Turner syndrome is the most common genetic condition affecting women (Saenger, 1997, Curr. Ther. Endocrinol. Metab. 6: 239-243; Gravholt, 2004, Eur. J. Endocrinol. 151: 657-687; Ranke and Saenger, 2001, Lancet 358: 309-314). The incidence of Turner syndrome is 1 in 1,500 to 2,000 live female births (Saenger, 1997, Curr. Ther. Endocrinol. Metab. 6: 239-243; Gravholt, 2004, Eur. J. Endocrinol. 151: 657-687; Ranke and Saenger, 2001, Lancet 358: 309-314), and occurs when an entire, or a portion of an X chromosome is deleted (Saenger, 1997, Curr. Ther. Endocrinol. Metab. 6: 239-243; Ranke and Saenger, 2001, Lancet 358: 309-314). Phenotypic features include primary hypogonadism, renal abnormalities, difficulties with spatial perception, and structural cardiac problems (Saenger, 1997, Curr. Ther. Endocrinol. Metab. 6: 239-243; Ranke and Saenger, 2001, Lancet 358: 309-314). Girls with Turner syndrome are short and have an average adult height of 4 feet 6 inches tall (Ranke and Saenger, 2001, Lancet 358: 309-314; Saenger, 2000, Endocrine, 12: 183-187; Rosenfeld, et al., 1998, J. Pediatr. 132: 319-324). Neurological manifestations include problems with spatial perception and communication skills (Bordeleau, et al., 1998, J. Emerg. Med., 16: 593-596; Johnson, et al., 1993, Neurology 43: 801-808; Money, 1993, Soc. Biol., 40: 147-151; Haberecht, et al., 2001, Hum. Brain Mapp., 14: 96-107; Pennington, et al., 1985, Cortex 21: 391-404; Ross, et al., 1996, Pediatr. Neurol., 15: 317-322; Temple and Carney, 1993, Dev. Med. Child Neurol., 35: 691-698; Ross, et al., 1998, J. Clin. Endocrinol. Metab., 83: 3198-31204). Cardiac problems include coarctation of the aorta, single coronary vessels, bicuspid aortic valves, atrial and ventricular spatial defects, and abnormalities of great vessels. Renal problems include duplex, solitary, or horseshoe kidneys. Hearing problems may be secondary to a higher frequency of otitis media or sensorineural hearing loss.
Girls with Turner syndrome generally have normal intelligence. Yet, some girls may have problems with spatial perception and mathematical skills. Thus, a modified educational curriculum may be needed. Some girls with Turner syndrome have communication problems and social difficulties. This has been found to be related to whether the X-chromosome came from the mother or the father.
Of considerable importance, girls with Turner syndrome have an average adult height of 4 feet 6 inches, which is 10 inches below the average female adult height. Recent data suggest that the short stature may be related to mutations or deletions of the SHOX gene (encoded on the X-chromosome) in Turner syndrome (Blaschke and Rappold, 2000, Trends Endocrinol. Metab., 11: 227-230; Cormier-Daire, et al., 1999, Acta Paediatr. Suppl., 88: 55-59; Boucher, et al., 2001, J. Med. Genet., 38: 59159-8; Kosho, et al., 1999, J. Clin. Endocrinol. Metab. 84: 4613-4621). Short stature in Turner syndrome has been shown to result in significant long-term problems with self-esteem. Yet, with timely initiation of growth hormone therapy, acceptable adult stature can be achieved (Rosenfeld, et al., 1998, J. Pediatr. 132: 319-324; Hull and Harvey, 2003, J. Endocrinol. 179: 311-333).
Currently, many girls with Turner syndrome are diagnosed after 10 years of age (Parker, et al., 2003, J. Pediatr., 143: 133-135; Massa, et al., 2005, Arch. Dis. Child. 90: 267-268), and recognition of associated problems may be delayed (Savendahl and Davenport, 2000, J. Pediatr., 137: 455-459). Final height may be compromised by delayed adjunctive therapy with growth hormone (Savendahl and Davenport, 2000, J. Pediatr., 137: 455-459). With later recognition, however, replacement therapy with estrogen and progestin is delayed resulting in late pubertal development (Savendahl and Davenport, 2000, J. Pediatr., 137: 455-459; Bertelloni, et al., 2003, J. Pediatr. Endocrinol. Metab., 16 Suppl 2: 307-315).
Girls with Turner syndrome are at risk for gonadal tumor development if Y chromosomal material is present (Canto, et al., 2004, Cancer Genet. Cytogenet. 150: 70-72; Vlasak, et al., 1999, Klin. Padiatr., 211: 30-34). The failure to detect small fragments of Y chromosomal material by standard karyotype analysis (Longui, et al., 2002, Genet. Mol. Res., 1: 266-270) precludes recognition of girls with Turner syndrome with potential tumor risk.
Turner syndrome represents a constellation of features that occurs when an X-chromosome is either completely deleted (45×), or when portions of the X-chromosome are deleted (Hall and Gilchrist, 1990, Pediatr. Clin. North Am., 37: 1421-1440; Uehara, et al., 2001, J. Hum. Genet., 46: 126-131; Henn and Zang, 1997, Nature, 390: 569; Kleczkowska, et al., 1990, Genet. Couns., 1: 227-233; Lippe and Saenger, 2002, In: Sperling Mass., ed. Pediatric Endocrinology. Philadelphia: Saunders, 519-564). More than half of girls with Turner syndrome have a 45X genotype. In the remaining girls there is mosaicism with two populations of cells: a proportion of cells with the normal compliment of genes (46,XX), and a proportion of cells with an X-chromosome deletion (partial or complete) (Hall and Gilchrist, 1990, Pediatr. Clin. North Am., 37: 1421-1440; Uehara, et al., 2001, J. Hum. Genet., 46: 126-131; Henn and Zang, 1997, Nature, 390: 569; Kleczkowska, et al., 1990, Genet. Couns., 1: 227-233; Lippe and Saenger, 2002, In: Sperling Mass., ed. Pediatric Endocrinology. Philadelphia: Saunders, 519-564). Other complex rearrangement (e.g. ring abnormality of the X-chromosome) causing an imbalance in the normal complement of genes encoded on the X-chromosome, can also result in Turner syndrome (Hall and Gilchrist, 1990, Pediatr. Clin. North Am., 37: 1421-1440; Uehara, et al., 2001, J. Hum. Genet., 46: 126-131; Henn and Zang, 1997, Nature, 390: 569; Kleczkowska, et al., 1990, Genet. Couns., 1: 227-233; Lippe and Saenger, 2002, In: Sperling Mass., ed. Pediatric Endocrinology. Philadelphia: Saunders, 519-564).
Disorders of sexual differentiation (DSDs) also involve sex chromosome abnormalities and/or the need to determine the identification and number of sex chromosomes. These disorders include 46XY individuals with abnormal male gonadal or genital development, 46XX individuals with abnormal female gonadal or genital development, individuals with both testes and ovaries, and individuals with extra X and/or Y chromosomes, such as those with Klinefelter syndrome.
The gold standard for diagnosis of X chromosome anueploidies and DSDs remains cytogenetic analysis (karyotype) (Longui, et al., 2002, Genet. Mol. Res., 1: 266-270). While cytogenetic analysis by light microscopy has drastically advanced in resolution over the past 50 years, it remains a labor intensive and expensive method that is not practical for population screening. Testing of blood spot follicle-stimulating hormone (FSH) during early postnatal life has been tested in girls with Turner syndrome (Heinrichs, et al., 1994, J. Clin. Endocrinol. Metab. 78: 978-981). However, perinatal changes in FSH secretion are similar to those in normal girls, thus FSH measurement are not effective for neonatal screening of Turner syndrome (Heinrichs, et al., 1994, J. Clin. Endocrinol. Metab. 78: 978-981).
Over the past decade, genotyping techniques have become faster and less expensive. A quantitative method of genotyping based on the detection of single nucleotide polymorphisms (SNPs), may prove to be advantageous in identifying chromosome deletions or additions. Single nucleotide polymorphisms (SNPs) occur about every 100 nucleotide bases (Ronaghi, 2003, Methods Mol. Biol. 212: 189-195; Elahi and Ronaghi, 2004, Methods Mol. Biol. 255: 211-220). There are thousands of SNPs available to interrogate the full length, or any specific segment, of the X and Y chromosomes (Ronaghi, 2003, Methods Mol. Biol. 212: 189-195; Elahi and Ronaghi, 2004, Methods Mol. Biol. 255: 211-220). Pyrosequencing is especially advantageous for detecting SNPs due to a high degree of quantitative accuracy, ease-of-use, and high throughput capability (Ronaghi, 2003, Methods Mol. Biol. 212: 189-195).
Given that current methods for diagnosing Turner syndrome are not sufficient to detect the condition in neonates, and detection in girls does is not accurate until an age when symptoms of Turner syndrome are already manifest, there exists a long felt need for assays and methods to detect Turner syndrome quickly, efficiently, accurately and early. The present invention meets this need.