New KIT mutations in patients with piebaldism

Piebaldism with café-au-lait macules resulting from a novel mutation of KIT gene in a three-generation Chinese family

BACKGROUND

Piebaldism is a rare, autosomal dominant, and congenital pigmentary disorder characterized by stable depigmentation of the skin and white forelock. Mutations in KIT or SLUG genes result in piebaldism. Most individuals with piebaldism have a family history of the disorder.

METHODS

In this paper, we report a case of piebaldism with café-au-lait macules resulting from a novel mutation of KIT gene c.1982C > T (p.Thr661Ile) in a three-generation Chinese family. The whole-exome sequencing, mitochondrial gene 3000X, and bioinformatics tools were used to identify the mutation in this new-found pedigree. In addition, we searched the databases of "Punmed, Chinese National Knowledge Infrastructure, CMJD, WANFANG MED ONLINE", reviewed 88 cases of piebaldism caused by KIT gene mutation, and summarized the relationship between clinical phenotype and genotype of piebaldism through logistic regression and other statistical methods.

RESULTS

The proband and her affected mother carried a heterozygous c.1982C > T missense mutation (p.Thr661Ile) on KIT gene. Bioinformatics analysis hinted that it had potential pathogenicity. The data showed that piebaldism patients with cafè-au-lait macules had KIT mutations almost located in the intracellular tyrosine kinase domain and were mostly related to the severe clinical phenotype of piebaldism.

CONCLUSION

The new heterozygous c.1982C > T missense mutation on KIT caused piebaldism with café-au-lait macules in this Chinese family. This study provides a new reference index for clinicians to judge the severity of clinical phenotypes of piebaldism, broadens the understanding of the correlation between clinical phenotypes and genotypes of piebaldism, and provides reference of genetic counseling and prenatal diagnosis for affected families.

KIT Mutations Correlate with Higher Galectin Levels and Brain Metastasis in Breast and Non-Small Cell Lung Cancer

To investigate a potential role for galectins as biomarkers that enable diagnosis or prognostication of breast or non-small cell lung cancer, the serum levels of galectins -1, -3, -7, -8, and -9 of cancer patients determined by ELISA assays were compared to the mutation status of 50 known cancer-critical genes, which were determined using multiplex PCR in tumors of the same patients. Mutations in the KIT proto-oncogene, which codes for the c-Kit protein, a receptor tyrosine kinase, correlated with higher levels of galectins -1, -3, -8, and -9 in breast cancer patients and galectin-1 in non-small cell lung cancer patients. Mutations in the KIT gene were more likely found in brain metastases from both of these primary cancers. The most common KIT mutation in our panel was p.M541L, a missense mutation in the transmembrane domain of the c-Kit protein. These results demonstrate an association between KIT oncogenic signaling and elevated serum galectins in patients with metastatic disease. Changes in protein trafficking and the glycocalyx composition of cancer cells may explain the observed alterations in galectin expression. This study can be useful for the targeted selection of receptor tyrosine kinase and galectin inhibitor anti-cancer treatments.

Primary leptomeningeal melanoma: the prognostic significance of its genetic signature and embryological origin

Primary leptomeningeal melanomas are rare, comprising less than one percent of all brain tumours. They are aggressive and radioresistant tumours, with a poor prognosis. The mainstay of treatment is complete surgical resection and chemotherapy with limited success. Distinguishing a primary leptomeningeal melanoma from the more common metastatic disease can be difficult, and often requires the use of ancillary molecular testing. Primary central nervous system melanomas, including uveal melanomas, frequently exhibit mutations in GNAQ and GNA11, rare in the cutaneous and mucosal counterparts.A case of a primary leptomeningeal melanoma of the cerebellopontine angle is described. Molecular studies identified a GNA11 p.Q209L and a KIT p.M541L missense variant, with losses of chromosomes 1p and 3p demonstrated with cytogenetic studies. Complete surgical resection was not possible and leptomeningeal metastatic disease rapidly ensued despite immunotherapy. Further understanding of the molecular signature may translate to improved diagnosis, prognostication and development of targeted therapies.

Repigmentation of White Forelock in a Familial Case of Piebaldism Reported via Teledermatology in the COVID-19 Era

Piebaldism is a rare autosomal dominant disorder characterized by leucoderma with leucotrichia. We describe a case of white forelock repigmentation in an infant with piebaldism, thanks to a photograph sent by the patient's mother to our dermatology clinic, during COVID-19 pandemic.

Pigment Intensity in Dogs is Associated with a Copy Number Variant Upstream of KITLG

Dogs exhibit a wide variety of coat color types, and many genes have been identified that control pigment production, appearance, and distribution. Some breeds, such as the Nova Scotia Duck Tolling Retriever (NSDTR), exhibit variation in pheomelanin pigment intensity that is not explained by known genetic variants. A genome-wide association study comparing light red to dark red in the NSDTR identified a significantly associated region on canine chromosome 15 (CFA 15:23 Mb–38 Mb). Coverage analysis of whole genome sequence data from eight dogs identified a 6 kb copy number variant (CNV) 152 kb upstream of KITLG. Genotyping with digital droplet PCR (ddPCR) confirmed a significant association between an increased copy number with the dark-red coat color in NSDTR (p = 6.1 × 10⁻⁷). The copy number of the CNV was also significantly associated with coat color variation in both eumelanin and pheomelanin-based Poodles (p = 1.5 × 10⁻⁸, 4.0 × 10⁻⁹) and across other breeds. Moreover, the copy number correlated with pigment intensity along the hair shaft in both pheomelanin and eumelanin coats. KITLG plays an important role in melanogenesis, and variants upstream of KITLG have been associated with coat color variation in mice as well as hair color in humans consistent with its role in the domestic dog.

In-frame Val216-Ser217 deletion of KIT in mild piebaldism causes aberrant secretion and SCF response

BACKGROUND

Piebaldism is a pigmentary disorder characterized by a white forelock and depigmented patches. Although the loss-of-function mutations in the KIT gene underlie the disease, the intracellular dynamics of the mutant KIT are largely unknown. We herein report a Japanese family with piebaldism in which the affected members showed a mild phenotype.

OBJECTIVE

The objective of this study is to investigate the functions and intracellular dynamics of the mutant KIT protein.

METHODS

We performed genetic analyses of the KIT gene using peripheral blood cells. We analyzed the intracellular localization of the mutant KIT protein in HEK293T cells transfected with wild-type (Wt) and/or mutant KIT genes. Immunoprecipitation analyses, immunoblotting and immunofluorescence studies were performed using antibodies against KIT and downstream signaling proteins. Glycosidase digestion analysis was performed to clarify the intracellular localization of KIT protein.

RESULTS

A genetic analysis revealed a novel heterozygous mutation c.645_650delTGTGTC which results in the in-frame deletion of Val²¹⁶ and Ser²¹⁷ in the extracellular domain of KIT. Immunoprecipitation analyses confirmed that the wild and mutant KIT formed a heterodimer after treatment with stem cell factor (SCF); however, the phosphorylation of the downstream signaling factors was decreased. In an immunofluorescence study, the mutant KIT accumulated predominantly in the endoplasmic reticulum (ER) and was sparsely expressed on the cell surface. A glycosidase digestion study revealed that the mutant KIT is predominantly localized in the ER.

CONCLUSION

These data reveal an aberrant function and intracellular localization of mutant KIT protein in piebaldism.

Molecular characterization of piebaldism in a Tunisian family

OBJECTIVE

The present study is aimed at performing the molecular characterization of a Tunisian family with piebaldism.

METHODS

As the proband and her mother showed a severe phenotype, we first chose to screen exons 10, 11, 12, 13, 16, 17 and 18 of the KIT proto-oncogene by direct sequencing.

RESULTS

Direct sequencing analysis showed a C to T substitution at 1939 in exon 13 (c.1939C>T) in heterozygous state in the patient and her mother. The mutation was not found in their unaffected family members or normal controls.

CONCLUSION

Our results provide additional support that mutations in the tyrosine kinase domain of the KIT gene are responsible for the severe form of piebaldism.

A novel splicing mutation of KIT results in piebaldism and auburn hair color in a Chinese family

Piebaldism is a rare autosomal dominant disorder of melanocyte development, which is mostly caused by KIT gene. The key characteristics of piebaldism include localized poliosis, congenital leukoderma, and other variable manifestations. The previous study has illustrated that the homogeneous MC1R (a gene which is associated with the hair color) variant (p.I120T) coordinating with KIT mutation may lead to auburn hair color and piebaldism. In this study, we have investigated a Chinese family with piebaldism and auburn hair color; the mutation screening of KIT and MC1R genes identified that only a splicing mutation (c. 2484+1G>A) of KIT gene cosegregated with the auburn hair color and piebaldism. The data of this study and others suggests that the KIT mutation may causes of the auburn hair color in the piebaldism patients.

Piebaldism

Piebaldism is an uncommon autosomal dominantly inherited pigment anomaly characterized by a congenital white forelock and leukoderma on the frontal scalp, forehead, ventral trunk and extremities. It is caused by a loss-of-function mutation in the KIT gene. Genetic analyses reveal a consistent genotype-phenotype relationship in piebaldism. However, recently reported cases of piebaldism that are milder or severer than genetically expected indicate that other factors, such as a modifier gene of MC1R, influence skin and hair color. The KIT ligand/KIT that triggers the Ras/mitogen-activated protein kinase signaling pathway play essential functions in the migration, proliferation, survival, melanogenesis and melanosome transfer of the melanocytes. We summarize current research progress in piebaldism and related disorders.

A novel KIT missense mutation in one Chinese family with piebaldism

Piebaldism is an autosomal dominant disorder characterized by congenital leukoderma, mostly affecting forehead, abdomen and knee. Previous studies have revealed that piebaldism is caused by mutations of the KIT gene, which encodes the cell surface transmembrane tyrosine kinase receptor for KIT ligand. We reported here a Chinese Han family with piebaldism, and performed mutation detection of KIT gene by direct sequencing. A novel missense mutation C58G was identified in the patients, but not in the healthy individuals from the family and 100 unrelated controls. This study contributes to the database on KIT in piebaldism and enriches the knowledge about the genotype/phenotype correlation.

Gastrointestinal stromal tumors (GISTs): a review

Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal neoplasms in the gastrointestinal tract, which, over the last 10 years, have emerged from a poorly understood neoplasm to a well-defined tumor entity exhibiting particular molecular abnormalities and for which promising novel treatment modalities have been developed. GISTs probably arise from the precursor cell of the interstitial cell of Cajal, express KIT tyrosine kinase in most of the cases and harbor mutations of importance for individualized treatment. The molecular targets for therapeutic interventions are not only of importance for the treatment of GIST patients but also useful for in the development of novel drug modalities and new strategies in basic cancer therapy.

Association of paediatric mastocytosis with a polymorphism resulting in an amino acid substitution (M541L) in the transmembrane domain of c-KIT

BACKGROUND

The receptor tyrosine kinase c-KIT plays a key role in normal mast cell development. Point mutations in c-KIT have been associated with sporadic or familial mastocytosis.

OBJECTIVES

Two unrelated pairs of apparently identical twins affected by cutaneous mastocytosis attending the Mastocytosis Clinic at the Royal Children's Hospital, Melbourne, provided an opportunity to assess the possible contribution of c-KIT germline mutations or polymorphisms in this disease.

METHODS

Tissue biopsy, blood and/or buccal swab specimens were collected from 10 children with mastocytosis. To detect germline mutations/polymorphisms in c-KIT, we studied all coding exons by denaturing high pressure liquid chromatography. Exons showing mismatches were examined by direct sequencing. The influence of the substitution identified was further examined by expressing the variant form of c-KIT in factor-dependent FDC-P1 cells.

RESULTS

In both pairs of twins, a heterozygous ATG to CTG transition in codon 541 was observed, resulting in the substitution of a methionine residue in the transmembrane domain by leucine (M541L). In each case, one parent was also heterozygous for this allele. Expression of M541L KIT in FDC-P1 cells enabled them to grow in human KIT ligand (stem cell factor, SCF) but did not confer factor independence. Compared with cells expressing wild-type KIT at a similar level, M541L KIT-expressing cells displayed enhanced growth at low levels of SCF, and heightened sensitivity to the KIT inhibitor, imatinib mesylate.

CONCLUSIONS

The data suggest that the single nucleotide polymorphism resulting in the substitution M541L may predispose to paediatric mastocytosis.

Recent advances in the understanding of mastocytosis: the role of KIT mutations

Mastocytosis is a heterogeneous disorder characterised by the expansion and accumulation of mast cells in different organs and tissues. Mast cell physiology is closely dependent on activation of the stem cell factor/Kit signalling pathways and accumulating evidences confirm the physiopathological key role of activating KIT mutations (typically D816V) in mastocytosis and their relationship with the clinical manifestations of the disease. This paper reviews the most recent advances in the understanding of the molecular mechanisms associated with KIT mutations in mastocytosis, including recent data about the use of new therapies targeting the Kit molecule and its associated downstream signalling pathways.

Piebald Trait: Implication of kit Mutation on In Vitro Melanocyte Survival and on the Clinical Application of Cultured Epidermal Autografts

Piebald trait leukoderma results from "loss-of-function" mutations in the kit gene. Correlations between mutation type and clinical phenotype have been reported. However, mutation classification has been mainly based on the clinical features of patients. The aim of this study was to get a better understanding of the pathogenesis of human piebaldism by establishing whether the kit mutation type may affect the in vitro survival/proliferation of patient melanocytes. Overall, the research was finalized to implement the clinical application of the autologous cultured epidermis in the treatment of piebald patients. Seven patients, who were transplanted with autologous in vitro reconstituted epidermis, showed an average percentage of repigmentation of 90.7. Six novel and one previously reported mutations were found and their postulated effects discussed in relation to the clinical phenotype and in vitro behavior of epidermal cells. Although mutation type did not impair repigmentation given by autotransplantation, it was shown to influence the survival/proliferation of co-cultured melanocytes and keratinocytes. In particular, tyrosine kinase domain mutations were found with melanocyte loss and keratinocyte senescence during expansion of epidermal cultures. Results indicate that the clinical application of cultured epidermis in piebald patients may be optimized by investigating mutation functional effects before planning surgical operations.

Mice Transgenic for KitV620A: Recapitulation of Piebaldism but not Progressive Depigmentation Seen in Humans with this Mutation

Piebaldism is an autosomal dominant genetic pigmentary disorder, characterized by congenital white hair and patches located on the forehead, anterior trunk, and extremities. Most piebald patients have a mutation of the KIT gene, which encodes a tyrosine kinase receptor involved in pigment cell development. The white hair and patches of such patients are already completely formed at birth and do not usually expand thereafter. This stability of pigmented spots also applies to Kit(W) and Kitl(Sl) mutant mice. However, two novel cases of piebaldism were reported in 2001, in which both mother and daughter having a novel Val620Ala mutation in their KIT gene showed progressive depigmentation. To prepare an animal model of this mutation, to explore undefined functions of KIT signaling for maintaining pigmented melanocytes in the skin or more specifically the integrity of the melanocyte stem cell system in the postnatal skin, we produced transgenic mice expressing Val620Ala Kit. These mice well mimicked the white spotting pattern of patients; however, no change in this pattern was observed after birth, even after increasing the transgene expression by various means. Here, we report the unexpectedly extremely stable maintenance of the melanocyte stem cell system under stringent conditions for KIT signaling.