People with the 47,XYY karyotype have an increased growth rate from early childhood, with an average final height approximately 7 cm (3") above expected final height. In Edinburgh, Scotland, eight 47, XYY boys born 1967–1972 and identified in a newborn screening programme had an average height of 188.1 cm (6'2") at age 18—their fathers' average height was 174.1 cm (5'8½"), their mothers' average height was 162.8 cm (5'4"). The increased gene dosage of three X/Y chromosome pseudoautosomal region (PAR1) SHOX genes has been postulated as a cause of the increased stature seen in all three sex chromosome trisomies: 47,XXX, 47,XXY, and 47,XYY.