Department of Biologic and Materials Sciences, University of Michigan School of Dentistry, Ann Arbor, MI, USA.
Department of Pedodontics, Faculty of Dentistry, Istanbul University, Istanbul, Turkey.
Mol Genet Genomic Med. 2019 Oct;7(10):e00928. doi: 10.1002/mgg3.928. Epub 2019 Sep 2.
ENAM mutations cause autosomal dominant or recessive amelogenesis imperfecta (AI) and show a dose effect: enamel malformations are more severe or only penetrant when both ENAM alleles are defective.
Whole exome sequences of recruited AI probands were initially screened for mutations in known AI candidate genes. Sanger sequencing was used to confirm sequence variations and their segregation with the disease phenotype. The co-occurrence of ENAM and LAMA3 mutations in one family raised the possibility of digenic inheritance. Enamel formed in Enam Ambn , Enam , Ambn , and Enam Ambn mice was characterized by dissection and backscattered scanning electron microscopy (bSEM).
ENAM mutations segregating with AI in five families were identified. Two novel ENAM frameshift mutations were identified. A single-nucleotide duplication (c.395dupA/p.Pro133Alafs13) replaced amino acids 133-1142 with a 12 amino acid (ATTKAAFEAAIT) sequence, and a single-nucleotide deletion (c.2763delT/p.Asp921Glufs32) replaced amino acids 921-1142 with 31 amino acids (ESSPQQASYQAKETAQRRGKAKTLLEMMCPR). Three families were heterozygous for a previously reported single-nucleotide ENAM deletion (c.588+1delG/p.Asn197Ilefs*81). One of these families also harbored a heterozygous LAMA3 mutation (c.1559G>A/p.Cys520Tyr) that cosegregated with both the AI phenotype and the ENAM mutation. In mice, Ambn maxillary incisors were normal. Ambn molars were also normal, except for minor surface roughness. Ambn mandibular incisors were sometimes chalky and showed minor chipping. Enam incisor enamel was thinner than normal with ectopic mineral deposited laterally. Enam molars were sometimes chalky and rough surfaced. Enam Ambn enamel was thin and rough, in part due to ectopic mineralization, but also underwent accelerated attrition.
Novel ENAM mutations causing AI were identified, raising to 22 the number of ENAM variations known to cause AI. The severity of the enamel phenotype in Enam Ambn double heterozygous mice is caused by composite digenic effects. Digenic inheritance should be explored as a cause of AI in humans.
ENAM 突变导致常染色体显性或隐性牙釉质不全（AI），并表现出剂量效应：当两个 ENAM 等位基因均有缺陷时，牙釉质畸形更严重或仅表现为外显。
招募的 AI 先证者的全外显子组序列最初在已知的 AI 候选基因中筛选突变。Sanger 测序用于确认序列变异及其与疾病表型的分离。一个家庭中同时存在 ENAM 和 LAMA3 突变的可能性引发了双基因遗传的可能性。通过解剖和背散射扫描电子显微镜（bSEM）对 Enam Ambn 、Enam 、Ambn 和 Enam Ambn 小鼠形成的牙釉质进行了特征描述。
在五个家庭中发现了与 AI 共分离的 ENAM 突变。鉴定出两个新的 ENAM 移码突变。一个单核苷酸重复（c.395dupA/p.Pro133Alafs13）取代氨基酸 133-1142 与 12 个氨基酸（ATTKAAFEAAIT）序列，一个单核苷酸缺失（c.2763delT/p.Asp921Glufs32）取代氨基酸 921-1142 与 31 个氨基酸（ESSPQQASYQAKETAQRRGKAKTLLEMMCPR）。三个家庭为先前报道的 ENAM 缺失的杂合子（c.588+1delG/p.Asn197Ilefs*81）。其中一个家庭还携带有杂合 LAMA3 突变（c.1559G>A/p.Cys520Tyr），该突变与 AI 表型和 ENAM 突变共分离。在小鼠中，Ambn 上颌切牙正常。Ambn 磨牙也正常，除了表面粗糙度略有增加。Ambn 下颌切牙有时呈粉笔状，并有轻微的碎裂。Enam 切牙牙釉质比正常牙釉质薄，侧向异位沉积矿物质。Enam 磨牙有时呈粉笔状和粗糙表面。Enam Ambn 牙釉质薄且粗糙，部分原因是异位矿化，也加速了磨损。
发现了导致 AI 的新的 ENAM 突变，使已知导致 AI 的 ENAM 变异数增加到 22。Enam Ambn 双杂合子小鼠牙釉质表型的严重程度是由复合双基因效应引起的。双基因遗传应作为人类 AI 的病因进行探讨。
