Familial progressive hyper- and hypopigmentation and malignancy in two families with new mutations in KITLG

Therapeutic modulation of KIT ligand in melanocytic disorders with implications for mast cell diseases

KIT ligand and its associated receptor KIT serve as a master regulatory system for both melanocytes and mast cells controlling survival, migration, proliferation and activation. Blockade of this pathway results in cell depletion, while overactivation leads to mastocytosis or melanoma. Expression defects are associated with pigmentary and mast cell disorders. KIT ligand regulation is complex but efficient targeting of this system would be of significant benefit to those suffering from melanocytic or mast cell disorders. Herein, we review the known associations of this pathway with cutaneous diseases and the regulators of this system both in skin and in the more well-studied germ cell system. Exogenous agents modulating this pathway will also be presented. Ultimately, we will review potential therapeutic opportunities to help our patients with melanocytic and mast cell disease processes potentially including vitiligo, hair greying, melasma, urticaria, mastocytosis and melanoma.

Overexpression of KITLG predicts unfavorable clinical outcomes and promotes lymph node metastasis via the JAK/STAT pathway in nasopharyngeal carcinoma

Lymph node metastasis (LNM) is an early clinical sign and a contributor to the treatment failure in patients with nasopharyngeal carcinoma (NPC). The molecular mechanisms of LNM in NPC remain unclear. We aimed to identify and validate the possible key genes that play a crucial role in the LNM of NPC. The study included a discovery and validation phase. In the discovery phase, the key gene was identified by bioinformatics analysis. In the validation phase, the mRNA and protein expression of the key gene was detected by RT-PCR in NPC cells and by immunohistochemistry in a tissue microarray. Then, the effect of the key gene expression on cell invasion and migration was explored in vitro and in vivo. As a result, KITLG was identified as the key gene. The overexpression of KITLG was detected in NPC cells, which was correlated with neck lymph node metastasis and poor prognosis in patients with NPC. The suppression of KITLG inhibited the proliferation, invasion, and metastasis of NPC cells in vitro and in vivo. JAK/STAT signaling pathway might mediate the enhancement of cell invasion and metastasis caused by KITLG. In summary, the overexpression of KITLG in NPC cells might play a crucial role in the LNM of NPC, raising the possibility of KITLG as a prognostic factor and a potential target for NPC treatment.

Genome-Wide Association Study Identifies Candidate Genes for Stripe Pattern Feather Color of Rhode Island Red Chicks

Feather colors of chickens are not only characteristics of breeds but also as phenotypic markers in chicken breeding. Pure-bred Rhode Island Red (RIR) chicks have a stripe pattern and a non-stripe pattern on the back. The stripe pattern of RIR is generally shown as four longitudinal black stripes on the back and is more likely to appear in females. In this study, we performed a genome-wide association study (GWAS) to identify candidate genes controlling the stripe pattern of RIR chicks, and then, based on physical location and biological functions, quantitative RT-PCR analysis was used to validate the differential expression of candidate genes between stripe pattern and non-stripe pattern back skin tissue. The GWAS showed that a major signal contains 768 significant single nucleotide polymorphisms (SNPs) and 87 significant small insertions-deletions (INDELs) spanning 41.78 to 43.05 Mb (~1.27 Mb) on GGA1, corresponding to 16 genes associated with stripe pattern phenotype. Among these 16 genes, KITLG and TMTC3 could be considered candidate genes as they showed different expressions between back skin tissues of stripe pattern and non-stripe pattern chicks in value (p = 0.062) and the significant level (p < 0.05), respectively. This study provided novel insight into the mechanisms underlying feather pigmentation and stripe formation in RIR chicks.

De novo mutation in KITLG gene causes a variant of Familial Progressive Hyper- and Hypo-pigmentation (FPHH)

Familial Progressive Hyper‐ and Hypopigmentation is a pigmentary disorder characterized by a mix of hypo‐ and hyperpigmented lesions, café‐au‐lait spots and hypopigmented ash‐leaf macules. The disorder was previously linked to KITLG and various mutations have been reported to segregate in different families. Furthermore, association between KITLG mutations and malignancies was also suggested. Exome and SANGER sequencing were performed for identification of KITLG mutations. Functional in silico analyses were additionally performed to assess the findings. We identified a de novo mutation in exon 4 of KITLG gene causing NM_000899.4:c.[329A>T] (chr12:88912508A>T) leading to NP_000890.1:p.(Asp110Val) substitution in the 3rd alpha helix. It was predicted as pathogenic, located in a conserved region and causing an increase in hydrophobicity in the KITLG protein. Our findings clearly confirm an additional hot spot of KITLG mutations in the 3rd alpha helix, which very likely increases the risk of malignancies. To our knowledge the present study provides the strongest evidence of association of the KITLG mutation with both Familial Progressive Hyper‐ and Hypopigmentation and malignancy due to its’ location on somatic cancer mutation locus. Additionally we also address difficulties with classification of the unique phenotype and propose a subtype within broader diagnosis.

Identification of a novel mutation in the KITLG gene in a Chinese family with familial progressive hyper- and hypopigmentation

BACKGROUND

Familial progressive hyper- and hypopigmentation (FPHH, MIM 145250) is a rare hereditary skin disorder that is predominantly characterized by progressive, diffuse, partly blotchy hyperpigmented lesions intermingled with scattered hypopigmented spots, lentigines and sometimes Cafe-au-lait spots (CALs). Heterozygous mutations of the KIT ligand (KITLG, MIM 184745) gene are responsible for FPHH. To date, only eight KITLG mutations have been reported to be associated with FPHH, and no clear genotype-phenotype correlations have been established. This study aimed to identify the causative mutations in the KITLG gene in two Chinese FPHH patients.

METHODS

Direct sequencing of the coding regions of KITLG was performed. Pathogenicity prediction was performed using bioinformatics tools, including SIFT, Polyphen2, and SWISS-MODEL, and the results were further evaluated according to the 2015 American College of Medical Genetics and Genomics (ACMG) guidelines.

RESULTS

The novel mutation c.104A > T (p.Asn35Ile) and the recurrent mutation c.101C > T (p.Thr34Ile) in KITLG were identified. As shown using SIFT and Polyphen-2 software, both mutations identified in this study were predicted to be detrimental variations. Three-dimensional protein structure modeling indicated that the mutant KITLG proteins might affect the affinity of KITLG for its receptor, c-KIT. According to the 2015 ACMG guidelines, the novel mutation c.104A > T was 'likely pathogenic'.

CONCLUSIONS

To date, most of the identified KITLG mutations have been clustered within the conserved VTNNV motif (amino acids 33-37) in exon 2. The known mutations are only involved in 33 V, 34 T, 36 N, and 37 V but not 35 N. We have now identified a novel mutation in KITLG, c.104A > T, that was first reported in FPHH within the conserved 35 N motif. These results strengthen our understanding of FPHH and expand the mutational spectrum of the KITLG gene.

Mosaicism in genodermatoses

Genodermatoses are inherited disorders presenting with cutaneous manifestations with or without the involvement of other systems. The majority of these disorders, particularly in cases that present with a cutaneous patterning, may be explained in the context of genetic mosaicism. Despite the barriers to the genetic analysis of mosaic disorders, next-generation sequencing has led to a substantial progress in understanding their pathogenesis, which has significant implications for the clinical management and genetic counseling. Advances in paired and deep sequencing technologies in particular have made the study of mosaic disorders more feasible. In this review, we provide an overview of genetic mosaicism as well as mosaic cutaneous disorders and the techniques required to study them.

Novel mutation in the KITLG gene in familial progressive hyperpigmentation with or without hypopigmentation

We herein report a novel mutation in familial progressive hyper- and hypopigmentation (FPHH). The KITLG gene encoding the KIT ligand protein is a disease-causing gene for FPHH. Various disease-causing gain-of-function mutations, which reside within or adjacent to the conserved VTNN motif of this gene, have been described to date. We have now identified a novel KITLG mutation, c.337G>A (p.Glu113Lys), in FPHH which is located within another ligand-receptor interaction site.

Darwinian Positive Selection on the Pleiotropic Effects of KITLG Explain Skin Pigmentation and Winter Temperature Adaptation in Eurasians

Human skin color diversity is considered an adaptation to environmental conditions such as UV radiation. Investigations into the genetic bases of such adaptation have identified a group of pigmentation genes contributing to skin color diversity in African and non-African populations. Here, we present a population analysis of the pigmentation gene KITLG with previously reported signal of Darwinian positive selection in both European and East Asian populations. We demonstrated that there had been recurrent selective events in the upstream and the downstream regions of KITLG in Eurasian populations. More importantly, besides the expected selection on the KITLG variants favoring light skin in coping with the weak UV radiation at high latitude, we observed a KITLG variant showing adaptation to winter temperature. In particular, compared with UV radiation, winter temperature showed a much stronger correlation with the prevalence of the presumably adaptive KITLG allele in Asian populations. This observation was further supported by the in vitro functional test at low temperature. Consequently, the pleiotropic effects of KITLG, that is, pigmentation and thermogenesis were both targeted by natural selection that acted on different KITLG sequence variants, contributing to the adaptation of Eurasians to both UV radiation and winter temperature at high latitude areas.

Familial progressive hyper- and hypopigmentation: a report on a Chinese family and evidence for genetic heterogeneity

BACKGROUND

Familial progressive hyper- and hypopigmentation (FPHH) is a rare genodermatosis that is characterized by diffuse hyper- and hypopigmented spots on the skin and mucous membranes. It is caused by a pathogenic mutation of the KITLG gene.

OBJECTIVES

To investigate the clinical features and mutation of the KITLG gene in a Chinese family with FPHH.

METHODS

Histopathological and immunohistochemical analysis of lesions from the proband was performed. The KITLG gene was screened for the presence of mutations.

RESULTS

A Chinese family containing 14 individuals with FPHH was described, and the proband was a 5-year-old girl showing diffuse hyper- and hypopigmented lesions on her extremities and trunk. Histopathological and immunohistochemical staining for S100 and HMB45 of skin biopsy specimens from the hyperpigmented areas showed a striking increase in melanin throughout the epidermis, especially in the basal cell layer, and staining of hypopigmented area specimens displayed lower levels of melanin in the epidermis. Mutation analysis of the KITLG gene was performed, but no mutation was found.

STUDY LIMITATIONS

The new pathogenic gene was not found.

CONCLUSION

A family with FPHH was described. Analysis revealed that its members did not have any mutations of the KITLG gene, which provided evidence for genetic heterogeneity of this genodermatosis.