Whole exome sequencing identifies a novel dominant missense mutation underlying leukonychia in a Pakistani family

Activation Mechanisms and Diverse Functions of Mammalian Phospholipase C

Phospholipase C (PLC) plays pivotal roles in regulating various cellular functions by metabolizing phosphatidylinositol 4,5-bisphosphate in the plasma membrane. This process generates two second messengers, inositol 1,4,5-trisphosphate and diacylglycerol, which respectively regulate the intracellular Ca²⁺ levels and protein kinase C activation. In mammals, six classes of typical PLC have been identified and classified based on their structure and activation mechanisms. They all share X and Y domains, which are responsible for enzymatic activity, as well as subtype-specific domains. Furthermore, in addition to typical PLC, atypical PLC with unique structures solely harboring an X domain has been recently discovered. Collectively, seven classes and 16 isozymes of mammalian PLC are known to date. Dysregulation of PLC activity has been implicated in several pathophysiological conditions, including cancer, cardiovascular diseases, and neurological disorders. Therefore, identification of new drug targets that can selectively modulate PLC activity is important. The present review focuses on the structures, activation mechanisms, and physiological functions of mammalian PLC.

Identification of two novel mutations in the PLCD1 gene in Chinese patients with hereditary leukonychia

Hereditary leukonychia (HL) is a rare nail dystrophy disease, and several different clinical manifestations and mutations in the phospholipase C δ 1 (PLCD1) gene have been reported. The present study reports on one Chinese family and one sporadic case of with HL. The family members exhibited an autosomal dominant pattern of inheritance with the involvement of all the fingers and toenails in all the patients. Of interest, most of the affected members had koilonychia during their childhood. Thus, the present study first used gene mapping with an aim to identify the pathogenic gene underlying koilonychia. Through genome‑wide linkage analysis, the pathogenic area of koilonychia was identified on chromosome 3 with multipoint Log of Odds scores >2. A novel pathogenic mutation c.1384G>A (p.E462K) was identified in the PLCD1 gene in all the patients in the family, which confirmed the diagnosis of hereditary leukonychia. A novel mutation c.770G>A (p.R257H) was also detected in one sporadic case of leukonychia. On the basis of these findings and of previous studies, it is suggested that hereditary leukonychia may initially present as koilonychia, whereas hereditary koilonychia does not progress to leukonychia. Moreover, the present study identified two pathogenic variants of the PLCD1 associated with hereditary leukonychia, and highlights the significance of genetic diagnosis.

Phospholipase C families: Common themes and versatility in physiology and pathology

Phosphoinositide-specific phospholipase Cs (PLCs) are expressed in all mammalian cells and play critical roles in signal transduction. To obtain a comprehensive understanding of these enzymes in physiology and pathology, a detailed structural, biochemical, cell biological and genetic information is required. In this review, we cover all these aspects to summarize current knowledge of the entire superfamily. The families of PLCs have expanded from 13 enzymes to 16 with the identification of the atypical PLCs in the human genome. Recent structural insights highlight the common themes that cover not only the substrate catalysis but also the mechanisms of activation. This involves the release of autoinhibitory interactions that, in the absence of stimulation, maintain classical PLC enzymes in their inactive forms. Studies of individual PLCs provide a rich repertoire of PLC function in different physiologies. Furthermore, the genetic studies discovered numerous mutated and rare variants of PLC enzymes and their link to human disease development, greatly expanding our understanding of their roles in diverse pathologies. Notably, substantial evidence now supports involvement of different PLC isoforms in the development of specific cancer types, immune disorders and neurodegeneration. These advances will stimulate the generation of new drugs that target PLC enzymes, and will therefore open new possibilities for treatment of a number of diseases where current therapies remain ineffective.

Acquired Leukonychia of the Distal Nail Plate: A Morphologic and Proteomic Analysis

Leukonychia, or whitening of the nail plate, is a common disease that was first described in 1919. Leukonychia is classified as acquired or congenital and may be due to abnormality of the nail bed (pseudoleukonychia) or nail plate (true leukonychia). The distal whitened area of the nail plate was clipped from a 31-year-old woman with striated leukonychia and a 32-year-old man and 34-year-old woman with punctate leukonychia. Routine hematoxylin and eosin staining of all clipped samples was performed. A piece of nail with leukonychia and a normal nail from case 2 were sent to the Mayo Clinic for mass spectrometric analysis. On hematoxylin and eosin examination, all leukonychia samples showed odd-appearing eosinophilic linear parakeratinization in the mid-segment of the nail plate. Mass spectrometric analysis of case 2 revealed serum proteins (albumin, serotransferrin IgG, gamma chain, IgG lambda chain, and haptoglobulin) and hair proteins that were not found in the keratin content of the normal nail (keratin type Ha1 and cuticular keratin Ha4). This is the first description of odd-appearing linear parakeratosis and the first proteomic analysis showing abnormal protein content in acquired leukonychia.