WBR0114
| Author | [[PageAuthor::William J Gibson (Reviewed by Yazan Daaboul, M.D.)]] |
|---|---|
| Exam Type | ExamType::USMLE Step 1 |
| Main Category | MainCategory::Genetics |
| Sub Category | SubCategory::Endocrine, SubCategory::Reproductive |
| Prompt | [[Prompt::A 14-year-old girl is evaluated for failure to experience menarche. The patient is 1.45 m (4’ 9”) tall, has downward slanting of the eyes, low hairline, and a webbed neck. Further inspection reveals a broad chest and increased carrying angle of the elbow. Which of the following findings are most likely associated with this patient's condition?]] |
| Answer A | AnswerA::Elevated LH and FSH levels with absence of functional ''SRY'' gene |
| Answer A Explanation | [[AnswerAExp::The SRY gene encodes the SRY protein, which is also known as testis determining factor (TDF). It is located on the Y chromosome and is responsible for the initiation of male sex determination. Absence of functional SRY gene in an otherwise genetic male would cause Swyer syndrome, which is characterized by presence of phenotypic females with gonadal dysgenesis.]] |
| Answer B | AnswerB::Decreased LH and FSH levels with absence of Barr body |
| Answer B Explanation | [[AnswerBExp::While Turner syndrome is caused by the absence of a Barr body in somatic cells of females, these patients typically have increased FSH and LH due to loss of feedback inhibition by gonadal hormones.]] |
| Answer C | AnswerC::Elevated estrogen levels with preductal coarctation of the aorta |
| Answer C Explanation | AnswerCExp::While preductal coarction of the aorta is associated with Turner syndrome, patients typically have decreased levels of estrogen due to ovarian dysgenesis. |
| Answer D | AnswerD::Decreased estrogen levels with a renal fusion anomaly |
| Answer D Explanation | [[AnswerDExp::Turner syndrome is associated with presence of a horseshoe kidney and decreased estrogen due to gonadal dysgenesis.]] |
| Answer E | AnswerE::Elevated LH and FSH levels with ovarian dysgenesis and a normal uterus |
| Answer E Explanation | [[AnswerEExp::Patients with Turner syndrome have elevated FSH and LH due to loss of feedback inhibition caused by abnormally low estrogen levels. Most patients have a form of ovarian dysgenesis (or less commonly agenesis). Ovaries eventually become fibrotic, resulting in "streak ovaries". Although present, the uterus of patients with Turner syndrome is typically hypoplastic due to persistently low levels of estrogen during childhood.]] |
| Right Answer | RightAnswer::D |
| Explanation | [[Explanation::Turner syndrome is caused by the a complete or partial loss of one copy of the X chromosome, an abnormal structure of the X chromosome, or mosaicim of a 45,XO cell line with another cell line. The karyotype of patients with Turner syndrome is 45,XO. It affects 1/2000 to 1/3000 live-born girls.
Turner syndrome has a variable phenotypic expression, but some features are common. Facial characteristics have features due to lymphatic obstruction, such redundant neck folds, low posterior hairlines, and neck webbing (pterygium colli). Other signs of obstructive lymphedema include cystic hygroma, acral congenital lymphedema, and interstitial congestion. Also, patients have posteriorly rotated ears, downward slanting of the eyes, and epicanthal folds. Skeletal features include short stature, congenital hip dislocation, scoliosis, broad shield-shaped chest with a square torso and interspaced nipples, and cubitus valgus (increased carrying angle of the elbow). They often also have dental crowding, micrognathia or prognathia, and a posterior rotation of the mandible. Females with Turner syndrome typically experience gonadal dysgenesis (or less commonly agenesis), which results in amenorrhea, infertility, and the presence of a hypoplastic uterus, due to low estrogen levels. Consequently, the loss of negative feedback inhibition results in elevated FSH and LH levels. Turner syndrome is also associated with cardiac abnormalities such as pre-ductal coarctation of the aorta, and bicuspid aortic valve. Turner syndrome is also associated with the presence of a horseshoe kidney, a renal fusion anomaly that leads to trapping of the fused kidney low in the abdomen under the inferior mesenteric artery. First Aid 2014 page 574]] |
| Approved | Approved::Yes |
| Keyword | WBRKeyword::Reproductive, WBRKeyword::Chromosome, WBRKeyword::Karyotype, WBRKeyword::Turner syndrome, WBRKeyword::Ovulation, WBRKeyword::Genetics |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |