Nature Genetics pp 437 - 441

Fossil evidence indicates that modern humans originated in Africa and then expanded from North Africa into the Middle East about 100,000 years ago. Silvana Santachiara-Benerecetti (of the University of Pavia) and colleagues now provide evidence that supports a second route of exit from Africa, whereby ancient peoples dispersed from eastern Africa and migrated along the coast to South Asia.

Mitochondria are tiny intracellular bodies that generate the energy needed to drive the activities of a cell. They have their own DNA, distinct and independent from nuclear DNA. Mitochondrial DNA can be 'fingerprinted' according to small variations in sequence and, because mitochondria are only inherited from the mother, used to trace maternal ancestry. Closely related mitochondrial DNA sequences fall within the same 'haplogroup', and insinuate -- but do not prove -- a close genetic relationship between the people who carry them. People in Asia and Ethiopia carry the 'M' mitochondrial haplogroup, which raises the question: how has this come about? Have their mitochondrial DNAs evolved independently, but, through coincidence, converged onto the same haplotype? Or does the similarity reflect a genetic relationship?

On scrutinizing the region of mitochondrial sequence in Africans and Indians, Santachiara-Benerecetti and coworkers ruled out the possibility that the M haplogroups in eastern-African and Asian populations arose independently -- rather, they have a common African origin. These findings, together with the observation that the M haplogroup is virtually absent in Middle-Eastern populations, support the idea that there was a second route of migration out of Africa, approximately 60,000 years ago, exiting from eastern Africa along the coast towards Southeast Asia, Australia and the Pacific Islands.

Nature Genetics pp 429 - 432

Faulty sperm production, leading to infertility, can be caused by defects in the Y chromosome. Deletions that encompass any one of three regions of the Y chromosome are found in some infertile men, but critical genes within these regions have not, until now, been identified. David Page (of the Whitehead Institute) and colleagues now report mutations in the gene USP9Y in two infertile men. This is the first identification of a gene on the Y chromosome that, when mutated, results in failure to make sperm. These findings raise the possibility that mutations in USP9Y that lead to only a partial loss of function may underlie milder fertility problems in men.

Nature Genetics pp 421 - 424 and pp 378 - 380

As any dentist will tell you, regular brushing, flossing and swilling of mouthwash make for a sound set of teeth. But Nalin Thakker (of the University of Manchester) and colleagues now reveal that cathepsin C may prevent the pockets of infection that can occur around teeth -- a condition called periodontitis. The authors have discovered that people with Papillon-Lefevre syndrome (PLS), a hereditary disorder characterized by severe early-onset periodontitis, have mutations in the gene CTSC, encoding cathepsin C.

Cathepsin C is made by cells of the immune system to activate the enzymes needed to destroy diseased or infected cells, and minimize inflammation at sites of infection. People with PLS are susceptible to infection and inflammation of the gums, resulting in premature tooth loss (with loss of teeth by age fourteen). In addition, people with PLS have thick, scaly skin on their palms and soles, indicating that cathepsin C is also required for correct maturation and shedding of skin cells. The gums are attached to the teeth by a lining similar to the skin, so it is also possible that lack of cathepsin C in PLS sufferers weakens this mechanical barrier to microbial invasion, increasing susceptibility to periodontitis.

As suggested by Glen Nuckolls and Harold Slavkin (of the National Institutes of Heath) in an accompanying News & Views article, late-onset periodontitis, which affects more than 30% of the population, might be caused by mutations in CTSC that result in slight loss of cathepsin C activity. Cathepsin C may be a target for preventing and treating more common forms of gum disease.