translocations, have been reported. Isodicentric X chromosomes are formed presumably by end-to-end fusion of chromatids after a break, with subsequent loss of an acentric fragment. These chromosomes in general have phenotypes characteristic of the resultant X deletions. We present a case of a 14-year-old female diagnosed with Turner syndrome and with 2 abnormal cell lines. Case Presentation: This is a case of a 14-year-old female referred to pediatric endocrinology for concerns of short stature and delayed puberty. She denied any food intolerance, bloating and diarrhea. She is otherwise healthy with unremarkable past medical history. Her weight was normal at 15th percentile. Her height was 137cm or 0.01 percentile with a Z score of –3.6. Work up revealed hypothyroidism with TSH 16.3 mcIU/mL (0.4-4.7 mcIU/mL), positive thyroid peroxidase antibody >900 IU/ml and thyroglobulin antibody 14 IU/mL (< 1.8IUm/mL) and celiac disease (tissue transglutaminase IgA > 100 U/mL) both without associated symptoms. Estradiol level was undetectable, and LH and FSH were 9.89 mIU/ml and 52.69 mIU/ml respectively. The rest of her labs including growth factors were normal. Bone age was normal at 13 years for chronological age of 14 years old. Chromosomal microarray revealed 2 abnormal cell lines: one with monosomy X, the other with a normal X chromosome and an isodicentric X chromosome involving the Xp11.22-q28 region resulting in trisomy of the latter cell line. Levothyroxine was started. Plan is to start growth hormone therapy and initiate puberty after. Patient referred to necessary subspecialties for hearing evaluation as well as cardiac evaluation Conclusion Turner syndrome usually presents as females with short stature, gonadal dysgenesis and 45,X cell line that is either singly or in combination with another mosaic cell line. Our patient presented with short stature and absence of puberty. Initial investigation revealed hypothyroidism and highly positive celiac antibodies, but unable to attribute her short stature to both diagnoses given the lack of other symptoms. This case emphasizes the importance of checking the karyotype in females presenting with short stature and more importantly delayed puberty as part of the diagnostic algorithm. In addition, checking thyroid and celiac panel are also imperative as treatment of these are treatable etiologies of short stature.