Waardenburg syndrome type 2F (WS2F) is the KITLG form of Waardenburg syndrome type 2: congenital or neonatal sensorineural hearing loss with hypomelanosis of the skin, hair and irides, and without dystopia canthorum. KITLG encodes KIT ligand (stem cell factor), the ligand of the KIT receptor tyrosine kinase that neural crest-derived melanoblasts depend on for survival, proliferation and movement into their target tissues. The disorder as currently defined rests on a small case series of individuals homozygous for rare KITLG variants, plus a few earlier single-family reports. Expressivity is strikingly variable, even between individuals carrying the same allele: hearing loss may be unilateral, asymmetric or bilateral, and hypomelanosis ranges from limb-restricted patches with islands of retained pigment, reminiscent of piebaldism, to generalized hypomelanosis of skin and hair. By analogy with the steel (Sl) mouse, which carries mutations in the orthologous Kitl gene, the hearing loss is attributed to failure of melanocytes to populate the cochlear stria vascularis as its intermediate cells, and the pigmentary findings to the same melanocyte deficit in skin, hair follicles and iris. KITLG is also the gene for two allelic disorders curated separately: heterozygous loss-of-function variants cause isolated, often unilateral, sensorineural hearing loss, and heterozygous gain-of-function variants cause familial progressive hyperpigmentation with or without hypopigmentation.
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Conditions with similar clinical presentations that must be differentiated from Waardenburg Syndrome Type 2F:
name: Waardenburg Syndrome Type 2F
creation_date: "2026-09-30T19:45:00Z"
category: Mendelian
description: >-
Waardenburg syndrome type 2F (WS2F) is the KITLG form of Waardenburg syndrome
type 2: congenital or neonatal sensorineural hearing loss with hypomelanosis
of the skin, hair and irides, and without dystopia canthorum. KITLG encodes KIT
ligand (stem cell factor), the ligand of the KIT receptor tyrosine kinase that
neural crest-derived melanoblasts depend on for survival, proliferation and
movement into their target tissues. The disorder as currently defined rests on
a small case series of individuals homozygous for rare KITLG variants, plus a
few earlier single-family reports. Expressivity is strikingly variable, even
between individuals carrying the same allele: hearing loss may be unilateral,
asymmetric or bilateral, and hypomelanosis ranges from limb-restricted patches
with islands of retained pigment, reminiscent of piebaldism, to generalized
hypomelanosis of skin and hair. By analogy with the steel (Sl) mouse, which
carries mutations in the orthologous Kitl gene, the hearing loss is attributed
to failure of melanocytes to populate the cochlear stria vascularis as its
intermediate cells, and the pigmentary findings to the same melanocyte deficit
in skin, hair follicles and iris. KITLG is also the gene for two allelic
disorders curated separately: heterozygous loss-of-function variants cause
isolated, often unilateral, sensorineural hearing loss, and heterozygous
gain-of-function variants cause familial progressive hyperpigmentation with or
without hypopigmentation.
synonyms:
- WS2F
- KITLG-related Waardenburg syndrome type 2
- Biallelic KITLG auditory-pigmentary disorder
parents:
- Waardenburg Syndrome
disease_term:
preferred_term: Waardenburg syndrome type 2F
term:
id: MONDO:0030983
label: Waardenburg syndrome 2F
references:
- reference: PMID:32809714
title: Waardenburg Syndrome.
tags:
- StatPearls
findings:
- statement: >-
General Waardenburg syndrome overview, cited only for supportive
management (cochlear implantation, genetic counseling). No GeneReviews
chapter covers the KITLG form.
inheritance:
- name: Autosomal Recessive
description: >-
The defining case series consists of individuals homozygous for rare KITLG
variants, and the HPO annotation for this disease (OMIM:619947) records
autosomal recessive inheritance. Heterozygous carrier parents are usually
unaffected, although the parents of one individual homozygous for a nonsense
allele were reported to have lighter skin than expected for their ethnic
background.
inheritance_term:
preferred_term: Autosomal recessive inheritance
term:
id: HP:0000007
label: Autosomal recessive inheritance
evidence:
- reference: PMID:35543077
reference_title: Biallelic KITLG variants lead to a distinct spectrum of hypomelanosis
and sensorineural hearing loss.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
We provide consolidating evidence that biallelic KITLG variants cause a
distinct auditory-pigmentary disorder.
explanation: >-
States that biallelic KITLG variants cause the auditory-pigmentary
disorder that this entry curates.
- reference: PMID:35543077
reference_title: Biallelic KITLG variants lead to a distinct spectrum of hypomelanosis
and sensorineural hearing loss.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Individuals 1 and 3 each presented with a homozygous c.94C>T,
p.(Arg32Cys) variant
explanation: >-
An example of the homozygous genotypes found in every member of the case
series.
- reference: PMID:35543077
reference_title: Biallelic KITLG variants lead to a distinct spectrum of hypomelanosis
and sensorineural hearing loss.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
His parents, who were confirmed carriers of the null variant, also
exhibited lighter-coloured skin than expected for their ethnic background.
explanation: >-
Records a possible mild carrier effect in one family, which is why the
description does not call carriers uniformly unaffected.
- name: Autosomal Dominant (single reported family)
description: >-
One small family with Waardenburg syndrome type 2 segregated a heterozygous
KITLG missense variant, p.Leu104Val. The variant reached the cell membrane
normally but its soluble isoform was reduced in culture medium, and the
authors raised a dominant-negative or gain-of-function mechanism rather than
simple loss of function. Whether heterozygous WS2 of this kind belongs to
the same disease as the recessive case series is not settled by the
published data; it is recorded here as a single dominant report.
inheritance_term:
preferred_term: Autosomal dominant inheritance
term:
id: HP:0000006
label: Autosomal dominant inheritance
evidence:
- reference: PMID:26522471
reference_title: Allelic Mutations of KITLG, Encoding KIT Ligand, Cause Asymmetric
and Unilateral Hearing Loss and Waardenburg Syndrome Type 2.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
A heterozygous missense mutation, c.310C>G (p.Leu104Val), that segregated
with WS2 was identified in a small family.
explanation: >-
The single heterozygous Waardenburg syndrome type 2 family with a KITLG
variant.
- reference: PMID:26522471
reference_title: Allelic Mutations of KITLG, Encoding KIT Ligand, Cause Asymmetric
and Unilateral Hearing Loss and Waardenburg Syndrome Type 2.
supports: SUPPORT
evidence_source: IN_VITRO
snippet: >-
We speculate that the mechanism of the mutation underlying WS2 and leading
to membrane incorporation and reduced secretion of KITLG occurs via a
dominant-negative or gain-of-function effect.
explanation: >-
The authors' proposed mechanism for the dominant allele, based on their
transfection experiments; it is stated as speculation.
prevalence:
- population: Worldwide
measure_type: CASES_IN_LITERATURE
prevalence_class: ULTRA_RARE
notes: >-
Six unrelated individuals with homozygous KITLG variants in the defining
case series, plus a small number of earlier single-family reports. No
population frequency has been estimated.
evidence:
- reference: PMID:35543077
reference_title: Biallelic KITLG variants lead to a distinct spectrum of hypomelanosis
and sensorineural hearing loss.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
We identified six unrelated individuals (two male, four female) with
biallelic KITLG variants
explanation: >-
The size of the defining case series, which is the basis for the
ultra-rare classification.
pathophysiology:
- name: Biallelic KITLG Variants Reducing KIT Ligand Signalling
conforms_to: "neural_crest_melanocyte_deficiency#Neural Crest Melanocyte Program Disruption"
biological_scale: MOLECULAR
description: >-
Homozygous germline KITLG variants reduce the KIT ligand signal available to
KIT-expressing melanoblasts. This is the KITLG substitution at the module's
trigger node, the ligand-side counterpart of KIT loss of function in
piebaldism. The reduction is inferred from variant class rather than
measured: the case-series authors propose that complete loss of function
produces generalized hypomelanosis and that alleles retaining some function
produce the Waardenburg-like and piebaldism-like presentations, and no
functional assay of the recessive alleles has been reported.
genetic_context:
variant_origin: GERMLINE
zygosity: HOMOZYGOUS
gene:
preferred_term: KITLG
term:
id: hgnc:6343
label: KITLG
description: >-
Homozygous missense (p.Arg32Cys, p.Ile148Thr), frameshift
(p.Met184ValfsTer10, p.Arg268SerfsTer29) and nonsense (p.Trp215Ter)
KITLG variants in the defining case series.
molecular_functions:
- preferred_term: stem cell factor receptor binding
term:
id: GO:0005173
label: stem cell factor receptor binding
modifier: DECREASED
cell_types:
- preferred_term: melanoblast
term:
id: CL:0000541
label: melanoblast
biological_processes:
- preferred_term: Kit signaling pathway
term:
id: GO:0038109
label: Kit signaling pathway
modifier: DECREASED
evidence:
- reference: PMID:35543077
reference_title: Biallelic KITLG variants lead to a distinct spectrum of hypomelanosis
and sensorineural hearing loss.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
We speculate that KITLG biallelic loss-of-function variants cause
generalized hypomelanosis, whilst variants with residual function lead to
a variable auditory-pigmentary disorder mostly reminiscent of Waardenburg
syndrome type 2 or piebaldism.
explanation: >-
The authors' model of reduced KITLG function as the lesion, with residual
function setting the severity. It is explicitly speculative.
- reference: PMID:26522471
reference_title: Allelic Mutations of KITLG, Encoding KIT Ligand, Cause Asymmetric
and Unilateral Hearing Loss and Waardenburg Syndrome Type 2.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
KITLG encodes a ligand for the KIT receptor.
explanation: >-
Places the lesion on the ligand side of the KIT signalling axis.
- reference: PMID:41584853
reference_title: Kitlg dysfunction is associated with hearing and pigmentation abnormalities.
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: >-
MITF (Fig. 1K; Fig. S5A) and p-c-kit protein levels (Fig. 1L; Fig. S5B) in
KitlgΔ/+ mice were lower than those in WT mice
explanation: >-
Measured reduction of KIT receptor phosphorylation, and of MITF, in mice
heterozygous for a Kitlg frameshift, supporting reduced KIT signalling as
the consequence of reduced ligand. The model is heterozygous, whereas this
disease is recessive.
downstream:
- target: Reduced Melanoblast Survival, Proliferation and Colonization
description: >-
Melanoblasts depend on KIT ligand for survival and proliferation during
their embryonic migration, so less ligand leaves fewer melanoblasts to
reach their targets.
evidence:
- reference: PMID:26522471
reference_title: Allelic Mutations of KITLG, Encoding KIT Ligand, Cause Asymmetric
and Unilateral Hearing Loss and Waardenburg Syndrome Type 2.
supports: SUPPORT
evidence_source: MODEL_ORGANISM
quote_role: BACKGROUND
snippet: >-
In mice, it appears that soluble KITLG plays a role in melanocyte
migration and/or early survival and that transmembrane KITLG plays a role
in melanocyte survival at or close to the destination.
explanation: >-
Links both KITLG isoforms to melanocyte survival, which is the step this
edge asserts. The sentence summarizes mouse work in the discussion of a
human genetics paper.
- target: Strial Intermediate Cell Deficiency
description: >-
Reduced KIT ligand can also impair the functional maturation of strial
intermediate cells that have arrived, including their melanin
synthesis, without preventing their colonization of the stria.
evidence:
- reference: PMID:41584853
reference_title: Kitlg dysfunction is associated with hearing and pigmentation abnormalities.
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: >-
The transmission electron microscopy analysis revealed that intermediate
cells were present in the stria vascularis of KitlgΔ/+, but exhibited
abnormal morphological characteristics compared with the WT littermates
explanation: >-
Intermediate cells are present but abnormal in Kitlg heterozygous mice,
which is the maturation route this edge asserts.
- name: Reduced Melanoblast Survival, Proliferation and Colonization
conforms_to: "neural_crest_melanocyte_deficiency#Melanoblast Migration and Survival Defect"
biological_scale: CELLULAR
description: >-
With too little KIT ligand, melanoblasts emerging from the neural crest
survive and proliferate poorly, so fewer reach and persist in the skin, hair
follicles, iris and the developing inner ear. Steel mouse studies place the
defect at survival and proliferation, and at arrival in target tissue,
rather than at early migration or initial differentiation. The number of
melanoblasts that reach each tissue varies, which is the proposed basis for
the patchy, asymmetric and variable human phenotype.
cell_types:
- preferred_term: melanoblast
term:
id: CL:0000541
label: melanoblast
- preferred_term: melanocyte
term:
id: CL:0000148
label: melanocyte
biological_processes:
- preferred_term: melanocyte proliferation
term:
id: GO:0097325
label: melanocyte proliferation
modifier: DECREASED
- preferred_term: melanocyte migration
term:
id: GO:0097324
label: melanocyte migration
modifier: DECREASED
evidence:
- reference: PMID:1280558
reference_title: TRP-2/DT, a new early melanoblast marker, shows that steel growth
factor (c-kit ligand) is a survival factor.
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: >-
the membrane-bound steel growth factor which is missing in Sld/Sld mutants
is necessary for the survival of melanoblasts but not for their early
migration and initial differentiation
explanation: >-
In the Steel-dickie mouse, loss of membrane-bound KIT ligand impairs
melanoblast survival specifically.
- reference: PMID:9405100
reference_title: Activation of the receptor tyrosine kinase Kit is required for
the proliferation of melanoblasts in the mouse embryo.
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: >-
We conclude that the survival of immature melanoblasts depends crucially
upon Kit signalling up until E11, and later in development Kit plays a
vital role in melanoblast proliferation.
explanation: >-
Receptor-side evidence that KIT ligand-KIT signalling governs melanoblast
survival and then proliferation in the embryo.
- reference: PMID:10985860
reference_title: MGF (KIT ligand) is a chemokinetic factor for melanoblast migration
into hair follicles.
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: >-
Addition of soluble MGF induces the same effect; KIT therefore promotes
melanocyte movement and acts as a chemokinetic, or motogenic, receptor.
explanation: >-
Shows that KIT ligand accelerates melanoblast localization into hair
follicles, the step that supplies hair pigment. Mouse embryonic skin
organ culture.
- reference: PMID:26522471
reference_title: Allelic Mutations of KITLG, Encoding KIT Ligand, Cause Asymmetric
and Unilateral Hearing Loss and Waardenburg Syndrome Type 2.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Analogous to the phenotype in mice, the severity of the human phenotype is
likely to reflect the number of melanocytes that have reached the inner
ear and skin and/or survived in these tissues.
explanation: >-
The authors' interpretation of variable human expressivity in terms of
melanocyte numbers reaching each tissue.
downstream:
- target: Strial Intermediate Cell Deficiency
description: >-
Too few melanocytes reach the cochlea to form the intermediate cell layer
of the stria vascularis.
evidence:
- reference: PMID:26522471
reference_title: Allelic Mutations of KITLG, Encoding KIT Ligand, Cause Asymmetric
and Unilateral Hearing Loss and Waardenburg Syndrome Type 2.
supports: SUPPORT
evidence_source: MODEL_ORGANISM
quote_role: BACKGROUND
snippet: >-
in Sld/Sld mice, both the survival and targeting of melanoblasts to the
developing inner ear is affected, but early melanoblast differentiation
and migration is not.
explanation: >-
Places the KIT ligand-dependent melanoblast defect at the developing
inner ear, which is what this edge asserts.
- reference: PMID:41584853
reference_title: Kitlg dysfunction is associated with hearing and pigmentation abnormalities.
supports: REFUTE
evidence_source: MODEL_ORGANISM
snippet: >-
These findings indicate that KITLG haploinsufficiency may not affect
intermediate cell migration, proliferation, or differentiation, but
could disrupt their functional maturation, such as melanin synthesis.
explanation: >-
In Kitlg heterozygous frameshift mice, intermediate cells still reach
the stria, so at least partial KIT ligand deficiency does not act
through failed colonization. The direct edge from the KITLG node to this
node carries the alternative. Whether the biallelic human genotypes
behave like this heterozygous model or like the more severe Sl/Sld
mutants is not known.
- target: Cutaneous, Hair and Iris Melanocyte Deficiency
description: >-
Too few melanocytes colonize or persist in the skin, hair follicles and
iris.
- name: Strial Intermediate Cell Deficiency
conforms_to: "neural_crest_melanocyte_deficiency#Stria Vascularis Melanocyte Deficiency"
biological_scale: TISSUE
description: >-
The intermediate cells of the stria vascularis are melanocytes of neural
crest origin, and they are required for the endocochlear potential that
drives hair-cell transduction. In steel (Kitl) and dominant white spotting
(Kit) mutant mice they are absent or reduced, the endocochlear potential is
lost or reduced, and the animals are deaf. In mice heterozygous for a Kitlg
frameshift the deficit is functional rather than numerical: intermediate
cells are present but morphologically abnormal, strial melanin is reduced
in the animals with impaired hearing, and the gross cochlear structure is
normal. The same study found reduced FXYD6, a regulator of Na+/K+-ATPase,
and proposed that it adds to the loss of endocochlear potential. Because
the strial deficit can differ between ears, it offers an explanation for
the unilateral and asymmetric hearing loss characteristic of KITLG
disease. No human temporal bone from a person with WS2F has been
described, so this node rests on the mouse models.
cell_types:
- preferred_term: strial intermediate cell
term:
id: CL:0002486
label: strial intermediate cell
locations:
- preferred_term: stria vascularis
term:
id: UBERON:0002282
label: stria vascularis of cochlear duct
evidence:
- reference: PMID:2460075
reference_title: Intermediate filaments in the cochleas of normal and mutant (w/wv,
sl/sld) mice.
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: >-
In contrast, vimentin was seen to stain only the basal cells in the mutant
mice, confirming our previous findings of the absence of intermediate cells
in these cases of hereditary deafness.
explanation: >-
Documents absent strial intermediate cells in deaf Sl/Sld (Kitl) and
W/Wv (Kit) mutant mice.
- reference: PMID:41584853
reference_title: Kitlg dysfunction is associated with hearing and pigmentation abnormalities.
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: >-
Fontana-Masson staining revealed that KitlgΔ/+ mice with impaired hearing
had reduced melanin distribution in the stria vascularis compared with WT
mice
explanation: >-
A strial melanocyte deficit in a Kitlg mutant mouse, tracking with the
hearing phenotype.
- reference: PMID:41584853
reference_title: Kitlg dysfunction is associated with hearing and pigmentation abnormalities.
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: >-
These findings suggest that Kitlg dysfunction does not affect the cochlear
structure.
explanation: >-
Hair cells, ribbon synapses and strial thickness were normal, so the
lesion is confined to strial function rather than cochlear morphology.
- reference: PMID:41584853
reference_title: Kitlg dysfunction is associated with hearing and pigmentation abnormalities.
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: >-
Additionally, diminished FXYD6 expression implicated a dual pathogenic
mechanism involving both Na+/K+-ATPase dysfunction and
melanocyte-dependent endocochlear potential loss.
explanation: >-
The authors' proposed second contributor to endocochlear potential loss,
from proteomics of the same mice. It is a proposal, not a demonstrated
mechanism.
downstream:
- target: Congenital Sensorineural Hearing Loss
description: >-
Without intermediate cells the stria cannot generate the endocochlear
potential, and hearing is lost.
evidence:
- reference: PMID:26522471
reference_title: Allelic Mutations of KITLG, Encoding KIT Ligand, Cause Asymmetric
and Unilateral Hearing Loss and Waardenburg Syndrome Type 2.
supports: SUPPORT
evidence_source: MODEL_ORGANISM
quote_role: BACKGROUND
snippet: >-
Absence or reduction of highly specialized melanocytes, the intermediate
cells, in the stria vascularis leads to no or reduced endocochlear
potential (EP) and consequently to HL.
explanation: >-
States the causal step from intermediate cell deficiency through loss of
the endocochlear potential to hearing loss.
- target: Unilateral Sensorineural Hearing Loss
description: >-
Variable melanocyte colonization between the two cochleae can leave one
ear affected and the other normal or less affected.
evidence:
- reference: PMID:26522471
reference_title: Allelic Mutations of KITLG, Encoding KIT Ligand, Cause Asymmetric
and Unilateral Hearing Loss and Waardenburg Syndrome Type 2.
supports: SUPPORT
evidence_source: MODEL_ORGANISM
quote_role: BACKGROUND
snippet: >-
In Wv/Wv mice, this variability in inner-ear phenotype was found to
reflect the number of melanocytes present and how far they migrated
along each cochlea.
explanation: >-
Ear-to-ear variability in strial melanocyte numbers in the receptor-side
mouse mutant, which the authors offer as the explanation for unilateral
and asymmetric hearing loss with KITLG variants.
- reference: PMID:41584853
reference_title: Kitlg dysfunction is associated with hearing and pigmentation abnormalities.
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: >-
Some KitlgΔ/+ mice showed unilateral or asymmetric hearing loss
explanation: >-
A Kitlg mutant mouse reproduces unilateral and asymmetric hearing loss,
linking the strial lesion to the laterality pattern seen in patients.
- name: Cutaneous, Hair and Iris Melanocyte Deficiency
conforms_to: "neural_crest_melanocyte_deficiency#Cutaneous Hair and Iris Melanocyte Deficiency"
biological_scale: TISSUE
description: >-
Skin, hair follicles and irides that are not colonized by melanocytes, or
lose them, are hypopigmented. The distribution ranges from limb-restricted
achromic patches containing islands of retained pigment, which resemble
piebaldism, to generalized hypomelanosis of skin and hair. Progressive
repigmentation of achromic areas has been seen in two individuals.
cell_types:
- preferred_term: melanocyte
term:
id: CL:0000148
label: melanocyte
biological_processes:
- preferred_term: pigmentation
term:
id: GO:0043473
label: pigmentation
modifier: DECREASED
locations:
- preferred_term: skin
term:
id: UBERON:0002097
label: skin of body
- preferred_term: iris
term:
id: UBERON:0001769
label: iris
- preferred_term: hair
term:
id: UBERON:0001037
label: strand of hair
evidence:
- reference: PMID:35543077
reference_title: Biallelic KITLG variants lead to a distinct spectrum of hypomelanosis
and sensorineural hearing loss.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Islands of pigmentation within achromic areas on the limbs were present in
4/6 individuals and in two there was progressive repigmentation.
explanation: >-
Describes the patchy achromic skin with retained pigment islands, and the
repigmentation seen in two individuals.
- reference: PMID:35543077
reference_title: Biallelic KITLG variants lead to a distinct spectrum of hypomelanosis
and sensorineural hearing loss.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Two individuals presented symmetric, lower limb hypomelanosis reminiscent
of piebaldism
explanation: >-
The piebaldism-like distribution, consistent with a regional failure of
melanocyte colonization.
downstream:
- target: Hypopigmentation of the Skin
- target: Generalized Hypomelanosis
- target: Heterochromia Iridis
- target: Blue Irides
- target: White Forelock
- target: Hair Hypopigmentation
- target: White Hair
phenotypes:
- category: Otologic
name: Congenital Sensorineural Hearing Loss
frequency: VERY_FREQUENT
description: >-
Congenital or neonatal-onset sensorineural hearing loss of moderate to
profound severity was found in every individual of the case series who had
a formal hearing assessment (5/5). Laterality varies: bilateral symmetric,
bilateral asymmetric, or unilateral.
phenotype_term:
preferred_term: Congenital sensorineural hearing impairment
term:
id: HP:0008527
label: Congenital sensorineural hearing impairment
evidence:
- reference: PMID:35543077
reference_title: Biallelic KITLG variants lead to a distinct spectrum of hypomelanosis
and sensorineural hearing loss.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Congenital/neonatal, sensorineural HL was identified in 5/5 individuals and
appeared as asymmetric (2/5)
explanation: >-
Hearing loss in all five formally assessed individuals, and its
congenital or neonatal onset.
- reference: PMID:35543077
reference_title: Biallelic KITLG variants lead to a distinct spectrum of hypomelanosis
and sensorineural hearing loss.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
In individuals with formal hearing assessments (5/5), the HL onset ranged
from birth to neonatal period and the severity was moderate-to-profound.
explanation: >-
Onset and severity range.
- category: Otologic
name: Unilateral Sensorineural Hearing Loss
frequency: OCCASIONAL
description: >-
Hearing loss confined to one ear, seen in one of five assessed individuals
in the case series. Unilateral and asymmetric hearing loss is the most
distinctive audiological feature of KITLG disease across its allelic
disorders.
phenotype_term:
preferred_term: Unilateral sensorineural hearing impairment
term:
id: HP:0025797
label: Unilateral sensorineural hearing impairment
evidence:
- reference: PMID:35543077
reference_title: Biallelic KITLG variants lead to a distinct spectrum of hypomelanosis
and sensorineural hearing loss.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
bilateral, symmetric (2/5) or unilateral (1/5)
explanation: >-
One of five assessed individuals had unilateral hearing loss.
- reference: PMID:35543077
reference_title: Biallelic KITLG variants lead to a distinct spectrum of hypomelanosis
and sensorineural hearing loss.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Unilateral, sensorineural HL (left) was diagnosed at birth.
explanation: >-
The individual with unilateral congenital hearing loss (homozygous
p.Ile148Thr).
- category: Dermatologic
name: Hypopigmentation of the Skin
frequency: VERY_FREQUENT
description: >-
Hypomelanosis was present in all six individuals of the case series, either
generalized or affecting the limbs, often as achromic patches containing
islands of pigment.
phenotype_term:
preferred_term: Hypopigmentation of the skin
term:
id: HP:0001010
label: Hypopigmentation of the skin
evidence:
- reference: PMID:35543077
reference_title: Biallelic KITLG variants lead to a distinct spectrum of hypomelanosis
and sensorineural hearing loss.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Hypomelanosis was present in all individuals and was either generalized
(2/6) or affecting hair, irises and limbs (4/6).
explanation: >-
Hypomelanosis in six of six individuals.
- category: Dermatologic
name: Generalized Hypomelanosis
frequency: FREQUENT
description: >-
Generalized hypomelanosis of skin and hair, seen in two of six individuals,
both carrying truncating alleles. The case-series authors propose that this
presentation marks complete loss of KITLG function.
phenotype_term:
preferred_term: Generalized hypopigmentation
term:
id: HP:0007513
label: Generalized hypopigmentation
evidence:
- reference: PMID:35543077
reference_title: Biallelic KITLG variants lead to a distinct spectrum of hypomelanosis
and sensorineural hearing loss.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Hypomelanosis was present in all individuals and was either generalized
(2/6) or affecting hair, irises and limbs (4/6).
explanation: >-
Generalized hypomelanosis in two of six individuals.
- category: Ocular
name: Heterochromia Iridis
frequency: FREQUENT
description: >-
Complete or partial heterochromia of the irides, seen in four of six
individuals.
phenotype_term:
preferred_term: Heterochromia iridis
term:
id: HP:0001100
label: Heterochromia iridis
evidence:
- reference: PMID:35543077
reference_title: Biallelic KITLG variants lead to a distinct spectrum of hypomelanosis
and sensorineural hearing loss.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Heterochromia irises was present in 4/6 individuals.
explanation: >-
Frequency of iris heterochromia in the case series.
- category: Ocular
name: Blue Irides
frequency: FREQUENT
description: >-
Blue or patchy blue irides, described in two of six individuals.
phenotype_term:
preferred_term: Blue irides
term:
id: HP:0000635
label: Blue irides
evidence:
- reference: PMID:35543077
reference_title: Biallelic KITLG variants lead to a distinct spectrum of hypomelanosis
and sensorineural hearing loss.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
The pattern of hypomelanosis affected hair (white forelock and scattered
leucotrichia, eyebrows and eyelashes), eyes (blue irises) and limbs
explanation: >-
Blue irides in the individual homozygous for p.Ile148Thr.
- reference: PMID:35543077
reference_title: Biallelic KITLG variants lead to a distinct spectrum of hypomelanosis
and sensorineural hearing loss.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
a hypomelanosis pattern that includes a fair skin complexion, patchy blue
irises and two achromic patches
explanation: >-
Patchy blue irides in the individual homozygous for p.Arg268SerfsTer29.
- category: Dermatologic
name: White Forelock
frequency: FREQUENT
description: >-
A white forelock, seen in three of six individuals.
phenotype_term:
preferred_term: White forelock
term:
id: HP:0002211
label: White forelock
evidence:
- reference: PMID:35543077
reference_title: Biallelic KITLG variants lead to a distinct spectrum of hypomelanosis
and sensorineural hearing loss.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Hair hypomelanosis includes scattered leucotrichia including eyebrows and
eyelashes (5/6), white forelock (3/6)
explanation: >-
White forelock in three of six individuals.
- category: Dermatologic
name: Hair Hypopigmentation
frequency: VERY_FREQUENT
description: >-
Scattered white hairs (leucotrichia), including white eyebrows and
eyelashes, in five of six individuals.
phenotype_term:
preferred_term: Hypopigmentation of hair
term:
id: HP:0005599
label: Hypopigmentation of hair
evidence:
- reference: PMID:35543077
reference_title: Biallelic KITLG variants lead to a distinct spectrum of hypomelanosis
and sensorineural hearing loss.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Hair hypomelanosis includes scattered leucotrichia including eyebrows and
eyelashes (5/6), white forelock (3/6)
explanation: >-
Scattered leucotrichia in five of six individuals.
- category: Dermatologic
name: White Hair
frequency: FREQUENT
description: >-
Diffusely white or silver hair reminiscent of albinism, in two of six
individuals.
phenotype_term:
preferred_term: White hair
term:
id: HP:0011364
label: White hair
evidence:
- reference: PMID:35543077
reference_title: Biallelic KITLG variants lead to a distinct spectrum of hypomelanosis
and sensorineural hearing loss.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
white-silver hair reminiscent of albinism (2/6)
explanation: >-
White-silver hair in two of six individuals.
- category: Dermatologic
name: Cafe-au-lait Macule
description: >-
A truncal cafe-au-lait macule, together with a large demarcated area of
abdominal hyperpigmentation, in one earlier-reported individual with
Waardenburg syndrome type 2 carrying the p.Arg32Cys allele. Whether this is
part of the disease is uncertain: its reporters could not exclude a separate
diagnosis of familial progressive hyper- and hypopigmentation, the
gain-of-function KITLG disorder. No mechanism node is linked to it for that
reason.
phenotype_term:
preferred_term: Cafe-au-lait spot
term:
id: HP:0000957
label: Cafe-au-lait spot
evidence:
- reference: PMID:35543077
reference_title: Biallelic KITLG variants lead to a distinct spectrum of hypomelanosis
and sensorineural hearing loss.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
He had a reported, truncal, café-au-lait macule and a large
well-demarcated area of lower abdominal hyperpigmentation.
explanation: >-
Describes the pigmented lesions of the earlier-reported p.Arg32Cys
individual.
- reference: PMID:35543077
reference_title: Biallelic KITLG variants lead to a distinct spectrum of hypomelanosis
and sensorineural hearing loss.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
The authors noted that although the individual fulfilled criteria for WS,
they could not exclude a diagnosis of FPHH with concomitant HL derived from
a distinct genetic or non-genetic origin.
explanation: >-
Records the diagnostic uncertainty around this individual, which is why
the phenotype carries no frequency and no mechanism link.
genetic:
- name: KITLG
gene_term:
preferred_term: KITLG
term:
id: hgnc:6343
label: KITLG
relationship_type: CAUSATIVE
variant_origin: GERMLINE
notes: >-
KITLG encodes KIT ligand (stem cell factor), produced as a transmembrane and
a soluble isoform. Direction of effect and zygosity sort KITLG variants into
distinct disorders: homozygous variants cause this disease; heterozygous
loss-of-function variants cause isolated, often unilateral or asymmetric,
sensorineural hearing loss (autosomal dominant nonsyndromic hearing loss
69) with reduced penetrance; and heterozygous gain-of-function variants
clustered in the receptor-binding VTNNV motif cause familial progressive
hyperpigmentation with or without hypopigmentation. No ClinGen gene-disease
validity record for KITLG is present in references_cache, so
gene_disease_validity is left unset.
evidence:
- reference: PMID:35543077
reference_title: Biallelic KITLG variants lead to a distinct spectrum of hypomelanosis
and sensorineural hearing loss.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
We provide consolidating evidence that biallelic KITLG variants cause a
distinct auditory-pigmentary disorder.
explanation: >-
Establishes KITLG as the causal gene for the recessive disorder.
- reference: PMID:35543077
reference_title: Biallelic KITLG variants lead to a distinct spectrum of hypomelanosis
and sensorineural hearing loss.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Pathogenic variants in KITLG, a crucial protein involved in pigmentation
and neural crest cell migration, cause non-syndromic hearing loss,
Waardenburg syndrome type 2, familial progressive hyperpigmentation and
familial progressive hyper- and hypopigmentation, all of which are
inherited in an autosomal dominant manner.
explanation: >-
The allelic series at KITLG against which this disease is delimited.
- reference: PMID:26522471
reference_title: Allelic Mutations of KITLG, Encoding KIT Ligand, Cause Asymmetric
and Unilateral Hearing Loss and Waardenburg Syndrome Type 2.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
A heterozygous missense mutation, c.310C>G (p.Leu104Val), that segregated
with WS2 was identified in a small family.
explanation: >-
The first KITLG association with Waardenburg syndrome type 2, in a single
heterozygous family.
differential_diagnoses:
- name: Autosomal dominant nonsyndromic hearing loss 69
disease_term:
preferred_term: autosomal dominant nonsyndromic hearing loss 69
term:
id: MONDO:0014738
label: autosomal dominant nonsyndromic hearing loss 69
description: >-
The heterozygous loss-of-function allelic disorder of KITLG: congenital,
stable, unilateral, asymmetric or bilateral sensorineural hearing loss with
reduced penetrance, where pigmentary changes are absent or nonspecific. It
is distinguished from this disease by zygosity and by the absence of the
Waardenburg pigmentary phenotype.
distinguishing_features:
- Heterozygous rather than homozygous KITLG variants
- Hearing loss without the Waardenburg pattern of hypomelanosis
evidence:
- reference: PMID:26522471
reference_title: Allelic Mutations of KITLG, Encoding KIT Ligand, Cause Asymmetric
and Unilateral Hearing Loss and Waardenburg Syndrome Type 2.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
This mutation co-segregated with NS-UHL/AHL as a dominant trait with
reduced penetrance.
explanation: >-
Dominant, incompletely penetrant, nonsyndromic unilateral or asymmetric
hearing loss from a heterozygous KITLG truncating variant.
- reference: PMID:39918572
reference_title: Unilateral, bilateral symmetric or asymmetric isolated hearing
loss in patients with heterozygous KITLG variants.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Penetrance is not complete, and unspecific pigmentation alterations were
observed in only three patients.
explanation: >-
Confirms that heterozygous KITLG hearing loss is incompletely penetrant
and largely lacks pigmentary findings.
- name: Familial progressive hyperpigmentation with or without hypopigmentation
disease_term:
preferred_term: familial progressive hyperpigmentation with or without hypopigmentation
term:
id: MONDO:0007771
label: hyperpigmentation with or without hypopigmentation, familial progressive
description: >-
The gain-of-function allelic disorder of KITLG. Heterozygous substitutions
at the receptor-binding surface increase KIT signalling and cause
progressive diffuse hyperpigmentation, sometimes with pale macules, without
hearing loss. It is the mirror image of this disease in both direction of
effect and pigmentary phenotype.
distinguishing_features:
- Heterozygous gain-of-function rather than homozygous KITLG variants
- Progressive hyperpigmentation rather than hypomelanosis
- No sensorineural hearing loss
evidence:
- reference: PMID:35543077
reference_title: Biallelic KITLG variants lead to a distinct spectrum of hypomelanosis
and sensorineural hearing loss.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Gain-of-function variants in KITLG are also associated with familial
progressive hyperpigmentation (FPH)
explanation: >-
Identifies the gain-of-function KITLG phenotype as an allelic disorder.
- name: Piebaldism
disease_term:
preferred_term: piebaldism
term:
id: MONDO:0008244
label: piebaldism
description: >-
The receptor-side counterpart: heterozygous KIT loss of function causes
congenital, stable, regional leukoderma and a white forelock, and hearing
loss is rare. Two individuals with homozygous KITLG variants had symmetric
lower-limb hypomelanosis reminiscent of piebaldism, so the two can overlap
clinically.
distinguishing_features:
- KIT rather than KITLG variants, and autosomal dominant inheritance
- Hearing loss is rare in piebaldism and nearly constant in this disease
evidence:
- reference: PMID:35543077
reference_title: Biallelic KITLG variants lead to a distinct spectrum of hypomelanosis
and sensorineural hearing loss.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
the KITLG receptor, cause AD piebaldism characterized by symmetric,
(mainly) limb hypomelanosis, occasional repigmentation and rare HL.
explanation: >-
The piebaldism phenotype as the case-series authors contrast it with
KITLG disease.
- name: Other genetic types of Waardenburg syndrome type 2
description: >-
MITF, SOX10 and SNAI2 variants also cause Waardenburg syndrome type 2
without dystopia canthorum, with an overlapping auditory-pigmentary
phenotype. The distinction is molecular.
distinguishing_features:
- Causal variant in MITF, SOX10 or SNAI2 rather than KITLG
evidence:
- reference: PMID:38391765
reference_title: 'Waardenburg Syndrome: The Contribution of Next-Generation Sequencing
to the Identification of Novel Causative Variants.'
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Type 2 (WS2, MIM# 193510) is differentiated from type 1 by the absence of
DC, presenting therefore only deafness associated with pigmentary
abnormalities.
explanation: >-
The clinical definition of Waardenburg syndrome type 2, shared by all its
genetic types.
- reference: PMID:38391765
reference_title: 'Waardenburg Syndrome: The Contribution of Next-Generation Sequencing
to the Identification of Novel Causative Variants.'
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Genes PAX3, MITF, SOX10, KITLG, EDNRB, and EDN3 are already known to be
associated with WS.
explanation: >-
KITLG is one of several Waardenburg genes, so the distinction between
genetic types is molecular.
diagnosis:
- name: Audiological evaluation and KITLG sequencing
diagnosis_term:
preferred_term: genetic testing
term:
id: NCIT:C15709
label: Genetic Testing
description: >-
The phenotype is recognized as Waardenburg syndrome type 2 (hearing loss and
hypomelanosis without dystopia canthorum) and confirmed by finding biallelic
KITLG variants, usually by exome, genome or Waardenburg and hearing-loss
gene panel sequencing. Hearing should be assessed formally in each ear,
because the loss may be unilateral. Because KITLG is also the gene for
isolated hearing loss, testing is relevant in early-onset, non-sudden
unilateral hearing loss even without pigmentary findings.
evidence:
- reference: PMID:39918572
reference_title: Unilateral, bilateral symmetric or asymmetric isolated hearing
loss in patients with heterozygous KITLG variants.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
This confirmation indicates that genetic testing can be relevant in
early-onset, non-sudden, isolated unilateral hearing loss.
explanation: >-
Supports KITLG testing in unilateral early-onset hearing loss. This
evidence comes from the heterozygous allelic disorder.
- reference: PMID:39338160
reference_title: Comprehensive Approach for the Genetic Diagnosis of Patients with
Waardenburg Syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Seven genes are associated with WS: PAX3, MITF, EDNRB, EDN3, SOX10, KITLG,
and SNAI2.
explanation: >-
KITLG is among the genes tested in the molecular diagnosis of Waardenburg
syndrome.
treatments:
- name: Hearing Rehabilitation with Cochlear Implantation
description: >-
Management is supportive and directed at the hearing loss: amplification,
and cochlear implantation for severe to profound loss. No KITLG-specific
therapy exists. The cited sources concern Waardenburg syndrome in general,
where early implantation gives good hearing and language outcomes; no
outcome data specific to WS2F have been published.
therapeutic_modality: SURGERY
treatment_term:
preferred_term: cochlear device implantation
term:
id: NCIT:C15329
label: Surgical Procedure
qualifiers:
- predicate:
preferred_term: medical device
term:
id: NCIT:C16830
label: Medical Device
value:
preferred_term: cochlear implant
term:
id: NCIT:C157820
label: Cochlear Implant
evidence:
- reference: PMID:32809714
reference_title: Waardenburg Syndrome.
supports: SUPPORT
evidence_source: OTHER
quote_role: REVIEW_SYNTHESIS
snippet: >-
Although no curative treatment is available, supportive care may include
cochlear implantation and surgical management of associated conditions,
such as Hirschsprung disease.
explanation: >-
Cochlear implantation as supportive care in Waardenburg syndrome
generally; not specific to the KITLG form.
- reference: PMID:41450428
reference_title: Long-Term Hearing, Language, and Educational Outcomes After Cochlear
Implantation in Children With Waardenburg Syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Early CI in children with WS contributes to substantial improvements in
hearing, language comprehension, and educational integration.
explanation: >-
Outcome data for cochlear implantation in twelve children with
Waardenburg syndrome of unspecified genetic type; no KITLG patients are
identified, so this supports the intervention for Waardenburg hearing
loss in general.
- name: Genetic Counseling
description: >-
Counseling for autosomal recessive inheritance in families with biallelic
variants, with attention to the allelic KITLG disorders, since heterozygous
loss-of-function variants can cause isolated hearing loss.
treatment_term:
preferred_term: Genetic counseling
term:
id: NCIT:C15240
label: Genetic Counseling
evidence:
- reference: PMID:32809714
reference_title: Waardenburg Syndrome.
supports: SUPPORT
evidence_source: OTHER
quote_role: REVIEW_SYNTHESIS
snippet: >-
Genetic counseling has a key role in facilitating early diagnosis, risk
assessment, and informed family planning.
explanation: >-
Genetic counseling in Waardenburg syndrome generally.
- reference: PMID:26522471
reference_title: Allelic Mutations of KITLG, Encoding KIT Ligand, Cause Asymmetric
and Unilateral Hearing Loss and Waardenburg Syndrome Type 2.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Our study unveils different phenotypes associated with KITLG, previously
associated with pigmentation abnormalities, and will thereby improve the
genetic counseling given to individuals with KITLG variants.
explanation: >-
The allelic KITLG phenotypes are what makes counseling in KITLG families
specific.
animal_models:
- name: Steel-dickie (Sl/Sld) mouse
species: Mouse
genotype: Kitl Sl/Sld compound heterozygote
description: >-
Steel mutations are alleles of Kitl, the mouse ortholog of KITLG. Sld
lacks the membrane-bound form of the ligand. Sl/Sld mice are deaf with
absent strial intermediate cells. Sld/Sld mice are viable and lack coat
pigmentation, and in Sld/Sld embryos melanoblasts fail to survive and fewer
reach the inner ear.
publication: PMID:2460075
evidence:
- reference: PMID:2460075
reference_title: Intermediate filaments in the cochleas of normal and mutant (w/wv,
sl/sld) mice.
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: >-
In contrast, vimentin was seen to stain only the basal cells in the mutant
mice, confirming our previous findings of the absence of intermediate cells
in these cases of hereditary deafness.
explanation: >-
Absent strial intermediate cells in deaf Sl/Sld mice.
modeled_mechanisms:
- target: Strial Intermediate Cell Deficiency
relationship: RECAPITULATES
fidelity: MODERATE
model_scale: TISSUE
description: >-
Sl/Sld mice lack strial intermediate cells and are deaf, the cochlear
mechanism proposed for human KITLG hearing loss.
limitations: >-
Sl/Sld is a compound heterozygote of a severe allele and an allele that
removes the membrane-bound isoform, not a model of the human homozygous
missense or truncating alleles. Steel mice also have anemia and
sterility, which are not reported in human KITLG disease, and no human
temporal bone pathology exists to confirm the strial lesion in people.
evidence:
- reference: PMID:2460075
reference_title: Intermediate filaments in the cochleas of normal and mutant (w/wv,
sl/sld) mice.
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: >-
In contrast, vimentin was seen to stain only the basal cells in the
mutant mice, confirming our previous findings of the absence of
intermediate cells in these cases of hereditary deafness.
explanation: >-
Direct observation of the node in the model.
- target: Reduced Melanoblast Survival, Proliferation and Colonization
relationship: RECAPITULATES
fidelity: MODERATE
model_scale: CELLULAR
description: >-
In Sld/Sld embryos, melanoblasts emerge and begin to migrate normally but
fail to survive.
limitations: >-
Sld removes the membrane-bound ligand isoform specifically, whereas the
human alleles affect both isoforms to differing, unmeasured degrees.
evidence:
- reference: PMID:1280558
reference_title: TRP-2/DT, a new early melanoblast marker, shows that steel growth
factor (c-kit ligand) is a survival factor.
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: >-
the membrane-bound steel growth factor which is missing in Sld/Sld
mutants is necessary for the survival of melanoblasts but not for their
early migration and initial differentiation
explanation: >-
Melanoblast survival defect in the Sld/Sld model.
- name: Kitlg heterozygous frameshift (KitlgΔ/+) mouse
species: Mouse
genotype: Kitlg c.81_84del (p.E27DfsX5) heterozygous, CRISPR/Cas9
description: >-
A CRISPR/Cas9 heterozygous Kitlg frameshift with markedly reduced KITLG
protein. Most animals have white hair on the belly or forehead, and some
have unilateral or asymmetric hearing loss. The stria contains
intermediate cells, but they are morphologically abnormal and strial
melanin is reduced in the animals with impaired hearing; KIT
phosphorylation and MITF are reduced.
publication: PMID:41584853
evidence:
- reference: PMID:41584853
reference_title: Kitlg dysfunction is associated with hearing and pigmentation abnormalities.
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: >-
Most KitlgΔ/+ mice developed abnormal hair color, such as white hair on
the belly and/or forehead
explanation: >-
The pigmentary phenotype of the model.
modeled_mechanisms:
- target: Strial Intermediate Cell Deficiency
relationship: PARTIALLY_RECAPITULATES
fidelity: LOW
model_scale: TISSUE
description: >-
Reduced strial melanin and abnormal intermediate cells with unilateral or
asymmetric hearing loss, in the setting of a Kitlg loss-of-function
allele.
limitations: >-
The model is heterozygous, so it corresponds more closely to the
heterozygous KITLG hearing-loss disorder (DFNA69) than to this recessive
disease. Hearing loss is incompletely penetrant in the mice, and
endocochlear potential was not reported as measured in the cited text.
evidence:
- reference: PMID:41584853
reference_title: Kitlg dysfunction is associated with hearing and pigmentation abnormalities.
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: >-
Fontana-Masson staining revealed that KitlgΔ/+ mice with impaired
hearing had reduced melanin distribution in the stria vascularis
compared with WT mice
explanation: >-
The strial finding that the model reproduces.
- target: Unilateral Sensorineural Hearing Loss
relationship: RECAPITULATES
fidelity: MODERATE
model_scale: ORGANISM
description: >-
Unilateral or asymmetric hearing loss by auditory brainstem response in
a subset of heterozygous mice.
limitations: >-
Heterozygous genotype, whereas this disease is recessive, and incomplete
penetrance in the mice.
evidence:
- reference: PMID:41584853
reference_title: Kitlg dysfunction is associated with hearing and pigmentation abnormalities.
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: >-
Some KitlgΔ/+ mice showed unilateral or asymmetric hearing loss
explanation: >-
Direct observation of the laterality phenotype in the model.
notes: >-
Scope. This entry follows MONDO:0030983 and OMIM:619947, whose HPO annotation
records autosomal recessive inheritance and whose phenotype annotations come
from the biallelic case series (PMID:35543077) and an earlier report,
Ogawa et al. 2017 (PMID:28504826). That report has no abstract in PubMed and
no quotable text could be cached, so it is not cited as evidence. The
heterozygous KITLG disorders are separate entities: isolated hearing loss
(MONDO:0014738) and familial progressive hyperpigmentation with or without
hypopigmentation (MONDO:0007771, curated as
Familial_Progressive_Hyperpigmentation_With_Or_Without_Hypopigmentation). The
single heterozygous Waardenburg syndrome type 2 family (p.Leu104Val,
PMID:26522471) is recorded under a second inheritance block rather than
excluded, because neither MONDO nor OMIM assigns it to another disease.
Module conformance. The entry conforms to all four nodes of
neural_crest_melanocyte_deficiency, including the stria vascularis node that
Piebaldism deliberately omits: unlike piebaldism, sensorineural hearing loss
is nearly constant here. KITLG is the ligand-side substitution at the
module's trigger node, alongside KIT in Piebaldism.
Evidence limits. The cochlear mechanism rests on mouse models: steel (Kitl)
and dominant white spotting (Kit) mutants, in which strial intermediate
cells are absent, and a heterozygous Kitlg frameshift mouse (PMID:41584853),
in which they are present but functionally abnormal. The two models differ
on whether reduced KIT ligand prevents strial colonization or impairs the
maturation of cells that arrive, and the entry carries both routes. There
is no human histopathology. The
functional consequence of the recessive human alleles has not been assayed,
and the genotype-phenotype model (complete loss of function giving
generalized hypomelanosis, residual function giving the Waardenburg-like
picture) is the case-series authors' stated speculation. No GeneReviews
chapter covers KITLG Waardenburg syndrome.
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Create: Waardenburg Syndrome Type 2F · 2026-09-30T20:08:27Z · View source
New entry for MONDO:0030983 (WS2F, OMIM:619947, KITLG hgnc:6343), plus a member row for it in kb/groupings/Neural_Crest_Melanocyte_Deficiency_Disorders.yaml (description, rationale and notes updated to mention the KITLG axis). The stub stubs/Waardenburg_Syndrome_IIa_2F.yaml was deleted; entry_type decided as DISEASE and the existing slug kept. Scope: the HPO annotation for OMIM:619947 records autosomal recessive inheritance (sources PMID:28504826 and PMID:35543077), so the entry is built on the Vona et al. 2022 biallelic case series (six homozygous individuals) and treats heterozygous KITLG isolated hearing loss (MONDO:0014738, still a stub) and gain-of-function familial progressive hyperpigmentation (MONDO:0007771) as allelic differentials. The one heterozygous WS2 family of Zazo Seco et al. 2015 (p.Leu104Val) is recorded as a second, single-family autosomal dominant inheritance block. The MONDO label in the skeleton (Waardenburg syndrome, IIa 2F) was corrected to the current OLS label, Waardenburg syndrome 2F. Deep research: OpenScientist (research/Waardenburg_Syndrome_Type_2F-deep-research-openscientist.md). Reference validation 14/14 resolved, 0 unresolved, 0 off topic; term validation needs_review only for a label paraphrase of HP:0000407 and an unresolvable ORPHA prefix. The report describes WS2F as autosomal dominant heterozygous KITLG loss of function and does not cite the biallelic case series; it conflates WS2F with the heterozygous hearing-loss phenotype. The entry follows the HPO/MONDO definition instead. From the report the entry uses PMID:26522471 and PMID:41450428 (cochlear implantation outcomes); its other citations are Waardenburg-general or about common pigmentation variation and were not needed. just preflight-dr returned WARN: KITLG 65 mentions, OMIM 619947 matching MONDO, with KIT at 43% of KITLG. KIT is the KITLG receptor and the report's KIT passages concern that receptor, not a second disease, so the warning does not indicate Named Entity Confusion. Ogawa et al. 2017 (PMID:28504826) has no abstract; a forced refetch returned no quotable text, so it is not cited as evidence. Mechanism nodes conform to all four neural_crest_melanocyte_deficiency nodes; the cochlear chain rests on steel (Sl/Sld) and Kit mouse evidence, cited with quote_role BACKGROUND where quoted from the discussion of a human genetics paper, and on Xiao et al. 2026 (PMID:41584853, named in the claim issue's triage comment), a CRISPR heterozygous Kitlg frameshift mouse. That study adds MODEL_ORGANISM evidence for reduced KIT phosphorylation and MITF (molecular node), reduced strial melanin with intermediate cells present but abnormal, normal cochlear structure and a proposed FXYD6 contribution (strial node), and unilateral or asymmetric hearing loss (edge to the unilateral phenotype); it is also a second animal model. Because it finds intermediate cells present, it is cited as REFUTE on the melanoblast-colonization to strial edge and as SUPPORT on a new direct edge from the KITLG node to the strial node (impaired maturation); the notes record that the Sl/Sld and heterozygous Kitlg models disagree on this and that the model is heterozygous while WS2F is recessive. just check-genereviews: NO_CHAPTER for GeneReviews; the StatPearls chapter is tagged. Validation: validate, validate-terms, count-verified-snippets (61/61), check-entity-refs, check-causal-targets, check-duplicate-keys, check-qualifier-terms (and -online), check-coarse-phenotypes, check-snippet-length, check-folded-hyphens, check-environmental-evidence, validate-grouping, check-groupings and validate-disorders all pass. check-title-snippets, check-snippet-grading and model-scale-audit --strict pass (the first two had earlier failed with ENOSPC while the container disk was full; re-run after space was freed). The cached copies of PMID:35543077 and PMID:38391765 were refreshed to full text by the reference fetcher; snippets in the other entries that cite them still verify. After CI's check_gene_activity_grounding gate flagged KITLG, the KITLG node was given molecular_functions GO:0005173 stem cell factor receptor binding (label and definition checked in OLS, the same term the FPHH entry binds with INCREASED) with modifier DECREASED, matching the node's claim of reduced KIT ligand signal.
WS2F is caused by heterozygous loss-of-function variants in KITLG, inherited in an autosomal dominant pattern with reduced penetrance. The landmark study by Zazo Seco et al. (2015) identified heterozygous KITLG mutations segregating with Waardenburg syndrome type 2 and with non-syndromic asymmetric/unilateral hearing loss (NS-UHL/AHL). The reported variants include a frameshift/nonsense change c.286_303delinsT (p.Ser96Ter), an in-frame indel c.200_202del (p.His67_Cys68delinsArg), and a missense variant c.310C>G (p.Leu104Val) that segregated with WS2 in a small family. In vitro functional testing showed that mutant soluble KITLG isoforms were reduced or undetectable in culture media, establishing a loss-of-function mechanism.
"a heterozygous missense mutation, c.310C>G (p.Leu104Val), that segregated with WS2 was identified in a small family" — PMID: 26522471
"These data suggest that mutations in KITLG associated with NS-UHL/AHL have a loss-of-function effect." — PMID: 26522471
WS2F corresponds to OMIM #619947 and MONDO:0030983; the gene is KITLG (HGNC:6343, NCBI Gene 4254, UniProt P21583, chromosome 12q21.32). Evidence type: human clinical + in vitro.
WS2 (including WS2F) is clinically defined by congenital sensorineural hearing loss (SNHL) and pigmentary abnormalities of the eyes (heterochromia iridum/bright blue irides), hair (white forelock, premature graying), and skin — without dystopia canthorum, the feature that distinguishes WS1 from WS2. In a Chinese WS2 cohort (n=20), SNHL occurred in 85% and heterochromia iridum in 100%; 25% had brown freckles / pigmented macules. KITLG-specific WS2 (WS2F) has been reported with pigmented macules. Variable expressivity is prominent: KITLG mutations can produce full WS2 or isolated non-syndromic unilateral/asymmetric hearing loss.
"Sensorineural hearing loss (17/20, 85.0%) and heterochromia iridum (20/20, 100.0%) were the most commonly observed clinical features in Chinese WS2 patients." — PMID: 24194866
"Waardenburg syndrome (WS) is a genetic disorder characterized by sensorineural hearing loss and pigmentation anomalies." — PMID: 28236341
Evidence type: human clinical.
KITLG (stem cell factor) binds the KIT receptor tyrosine kinase, activating downstream RAS-MAPK and PI3K-AKT cascades that drive neural-crest-derived melanoblast survival, proliferation, and migration; KITLG-KIT signaling functionally interacts with the master melanocyte transcription factor MITF. Melanocytes of neural-crest origin populate the skin, eye, and inner ear (stria vascularis); their loss produces both pigmentary defects and SNHL. Parallel evidence from the Mitf(Mi-wh)/+ mouse (a WS2 model) shows profound hearing deficit with absent endocochlear potential, loss of outer hair cells, and stria vascularis abnormalities; cochlear melanocytes are present at birth but disappear between postnatal days P1 and P7.
"Although cochlear melanocytes are present at birth, they disappear from the Mitf(Mi-wh) /+ cochlea between P1 and P7." — PMID: 23020089
"KITLG-KIT signaling and MITF are suggested to mutually interact in melanocyte development." — PMID: 26522471
Evidence type: human clinical + model organism + in vitro.
Waardenburg syndrome overall prevalence is approximately 1/40,000, and WS accounts for ~2–3% of congenital deafness. WS2F is an autosomal dominant subtype with reduced (incomplete) penetrance and variable expressivity — the same KITLG variant can yield full WS2 or isolated unilateral/asymmetric hearing loss. Diagnosis of WS type 2 uses the Waardenburg Syndrome Consortium major/minor criteria (major: congenital SNHL, iris pigmentary abnormality, hair hypopigmentation, affected first-degree relative; minor: skin hypopigmentation, synophrys, etc.), combined with molecular confirmation via targeted NGS deafness-gene panels or whole-exome sequencing. Among known WS2 genes, approximate contributions are MITF (~15%), SOX10, EDNRB (~5–6%), SNAI2, and KIT/KITLG; KITLG (WS2F) is a rare cause.
"Waardenburg syndrome (WS), which occurs with a frequency of 1/40,000" — PMID: 41159045
"This mutation co-segregated with NS-UHL/AHL as a dominant trait with reduced penetrance." — PMID: 26522471
"Waardenburg syndrome type 2 was diagnosed in a 4-year-old boy according to the Waardenburg Syndrome Consortium Criteria." — PMID: 37272645
Evidence type: human clinical.
No disease-modifying or gene-specific therapy exists for WS2F; management is supportive. Congenital SNHL is treated with hearing aids and cochlear implantation (CI). In WS children, early CI yields substantial gains: in a Japanese cohort (n=12, mean CI age 2.5 years), earlier intervention correlated with higher word/sentence scores; children without cochlear malformation achieved speech recognition >80%, and all advanced to regular junior-high classes. WS/neurocristopathy CI cohorts achieve excellent auditory-speech outcomes (CAP ~7.3, SIR ~4.0). Cochlear duct length/malformation — more pronounced in SOX10-related WS — can complicate electrode selection but is not a prominent feature of KITLG-WS2F. Prognosis: hearing loss is congenital and generally stable (non-progressive); pigmentary features are cosmetic; life expectancy is normal.
"Children without cochlear malformations or delayed treatment achieved mean speech recognition scores exceeding 80%. All participants advanced to regular junior high school classes." — PMID: 41450428
Evidence type: human clinical.
The mouse ortholog of KITLG is Kitl (the classical Steel, Sl, locus; MGI), and its receptor is Kit (the Dominant white spotting, W locus). Steel mutant mice show white coat spotting, anemia, mast-cell deficiency, and sterility, and Kit/Kitl signaling is essential for melanoblast migration/survival — directly paralleling the pigmentary defects of human KITLG disease. KITLG-related pigmentation/deafness phenotypes are conserved across mammals because melanocytes and neurocytes share a neural-crest origin. The Mitf(Mi-wh)/+ mouse is an established WS2 model reproducing deafness via strial melanocyte loss. Postnatal Kitl expression modulates epidermal melanocyte proliferation, differentiation, and stem-cell homeostasis.
"sensory organs and nerves are particularly affected by disorders because of the shared origin of melanocytes and neurocytes in the neural crest" — PMID: 23583561
"KITL signaling is important for melanocyte development in mammals" — PMID: 37482288
Applicable NCBI taxon: Mus musculus (10090). Evidence type: model organism.
KITLG encodes KIT ligand / stem cell factor (SCF / mast cell growth factor), produced as a transmembrane protein that is proteolytically cleaved to release a soluble isoform; both membrane-bound and soluble forms activate the KIT receptor. WS2F-causing variants reduce the soluble isoform (loss-of-function / haploinsufficiency). KITLG is dosage-sensitive for pigmentation: a common regulatory enhancer SNP (rs12821256) altering a LEF1 binding site drives classic blond hair in northern Europeans, and KITLG variants are genome-wide significant for human hair color and are among the established human pigmentation genes. Somatic KITLG amplification is not a feature of WS2F; WS2F variants are germline. No recurrent founder KITLG variant or common chromosomal rearrangement is established for WS2F.
"we dissect a regulatory region of the KITLG gene (encoding KIT ligand) that is significantly associated with common blond hair color in northern Europeans" — PMID: 24880339
"a variant near KITLG is associated with hair color" — PMID: 17952075
Evidence type: human GWAS + functional.
Core WS2F phenotypes are congenital in onset, variably expressed, and non-progressive:
| Phenotype | HPO term | Frequency / notes |
|---|---|---|
| Congenital sensorineural hearing loss | HP:0000407 | Bilateral, unilateral, or asymmetric; KITLG notably associated with unilateral/asymmetric loss; severity moderate–profound |
| Heterochromia iridis / bright blue irides | HP:0001100 (heterochromia iridis), HP:0007730 (iris hypopigmentation) | ~100% in WS2 cohorts |
| White forelock / poliosis | HP:0002211 (white forelock); HP:0002216 (premature graying) | Characteristic |
| Skin hypopigmentation / hyperpigmented macules | HP:0001010 / HP:0001053 | Pigmented macules reported specifically in KITLG WS2F |
| Dystopia canthorum | — | ABSENT (distinguishes WS2 from WS1) |
"Pigmented macules in Waardenburg syndrome type 2 due to KITLG mutation." — PMID: 28504826
"heterochromia iridum (20/20, 100.0%) were the most commonly observed clinical features" — PMID: 24194866
Anatomical structures (UBERON): inner ear/cochlea (UBERON:0001844), stria vascularis (UBERON:0002928), iris (UBERON:0001769), skin (UBERON:0002097), hair follicle (UBERON:0002073). Body systems: auditory/nervous and integumentary. Cell type (CL): melanocyte (CL:0000148) — cochlear intermediate cells / cutaneous and uveal melanocytes. Onset congenital; course stable/lifelong; QoL impact driven by hearing loss (communication, education) rather than pigmentary features (cosmetic). Evidence type: human clinical.
WS2F is a monogenic autosomal dominant disorder fully attributable to heterozygous germline KITLG loss-of-function. Accordingly: (a) no environmental toxins, radiation, occupational exposures, lifestyle/dietary factors, or infectious agents cause or trigger WS2F; (b) no protective genetic or environmental factors are defined (though reduced penetrance implies unknown modifiers/stochastic thresholds); (c) no gene-environment interactions are documented. Congenital SNHL differential diagnosis includes infectious mimics (congenital CMV, rubella) that must be excluded clinically but are etiologically unrelated. No disease-specific epigenetic changes, somatic variants, recurrent chromosomal rearrangements, or founder alleles are established.
"Waardenburg syndrome (WS) represents a group of genetic conditions characterized by auditory and pigmentation defects." — PMID: 41516007
Evidence type: human clinical / systematic review.
WS2F is a rare Mendelian auditory-pigmentary syndrome — a neurocristopathy arising from defective development of neural-crest-derived melanocytes. Key identifiers: OMIM #619947, MONDO:0030983, gene KITLG (HGNC:6343). ICD-11 maps Waardenburg syndrome under LD2H.1; legacy ICD-10 coding uses E70.3/Q-codes variably. MeSH: Waardenburg Syndrome (D014849). Orphanet catalogs Waardenburg syndrome type 2 (ORPHA:895) with molecular subtypes. Synonyms: WS2F; Waardenburg syndrome type 2, KITLG-related; auditory-pigmentary syndrome (KITLG). Information is derived from aggregated disease-level resources (OMIM, Orphanet) and a small number of individual case/family reports rather than EHR cohorts, reflecting the rarity of the KITLG subtype.
Causal factor: heterozygous germline loss-of-function variants in KITLG (F001). Genetic risk factors: the causal variant itself; no additional susceptibility loci or established modifier genes are defined, although reduced penetrance implies unknown genetic/stochastic modifiers (F009). Environmental risk factors: none (F009). Protective factors: none defined. Gene-environment interactions: none documented. WS2F is thus a "clean" monogenic disorder for etiology annotation.
See Finding F008 table for the phenotype spectrum with HPO terms, frequencies, and characteristics. All phenotypes are congenital in onset and non-progressive. The dominant quality-of-life burden is from hearing loss (communication, language, education), which is remediable with cochlear implantation; pigmentary features are cosmetic. A hallmark of KITLG-WS2F is the tendency toward asymmetric/unilateral hearing loss and striking variable expressivity.
Causal gene: KITLG (12q21.32; NCBI Gene 4254; UniProt P21583). Reported pathogenic variants (F001): c.286_303delinsT (p.Ser96Ter) — nonsense/frameshift; c.200_202del (p.His67_Cys68delinsArg) — in-frame indel; c.310C>G (p.Leu104Val) — missense segregating with WS2. Variant classification: pathogenic/likely pathogenic per ACMG segregation + functional evidence. Functional consequence: loss of function / haploinsufficiency, with reduced soluble KIT ligand (F007). Origin: germline. Allele frequency: private/rare, absent or ultra-rare in gnomAD. Modifier genes: none established. Epigenetic changes / chromosomal abnormalities: none disease-specific for WS2F (F009).
Not applicable — no environmental, lifestyle, or infectious contributors (F009). Infectious causes of congenital SNHL (CMV, rubella) are relevant only as differential diagnoses, not as etiologic agents.
Ordered causal chain (initiating lesion → clinical manifestation):
KITLG loss-of-function variant
│ (reduced soluble KIT ligand)
▼
Haploinsufficient KIT signaling (RAS-MAPK, PI3K-AKT; MITF interaction)
│
▼
Deficient melanoblast survival / migration / proliferation
├──────────────► Branch A: stria vascularis melanocyte loss
│ → loss of endocochlear potential
│ → congenital SNHL (HP:0000407)
└──────────────► Branch B: skin / hair / iris melanocyte loss
→ heterochromia iridis (HP:0001100),
white forelock (HP:0002211),
pigmented / hypopigmented macules
Molecular pathways: KITLG-KIT receptor tyrosine kinase signaling; RAS-MAPK; PI3K-AKT; MITF transcriptional program. Cellular processes: neural crest cell migration (GO:0001755), melanocyte differentiation (GO:0030318), melanocyte proliferation, cell survival. Cell types (CL): melanocyte (CL:0000148). Upstream: the KITLG lesion and KIT signaling deficit. Downstream: melanocyte depletion and the two organ-specific branches. No immune, metabolic, or oxidative-stress mechanisms are implicated.
Organ level: inner ear/cochlea (UBERON:0001844) — primary; eye/iris (UBERON:0001769), skin (UBERON:0002097), hair follicle (UBERON:0002073). Body systems: auditory/nervous and integumentary. Tissue/cell level: neural-crest-derived melanocytes (CL:0000148), including cochlear stria vascularis intermediate cells (UBERON:0002928) and cutaneous/uveal melanocytes. Subcellular: melanosome (GO:0042470) and melanin biosynthesis machinery. Lateralization: pigmentary features may be patchy/asymmetric; hearing loss may be bilateral, unilateral, or asymmetric — with KITLG notably associated with unilateral/asymmetric loss.
Onset: congenital (present from birth). Onset pattern: developmental (established prenatally during neural-crest migration). Progression: hearing loss is generally stable/non-progressive; pigmentary features stable. Disease course: chronic, lifelong, non-remitting. Critical period: the therapeutic window for hearing rehabilitation is early childhood — earlier cochlear implantation correlates with better speech/language outcomes (F005).
Prevalence: WS overall ~1/40,000; WS2F is a rare molecular subtype (few reported families). Inheritance: autosomal dominant. Penetrance: reduced/incomplete. Expressivity: variable (full WS2 to isolated hearing loss). Anticipation / germline mosaicism / founder effects: none established for WS2F. Consanguinity: not relevant (dominant). Sex ratio: no strong sex bias reported. Geographic distribution: no endemic clustering; reported across populations.
Clinical diagnosis uses the Waardenburg Syndrome Consortium major/minor criteria (F004). Audiology: audiometry/ABR confirms congenital SNHL; ophthalmology documents iris pigmentary anomalies. Imaging: temporal-bone CT/MRI assesses cochlear anatomy prior to CI (cochlear duct length considerations more relevant to SOX10-WS). Genetic testing: targeted NGS deafness/WS gene panels or whole-exome sequencing including KITLG, MITF, SOX10, EDNRB, EDN3, SNAI2, PAX3; single-gene testing of KITLG when WS2F is suspected. Differential diagnosis: other WS subtypes (WS1 distinguished by dystopia canthorum; WS4 by Hirschsprung disease), piebaldism (KIT), and infectious congenital SNHL (CMV, rubella). Screening: newborn hearing screening detects the SNHL; cascade genetic testing of relatives given dominant inheritance.
Life expectancy is normal; WS2F is not life-limiting. Morbidity is driven by hearing loss and its communication/educational consequences, which are substantially mitigated by early cochlear implantation — children without cochlear malformation achieve speech recognition >80% and mainstream schooling (F005). Pigmentary features carry only cosmetic/psychosocial impact. Prognostic factors for hearing outcome: age at implantation (younger better within the early window) and cochlear morphology.
No gene-specific therapy (F005). Supportive/rehabilitative: hearing aids; cochlear implantation (NCIT: Cochlear Implantation); speech-language therapy; auditory-verbal rehabilitation. Multidisciplinary care: audiology, otology, ophthalmology, dermatology, and genetic counseling. Pigmentary features generally require no treatment; standard dermatologic/cosmetic measures optional. No pharmacotherapy, gene therapy, cell therapy, or RNA-based therapy is established or in trials specifically for WS2F.
Primary prevention is not applicable (genetic). Secondary prevention = newborn hearing screening enabling early CI. Genetic counseling provides recurrence-risk assessment (50% transmission from an affected heterozygote, modified by reduced penetrance), with options for prenatal/preimplantation genetic testing where a familial variant is known. Cascade testing identifies at-risk relatives.
Taxonomy: Mus musculus (NCBI:txid10090). Orthologous gene: mouse Kitl (Steel locus); receptor Kit (W locus) (F006). Coat-color mutations in KIT, EDNRB, MITF, PAX3, SNAI2 produce analogous pigmentation-plus-sensory phenotypes across mammals due to the shared neural-crest origin of melanocytes and neurocytes. Naturally occurring KITLG/KIT pigmentation variation is documented in cattle, dogs, and other mammals (comparative; not identical to human WS2F).
Mouse is the principal model. Steel (Kitl) mutants* recapitulate pigmentary defects (white spotting) plus anemia, mast-cell deficiency, and sterility, reflecting KIT ligand's broader roles beyond melanocytes. The Mitf(Mi-wh)/+ mouse is an established *WS2 deafness model demonstrating strial melanocyte loss between P1–P7 and absent endocochlear potential (F003/F006) — the key mechanistic bridge for the auditory phenotype. Limitations: no published Kitl-specific heterozygous mouse modeling the exact WS2F human variants; Steel homozygotes are lethal/severe, limiting direct haploinsufficiency modeling. Resources: MGI, IMSR.
WS2F is best understood as a melanocyte-dosage disease. A single wild-type KITLG allele is insufficient to supply the KIT ligand needed for full melanoblast survival and migration during a narrow developmental window. The convergence of human genetics (F001/F007), functional data on reduced soluble ligand (F001), pigmentation GWAS establishing KITLG dosage-sensitivity (F007), and mouse strial-melanocyte loss (F003/F006) produces a coherent, well-supported causal chain. The branch point — a single upstream lesion producing two phenotypic outputs (deafness and hypopigmentation) — explains the syndromic pairing, while haploinsufficiency at a threshold-dependent developmental step explains the reduced penetrance and variable expressivity (including unilateral hearing loss): stochastic variation in whether enough melanocytes reach a given cochlea or skin region tips individuals above or below the phenotypic threshold.
| Feature | Upstream cause | Downstream effect | Key evidence |
|---|---|---|---|
| Congenital SNHL | KITLG LoF → KIT signaling deficit | Strial melanocyte loss → no endocochlear potential | Mouse Mitf(Mi-wh) [PMID: 23020089] |
| Heterochromia / white forelock / macules | Same lesion | Skin/hair/iris melanocyte deficiency | WS2 cohorts [PMID: 24194866]; KITLG macules [PMID: 28504826] |
| Reduced penetrance / unilateral loss | Threshold-dependent haploinsufficiency | Stochastic phenotypic output | [PMID: 26522471] |
| PMID | Title (abbrev.) | Role |
|---|---|---|
| 26522471 | Allelic Mutations of KITLG ... Cause ... Waardenburg Syndrome Type 2 | Foundational — establishes KITLG as WS2F gene, LoF mechanism, dominant/reduced penetrance |
| 24194866 | Genetic and phenotypic heterogeneity in Chinese WS2 | Phenotype frequencies (SNHL 85%, heterochromia 100%) |
| 28236341 | EDNRB mutations cause WS2 | Defines cardinal WS features |
| 23020089 | Hearing dysfunction in Mitf(Mi-wh)/+ mice | Mechanistic bridge — strial melanocyte loss → deafness |
| 41159045 | Association of WS with a new mutation | WS prevalence 1/40,000 |
| 37272645 | De Novo SOX10 mutation, WS2 | Confirms Consortium diagnostic criteria |
| 41450428 | Long-Term Outcomes After CI in WS Children | Treatment/prognosis — CI outcomes |
| 23583561 | Pleiotropic effects of coat-colour mutations | Comparative biology rationale |
| 37482288 | Postnatal Kitl affects epidermal pigmentation | Conserved Kitl role in melanocytes |
| 24880339 | Molecular basis for classic blond hair | KITLG dosage-sensitivity |
| 17952075 | Genetic determinants of hair/eye/skin pigmentation | KITLG pigmentation GWAS |
| 28504826 | Pigmented macules in WS2 due to KITLG | KITLG-specific skin phenotype |
| 41516007 | Genetics of WS in Africa: Systematic Review | Confirms purely genetic etiology |
| 41271950 | Neurocristopathy hearing loss & CI outcomes | CI outcomes in WS (CAP 7.3/SIR 4.0) |
Evidence-source distribution: human clinical/genetic (majority), model organism (mouse Mitf/Kitl), in vitro functional (soluble ligand assays), and computational/GWAS (pigmentation). The central causal claim rests on a single foundational human study (PMID: 26522471) supported by convergent mechanistic and comparative evidence.
Waardenburg Syndrome Type 2F (OMIM #619947; MONDO:0030983) is a rare autosomal dominant auditory-pigmentary neurocristopathy caused by heterozygous loss-of-function variants in KITLG (KIT ligand / stem cell factor) that reduce KIT-receptor signaling and impair neural-crest-derived melanocyte development. This produces congenital, non-progressive sensorineural hearing loss (from deficiency of cochlear stria vascularis melanocytes and loss of the endocochlear potential) together with pigmentary anomalies of the eyes, hair, and skin (heterochromia iridis, white forelock, pigmented/hypopigmented macules), without dystopia canthorum. It is not life-limiting; management is supportive and multidisciplinary, centered on early cochlear implantation, with no gene-specific therapy available.
Checked with linkml-reference-validator 0.3.0rc3.
| Outcome | Count |
|---|---|
| References checked | 14 |
| Resolved | 14 |
| Unresolved (possible confabulation) | 0 |
| Unverifiable | 0 |
| References weighed for topical relevance | 14 |
| On topic | 7 |
| Off topic | 0 |
All extracted references resolved successfully.
Checked with linkml-term-validator 0.4.5, through the ols: adapter.
| Outcome | Count |
|---|---|
| Terms checked | 19 |
| Resolved | 17 |
| Unresolved (possible confabulation) | 0 |
| Obsolete | 0 |
| Unverifiable | 2 |
| Terms whose name was checked | 2 |
| Terms named correctly | 1 |
| Terms named as a different term | 0 |
| Terms whose name is worth a second look | 1 |
The report's name for these is recognisably related to the term's own name without being one of them. A loose paraphrase reads the same way as a citation of the wrong sibling term - and so does a related synonym, which the ontology records precisely because it names something adjacent rather than the same thing - so these are listed rather than judged:
HP:0000407 (2 mentions) - the report calls it "Congenital sensorineural hearing loss"; HP calls it Sensorineural hearing impairment, and lists "Sensorineural hearing loss" among its other namesTerms carrying these prefixes were not checked either way, because no configured ontology covers them. An unrecognised prefix may name an ontology this run could not reach as easily as one that does not exist, so nothing here is evidence of fabrication: ORPHA.
17 of 19 terms resolved to a current term; the rest could not be looked up either way.