Our results are consistent with REE being the principal cause of obesity in PHP1A rather than it being caused by excessive energy intake or endocrine dysfunction.

Context Patients with pseudohypoparathyroidism type 1b (PHP1b) show disordered imprinting of the maternal GNAS allele or paternal uniparental disomy (UPD). Genetic deletions in STX16 or in upstream exons of GNAS are present in many familial but not sporadic cases. Objective Characterization of epigenetic and genetic defects in patients with PHP1b. Design and Patients DNA from 84 subjects, including 26 subjects with sporadic PHP1b, 27 affected subjects and 17 unaffected and/or obligate gene carriers from 12 PHP1b families, 11 healthy individuals, and 3 subjects with PHP1a was subjected to quantitative pyrosequencing of GNAS differentially methylated regions (DMRs), microarray analysis, and microsatellite haplotype analysis. Setting Academic medical center. Main Outcome Measurements Molecular pathology of PHP1b. Results Healthy subjects, unaffected family members and obligate carriers of paternal PHP1b alleles, and subjects with PHP1a showed normal methylation of all DMRs. All PHP1b subjects showed loss of methylation (LOM) at the exon A/B DMR. Affected members of nine PHP1b kindreds showed LOM only at the exon A/B DMR, which was associated with a 3-kb deletion of STX16 exons 4-6 in seven families and a novel deletion of STX16 and adjacent NEPEPL1 in one family. A novel NESP deletion was found in one of two other families with more extensive methylation defects. One sporadic PHP1b had UPD of 20q, two had 3-kb STX16 deletions, and five had apparent epigenetic mosaicism. Conclusions We found diverse patterns of defective methylation and identified novel or previously known mutations in 9 of 12 PHP1b families.

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