A study of 45,X/46,XX mosaicism in Turner syndrome females: a novel primer pair for the (CAG)n repeat within the androgen receptor gene

X‑chromosome loss rescues Sertoli cell maturation and spermatogenesis in Klinefelter syndrome

Klinefelter syndrome (47,XXY) causes infertility with a testicular histology comprising two types of Sertoli cell-only tubules, representing mature and immature-like Sertoli cells, and occasionally focal spermatogenesis. Here, we show that the immature-like Sertoli cells highly expressed XIST and had two X-chromosomes, while the mature Sertoli cells lacked XIST expression and had only one X-chromosome. Sertoli cells supporting focal spermatogenesis also lacked XIST expression and the additional X-chromosome, while the spermatogonia expressed XIST despite having only one X-chromosome. XIST was expressed in Sertoli cells until puberty, where a gradual loss was observed. Our results suggest that a micro-mosaic loss of the additional X-chromosome is needed for Sertoli cells to mature and to allow focal spermatogenesis.

Mechanisms of mosaicism, chimerism and uniparental disomy identified by single nucleotide polymorphism array analysis

Mosaic aneuploidy and uniparental disomy (UPD) arise from mitotic or meiotic events. There are differences between these mechanisms in terms of (i) impact on embryonic development; (ii) co-occurrence of mosaic trisomy and UPD and (iii) potential recurrence risks. We used a genome-wide single nucleotide polymorphism (SNP) array to study patients with chromosome aneuploidy mosaicism, UPD and one individual with XX/XY chimerism to gain insight into the developmental mechanism and timing of these events. Sixteen cases of mosaic aneuploidy originated mitotically, and these included four rare trisomies and all of the monosomies, consistent with the influence of selective factors. Five trisomies arose meiotically, and three of the five had UPD in the disomic cells, confirming increased risk for UPD in the case of meiotic non-disjunction. Evidence for the meiotic origin of aneuploidy and UPD was seen in the patterns of recombination visible during analysis with 1-3 crossovers per chromosome. The mechanisms of formation of the UPD included trisomy rescue, with and without concomitant trisomy, monosomy rescue, and mitotic formation of a mosaic segmental UPD. UPD was also identified in an XX/XY chimeric individual, with one cell line having complete maternal UPD consistent with a parthenogenetic origin. Utilization of SNP arrays allows simultaneous evaluation of genomic alterations and insights into aneuploidy and UPD mechanisms. Differentiation of mitotic and meiotic origins for aneuploidy and UPD supports existence of selective factors against full trisomy of some chromosomes in the early embryo and provides data for estimation of recurrence and disease mechanisms.

Microsatellite analysis in Turner syndrome: parental origin of X chromosomes and possible mechanism of formation of abnormal chromosomes

Turner syndrome is a chromosomal disorder in which all or part of one X chromosome is missing. The meiotic or mitotic origin of most cases remains unknown due to the difficulty in detecting hidden mosaicism and to the lack of meiotic segregation studies. We analyzed 15 Turner patients, 10 with a 45,X whereas the rest had a second cell line with abnormal X-chromosomes: a pseudodicentric, an isochromosome, one large and one small ring, and the last with a long arm deletion. Our aims were: to detect X cryptic mosaicism in patients with a 45,X constitution; to determine the parental origin of the abnormality; to infer the zygotic origin of the karyotype and to suggest the timing and mechanism of the error(s) leading to the formation of abnormal X chromosomes from maternal origin. Molecular investigation did not revealed heterozygosity for any microsatellite, excluding X mosaicism in the 45,X cases. Parental origin of the single X chromosome was maternal in 90% of these patients. Three of the structurally abnormal Xs were maternally derived whereas the other two were paternal. These results allowed us to corroborate breakpoints in these abnormal X chromosomes and suggest that the pseudodicentric chromosome originated from post-zygotic sister chromatid exchange, whereas the Xq deleted chromosome probably arose after a recombination event during maternal meiosis.

Ear and hearing in relation to genotype and growth in Turner syndrome

Hearing loss, auricular anomalies and middle ear infections are common findings in many genetic disorders, but the mechanisms have remained unknown. We studied ear and hearing problems in Turner's syndrome (TS) in relation to the degree of X chromosome loss (i.e. degree of mosaicism) and growth. One hundred and nineteen girls and women with TS were studied regarding audiometry, fluorescent in situ hybridisation, serum concentration of insulin-like growth factor-1 (IGF-1) and body height. It was found that sensorineural hearing loss and occurrence of auricular anomalies were significantly increased the greater the proportion of 45,X cells in a particular individual (P<0.05 and P<0.001, respectively). Middle ear infections and sensorineural hearing loss were negatively correlated with IGF-1 (P<0.05 and P<0.001, respectively). Hearing correlated positively with height (P<0.01) and IGF-1 independently of age (P<0.05). Height correlated positively with IGF-1 (P<0.001). Auricular malformations, middle ear infections and hearing impairment in TS were interpreted as due to growth disturbances during development. A new hypothesis on the pathophysiology of external, middle and inner ear disorders due to a delayed cell cycle caused by chromosomal aberrations per se and not only to the specific X chromosome deletion is presented.