Review Article

Recent Developments in Diagnosis and Care for Girls in Turner Syndrome

Figure 2

X chromosome single-nucleotide polymorphism (SNP) array from a patient with TS. Beta allele frequency is shown in the top panel. This analysis quantifies detection of polymorphic sites along the X chromosome. For example, homozygosity for a hypothetic SNP allele (AA) is reported as zero, heterozygosity (Aa) is reported as 0.5, and homozygosity for the alternative allele (aa) is reported as 1. When two parental chromosomes are present, the betal allele frequency averages 0.5. Log  ratios are shown on the lower panel. This measures copy number variation for the chromosome segments represented on the array. When test subject value is equal to the reference control (1 : 1 ratio), the log  (LRR) ratio is zero. Copy number loss shows a negative LRR, while copy number gain shows a positive LRR. The X chromosome physical structure is diagrammed below the graphs. In this example, there is loss of heterozygosity and negative (~−.45) LRR beginning at Xp11.22 to Xpter, indicating segmental monosomy for the X chromosome short arm from Xpter-Xp11.22. The abrupt increase of LRR to 0.26 and division of BAF into four tracks (1.00, 0.66, 0.34, and 0) indicate trisomy of Xp11-Xqter. The 50-cell standard karyotype revealed 46,X,isoXp11. This figure is adapted from [22].