Autosomal recessive osteopetrosis: report of 41 novel mutations in the TCIRG1 gene and diagnostic implications

Here we report 41 novel mutations in the TCIRG1 gene that is responsible for the disease in more than 50% of ARO patients. The characterisation of mutations in this gene might be useful in the process of drug design for osteoporosis treatment.

INTRODUCTION

Autosomal recessive osteopetrosis (ARO) is a genetically heterogeneous disorder due to reduced bone resorption by osteoclasts. In this process, a crucial role is played by the proton pump V-ATPase. Biallelic mutations in the TCIRG1 gene, encoding for the a3 subunit of this pump, are responsible for more than one half of ARO patients.

METHODS

Patients with a clinical diagnosis of ARO have been collected for 7 years and mutation analysis of the TCIRG1 gene was performed using direct DNA sequencing of PCR-amplified exons according to both a standard protocol and a modified one.

RESULTS

We report here 41 novel mutations identified in 67 unpublished patients, all with biallelic mutations. In particular, we describe two novel large genomic deletions and two splice site mutations in the 5' UTR of the TCIRG1 gene, in patients previously classified as mono-allelic.

CONCLUSIONS

Our data highlights the importance of two large genomic deletions and mutations in the 5' UTR with respect to patient management and, more critically, to prenatal diagnosis. With the present work, we strongly contribute to the molecular dissection of TCIRG1-deficient ARO and identify several protein residues which are fundamental for proton pump function and could thus be the target of future drugs designed to inhibit osteoclast resorptive activity.

Human Y-chromosome variation in the western Mediterranean area: implications for the peopling of the region

Y-chromosome variation was analyzed in a sample of 1127 males from the Western Mediterranean area by surveying 16 biallelic and 4 multiallelic sites. Some populations from Northeastern Europe and the Middle East were also studied for comparison. All Y-chromosome haplotypes were included in a parsimonious genealogic tree consisting of 17 haplogroups, several of which displayed distinct geographic specificities. One of the haplogroups, HG9.2, has some features that are compatible with a spread into Europe from the Near East during the Neolithic period. However, the current distribution of this haplogroup would suggest that the Neolithic gene pool had a major impact in the eastern and central part of the Mediterranean basin, but very limited consequences in Iberia and Northwestern Europe. Two other haplogroups, HG25.2 and HG2.2, were found to have much more restricted geographic distributions. The first most likely originated in the Berbers within the last few thousand years, and allows the detection of gene flow to Iberia and Southern Europe. The latter haplogroup is common only in Sardinia, which confirms the genetic peculiarity and isolation of the Sardinians. Overall, this study demonstrates that the dissection of Y-chromosome variation into haplogroups with a more restricted geographic distribution can reveal important differences even between populations that live at short distances, and provides new clues to their past interactions.

Patterns of male-specific inter-population divergence in Europe, West Asia and North Africa

We typed 1801 males from 55 locations for the Y-specific binary markers YAP, DYZ3, SRY10831 and the (CA)n microsatellites YCAII and DYS413. Phylogenetic relationships of chromosomes with the same binary haplotype were condensed in seven large one-step networks, which accounted for 95% of all chromosomes. Their coalescence ages were estimated based on microsatellite diversity. The three largest and oldest networks undergo sharp frequency changes in three areas. The more recent network 3.1A clearly discriminates between Western and Eastern European populations. Pairwise Fst showed an overall increment with increasing geographic distance but with a slope greatly reduced when compared to previous reports. By sectioning the entire data set according to geographic and linguistic criteria, we found higher Fst-on-distance slopes within Europe than in West Asia or across the two continents.