Female Hunter syndrome caused by a single mutation and familial XCI skewing: implications for other X-linked disorders. 
Familial X-chromosome inactivation (XCI) skewing was investigated in a family in which a female mucopolysaccharidosis type II (MPS II) (Hunter syndrome, an X-linked genetic disease) occurred.  Among eight related females aged under 60 years from three generations who were tested, four revealed a non-random pattern of XCI.  Detailed genetic analysis failed to find mutations in genes that were previously reported as important for the XCI process.  Haplotype analysis excluded linkage of non-random XCI with genes localized on the X-chromosome.  We propose that analysis of the XCI pattern should be taken into consideration when assessing risk factors for X-linked recessive genetic disorders.