Rischewski J R, Clausen H, Leber V, Niemeyer C, Ritter J, Schindler D, Schneppenheim R
University Children's Hospital, Hamburg, Germany.
Klin Padiatr. 2000 Jul-Aug;212(4):174-6. doi: 10.1055/s-2000-9673.
Patients with Fanconi Anemia (FANC) have a well documented increased risk to develop malignancies, especially Acute Myeloid Leukemia (AML) and Myelodysplastic Syndrome (MDS). The risk for heterozygous individuals is not clear, epidemiological data are inconsistent. If the risk for heterozygous individuals to develop malignancies was increased, they should be found in groups of patients with AML or MDS at higher proportion than in the normal population. We are currently screening a pediatric population with hematologic malignancies for mutations in the FANCA, FANCC and FANCG gene, and report here on siblings carrying a heterozygous frameshift mutation in the FANCC Gene.
Using PCR based single strand conformational analysis we screened the DNA from pediatric patients suffering from 1 degree or 2 degrees MDS, CMML/JMML or AML for mutations in the FANCA (43 exons), FANCC (14 exons) and FANCG (14 exons) gene, and included one patient with refractory T-ALL, being the brother of a patient with T-ALL and MDS transforming into AML. Aberrant PCR products were directly sequenced. Flowcytometric measurement of mitogen-sensitivity and G2-phase arrest is used to evaluate cultured stimulated lymphocytes from individuals carrying FANC-mutations.
A novel heterozygous frame-shift mutation, 377-378delGA in the FANCC gene was found in 2 siblings, both suffering from T-ALL with subsequent MDS transforming to AML in one of them. No other mutation was found by direct sequencing of the complete FANCC gene. Both patients died under therapy. The parents (first degree cousins) and one healthy brother are also carriers. Their lymphocytes show a higher mutagen sensitivity than normal, but do not get blocked in G2 phase as being typical for Fanconi Anemia.
As the mutation causes a premature Stopcodon within exon 4 of the FANCC gene it has to be regarded as a causal FANCC gene defect. The findings within this family support the hypothesis of an increased risk to develop malignancies in heterozygous carriers of FANC-mutations. A systematic screening of further patients is needed, and we are currently examining a larger cohort to get a better estimate of the true risk of heterozygosity.
范可尼贫血（FANC）患者发生恶性肿瘤的风险增加，这已得到充分证实，尤其是急性髓系白血病（AML）和骨髓增生异常综合征（MDS）。杂合子个体的风险尚不清楚，流行病学数据并不一致。如果杂合子个体发生恶性肿瘤的风险增加，那么在AML或MDS患者群体中发现他们的比例应该高于正常人群。我们目前正在对患有血液系统恶性肿瘤的儿科人群进行FANCA、FANCC和FANCG基因突变筛查，并在此报告携带FANCC基因杂合移码突变的同胞情况。
我们采用基于聚合酶链反应（PCR）的单链构象分析方法，对患有1级或2级MDS、慢性粒-单核细胞白血病/幼年型粒-单核细胞白血病（CMML/JMML）或AML的儿科患者的DNA进行FANCA（43个外显子）、FANCC（14个外显子）和FANCG（14个外显子）基因突变筛查，纳入一名难治性T淋巴细胞白血病（T-ALL）患者，该患者是一名T-ALL且MDS转化为AML患者的兄弟。对异常的PCR产物进行直接测序。采用流式细胞术检测有丝分裂原敏感性和G2期阻滞，以评估携带FANC突变个体的培养刺激淋巴细胞。
在2名同胞中发现了FANCC基因的一种新的杂合移码突变，即377-378delGA，两人均患有T-ALL，其中一人随后发生MDS转化为AML。对完整的FANCC基因进行直接测序未发现其他突变。两名患者均在治疗过程中死亡。其父母（一级表亲）和一名健康兄弟也是携带者。他们的淋巴细胞显示出比正常人更高的诱变敏感性，但不像典型的范可尼贫血那样在G2期阻滞。
由于该突变导致FANCC基因第4外显子内出现提前终止密码子，因此必须将其视为FANCC基因的因果缺陷。该家族的研究结果支持FANC突变杂合携带者发生恶性肿瘤风险增加的假说。需要对更多患者进行系统筛查，我们目前正在研究一个更大的队列，以更好地评估杂合性的真实风险。
