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    Progressive Osseous Heteroplasia: A Model for the Imprinting Effects of GNAS Inactivating Mutations in Humans

    J Clin Endocrinol Metab. 2010 Apr 28. [Epub ahead of print]


    Inactivating mutations in GNAS, the gene that encodes the stimulatory G-protein alpha subunit (Gs-α), produce different phenotypes in humans depending on whether they are inherited maternally or paternally. Inactivating GNAS mutations that are paternally inherited cause Progressive Osseous Heteroplasia, syndrome, which is characterized by progressive heterotopic ossification during infancy. This paper characterized gene expression in patients with POH and similar patients who had the same GNAS mutation but had the phenotype of pseudohypoparathyroidism type 1a. However, it was unclear why the same gene mutation transmitted paternally produced different phenotypes in different patients.
      
    Authors: Lebrun M, Richard N, Abeguilé G, et. al

    Heterozygous GNAS inactivating mutations are known to induce pseudohypoparathyroidism type 1a when maternally inherited and pseudopseudohypoparathyroidism when paternally inherited. Progressive osseous heteroplasia (POH) is a rare disease of ectopic bone formation, and studies in different families have shown that POH is also caused by paternally inherited GNAS mutations. Objective: Our purpose was to characterize parental origin of the mutated allele in de novo cases of POH and to draw phenotype/genotype correlations according to maternal or paternal transmission of a same GNAS mutation. Design and Setting: We conducted a retrospective study on patients addressed to our referral center for the rare diseases of calcium and phosphorus metabolism. Patients and Methods: We matched 10 cases of POH with cases of pseudohypoparathyroidism type 1a carrying the same GNAS mutations. Main Outcome Measures: The parental origin of the mutated allele was studied using informative intragenic polymorphisms and subcloning of PCR products. Results: Paternal origin of GNAS mutations was clearly demonstrated in eight POH cases including one patient with mutation in exon 1. Genotype/phenotype analyses suggest that there is no direct correlation between the ossifying process and the position of the inactivating GNAS mutation. It is, however, more severe in patients in whom origin of the mutation is paternal. Severe intrauterine growth retardation was clearly evidenced in paternally inherited mutations. Conclusions: Clinical heterogeneity makes genetic counseling a delicate matter, especially in which paternal inheritance is concerned because it can lead to either a mild expression of pseudopseudohypoparathyroidism or a severe expression of POH.

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