Departamento de Ciencias Biomédicas Básicas de la Facultad de Ciencias Biomédicas y de la Salud de la Universidad Europea de Madrid.

Three X makes you a superwoman, but only one doesn’t.

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Biología CelularBC
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24-09-2018

Turner syndrome is a chromosomic condition characterized by the presence of only one sexual
chromosome X. The X monosomy is the only monosomy of the sexual chromosomes possible
because the presence of only Y is not viable. The phenotype of a 45 X karyotype is nearly always
feminine because the absence of the SRY gene expression on the Y chromosome leads to the
evolution of feminine characteristics. The frequency of this disease could be considered high
representing 1/2500 girls and 1/5000 boys but still, the frequency is said low because nearly 98% of the embryos having this monosomy will not reach maturity.

 

What are the odds on Turner’s syndrome?
To have a better understanding of the frequency and prevalence of Turner’s syndrome we oriented ourselves on two articles. The first article is a result sum-up obtained on different studies, while the second presents results obtained in Denmark in 2006. This said, we can observe different population samples, one of them are 478 patients that have been studied in 1990, a second sample consisting of 211 patients studied in 1997, and a third sample of 781 patients studied in 2006. Results confirm that this syndrome particularly affects women (1/2500 birth worldwide). Turner’s syndrome is undoubtedly from genetic origin and there are several variations of it following particular genetic patterns. Individuals affected by Turner’s follow two main genetic patterns: absence of the second X chromosome or presence of both X chromosomes with anomalies in the rearrangement or missing parts. The most recurrent karyotype seems to be Karyotype 45, X representing 52.1% of the cases in the first study, 46% in the second, and 45% in the last one. This karyotype has a monosomy of the X chromosome. It also seems that the karyotypes revealing X isochromosomes, with 16.1% of cases in the first study, and 11% of cases in the 3rd study is one of the reasons Turner syndrome. It should be noted that isochromosomes are chromosomes that lost one of its arms to replace it by an exact figure of the other arm: in this case they are noted Xp or Xq. Turner syndrome may also manifest as mosaicism, which consist in a chromosomal change in some cells only not the whole set, those forms are called “mosaic Turner syndromes”. The gene responsible has not been determined yet, but a gene important in cell growth called SHOX has been identified among those responsible in the skeletal features of people affected. The first article shows a prevalence of mosaic karyotypes of 19.5% (karyotype 45, X / 46, XX prevailing over others) and the second article has a prevalence of 7% for karyotypes 45 , X / 46, XX and 45, X / 47, XXX.

How to know : symptomatic and genetic approach

Multiple diagnosis resources are available for the detection of Turner syndrome. Symptomatically speaking the leading signs are a short stature visible from a young age and generally the absence of ovarian function leading to development problems. Other symptoms include a wide neck, a narrow roof of the mouth, a lower back hairline. Preliminary tests include blood hormone levels,
echocardiogram (because about one third of turner’s syndrome are born with a heart defect) and ultrasound of reproductive organs. The genetic diagnostic can be done with the help of cytogenetic tests such as a FISH-interphase, FISH-metaphase or a Karyotype combined with molecular genetic tests such as detection of homozygosity or variation analysis and sequence analysis.

Management of Turner’s syndrome

Having Turner’s syndrome means a great number of management issues throughout life. A different onset of adjacent conditions and repercussions need to be monitored including cardiac problems, audition, reproductive capacity, thyroid dysfunctions and physical disruptions. There is no cure for Turner’s but certain treatments can be used to minimize the impulse, progression and symptoms.
- Administration of HGH (human growth hormone) at a young age.
- Oestrogen replacement therapy (to help acquire better secondary sexual characteristics).

Nevertheless, progress are made in research to promote a better quality of life for people with Turner’s.

References

  1. S. E. Levin, J. Harrisberg, a Kelly, Turner syndrome. Pediatrics . 87 , 745 (1991).K. Stochholm, S. Juul, K. Juel, R. W. Naeraa, C. H. Gravholt, Prevalence, incidence, diagnostic delay, and mortality in Turner syndrome. Journal of Clinical Endocrinology and Metabolism . 91 , 3897–3902 (2006).
  2. Bondy C. New Issues in the Diagnosis and Management of Turner Syndrome. Reviews in Endocrine and Metabolic Disorders. 2005;6(4):269-280.
  3. Lepage J, Dunkin B, Hong D, Reiss A. Impact of cognitive profile on social functioning in prepubescent females with  Turner syndrome. Child Neuropsychology. 2013;19(2):161-172.
  4. Morgan T. Turner syndrome: diagnosis and management. Am Fam Physician. 2007 Aug 1;76(3):405-10.

FIRMA: 
Chloé VERNEY, Gregoire LAFFOND, Francesco FERMANI, Nicolas FONS-CASENOVE, Melissa ETIENNE. Estudiantes 1º Odontología, Curso 2017-2018. Asignatura: Biología Celular y Genética Humana.

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