A novel frameshift mutation in the KIND1 gene in Turkish siblings with Kindler syndrome

A novel frameshift mutation in the FERMT1 gene in a Chinese patient with Kindler syndrome

Kindler syndrome (KS) is a rare subtype of epidermolysis bullosa that is inherited in an autosomal recessive manner with mutations in FERMT1. A number of mutations in FERMT1 have been identified in KS. The current study reported a 33-year-old Chinese man who exhibited a wide variety of clinical features, including formation of blisters, photosensitivity, cutaneous atrophy and poikiloderma, telangiectasia of the face and neck, contracture of the end limbs, nail dystrophy, muscle, eye and oral damage, tympanitis, esophagus narrowing, pneumothorax and palmoplantar keratoderma. The patient's parents were healthy and the patient had no siblings or children. Peripheral blood was obtained from the patient, his parents and 100 controls, who were admitted to the Dermatology Clinic of Shanghai Skin Disease Hospital, Shanghai, China. A multi-gene panel test consisting of 541 genetic loci of monogenic hereditary diseases was performed. The results identified one novel homogenous mutation in the patient: c.1885_1901del (p.Val629fs) on exon 15 in FERMT1. The patient's parents exhibited heterogeneous identical mutations. This mutation was absent in the control group. The results of the multi-gene panel test were further verified by Sanger sequencing. Based on the clinical manifestations and genetic analysis, KS was diagnosed in the patient. The current study reported a Chinese case of KS with one novel mutation c.1885_1901del in FERMT1 and presented a brief summary of all pathogenic mutations in FERMT1 that have been reported in KS between 1984 and May 2020 via a PubMed literature search.

Kindler syndrome: extension of FERMT1 mutational spectrum and natural history

Mutations in the FERMT1 gene (also known as KIND1), encoding the focal adhesion protein kindlin-1, underlie the Kindler syndrome (KS), an autosomal recessive skin disorder with an intriguing progressive phenotype comprising skin blistering, photosensitivity, progressive poikiloderma with extensive skin atrophy, and propensity to skin cancer. Herein we review the clinical and genetic data of 62 patients, and delineate the natural history of the disorder, for example, age at onset of symptoms, or risk of malignancy. Although most mutations are predicted to lead to premature termination of translation, and to loss of kindlin-1 function, significant clinical variability is observed among patients. There is an association of FERMT1 missense and in-frame deletion mutations with milder disease phenotypes, and later onset of complications. Nevertheless, the clinical variability is not fully explained by genotype-phenotype correlations. Environmental factors and yet unidentified modifiers may play a role. Better understanding of the molecular pathogenesis of KS should enable the development of prevention strategies for disease complications.

Loss-of-function FERMT1 mutations in kindler syndrome implicate a role for fermitin family homolog-1 in integrin activation

Kindler syndrome is an autosomal recessive disorder characterized by skin atrophy and blistering. It results from loss-of-function mutations in the FERMT1 gene encoding the focal adhesion protein, fermitin family homolog-1. How and why deficiency of fermitin family homolog-1 results in skin atrophy and blistering are unclear. In this study, we investigated the epidermal basement membrane and keratinocyte biology abnormalities in Kindler syndrome. We identified altered distribution of several basement membrane proteins, including types IV, VII, and XVII collagens and laminin-332 in Kindler syndrome skin. In addition, reduced immunolabeling intensity of epidermal cell markers such as beta1 and alpha6 integrins and cytokeratin 15 was noted. At the cellular level, there was loss of beta4 integrin immunolocalization and random distribution of laminin-332 in Kindler syndrome keratinocytes. Of note, active beta1 integrin was reduced but overexpression of fermitin family homolog-1 restored integrin activation and partially rescued the Kindler syndrome cellular phenotype. This study provides evidence that fermitin family homolog-1 is implicated in integrin activation and demonstrates that lack of this protein leads to pathological changes beyond focal adhesions, with disruption of several hemidesmosomal components and reduced expression of keratinocyte stem cell markers. These findings collectively provide novel data on the role of fermitin family homolog-1 in skin and further insight into the pathophysiology of Kindler syndrome.

Kindler syndrome: a focal adhesion genodermatosis

Kindler syndrome (OMIM 173650) is an autosomal recessive genodermatosis characterized by trauma-induced blistering, poikiloderma, skin atrophy, mucosal inflammation and varying degrees of photosensitivity. Although Kindler syndrome is classified as a subtype of epidermolysis bullosa, it has distinct clinicopathological and molecular abnormalities. The molecular pathology of Kindler syndrome involves loss-of-function mutations in a newly recognized actin cytoskeleton-associated protein, now known as fermitin family homologue 1, encoded by the gene FERMT1. This protein mediates anchorage between the actin cytoskeleton and the extracellular matrix via focal adhesions, and thus the structural pathology differs from other forms of epidermolysis bullosa in which there is a disruption of the keratin intermediate filament-hemidesmosome network and the extracellular matrix. In the skin, fermitin family homologue 1 is mainly expressed in basal keratinocytes and binds to the cytoplasmic tails of beta1 and beta3 integrins as well as to fermitin family homologue 2 and filamin-binding LIM protein 1. It also plays a crucial role in keratinocyte migration, proliferation and adhesion. In this report, we review the clinical, cellular and molecular pathology of Kindler syndrome and discuss the role of fermitin family homologue 1 in keratinocyte biology.