Rezwan Faisal I, Poole Rebecca L, Prescott Trine, Walker Joanna M, Karen Temple I, Mackay Deborah J G
Human Genetics and Genomic medicine, Faculty of Medicine, University of Southampton, Southampton, UK.
1] Human Genetics and Genomic medicine, Faculty of Medicine, University of Southampton, Southampton, UK [2] Wessex Regional Genetics Laboratory, Salisbury District Hospital, Salisbury NHS Foundation Trust, Salisbury, UK.
Eur J Hum Genet. 2015 Apr;23(4):494-9. doi: 10.1038/ejhg.2014.133. Epub 2014 Jul 9.
Pseudohypoparathyroidism (PHP) is caused by reduced expression of genes within the GNAS cluster, resulting in parathormone resistance. The cluster contains multiple imprinted transcripts, including the stimulatory G protein α subunit (Gs-α) and NESP55 transcript preferentially expressed from the maternal allele, and the paternally expressed XLas, A/B and antisense transcripts. PHP1b can be caused by loss of imprinting affecting GNAS A/B alone (associated with STX16 deletion), or the entire GNAS cluster (associated with deletions of NESP55 in a minority of cases). We performed targeted genomic next-generation sequencing (NGS) of the GNAS cluster to seek variants and indels underlying PHP1b. Seven patients were sequenced by hybridisation-based capture and fourteen more by long-range PCR and transposon-mediated insertion and sequencing. A bioinformatic pipeline was developed for variant and indel detection. In one family with two affected siblings, and in a second family with a single affected individual, we detected maternally inherited deletions of 40 and 33 bp, respectively, within the deletion previously reported in rare families with PHP1b. All three affected individuals presented with atypically severe PHP1b; interestingly, the unaffected mother in one family had the detected deletion on her maternally inherited allele. Targeted NGS can reveal sequence changes undetectable by current diagnostic methods. Identification of genetic mutations underlying epigenetic changes can facilitate accurate diagnosis and counselling, and potentially highlight genetic elements critical for normal imprint setting.
假性甲状旁腺功能减退症（PHP）是由GNAS基因簇内基因表达减少引起的，导致甲状旁腺激素抵抗。该基因簇包含多个印记转录本，包括优先从母本等位基因表达的刺激性G蛋白α亚基（Gs-α）和NESP55转录本，以及从父本表达的XLas、A/B和反义转录本。PHP1b可能由仅影响GNAS A/B的印记丢失（与STX16缺失相关）或整个GNAS基因簇（少数情况下与NESP55缺失相关）引起。我们对GNAS基因簇进行了靶向基因组下一代测序（NGS），以寻找PHP1b潜在的变异和插入缺失。7名患者通过基于杂交的捕获进行测序，另外14名患者通过长距离PCR和转座子介导的插入及测序进行检测。开发了一种用于变异和插入缺失检测的生物信息学流程。在一个有两名受影响兄弟姐妹的家庭以及另一个有一名受影响个体的家庭中，我们分别在先前报道的PHP1b罕见家庭的缺失区域内检测到母系遗传的40和33bp缺失。所有三名受影响个体均表现出非典型严重的PHP1b；有趣的是，一个家庭中未受影响的母亲在其母系遗传的等位基因上有检测到的缺失。靶向NGS可以揭示当前诊断方法无法检测到的序列变化。鉴定表观遗传变化背后的基因突变有助于准确诊断和咨询，并可能突出对正常印记设定至关重要的遗传元件。
