On the genetic length of the short arm of the human X chromosome

DNA analysis and recombination in X-linked retinitis pigmentosa

X-linked retinitis pigmentosa is a hereditary retinal degenerative disorder which has been localised to the proximal short arm of the X chromosome. Recent evidence suggests that the disorder is heterogeneous with two possible loci for the disease mutation. DNA analysis on the family presented in this paper showed that the mutation mapped to the more telomeric locus (RP3), thus enabling two flanking polymorphic DNA probes (XJ1.1 and M27 beta) to be used for the detection of female carriers in the family. In none of the carriers was a tapetal reflex (metallic sheen) observed.

Regional localisation of X chromosome short arm probes

Nine human X chromosome-specific clones have been isolated by screening an X-chromosomal genomic library with fetal muscle cDNA. Five of the clones have been localised to the short arm and four to the long arm. The short arm probes have been regionally assigned using a panel of somatic cell hybrids. They have been mapped further using a series of DNA samples from male patients with different deletions of the region Xp21, and having complex phenotypes including Duchenne muscular dystrophy. The use of these probes in the mapping of the short arm of the X chromosome is discussed.

A genetic linkage study of a kindred with X-linked retinitis pigmentosa

A large kindred with X-linked retinitis pigmentosa (XLRP) was investigated clinically and by means of genetic linkage with a view to developing methods of carrier detection and early diagnosis. A restriction fragment length polymorphism, identified by recombinant DNA probe L1.28, showed close genetic linkage to XLRP in this kindred and is a potentially useful marker for the purposes of genetic counselling.

X-linked dominant Charcot-Marie-Tooth disease: suggestion of linkage with a cloned DNA sequence from the proximal Xq

A large kindred with the X-linked dominant form of peroneal muscular atrophy (Charcot-Marie-Tooth disease) was analyzed for individual variation in the length of DNA fragments after restriction endonuclease digestion. A systematic search was performed for linkage with a series of cloned single-copy DNA sequences of known regional assignment to the human X chromosome. Close linkage was found with the pDP34 probe (DXYS1 locus, Xq13-q21), suggesting that the gene responsible for the disease is located on the proximal long arm of the X chromosome.

X-linked agammaglobulinemia and the red blood cell determinants Xg and 12E7 are not closely linked

Studies on the segregation of the red blood cell determinant Xg in 12 families with X-linked inheritance of agammaglobulinemia (XLA) in 3-4 generations suggested linkage of Xg with XLA. One extensive pedigree of a Dutch family with XLA in eight generations was investigated for Xg and the quantitative polymorphism 12E7. LIPED analysis indicated linkage disproven up to 25cM distance within this pedigree. Taken together with data obtained from two other informative XLA pedigrees and with published data, the results indicate no close linkage between XLA and Xg: 12E7, the distance between XLA and Xg being more than 20cM.

Close genetic linkage between X-linked retinitis pigmentosa and a restriction fragment length polymorphism identified by recombinant DNA probe L1.28

Retinitis pigmentosa (RP) is a group of retinal degeneration characterized by progressive visual field loss, night blindness and pigmentary retinopathy. Its prevalence is in the region of 1-2 in 5,000 of the general population, making it one of the commoner causes of blindness in early and middle life. Although 36-48% of RP patients are isolated cases, the remainder show autosomal dominant, autosomal recessive or X-linked modes of inheritance. The X-linked variety ( XLRP ) is found in 14-22% of RP families in the UK. In the present study, X chromosome-specific recombinant DNA probes which can detect restriction fragment length polymorphisms have been used to localize the XLRP gene(s) to a subregion of the X chromosome using linkage analysis. One of the probes, L1.28, has been shown to be closely linked to XLRP in five kindreds, with 95% confidence limits of 0-15 centimorgans (maximum LOD score of 7.89 at a distance of 3 centimorgans). This suggests that the XLRP locus lies on the proximal part of the short arm of the X chromosome. This probe is potentially useful for carrier detection and early diagnosis in about 40% of cases, provided that genetic heterogeneity can be excluded by analysis of further families.