Deletion of the KIT and PDGFRA genes in a patient with piebaldism

Genetic etiology of renal agenesis: fine mapping of Renag1 and identification of Kit as the candidate functional gene

Congenital anomalies of the kidney and urogenital tract (CAKUT) occur in approximately 0.5% of live births and represent the most frequent cause of end-stage renal disease in neonates and children. The genetic basis of CAKUT is not well defined. To understand more fully the genetic basis of one type of CAKUT, unilateral renal agenesis (URA), we are studying inbred ACI rats, which spontaneously exhibit URA and associated urogenital anomalies at an incidence of approximately 10%. URA is inherited as an incompletely dominant trait with incomplete penetrance in crosses between ACI and Brown Norway (BN) rats and a single responsible genetic locus, designated Renag1, was previously mapped to rat chromosome 14 (RNO14). The goals of this study were to fine map Renag1, identify the causal genetic variant responsible for URA, confirm that the Renag1 variant is the sole determinant of URA in the ACI rat, and define the embryologic basis of URA in this rat model. Data presented herein localize Renag1 to a 379 kilobase (kb) interval that contains a single protein coding gene, Kit (v-kit Hardy-Zukerman 4 feline sarcoma viral oncogene homolog); identify an endogenous retrovirus-derived long terminal repeat located within Kit intron 1 as the probable causal variant; demonstrate aberrant development of the nephric duct in the anticipated number of ACI rat embryos; and demonstrate expression of Kit and Kit ligand (Kitlg) in the nephric duct. Congenic rats that harbor ACI alleles at Renag1 on the BN genetic background exhibit the same spectrum of urogenital anomalies as ACI rats, indicating that Renag1 is necessary and sufficient to elicit URA and associated urogenital anomalies. These data reveal the first genetic link between Kit and URA and illustrate the value of the ACI rat as a model for defining the mechanisms and cell types in which Kit functions during urogenital development.

A novel Kit gene mutation in CF1 mice involved in the extracellular domain of the KIT protein

We screened for natural mutations in Crl:CF1 closed colony mice using an ordinary backcrossing system. Five of 30 CF1 males carried novel genes that caused white spots on colored coats. Their backcross progenies showed a white spot phenotype. The white spot gene was mapped to approximately 39 cM on chromosome 5, where the Kit gene is known to reside. Allelism testing between this spot gene and the Kit gene was performed using two already known Kit alleles, Kit(W), and Kit(W-v). We demonstrated that the spot mutation was semidominant and a novel allele of the Kit gene, which was tentatively named Kit(W-Ham). No infertility or anemia was observed in Kit(W-Ham) homozygotes. However, a reduced number of germ cells and mast cells was observed in Kit(W-Ham)/Kit(W) and Kit(W-Ham)/Kit(W-v) transheterozygotes. Sequencing of the 21 exons of the Kit gene in the Kit(W-Ham) mutants revealed that a unique guanine-to-adenine (G-A) transition at nucleotide position 545 (c.545G>A) of exon 3 changes arginine (R) to glutamine (Q) at position 182 in the extracellular domain of the KIT protein (p.R182Q). This extracellular KIT domain is a binding site for stem cell factors (SCF). It was concluded that the Kit(W-Ham) mutant may serve as a new model of human piebaldism.

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.

Transplante de melanócitos no piebaldismo: relato de caso

O piebaldismo é uma genodermatose rara onde as lesões acrômicas não respondem aos tratamentos tópico e fototerápico. Este artigo tem como objetivo demonstrar a importância do transplante de melanócitos, usando a técnica de minigrafting no tratamento do piebaldismo.

[4-t-butylphenyl]-N-(4-imidazol-1-yl phenyl)sulfonamide (ISCK03) inhibits SCF/c-kit signaling in 501mel human melanoma cells and abolishes melanin production in mice and brownish guinea pigs

It is well known that c-kit is related to pigmentation as well as to the oncology target protein. The objective of this study was to discover a skin-whitening agent that regulates c-kit activity. We have developed a high-throughput screening system using recombinant human c-kit protein. Approximately 10,000 synthetic compounds were screened for their effect on c-kit activity. Phenyl-imidazole sulfonamide derivatives showed inhibitory activity on c-kit phosphorylation in vitro. The effects of one derivative, [4-t-butylphenyl]-N-(4-imidazol-1-yl phenyl)sulfonamide (ISCK03), on stem-cell factor (SCF)/c-kit cellular signaling in 501mel human melanoma cells were examined further. Pretreatment of 501mel cells with ISCK03 inhibited SCF-induced c-kit phosphorylation dose dependently. ISCK03 also inhibited p44/42 ERK mitogen-activated protein kinase (MAPK) phosphorylation, which is known to be involved in SCF/c-kit downstream signaling. However ISCK03 did not inhibit hepatocyte growth factor (HGF)-induced phosphorylation of p44/42 ERK proteins. To determine the in vivo potency of ISCK03, it was orally administered to depilated C57BL/6 mice. Interestingly, oral administration of ISCK03 induced the dose-dependent depigmentation of newly regrown hair, and this was reversed with cessation of ISCK03 treatment. Finally, to investigate whether the inhibitory effect of ISCK03 on SCF/c-kit signaling abolished UV-induced pigmentation, ISCK03 was applied to UV-induced pigmented spots on brownish guinea pig skin. The topical application of ISCK03 promoted the depigmentation of UV-induced hyperpigmented spots. Fontana-Masson staining analysis showed epidermal melanin was diminished in spots treated with ISCK03. These results indicate that phenyl-imidazole sulfonamide derivatives are potent c-kit inhibitors and might be used as skin-whitening agents.

A Girl with del(4)(q33) And Occipital Encephalocele: Clinical Description And Molecular Genetic Characterization of A Rare Patient

We present clinical and developmental data on a girl with a de novo terminal deletion of the long arm of chromosome 4, del(4)(q33). The patient was evaluated at birth and followed up until 5 years of age. She showed facial and digital dysmorphism, a complex congenital heart defect, a large occipital encephalocele, and postnatal growth deficiency. Her neuropsychomotor milestones were delayed, and she developed learning difficulties. Apart from standard Giemsa banding, a molecular genetic analysis was performed using a comparative genomic hybridization (CGH) array. This revealed a terminal deletion at the band 4q32.3, which is directly adjacent to 4q33. The clinical findings in our patient differ from those described previously in patients with del(4)(q33) and del(4)(q32), respectively. In particular, the prominent occipital encephalocele has not been observed before in a terminal 4q deletion.

New KIT mutations in patients with piebaldism

BACKGROUND

Piebaldism is an autosomal dominantly inherited disorder characterized by congenital leukoderma, typically on the forehead, abdomen, and knees. The leukoderma is usually stable throughout life. KIT mutations have been demonstrated in about 75% of patients with piebaldism.

OBJECTIVES

To identify KIT mutations of the family with piebaldism and examine genotype-phenotype correlations in this disorder.

METHODS

PCR-direct-sequencing technique using genomic DNA from peripheral leukocytes.

RESULTS

We have studied 10 individuals within six piebaldism families and able to identify six novel mutations in the KIT gene in patients with piebaldism. These include four frameshift mutations: 142delG, 1768-1769delAG, 2139delC, 2246-2249delAAAG, and two missense mutations: M541L, Y870C.

CONCLUSIONS

These six new mutations are associated with phenotypes that are well in accordance with our knowledge of genotype-phenotype correlations in KIT.

Analphoid marker chromosome in a patient with hyper-IgE syndrome, autism, and mild mental retardation

Hyper-IgE syndrome with recurrent infections (HIES) is a primary immunodeficiency disease characterized by recurrent skin and lung abscesses and extreme elevations of serum IgE, but also involving dentition, bones, and connective tissue. Although the etiology of HIES is unknown, autosomal dominant inheritance has been observed in multiple kindreds. A 17 year old male with sporadic HIES, autism, and mild mental retardation was found to have a supernumerary marker chromosome in peripheral blood lymphocytes and skin fibroblasts. Microdissection and FISH analysis of the marker chromosome showed that it was derived from a small interstitial deletion of one homologue of chromosome 4q21. Lack of hybridization of probes specific for telomeres and alphoid centromeres, including a centromere 4 specific probe, established that the marker was an analphoid ring chromosome. Comparative genotyping of transformed B-cell subclones with (M+) and without (M-) the marker chromosome showed loss of the maternal alleles in M- cells between markers D4S1569 and D4S3010. FISH using YAC clones from 4q21 confirmed the size and location of the interstitial deletion. Thus our patient's phenotypes were associated with de novo formation of a marker chromosome containing 15-20 cM of DNA deleted from his maternally derived chromosome 4. Proximal chromosome 4q therefore is a candidate region for disease genes for both HIES and autism. Identification of genes disrupted or lost during the formation of the marker chromosome as well as linkage studies in kindreds with HIES or autism may help us to understand the etiology of these complex phenotypes.

Interstitial deletion of bands 4q12-->q13.1: case report and review of proximal 4q deletions

We report a 6 year old child with a small de novo interstitial deletion of proximal 4q, karyotype 46,XX,del(4)(pter-->q12::q13.1-->qter). She has made good developmental progress and attends normal school with minimal assistance. We review published reports and clinical findings in patients with proximal 4q deletions.

Molecular basis of human piebaldism

Piebaldism is an autosomal dominant genetic disorder of pigmentation characterized by congenital patches of white skin and hair that lack melanocytes. Piebaldism results from mutations of the KIT proto-oncogene, which encodes the cell-surface receptor transmembrane tyrosine kinase for an embryonic growth factor, Steel factor. Several pathologic mutations of the KIT gene have now been identified in different patients with piebaldism. Correlation of these mutations with the associated piebald phenotypes has led to the recognition of a hierarchy of three classes of mutations that result in a graded series of piebald phenotypes, and to improved understanding of the mechanisms that underlie dominant genetic disorders.

Structural analysis of chromosomal rearrangements associated with the developmental mutations Ph, W19H, and Rw on mouse chromosome 5

We are studying the chromosomal structure of three developmental mutations, dominant spotting (W), patch (Ph), and rump white (Rw) on mouse chromosome 5. These mutations are clustered in a region containing three genes encoding tyrosine kinase receptors (Kit, Pdgfra, and Flk1). Using probes for these genes and for a closely linked locus, D5Mn125, we established a high-resolution physical map covering approximately 2.8 Mb. The entire chromosomal segment mapped in this study is deleted in the W19H mutation. The map indicates the position of the Ph deletion, which encompasses not more than 400 kb around and including the Pdgfra gene. The map also places the distal breakpoint of the Rw inversion to a limited chromosomal segment between Kit and Pdgfra. In light of the structure of the Ph-W-Rw region, we interpret the previously published complementation analyses as indicating that the pigmentation defect in Rw/+ heterozygotes could be due to the disruption of Kit and/or Pdgfra regulatory sequences, whereas the gene(s) responsible for the recessive lethality of Rw/Rw embryos is not closely linked to the Ph and W loci and maps proximally to the W19H deletion. The structural analysis of chromosomal rearrangements associated with W19H, Ph, and Rw combined with the high-resolution physical mapping points the way toward the definition of these mutations in molecular terms and isolation of homologous genes on human chromosome 4.

Piebaldism in a mentally retarded girl with rare deletion of the long arm of chromosome 4

A 4-year-old mentally retarded girl had congenital depigmentations of ventrolateral parts of the chest, abdomen, and legs. She also showed dysmorphic features of the head, thorax, and extremities, a pigmented ring in both irises, and a hernia of the left obliquus muscle. Cytogenetic investigations revealed deletion of chromosome 4 for the long arm segment q12-q21. The typical depigmentations, reported in four other patients with a similar chromosomal deletion, correspond with those in the autosomal dominant piebald trait. Mutations in the Kit protooncogene (mapped to the chromosome (4q11-4q12 region) have been found in patients affected with this dominant disorder. Piebaldism in children with developmental delay and dysmorphic features should alert the physician to the possibility of a deletion of the long arm of chromosome 4.

Novel mutations of the KIT (mast/stem cell growth factor receptor) proto-oncogene in human piebaldism

Piebaldism is an autosomal dominant genetic disorder of pigmentation characterized by congenital patches of white skin and hair that lack melanocytes. Piebaldism results from mutations of the KIT proto-oncogene, which encodes the cellular receptor transmembrane tyrosine kinase for mast/stem cell growth factor. Here we describe two novel KIT mutations associated with human piebaldism. These amino acid substitutions, located in the most highly conserved sections of the KIT kinase domain, would be expected to dominant-negatively inhibit KIT-dependent signal transduction, resulting in aberrant melanocyte proliferation or migration during embryologic development.