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A Coruña, Spain

Perez-Nanclares G.,Endocrinology and Diabetes Research Group | Romanelli V.,Hospital Universitario La Paz | Romanelli V.,Institute Salud Carlos III | Mayo S.,Hospital Universitario La Paz | And 75 more authors.
Journal of Clinical Endocrinology and Metabolism | Year: 2012

Context: Genomic imprinting is the modification of the genomeso that genes from only one (rather than two) of the parental alleles are expressed.The mechanism underlying imprinting is epigenetic, occurring via changes in DNA methylation and histone modifications rather than through alterations in the DNA sequence. To date, nine different imprinting disorders have been clinically and genetically identified and a considerable research effort has been focused on determining the cause of the corresponding methylation defects. Objective: Our objective was to identify multilocus imprinting defects and characterize any mutations in trans-acting genes in patients with pseudohypoparathyroidism (PHP) caused by epigenetic alterations at GNAS locus. Design: We have investigated multilocus imprinting defects in 22 PHP patients with aberrant methylation at the GNAS locus not due to previously described deletions or to paternal uniparental disomy (UPD) of chromosome 20. Results: We found that, in contrast to what has been described in growth disorders, multilocus hypomethylation is an uncommon event in PHP patients. We were also unable to identify any genetic alteration causative of the epigenetic defects in the currently known methylation regulatory genes. Conclusion: Our work suggests that a trans-acting gene regulating the establishment or maintenance of imprinting at GNAS locus, if it exists, should be specific to PHP cases caused by epigenetic defects at GNAS. Copyright © 2012 by The Endocrine Society. Source

Fernandez-Rebollo E.,Endocrinology and Diabetes Research Group | Fernandez-Rebollo E.,Harvard University | Lecumberri B.,Hospital Universitario La Paz | Garin I.,Endocrinology and Diabetes Research Group | And 71 more authors.
European Journal of Endocrinology | Year: 2010

Purpose: Type I pseudohypoparathyroidism (PHP-I) can be subclassified into Ia and Ib, depending on the presence or absence of Albright's hereditary osteodystrophy's phenotype, diminished α-subunit of the stimulatory G protein (Gsα) activity and multihormonal resistance. Whereas PHP-Ia is mainly associated with heterozygous inactivating mutations in G sα-coding exons of GNAS, PHP-Ib is caused by imprinting defects of GNAS. To date, just one patient with PHP and complete paternal uniparental disomy (UPD) has been described. We sought to identify the underlining molecular defect in twenty patients with parathyroid hormone resistance, hypocalcemia and hyperphosphatemia, and abnormal methylation pattern at GNAS locus. Methods: Microsatellite typing and comparative genome hybridization were performed for proband and parents. Results: We describe four patients with partial paternal UPD of chromosome 20 involving pat20qUPD in one case, from 20q13.13-qter in two cases, and pat20p heterodisomy plus interstitial 20q isodisomy in one patient. Conclusions: These observations demonstrate that mitotic recombination of chromosome 20 can also give rise to UPD and PHP, a situation similar to other imprinting disorders, such as Beckwith-Wiedemann syndrome or neonatal diabetes. © 2010 European Society of Endocrinology. Source

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