Precise Microdeletion Detection of Prader-Willi Syndrome with Array Comparative Genome Hybridization

Objective Prader-Willi Sydrome （PWS） is a human disorder related to genomic imprinting defect on 15ql 1-13. It is characterized by a series of classic features such as hypotonia, hyperphagia, obesity, osteoporosis, typical facial and body dysmorphosis, hypogonadism, mental and behaviour disorders. Our study was designed to precisely detect the microdeletions, which accounts for 65%-70% of the PWS. Methods Physical and laboratory examinations were firstly performed to diagnose PWS clinically, and to discover novel clinical features. Then the patient was screened with bisulfite-specific sequencing and precisely delineated through high-density array CGH. Results With the bisulfite-specific sequencing, the detected CpG island in the PWS critical region was found homozygously hypermethylated. Then with array CGH, a 2.22 Mb type II microdeletion was detected, covering a region from MKRN3, MAGEL2, NDN, PWRN2, PWRN1, Cl2orf2, SNURF-SNRPN, C/D snoRNAs, to distal of UBE3A. Conclusions Array CGH, after the fast screening of Bisulfite-specific sequencing, is a feasible and precise method to detect microdeletions in PWS patients. A novel feature of metacarpophalangeal joint rigidity was also presented, which is the first time reported in PWS.

Intracellular Retention of Human Melanocortin-4 Receptor:A Molecular Mechanism Underlying Early-onset Obesity in F261S Pedigree of Chinese

Objective To investigate how F261S mutation identified from Chinese obese patients affects the function of melanocorfin 4 receptor (MC4R) and to analyze the obesity-related phenotypes in subjects carrying the F261S mutation. Methods F261S mutant of MC4R was generated by site-directed mutagenesis. Plasmids encoding wild-type or F261S mutant of MC4R were transfected into HEK293 and COS-7 cells to examine their functional characteristics. Signaling properties of F261S MC4R were assessed by measuring intracellular cAMP levels in response to α-MSH stimulation. Cell surface expression of F261S MC4R was compared with that of wild-type MC4R. Clinical examinations were performed in subjects carrying F261S mutation and in non-mutated controls. Results The a-MSH-stimulated reporter gene activity was significantly reduced in cells expressing F261S MC4R, with a maximal response equal to 57% of wild-type MC4R. The F261S mutation also led to a significant change in the EC50 value compared with the wild-type receptor (P〈0.01). Immunofluorescent assay revealed a marked reduction in plasma membrane localization of the MC4R in cells expressing the F261S mutant receptor. The resting metabolic rate and fat composition of the mutant carriers were not significantly different from those of the non-mutated obese controls. Conclusions The decreased response to α-MSH due to the intracellular retention of MC4R may cause early-onset obesity in the F261S pedigree of Chinese.