Turner syndrome

The fellowship mark goes to the candidate who thinks in three layers at once. The first layer is the girl in front of you: her height velocity, her pubertal staging, her cardiovascular anatomy, her renal ultrasound, her hearing, her thyroid function, and her school performance and mood. The second is the chromosomal mechanism: the karyotype class that determines the gonadoblastoma risk, the mosaicism that softens or hardens the phenotype, and the haploinsufficiency of SHOX and the lymphogenic genes that build the body. The third is the lifespan: the transition from paediatric to adult care, the fertility window that closes early, the aorta that dilates silently, and the osteoporosis that is preventable if oestrogen is given on time. [1] [8]

Overview & Definition

Turner syndrome is a chromosomal disorder of phenotypic females caused by the complete or partial absence of one X chromosome, with or without mosaicism. The classic karyotype, 45,X (monosomy X), accounts for roughly half of cases; the remainder are mosaics (45,X/46,XX being the most common) or harbour a structurally abnormal X chromosome — an isochromosome of the long arm, a ring X, or a partial deletion. The clinical consequence is a syndrome of short stature, gonadal dysgenesis, cardiovascular and renal anomalies, a characteristic lymphatic phenotype, and a distinctive but variable neurocognitive profile. [2] [1]

Two biological facts anchor the entire topic and recur in every examination. First, Turner syndrome is far more common at conception than at birth: an estimated 99 percent of 45,X conceptuses are lost spontaneously, and Turner syndrome accounts for approximately 10 percent of all first-trimester miscarriages. The live-birth prevalence is therefore about one in 2,500 females — high enough to be common, low enough that the diagnosis is missed when the phenotype is mild. Second, the phenotype is driven by haploinsufficiency of genes that escape X-inactivation and remain active on the single X chromosome, and the most important of these for stature and skeletal patterning is SHOX (short-stature homeobox-containing gene) in the pseudoautosomal region of Xp. [2] [1]

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1. [1]Gravholt CH, Andersen NH, Conway GS, Dekkers OM, Geffner ME, Klein KO, et al. Clinical practice guidelines for the care of girls and women with Turner syndrome: proceedings from the 2016 Cincinnati International Turner Syndrome Meeting. Eur J Endocrinol, 2017.PMID 28705803
2. [2]Sybert VP, McCauley E. Turner's syndrome. N Engl J Med, 2004.PMID 15371580
3. [3]Stephure DK Impact of growth hormone supplementation on adult height in Turner syndrome: results of the Canadian randomized controlled trial. J Clin Endocrinol Metab, 2005.PMID 15784709
4. [4]Hadnott TN, Gould HN, Gharib AM, Bondy CA. Outcomes of spontaneous and assisted pregnancies in Turner syndrome: the U.S. National Institutes of Health experience. Fertil Steril, 2011.PMID 21496813
5. [5]Sheanon NM, Backeljauw PF. Effect of oxandrolone therapy on adult height in Turner syndrome patients treated with growth hormone. Int J Pediatr Endocrinol, 2015.PMID 26322078
6. [6]Ostberg JE, Donald AE, Halcox JP, Storry C, McCarthy C, Conway GS. Vasculopathy in Turner syndrome: arterial dilatation and intimal thickening without endothelial dysfunction. J Clin Endocrinol Metab, 2005.PMID 15985480
7. [7]Cleemann L, Holm K, Fallentin E, et al. Effect of Dosage of 17beta-Estradiol on Uterine Growth in Turner Syndrome-A Randomized Controlled Trial. J Clin Endocrinol Metab, 2020.PMID 31613320
8. [8]Trolle C, Mortensen KH, Hjerrild BE, Cleemann L, Gravholt CH. Clinical care of adult Turner syndrome--new aspects. Pediatr Endocrinol Rev, 2012.PMID 22946288