Demonstration of a novel Xp22.2 microdeletion as the cause of familial extreme skewing of X-inactivation utilizing case-parent trio SNP microarray analysis.

BACKGROUND: We report a kindred referred for molecular investigation of severe hemophilia A in a young female in which extremely skewed X-inactivation was observed in both the proband and her clinically normal mother. METHODS: Bidirectional Sanger sequencing of all F8 gene coding regions and exon/intron boundaries was undertaken. Methylation-sensitive restriction enzymes were utilized to investigate skewed X-inactivation using both a classical human androgen receptor (HUMARA) assay, and a novel method targeting differential methylation patterns in multiple informative X-chromosome SNPs. Illumina Whole-Genome Infinium microarray analysis was performed in the case-parent trio (proband and both parents), and the proband's maternal grandmother. RESULTS: The proband was a cytogenetically normal female with severe hemophilia A resulting from a heterozygous F8 pathogenic variant inherited from her similarly affected father. No F8 mutation was identified in the proband's mother, however, both the proband and her mother both demonstrated completely skewed X-chromosome inactivation (100%) in association with a previously unreported 2.3 Mb deletion at Xp22.2. At least three disease-associated genes (FANCB, AP1S2, and PIGA) were contained within the deleted region. CONCLUSIONS: We hypothesize that true "extreme" skewing of X-inactivation (≥95%) is a rare occurrence, but when defined correctly there is a high probability of finding an X-chromosome disease-causing variant or larger deletion resulting in X-inactivation through a survival disadvantage or cell lethal mechanism. We postulate that the 2.3 Mb Xp22.2 deletion identified in our kindred arose de novo in the proband's mother (on the grandfather's homolog), and produced extreme skewing of X-inactivation via a "cell lethal" mechanism. We introduce a novel multitarget approach for X-inactivation analysis using multiple informative differentially methylated SNPs, as an alternative to the classical single locus (HUMARA) method. We propose that for females with unexplained severe phenotypic expression of an X-linked recessive disorder trio-SNP microarray should be undertaken in combination with X-inactivation analysis.

A consensus statement on the management of pregnancy and delivery in women who are carriers of or have bleeding disorders.

Pregnancy and delivery are critical times for women with bleeding disorders, with mothers, and possibly their affected infants, being exposed to a variety of haemostatic challenges. Management of women with bleeding disorders during pregnancy involves a multidisciplinary team including, but not limited to, an obstetrician, an anaesthetist and a haematologist. This consensus document from the Australian Haemophilia Centre Directors' Organisation (AHCDO) provides practical information for clinicians managing women with bleeding disorders during pregnancy. Included are: the expected physiological response in pregnancy in such women; management of pregnancy, labour and delivery, as well as obstetric anaesthesia issues, postpartum care, and reducing and treating postpartum haemorrhage; and management of infants at risk of a bleeding disorder and of bleeding in neonates. The guidelines were developed after extensive consultation, face-to-face meetings and revisions. The final document represents a consensus opinion of all AHCDO members. Where evidence is lacking, recommendations are based on clinical experience and consensus opinion.