Genetics

Turner's Syndrome

 

Introduction

Turner Syndrome (TS) is the most common sex chromosome abnormality in females. It is caused from the complete or partial monosomy of the X chromosome. TS has an incidence between 1 in 1500 and 1 in 2500 female births. It is estimated that 1% of TS embryos progress to term and it accounts for 15% of spontaneous miscarriages. About 50% of cases have the XO karyotype and the rest are mosaics and abnormalities of the X chromosome.

 

Clinical Features

 

Physical Features

  1. Low birth weight and length
  2. Short stature
  3. Low posterior hairline
  4. Webbed neck (due to cystic hygromas)
  5. Puffy hands and feet (due to lymphedema)
  6. Shield chest and wide spaced nipples
  7. Cubitus valgus – elbows turned inward with forearms deviated outwards
  8. Short fourth metacarpal
  9. Nail dysplasia
  10. High palate
  11. Low set ears

 

http://upload.wikimedia.org/wikipedia/commons/2/22/Neck_Turner.JPG

Figure 2: Webbed neck is a classic feature of Tuner Syndrome.  http://upload.wikimedia.org/wikipedia/commons/2/22/Neck_Turner.JPG

 

Endocrine

  1. Gonadal dysgenesis
  2. Sexual infantilism
  3. Hypothyroidism

Cardiovascular

  1. Cardiac defects
    1. Coarctation of the aorta
    2. Hypoplastic left heart
    3. Bicuspid aortic valve
  2. Essential hypertension

Renal

  1. Abnormal renal position
  2. Ureteropelvic junction obstruction
  3. Double collecting systems

Developmental

  1. IQ is generally normal although may have increased incidence of learning disabilities

Other

  1. Sensorineural hearing loss
  2. Orthopedic problems
  3. Increased otitis media
  4. Vision problems
  5. Obesity
  6. Inflammatory bowel disease

 

Diagnosis

Prenatal diagnosis

  • Prenatal diagnosis of TS is often incidental during chorionic villus sampling or amniocentesis
  • Prenatal ultrasonography may demonstrate typical findings: increase nuchal folds, cystic hygromas, cardiac/ renal anomalies
  • The degree of mosaicism found on prenatal karyotype analysis is generally NOT predictive of the resulting phenotype

Postnatal diagnosis

  • 1/5 to 1/3 of children with TS are diagnosed as newborns due to puffy hands or feet or redundant nuchal skin
  • Some are diagnosed as newborns due to characteristic heart anomalies
  • About 1/3 are diagnosed in midchildhood during a work up for short stature
  • The rest are usually diagnosed during adolescence during a work up for delayed puberty or during adulthood during a work up for recurrent pregnancy loss
  • Karyotyping of a blood sample is the test of choice
    • 45X on karyotype analysis or the 45X/46XX mosaic is diagnostic of Turner syndrome
    • Due to mosaicism, if a karyotype is normal but suspicion remains high, an extended FISH study should be performed

 

Management

Management of children with Turner syndrome requires a multidisciplinary approach.

  1. Cardiac management - Approximately 30% of patients with TS have a congenital heart defect, so at the time of diagnosis, all patients should have a cardiac exam and a screening echocardiogram. Blood pressure should be monitored annually in all patients with TS. If initial exam does not show congenital heart disease, a repeat cardiovascular exam and echocardiogram should be done during adolescence. Patients who are found to have a structural heart lesion must receive antibiotic prophylaxis for subacute bacterial endocarditis before any dental work. Patients found to have coarctation of the aorta should undergo surgical correction. Patients found to have other heart defects should be followed regularly with repeat cardiac exams and echocardiograms.
  2. Short stature - The height of all girls with TS should be plotted on growth curves specific for Turner syndrome. Growth hormone therapy for girls with TS should be considered when the height of the patient falls below the 5th percentile for her age; this usually occurs between 2 and 5 years. Treatment may be combined with anabolic steroids. With the early initiation of GH therapy, attainment of normal adult height is possible (usually around 150 cm). A pediatric endocrinologist should direct this therapy. Later onset therapy is usually less effective.
  3. Sexual Infantilism - Poor sexual development and lack of attainment of puberty are major complications in females with Turner’s syndrome. Most girls will require exogenous estrogen with a progestin to achieve sexual development, optimal skeletal development and normal bone density. Over 90% of females with Turner syndrome will have gonadal failure, but around 30% may have normal, spontaneous pubertal development. In most females with TS, estrogen therapy should be considered when the patient is between 13 and 15 years old. Progestin therapy must also be initiated in order to prevent endometrial hyperplasia.
  4. Urinary system – Approximately 30 – 40% of patients with TS have structural kidney anomalies.  These include both anomalies of the collecting system and structural/positional anomalies of the kidney.  Girls with a classic 45X karyotype are more likely to have a structural anomaly, while mosaics are more likely to have anomalies of the collecting system.  Renal ultrasonography should be obtained at the time of diagnosis.
  5. Vision – Hyperopia and strabismus each occur in approximately 25 – 35% of patients with TS.  All patients should have an ophthalmologic evaluation by 12 to 18 months of age.
  6. Hearing – Both conductive and sensorineural hearing loss is an issue in patients with TS.  A high level of suspicion should be used in regards to otitis media.  Conductive hearing loss can result from chronic otitis media.  Otoscopic examination with insufflation and tympanometry is indicated at least annually until at least 7 – 8 years of age.  A low threshold should be used for referral to an otolaryngologist.  Sensorineural hearing loss is usually seen in adults but can be seen in children.  Audiology evaluations should be performed yearly in children with identified hearing loss or chronic otitis media and every 2 – 3 years in all other children with TS.
  7. Orthodontics – In girls with TS and abnormal craniofacial development, tooth development can be abnormal and tooth eruption early.  Dental evaluation should be performed by 2 years of age and an orthodontic evaluation by 7 years.
  8. Autoimmunity – Hypothyroidism and celiac disease are seen more frequently in patients with TS.  These girls should receive annual thyroid screening starting at 4 years of age and celiac screening every 2 – 5 years beginning at 4 years of age.
  9. Lymphatics – The lymphedema associated with TS usually resolves by 2 years of age.  However, it can recur and may require treatments such as use of support stockings and elevation or decongestive physiotherapy.
  10. Behavioral - Psychological and emotional support is important. Establish contact with Turner's syndrome support groups.

 

Support

http://www.turnersyndrome.org/

The Turner Syndrome Society

 

References

  1. Siberry, G. The Harriet Lane Handbook. 16th Ed. 2002. Moseby. pp 278-279.
  2. Cotran. Robbins Pathologic Basis of Disease, 6th Ed. 1999, W.B. Saunders. Pp 169-176.
  3. Loscalzo, ML. Turner Syndrome. Pediatr. Rev. 2008; 29; 219-227.
  4. Saenger, P.Recommendations for the Diagnosis and Management of Turner Syndrome. Journal of Clinical Endocrinology and Metabolism. 2001: 86 (7): 3061-3069.
  5. Saenger, P. Turner�s Syndrome. NEJM. 1996; 335:1749.
  6. American Academy of Pediatrics. Health Supervison for Patients with Turner' Syndrome. Pediatrics March 200
  7. Sybert V.P. and McCauley. Medical Progress: Turner's Synrdome NEJM Sept 16 2004
  8. Ross JL. Growth Hormone plus Childhood Low-Dose Esstrogen in Turner's Syndrome.  NEJM March 31, 2011