Zimmermann-Laband Syndrome (ZLS; MIM 135500) is a rare genetic disorder with the main clinical manifestations of gingival fibromatosis and finger/toe nail hypoplasia. KCNH1 (potassium channel, voltage-gated, subfamily H, member-1), KCNN3 (potassium channel, voltage-gated, subfamily H, member-3) and ATP6V1B2 (ATPase H+ transporting V1 subunit B2) genes are considered causative genes for ZLS. However, there are limited reports about the diverse clinical presentation and genetic heterogeneity. Reporting more information on phenotype-genotype correlation and the treatment of ZLS is necessary. This case reported a 2-year-old patient with gingival enlargement that failure of eruption of the deciduous teeth and severe hypoplasia of nails. Based on a systemic examination and a review of the relevant literature, we made an initial clinical diagnosis of ZLS. A novel pathogenic variant in the KCNH1 gene was identified using whole-exome sequencing to substantiate our preliminary diagnosis. The histopathological results were consistent with gingival fibromatosis. Gingivectomy and gingivoplasty were performed under general anesthesia. After surgery, the gingival appearance improved significantly, and the masticatory function of the teeth was restored. After 2-year follow-up, the gingival showed slightly hyperplasia. Systemic examination and gene sequencing firstly contribute to provide information for an early diagnosis for ZLS, then timely removal of the hyperplastic gingival facilitates the establishment of a normal occlusal relationship and improves oral aesthetics.

Zimmermann-Laband Syndrome (ZLS) and infantile systemic hyalinosis (ISH) are rare genetic disorders. They are characterized by various spectrum manifestations. In spite of other case reports, this case with features of both syndromes was reported by oral medicine specialists and oral and maxillofacial surgeons.
In this study, we reported an 18-months old female patient with gingival overgrowth. This phenomenon completely embedded all the erupted teeth. In this case, the presence of multiple papulonodular cutaneous lesions is a newly observed aspect that has rarely been reported in the existing literature. Gingival overgrowth was excised under general anesthesia. At six months of follow-up after surgery, mastication and breathing problems were improved. Aesthetic aspects were ameliorated in terms of gingival appearance.
To date, due to the ambiguous presentations, both syndromes remain an enigma for specialists. A timely diagnosis could be crucial for prognosis and preventing severe further surcharge. Dentists could play an important role in the diagnosis of rare disorders.

Zimmermann-Laband syndrome is a rare, heterogeneous disorder characterized by gingival hypertrophy or fibromatosis, aplastic/hypoplastic nails, hypoplasia of the distal phalanges, hypertrichosis, various degrees of intellectual disability, and distinctive facial features. Three genes are considered causative for ZLS: KCNH1, KCNN3, and ATP6V1B2. We report on a pair of female concordant monozygotic twins, both carrying a novel pathogenic variant in the KCNN3 gene, identified using exome sequencing. Only six ZLS patients with the KCNN3 pathogenic variant have been reported so far. The twins show facial dysmorphism, hypoplastic distal phalanges, aplasia or hypoplasia of nails, and hypertrichosis. During infancy, they showed mild developmental delays, mainly speech. They successfully completed secondary school education and are socio-economically independent. Gingival overgrowth is absent in both individuals. Our patients exhibited an unusually mild phenotype compared to published cases, which is an important diagnostic finding for proper genetic counseling for Zimmermann-Laband syndrome patients and their families.