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Non-disjoined chromosomes 15 from 115 cases of uniparental disomy (ascertained through Prader-Willi syndrome) and 13 cases of trisomy of maternal origin were densely typed for microsatellite loci spanning chromosome 15q. Of these 128 cases a total of 97 meiosis I (MI) errors, 19 meiosis II (MII) errors and 12 mitotic errors were identified. The genetic length of a map created from the MI errors was 101 cM, as compared with a maternal length of 137 cM based on CEPH controls. No significant differences were detected in the distribution of recombination events along the chromosome arm and a reduction was seen for most of the chromosome 15 intervals examined. It was estimated that 21% of tetrads leading to MI non-disjunction were achiasmate, which may account for most or all of the reduction in recombination noted. The mean age of mothers of cases involving MI errors which showed no transitions from heterodisomy to isodisomy was significantly lower (32.7) than cases showing one or more observable transitions (36.3) (P < 0.003, t-test). However, even among chiasmate pairs the highest mean maternal age was seen for multiple exchange tetrads. Chromosome-specific differences in maternal age effects may be related to the normal distribution of exchanges (and their individual susceptibilities) for each chromosome. However, they may also reflect the presence of multiple factors which act to ensure normal segregation, each affected by maternal age in a different way and varying in importance for each chromosome

Workshops are an important part of the IFPA annual meeting as they allow for discussion of specialised topics. At IFPA meeting 2011 there were twelve themed workshops, five of which are summarized in this report. These workshops related to various aspects of placental biology: 1) immunology; 2) epigenetics; 3) comparative placentation; 4) trophoblast differentiation; 5) stem cells.

Workshops are an important part of the IFPA annual meeting as they allow for discussion of specialised topics. At IFPA meeting 2011 there were twelve themed workshops, five of which are summarized in this report. These workshops related to various aspects of placental biology: 1) immunology; 2) epigenetics; 3) comparative placentation; 4) trophoblast differentiation; 5) stem cells.

Meiotic recombination is a specifically timed and regulated process which does not occur randomly throughout the genome, but tends to be clustered in ‘hotspots'. There is extensive evidence that recombinatlon rate is influenced by chromatin conformation and that events are primarily initiated at gene promoter regions. In an effort to determine the pattern of chromatin condensation and recombinatlon at meiosis in an imprinted region, fine scale genetic mapping in the approximately 4 Mb Prader-Willi/Angelman syndrome deletion region was undertaken. The results Indicate that the male-female recombinatlon ratio can vary significantly over short regions. A male recombinatlon hotspot is localized to between the 3' end of GABRA5 and Dl 5S1 56, which Is adjacent to but outside the putative AS/PWS imprinted regions. In addition, a region of relatively high recombination In females is observed between Dl 5S1 28 and D15S97, which spans a domain of paternal allele-specific transcription implicated in the Prader-Willi syndrome. It is inferred that the Inactivation and relative condensation of this latter region on the maternal chromosome occurs as a post-meiotic modification

The association of an interstitial deletion of chromosome 15q11–13 with the Prader-Willi Syndrome (PWS) has been known since 1981 (Ledbetter et al, 1981 and 1982). However, about 37% of patients are cytogenetically normal (Ledbetter et al, 1987). The discovery of maternal heterodisomy for 15q11–13 in two patients with PWS (Nicholls et al, 1989) raised the question of whether such a phenomenon could explain many or even all non-deletion patients. To answer such a question requires a very good clinical diagnosis and reliable molecular data, and was the major impetus for the work presented here.

Non-disjoined chromosomes 15 from 115 cases of uniparental disomy (ascertained through Prader-Willi syndrome) and 13 cases of trisomy of maternal origin were densely typed for microsatellite loci spanning chromosome 15q. Of these 128 cases a total of 97 meiosis I (MI) errors, 19 meiosis II (MII) errors and 12 mitotic errors were identified. The genetic length of a map created from the MI errors was 101 cM, as compared with a maternal length of 137 cM based on CEPH controls. No significant differences were detected in the distribution of recombination events along the chromosome arm and a reduction was seen for most of the chromosome 15 intervals examined. It was estimated that 21% of tetrads leading to MI non-disjunction were achiasmate, which may account for most or all of the reduction in recombination noted. The mean age of mothers of cases involving MI errors which showed no transitions from heterodisomy to isodisomy was significantly lower (32.7) than cases showing one or more observable transitions (36.3) (P < 0.003, t-test). However, even among chiasmate pairs the highest mean maternal age was seen for multiple exchange tetrads. Chromosome-specific differences in maternal age effects may be related to the normal distribution of exchanges (and their individual susceptibilities) for each chromosome. However, they may also reflect the presence of multiple factors which act to ensure normal segregation, each affected by maternal age in a different way and varying in importance for each chromosome