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The absence of a protein involved in transcribing genes that are activated by androgens may cause some cases of androgen insensitivity. Androgen insensitivity is a sex-linked disorder that can affect men and women.

Duchenne muscular dystrophy (DMD) is perhaps the most well known of the muscular dystrophies. Many of these syndromes, including DMD, are sex-linked disorders and the genes are located on the short arm (p) of the X chromosome. In addition, it appears that there are a number of familial muscle abnormalities which also map to the Xp21 region of the chromosome, but are not as insidious as DMD and are not progressive, as is DMD. A family has now been identified in which nine male members in two generations were affected with muscle cramps during normal exercise; a few individuals also experienced muscle pain, or myalgia. The second generation patients were born only to females of the first generation, which is strongly suggestive of an X-linked trait. The affected males had high levels of creatine kinase in their blood, and there was no sign of muscle weakness. The patients had well developed muscles, and hypertrophy (overdevelopment) of the muscles in the calves. Like DMD, the syndrome developed in childhood, but unlike DMD it did not progress. Examination of muscle biopsies showed indications of myopathy (muscle disease), but nothing which could be regarded as specific. The apparent linkage of this familial myopathy to the X chromosome prompted a molecular analysis of the genes for dystrophin, a protein associated with muscular dystrophy. It was found that there was a deletion in the dystrophin gene in these patients, that is, a portion of the gene was simply missing. Using antibodies to analyze the muscle specimens for the presence of dystrophin, researchers detected a normal quantity of dystrophin, but the molecules were abnormally small, as might result from a gene deletion. This strongly suggests that this gene is indeed responsible for the observed muscle-cramping syndrome. Furthermore, it indicates that a portion consisting of at least 15 percent of the dystrophin molecule may be missing without seriously affecting the molecule's function. (Consumer Summary produced by Reliance Medical Information, Inc.)

Some serious problems have been discovered in the data presented by A.A.B. Bergen and A.J.L.G. Pinckers on X-linked progressive cone dystrophy. The LOD scores for the family showing linkage appear to be incorrect. The multipoint analysis LOD score should not be so much larger than the two-point LOD scores. In addition, the mapping of the locus to Xq27 is not definite.

The gap or break in the X chromosome is called the fragile X syndrome. This gap at location xq27 causes inherited mental retardation in about 4% of all cases. Scientists have discovered the fragile X mental retardation gene, expressed in the brain, the code for which is practically in the same region as the fragile X location. The current explanation is that imprinting may cause inactivation of this gene leading to mental retardation.

Genetic variation in nondisjunction frequency among X chromosomes from two Drosophila melanogaster natural populations is examined in a sensitized assay. A high level of genetic variation is observed (a range of 0.006-0.241). Two naturally occurring variants at the nod locus, a chromokinesin required for proper achiasmate chromosome segregation, are significantly associated with an increased frequency of nondisjunction. Both of these polymorphisms are found at intermediate frequency in widely distributed natural populations. To account for these observations, we propose a general model incorporating unique opportunities for meiotic drive during female meiosis. The ootid competition model can account for both high mean rates of female-specific nondisjunction in Drosophila and humans as well as the standing genetic variation in this critical fitness character in natural populations.

We have screened the Drosophila X chromosome for genes whose dosage affects the function of the homeotic gene Deformed. One of these genes, extradenticle, encodes a homeodomain transcription factor that heterodimerizes with Deformed and other homeotic Hox proteins. Mutations in the nejire gene, which encodes a transcriptional adaptor protein belonging to the CBP/p300 family, also interact with Deformed. The other previously characterized gene identified as a Deformed interactor is Notch, which encodes a transmembrane receptor. These three genes underscore the importance of transcriptional regulation and cell-cell signaling in Hox function. Four novel genes were also identified in the screen. One of these, rancor, is required for appropriate embryonic expression of Deformed and another homeotic gene, labial. Both Notch and nejire affect the function of another Hox gene, Ultrabithorax, indicating they may be required for homeotic activity in general.

A long-standing mystery associated with human gender differences is why girls are less vulnerable than boys to developmental disorders that affect social cognition. While such differences could be caused by the differing social roles of males and females, they could also be caused by their different genetic composition. A study of females with Turner's syndrome, in which all or part of one X chromosome is absent, shows that social functioning is influenced by paternally-derived X chromosomes.