Turner syndrome affects 3% of all females prior to birth, with only around 1% of these ‘in utero’ cases surviving to term; it is not inherited from either parent, but purely a ‘chance’ mutation. Despite this, it has become the most common genetically determined abnormality amongst females, and can have detrimental effects on systemic wellbeing throughout life. Turner Syndrome is a sex-linked genetic disorder which only affects females, and can present symptoms in several organ systems including the reproductive, cardiovascular and musculoskeletal systems, particularly in adult life (Elsheikh et al. 002).
The disorder is not inheritable maternally or paternally, but is a result of prenatal abnormalities in the chromosomes of an affected individual; it is characterised as a complete or partial loss of an X chromosome (called a monosomy) from one or more types of cell (Donaldson et al. 2006). The typical phenotype (physical characteristics) of a female with Turner syndrome includes shorter than average stature, webbed neck, undeveloped ovaries and lack of pubertal change when growing up, ultimately resulting in infertility (Tesch & Rosenfeld 1995).
Turner syndrome is often referred to as ’45, X’ or ’45, XO’ (Figure 1), meaning 45 chromosomes are present instead of 46, and that the genetic sex of the individual is X (XO), rather than XX in normal females. Turner syndrome is incident in about 1 in every 2000 female foetuses, with only a small percentage of those coming to term, and can vary widely in its effects and symptoms (Gravholt et al. 1996); if the X chromosome is missing in all of the woman’s cells, her genetic karyotype is definitively 45 X, and this occurs in around 50% of all postnatal sufferers (Sybert & McCauley 2004).
However if her X chromosome is missing in some types of cell while other cell types contain a full set (46, XX), this is known as chromosomal mosaicism. Individuals with mosaic Turner syndrome usually have a less abnormal phenotype, and are suffer less severe symptoms including carviovascular, gastrointestinal and gonanal dysfunctions later in life (Doger et al. 2015). Risk Factors and Symptoms Turner syndrome was the first known example of gonadal dysgenesis, in which there is a loss of gamete-producing (germ) cells known in females as oocytes.
This occurs due to the absence of an X chromosome in these germ cells, and results in the ovaries remaining under- or undeveloped, forming streaks, or complete ovarian failure, which can happen in utero or in the first months or years of life (Elsheikh et al. 2002; Conway 1997). Gonadal symptoms therefore include infertility, lack of- or insufficient production of oestrogen during puberty, and absent physical and sexual maturations such as breast development (Sybert & McCauley 2004).
A typical symptom and stigmata of Turner syndrome is a less than average height, peaking at a whole 8 inches less than a non-sufferer on average (Davenport et al. 2007); there is a large genetic element surrounding this, in the form of the short stature homeobox (SHOX) gene located on the allosomes (X and Y chromosomes). In females, SHOX requires both X chromosomes and their respective genes providing enough expression of the gene to regulate adequate growth necessary for normal postnatal growth and adolescent and pubescent growth spurts (Clement-Jones et al 2000).
Several cardiovascular symptoms are prevalent in Turner syndrome sufferers, and can be associated with the disorder itself; the karyotype of an affected individual has been shown to correlate with the severity of malfunctions. 45 X karyotypes have a greater risk and higher prevalence (than mosaic individuals) of defects including diseases of the bicuspid and aortic valves, and more importantly, the coarctation (narrowing) of the aorta which can implement further cardiovascular difficulties due to lessened blood flow and hypertension (Mazzanti et al. 1996; Gotzsche et al. 1994).
Diagnosis of Turner Syndrome Prenatal diagnosis or at least suspicion of Turner syndrome can occur during an ultrasound scan of the baby by a process called amniocentesis, observing heart or kidney defects, or swelling of the body, known as lymphoedema (Papp et al. 2006). Karyotype analysis is the current method of confirmating Turner syndrome in children and adults, as it can sometimes take until puberty is noticeably absent by undeveloped breasts or lack of menstruation to identify the syndrome (Elsheikh et al. 2002) when a slower growth rate is not identified in earlier years. Treatment and Management
There is no known cure for Turner Syndrome, but several treatments and procedures to manage the disease are in place to reduce the morbidity and improve the living quality of sufferers, the most common being oestrogen, to aid in fertility and puberty, and growth hormone therapy, to counteract SHOX deficiency (Donaldson et al. 2006). Oestrogen can be administered as part of hormone replacement therapy, and can be given as standard contraceptive pills or injections, while Human Growth Hormone can also be used to increase their final height, if given from an early age until early teenage years around the time of puberty (Bolar et al. 007).
Besides gonadal dysgenesis and slow growth rate, there is still a range of symptoms and abnormalities that stem from Turner syndrome that it is not possible for a single medical professional to manage, therefore treatment and management is optimised by utilising people of various disciplines to meet the many different requirements of a patient (Elsheikh et al. 2002)
This also differs in age group, from behavioural and hearing difficulties in childhood to osteoporosis, immune disorders and ovarian failure in adolescence to adulthood (Donaldson et al. 006). Finally, genetic counselling is available for monosomy and mosaic sufferers regarding the decreased chance of pregnancy, and chances of surviving to term (Doger et al. 2015). However cases can occur very rarely in sufferers not only of the woman undergoing puberty but conceiving naturally, despite the natural issues of infertility and miscarriage that are typical of Turner syndrome (Hovatta 1999; Livadas et al. 2005).?
