GENETIC STUDIES OF CRANIOFACIAL AND LIMB DISORDERS

Saethre-Chotzen综合征是最常见的常染色体显性遗传病之一， 人类颅缝早闭症的病症，其特征在于 颅面和肢体畸形Saethre-Chotzen综合征的发病部位 定位于染色体7 p21-p22。 我们已经评估了TWIST，一种基本的螺旋- 环螺旋转录因子，作为这种情况的候选基因 因为它在果蝇中的表达模式和突变表型， 小鼠与Saethre-Chotzen表型一致。我们绘制了TWIST 对人类染色体7 p21-p22进行了突变分析， 患者显示无义、错义、插入和缺失突变 （霍华德等人，1997年）。这些突变发生在基本的DNA中 结合，螺旋I和环结构域，或导致过早终止 蛋白质。 在Apert综合征中，以颅缝早闭和并指为特征， 手和脚，丝氨酸-脯氨酸二肽的反复突变 （FGFR 2 Ser 252 Trp或Pro253 Arg）， IgIII细胞外免疫球蛋白样结构域，已被记录 160多个无关个体的基因 我们做了产前诊断 在检测到与这种情况一致的特征的零星病例上 早在妊娠早期（Filkins et al. 1997）。 我们有 鉴定了该二肽的三种新的FGFR 2突变， 具有不同的颅缝早闭表型（Oldridge et al. 1997）。 的CG 在一个男孩中确定的预测Ser 252 Phe替换的T突变 轻度Crouzon综合征（正常肢体的颅缝早闭）也是 在他的三个临床上正常的家庭成员中存在。A CG->TT 预测Ser 252 Phe取代的突变导致表型 符合阿伯特综合征 最后，CGC->TCT突变， 预测双氨基酸取代（Ser 252 Phe和Pro253 Ser） 导致Pfeiffer综合征变异型，伴有轻度颅缝早闭，广泛 拇指和大脚趾，几个手指的固定延伸， 皮肤并指畸形 Treacher柯林斯综合征是人类最常见的 下颌骨面骨发育不全疾病。最近，一个部分TCOF 1 cDNA被克隆。 在TCS家族中鉴定并显示含有突变。这里我们 呈现完整的外显子/内含子基因组结构和完整的编码 TCOF 1-TCOF 1序列编码1411个氨基酸的低复杂性蛋白质， 酸，其预测的蛋白质结构揭示了重复的基序， 反映其外显子的组织。这些图案与 核仁运输蛋白在其他物种，并预测将是 被酪蛋白激酶高度磷酸化。与此相一致，完整的- 长度TCOFI蛋白序列还含有推定的核和 核仁定位信号。在整个开放式阅读框架中， 检测到另外8个突变和几个多态性， 筛选了超过50个TCS家族（Wise等，1997）。我们假设 TCS是由核仁运输蛋白缺陷引起的， 是人类颅面发育所必需的

Saethre-Chotzen syndrome is one of the most common autosomal dominant disorders of craniosynostosis in humans and is characterized by craniofacial and limb anomalies. The locus for Saethre-Chotzen syndrome maps to chromosome 7p21-p22. We have evaluated TWIST, a basic helix- loop-helix transcription factor, as a candidate gene for this condition because its expression pattern and mutant phenotypes in Drosophila and mouse are consistent with the Saethre-Chotzen phenotype. We mapped TWIST to human chromosome 7p21-p22, and mutational analysis on over 15 patients revealed nonsense, missense, insertion and deletion mutations (Howard et al. 1997). These mutations occur within the basic DNA binding, helix I and loop domains, or result in premature termination of the protein. In Apert syndrome, characterized by craniosynostosis and syndactyly of the hands and feet, recurrent mutations of the serine-proline dipeptide (either FGFR2 Ser252Trp or Pro253Arg) in the linker between the IgII and IgIII extracellular immunoglobulin-like domains, have been documented in more than 160 unrelated individuals. We performed prenatal diagnosis on a sporadic case with features consistent with this condition detected as early as the first trimester (Filkins et al. 1997). We have identified three novel FGFR2 mutations of this dipeptide, associated with distinct craniosynostotic phenotypes (Oldridge et al. 1997). A CG T mutation that predicts a Ser252Phe substitution, ascertained in a boy with mild Crouzon syndrome (craniosynostosis with normal limbs) is also present in three clinically normal members of his family. A CG->TT mutation that predicts a Ser252Phe substitution results in a phenotype consistent with Apert syndrome. Finally, a CGC->TCT mutation that predicts a double amino acid substitution (Ser252Phe and Pro253Ser) causes a Pfeiffer syndrome variant with mild craniosynostosis, broad thumbs and big toes, fixed extension of several digits, and only minimal cutaneous syndactyly. Treacher Collins syndrome is the most common of the human mandibulofacial dysostosis disorders. Recently, a partial TCOFl cDNA was identified and shown to contain mutations in TCS families. Here we present the entire exon/intron genomic structure and the complete coding sequence of TCOFl - TCOFl encodes a low complexity protein of 1411 amino acids, whose predicted protein structure reveals repeated motifs that mirror the organization of its exons. These motifs are shared with nucleolar trafficking proteins in other species and are predicted to be highly phosphorylated by casein kinase. Consistent with this, the full- length TCOFI protein sequence also contains putative nuclear and nucleolar localization signals. Throughout the open reading frame, we detected an additional eight mutations and several polymorphisms when over 50 TCS families were screened (Wise et al. 1997). We postulated that TCS results from defects in a nucleolar trafficking protein that is critically required during human craniofacial development.