Relationship of the sickle cell gene to the ethnic and geographic groups populating the Sudan

The presence of a geographical pattern in the distribution of the sickle cell gene (S gene) and its association with malaria is well documented. To study the distribution of the S gene among various ethnic and linguistic groups in the Sudan we analyzed a hospital-based sample of 189 sickle cell anemia (SCA) patients who reported to the Khartoum Teaching Hospital between June 1996 and March 2000 and 118 controls with other complaints, against their ethnic and linguistic affiliations and geographic origin. Electrophoresis for hemoglobin S and sickling tests were carried out on all patients and controls as a prerequisite for inclusion. The majority of patients (93.7%) belonged to families of single ethnic descent, indicating the high degree of within-group marriages and thus the higher risk of augmenting the gene. SCA was found to be predominant among the Afro-Asiatic-speaking groups (68.4%) including nomadic groups of Arab and non- Arab descent that migrated to the Sudan in various historical epochs. Those patients clustered in western Sudan (Kordofan and Darfur) from where 73% of all cases originate. The proportion of patients reporting from other geographic areas like the south (3.1%), which is primarily inhabited by Nilo-Saharan-speaking groups (19% of the whole sample) who populated the country in previous times, is disproportionate to their total population in the country (chi(2) = 71.6; p = 0.0001). Analysis of the haplotypes associated with the S gene indicated that the most abundant haplotypes are the Cameroon, Benin, Bantu and Senegal haplotypes, respectively. No relationship was seen between haplotypes and the various hematological parameters in the sub-sample analyzed for such association. These results provide an insight into the distribution of the sickle cell gene in the Sudan, and highlight the strong link of the middle Nile Valley with West Africa through the open plateau of the Sahel and the nomadic cattle herders and also probably the relatively young age of the S gene.     

X‐Ray Writing of Metallic Conductivity and Oxygen Vacancies at Silicon/SrTiO3 Interfaces

Tunable electronic properties of transition metal oxides and their interfaces offer remarkable functionalities for future devices. The interest in these materials has been boosted with the discovery of a 2D electron gas (2DEG) at SrTiO₃ (STO)‐based interfaces. For the majority of these systems, oxygen vacancies play a crucial role in the emergence of interface conductivity, ferromagnetism, and high electron mobility. Despite its great importance, controlling the density and spatial distribution of oxygen vacancies in a dynamic way remains extremely challenging. Here, lithography‐like writing of a metallic state at the interface between SrTiO₃ and amorphous Si using X‐ray irradiation is reported. Using a combination of transport techniques and in operando photoemission spectroscopy, it is revealed in real time that the X‐ray radiation induces transfer of oxygen across the interface leading to the on‐demand formation of oxygen vacancies and a 2DEG in STO. The formed 2DEG stays stable in ambient conditions as the interface oxygen vacancies are stabilized by the capping of Si. The study provides a fundamental understanding of X‐ray‐induced redox reactions at the SrTiO₃‐based interfaces and in addition shows the potential of X‐ray radiation for patterning stabile conductive pathways for future oxide‐based electronic devices.