Abnormalities of sex chromosomes are the most frequently detected rearrangements in postnatal and prenatal chromosome evaluation. They are estimated to occur in 1:400 newborns, and in 1:250 at prenatal diagnosis [1], that includes both numerical and structural rearrangements of X and Y chromosomes.
The incidence of 47, XYY in postnatal studies is 1:850 in European countries [2], 1:1000 in the USA [3], and 1:1520 in Japan [4]. The reason for these differences is that the patients have only minor dysmorphic stigmata and may not be referred for chromosomal analysis, thus underdiagnosis of the condition is common. Although this anomaly is present in both somatic and germ cells, the frequency of 24, XY and 24, YY in spermatozoa, confirmed by fluorescence in situ hybridization (FISH) studies, is less than 1% [5,6]. The Y chromosome in XYY individuals has been lost during the first meiotic division, thus the offspring has a normal chromosomal complement in most cases.
The 47, XYY phenotype includes tall stature, mild developmental delay, speech impairment and behavioral problems. Although minor malformations are described in 20% of cases [7], there is no specific pattern that enables early clinical recognition of this chromosomal abnormality. Most frequent minor malformations that, by definition, do not cause serious medical or cosmetic consequences, include wide forehead, prominent glabella, long ears with deformed helix, heavy eyebrows, protruded mandible, incurved fifth finger, and long fingers. The incidence of major congenital malformations (anomalies of the brain, cardiovascular tract and skeletal system) in these individuals does not differ when compared to the general population. The most frequent major anomaly of the skeletal system is radio ulnar synostosis [8]. The main reasons for chromosomal analysis of the patients are psychomotoric delay, speech impairment and specific behavior.