Turner syndrome
Updates to Article Attributes
Turner syndrome (or 45X) is the most common ofsex chromosome abnormalities in females.
Epidemiology
The incidence is estimated at 1:2000-5000 of live birth, although the the in utero rate is much higher (1-2% of conceptions) due to a significant proportion of foetusesfetuses with 45X aborting by the 2nd trimester.
Clinical presentation
In adults it is one of the most important causes of primary amenorrhoea and accounts for approximately one-third of such cases.
Pathology
Genetics
Turner syndrome is classically characterised with the absence of one X chromosome copy (45 XO), with the missing chromosome most frequently (two-thirds) being the paternal one. Most cases occur as a sporadic event.
However the classic genetic change is not present in all cases. Three main subtypes include:
- complete monosomy (45XO): ~60%
- even though it is relatively common, almost all 45 XO fetuses will spontaneously abort, with 70% lost between 16 weeks and term
- partial monosomy (structurally altered X chromosome): ~15%
- mosaicism (XO and another sex karyotype): ~30%
Unlike the commontrisomies, there is no association with maternal age.
Markers
- serum alpha feto protein (AFP): decreased
- beta HCG
- elevated if hydrops present
- decreased if no hydrops
- serum inhibin
- elevated if hydrops present
- absent if hydrops absent
Associations
- hypertension
- glucose intolerance
- inflammatory bowel disease
- hypothyroidism: due to formation of thyroid antibodies (most commonlyHashimoto thyroiditis)
- gonadal dysgenesis/ovarian dysgenesis
Complications
In utero complications complications include
- development ofhydrops fetalis: usually from fluid overload secondary to lymphatic failure
Radiographic features
Intra-uterine ultrasound findings
- cystic hygroma: may appear septated; one of the most typical features of Turner syndrome
- increasednuchal thickness
- increased nuchal translucency
- coarctation of the aorta: 15-20%
- bicuspid aortic valve
- horseshoe kidney/pelvic kidney
- mild IUGR
- features related to complicating hydrops fetalis
- short fetal limbs
Post partum to adulthood findings
Musculoskeletal
- scoliosis
- short 4th metacarpal: positive metacarpal sign
- narrowing scapholunate angle: positive carpal sign
- abnormal medial femoral condyle
- decreased carpal angle: Madelung deformity
- short stature
- webbed neck
- valgus deformity of elbow: increased carrying angle (cubitus valgus)
Pelvic ultrasound
Treatment and prognosis
Overall prognosis very variable is dependent on associated anomalies. While the vast majority of fetuses abort in the second trimester, some may have long life expectancy. Cases with mosiacism do much better. Mental development is unaffected.
History and etymology
It is named after Henry Turner who first described the syndrome in 1938.
Differential diagnosis
General differential considerations include
- Noonan syndrome: can have similar phenotypical features but normal karyotype
-<p><strong>Turner syndrome</strong> (or <strong>45X</strong>) is the most common of <a href="/articles/sex-chromosome">sex chromosome</a> abnormalities in females. </p><h4>Epidemiology</h4><p>The incidence is estimated at 1:2000-5000 of live birth, although the in utero rate is much higher (1-2% of conceptions) due to a significant proportion of foetuses with 45X aborting by the 2<sup>nd </sup>trimester. </p><h4>Clinical presentation</h4><p>In adults it is one of the most important causes of <a href="/articles/primary-amenorrhoea">primary amenorrhoea</a> and accounts for approximately one-third of such cases. </p><h4>Pathology</h4><h5>Genetics</h5><p>Turner syndrome is classically characterised with the absence of one X chromosome copy (45 XO), with the missing chromosome most frequently (two-thirds) being the paternal one. Most cases occur as a sporadic event.</p><p>However the classic genetic change is not present in all cases. Three main subtypes include:</p><ul>- +<p><strong>Turner syndrome</strong> (or <strong>45X</strong>) is the most common of <a href="/articles/sex-chromosome">sex chromosome</a> abnormalities in females. </p><h4>Epidemiology</h4><p>The incidence is estimated at 1:2000-5000 of live birth, although the in utero rate is much higher (1-2% of conceptions) due to a significant proportion of fetuses with 45X aborting by the 2<sup>nd </sup>trimester. </p><h4>Clinical presentation</h4><p>In adults it is one of the most important causes of <a href="/articles/primary-amenorrhoea">primary amenorrhoea</a> and accounts for approximately one-third of such cases. </p><h4>Pathology</h4><h5>Genetics</h5><p>Turner syndrome is classically characterised with the absence of one X chromosome copy (45 XO), with the missing chromosome most frequently (two-thirds) being the paternal one. Most cases occur as a sporadic event.</p><p>However the classic genetic change is not present in all cases. Three main subtypes include:</p><ul>
-</ul><p>Unlike the common <a href="/articles/trisomies">trisomies</a>, there is no association with maternal age.</p><h5>Markers</h5><ul>- +</ul><p>Unlike the common <a href="/articles/trisomies">trisomies</a>, there is no association with maternal age.</p><h5>Markers</h5><ul>
-<a href="/articles/hypothyroidism">hypothyroidism</a>: due to formation of thyroid antibodies (most commonly <a href="/articles/hashimoto-thyroiditis">Hashimoto thyroiditis</a>)</li>- +<a href="/articles/hypothyroidism">hypothyroidism</a>: due to formation of thyroid antibodies (most commonly <a href="/articles/hashimoto-thyroiditis">Hashimoto thyroiditis</a>)</li>
-</ul><h5>Complications</h5><p>In utero complications include</p><ul><li>development of <a href="/articles/hydrops-fetalis">hydrops fetalis</a>: usually from fluid overload secondary to lymphatic failure</li></ul><h4>Radiographic features</h4><h5>Intra-uterine ultrasound findings</h5><ul>- +</ul><h5>Complications</h5><p>In utero complications include</p><ul><li>development of <a href="/articles/hydrops-fetalis">hydrops fetalis</a>: usually from fluid overload secondary to lymphatic failure</li></ul><h4>Radiographic features</h4><h5>Intra-uterine ultrasound findings</h5><ul>
-<li>increased <a href="/articles/nuchal-fold-thickness-1">nuchal thickness</a>- +<li>increased <a href="/articles/nuchal-fold-thickness-1">nuchal thickness</a>
-<li><a href="/articles/streak-ovaries">streak ovary</a></li>- +<li><a href="/articles/streak-ovaries">streak ovary</a></li>