Nyamkhishig Sambuughin

High levels of mitochondrial DNA (mtDNA) diversity were determined for Mongolian populations, represented by the Mongol-speaking Khalkha and Dariganga. Although 103 samples were collected across Mongolia, low levels of genetic substructuring were detected, reflecting the nomadic lifestyle and relatively recent ethnic differentiation of Mongolian populations. mtDNA control region I sequence and seven additional mtDNA polymorphisms were assayed to allow extensive comparison with previous human population studies. Based on a comparative analysis, we propose that indigenous populations in east Central Asia represent the closest genetic link between Old and New World populations. Utilizing restriction/deletion polymorphisms, Mongolian populations were found to carry all four New World founding haplogroups as defined by WALLACE and coworkers. The ubiquitous presence of the four New World haplogroups in the Americas but narrow distribution across Asia weakens support for GREENBERG and coworkers' theory of New World colonization via three independent migrations. The statistical and geographic scarcity of New World haplogroups in Asia makes it improbable that the same four haplotypes would be drawn from one geographic region three independent times. Instead, it is likely that founder effects manifest throughout Asia and the Americas are responsible for differences in mtDNA haplotype frequencies observed in these regions.

Human DNA variation is currently a subject of intense research because of its importance for studying human origins, evolution, and demographic history and for association studies of complex diseases. A approximately 10-kb region on chromosome 1, which contains only four small exons (each <155 bp), was sequenced for 61 humans (20 Africans, 20 Asians, and 21 Europeans) and for 1 chimpanzee, 1 gorilla, and 1 orangutan. We found 52 polymorphic sites among the 122 human sequences and 382 variant sites among the human, chimpanzee, gorilla, and orangutan sequences. For the introns sequenced (8,991 bp), the nucleotide diversity (pi) was 0.058% among all sequences, 0.076% among the African sequences, 0.047% among the Asian sequences, and 0.045% among the European sequences. A compilation of data revealed that autosomal regions have, on average, the highest pi value (0.091%), X-linked regions have a somewhat lower pi value (0.079%), and Y-linked regions have a very low pi value (0.008%). The lower polymorphism in the present region may be due to a lower mutation rate and/or selection in the gene containing these introns or in genes linked to this region. The present region and two other 10-kb noncoding regions all show a strong excess of low-frequency variants, indicating a relatively recent population expansion. This region has a low mutation rate, which was estimated to be 0.74 x 10 per nucleotide per year. An average estimate of approximately 12,600 for the long-term effective population size was obtained using various methods; the estimate was not far from the commonly used value of 10,000. Fu and Li's tests rejected the assumption of an equilibrium neutral Wright-Fisher population, largely owing to the high proportion of low-frequency variants. The age of the most recent common ancestor of the sequences in our sample was estimated to be more than 1 Myr. Allowing for some unrealistic assumptions in the model, this estimate would still suggest an age of more than 500,000 years, providing further evidence for a genetic history of humans much more ancient than the emergence of modern humans. The fact that many unique variants exist in Europe and Asia also suggests a fairly long genetic history outside of Africa and argues against a complete replacement of all indigenous populations in Europe and Asia by a small Africa stock. Moreover, the ancient genetic history of humans indicates no severe bottleneck during the evolution of humans in the last half million years; otherwise, much of the ancient genetic history would have been lost during a severe bottleneck. We suggest that both the "Out of Africa" and the multiregional models are too simple to explain the evolution of modern humans.

BACKGROUND: Malignant hyperthermia (MH) is a life-threatening and frequently fatal disorder triggered by commonly used anesthetics. MH susceptibility is a genetically determined predisposition to the development of MH. Mutations in the ryanodine receptor type 1 (RYR1) gene are the major cause of MH susceptibility. The authors sought to develop a reliable genetic screening strategy based on efficient and relatively inexpensive mutation-detection procedures. METHODS: A cohort (n = 30) of North American MH patients and MH-susceptible individuals was studied. RNA and DNA extracted from muscle tissue or blood lymphocytes were used for analysis. The entire RYR1 coding region was amplified in 57 overlapping fragments and subjected to denaturing high-performance liquid chromatography analysis followed by direct nucleotide sequencing to characterize RYR1 alterations. RESULTS: Nine previously reported and nine unknown RYR1 mutations were identified in 21 of 30 studied patients (70%). Some of the new mutations were located outside of known mutational "hot spots," suggesting that RYR1 contains previously unknown mutation-prone areas requiring analysis. The North American MH/MH-susceptible population is characterized by a high RYR1 allelic heterogeneity. CONCLUSIONS: Denaturing high-performance liquid chromatography analysis of RNA samples extracted from the biopsied skeletal muscle followed by DNA sequencing is a highly efficient methodology for RYR1 mutation detection. This approach allows increasing the rate of mutation detection to 70% and identifying mutations in the entire RYR1 coding region.