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See relatedprovided Commentary by Elsevier -on Publisher page Connector v Genetic Heterogeneity of KID Syndrome: Identification of a Cx30 (GJB6) Mutation in a Patient with KID Syndrome and Congenital Atrichia

Amy Y. Jan,Ã Shivan Amin,w Paulina Ratajczak,w Gabriele Richard,w and Virginia P. Sybertz ÃDivision of Dermatology, Department of Medicine, University of Washington, Seattle, WA, USA; wDepartment of Dermatology and Cutaneous Biology and Jefferson Institute of Molecular Medicine, Thomas Jefferson University, Philadelphia, PA, USA; zDivision of Medical Genetics, Department of Medicine, University of Washington and Division of Dermatology, Group Health Permanente, Seattle, WA, USA

Connexins are integral membrane forming aqueous channels that allow the diffusional exchange of ions and small metabolites between cells, thus coordinating metabolic activities in multicellular tissues. Dominant mutations in the Cx26 gene GJB2 have been shown to cause keratitis-ichthyosis-deafness (KID) syndrome, palmoplantar keratoderma associated with hearing loss, and Vohwinkel syndrome. Missense mutations in the closely related Cx30 gene GJB6 underlie Clouston syndrome (autosomal dominant hidrotic ectodermal dysplasia). We report a 6-y-old boy with phenotypic characteristics of KID syndrome as well as atrichia. In contrast to other KID syndrome patients, molecular analysis of the gene GJB2 did not disclose a pathogenic mutation, although the patient was homozygous for a common polymorphism (V27I) in the coding sequence of Cx26. Nevertheless, screening of GJB6 revealed a heterozygous missense mutation (V37E) predicted to alter sequence and charge of the first transmembrane helix of Cx30, which was previously implicated in Clouston syndrome (Smith et al, 2002). The presence of a pathogenic Cx30 mutation and the lack of a pathologic molecular change in Cx26 in this patient, whose clinical features predominantly resemble KID syndrome, suggest genetic heterogeneity of KID syndrome and underscore that mutations in Cx30, similar to those in Cx26 or Cx31, can cause different phenotypes. Based on our results, connexin gene mutations should be considered in patients presenting with congenital sensorineural hearing loss and disorders of cornification, and screening of several connexin with known cutaneous phenotype, such as those for Cx26, Cx30, Cx30.3, and Cx31, may be required. Key words: connexin-30/connexin-26/hearing loss/palmoplantar keratoderma/gap junctions J Invest Dermatol 122:1108 –1113, 2004

Keratitis-ichthyosis-deafness (KID) syndrome (OMIM with photophobia, punctate keratitis, and progressive 148210) and Clouston syndrome (hidrotic ectodermal corneal vascularization that may later result in visual decline dysplasia; OMIM 129500) are rare autosomal dominant and blindness (Caceres-Rios et al, 1996). Many KID ectodermal dysplasias due to germline mutations in the syndrome patients were reported to have sparse or connexin genes GJB2 and GJB6, respectively, which cluster lusterless hair, but only approximately 10%–23% have at 13q11 and encode the closely related gap congenital absence of hair (Caceres-Rios et al, 1996; junction proteins Cx26 and Cx30 (Lamartine et al, 2000; Sundaram et al, 2003). Other findings that are variably Richard et al, 2002; van Steensel et al, 2002). KID and present include nail dystrophy, dental anomalies, hypohi- Clouston syndrome share a few overlapping features, such drosis, growth delay, increased susceptibility to cutaneous as nail dystrophy, hair loss, and palmoplantar keratoderma. infections, and a propensity for developing squamous cell Although the disorders are usually readily distinguishable on carcinomas (Caceres-Rios et al, 1996). KID syndrome is clinical grounds in patients with a full-blown picture, the caused by autosomal dominant missense mutations in the differentiation can be challenging in others. connexin gene GJB2. A common mutation that has been KID syndrome is a rare, mostly sporadic disorder with a reported in 12 of 15 unrelated patients tested results in the broad spectrum of cutaneous features, including erythro- replacement of aspartic acid 50 with asparagine (D50N) in keratoderma, follicular hyperkeratoses, psoriasiform or the first extracellular loop of Cx26 (Richard et al, 2002; van verrucous plaques, acanthosis, and palmoplantar kerato- Geel et al, 2002; van Steensel et al, 2002; Alvarez et al, derma (PPK) often described as reticulated or pitted 2003; Yotsumoto et al, 2003). This sequence motif is high- (reviewed in Caceres-Rios et al, 1996; Sundaram et al, ly conserved among all and any change in 2003). Between 90% and 93% of affected individuals have composition and charge is likely detrimental for the prelingual sensorineural hearing loss (SNHL) (Caceres-Rios formation and function of gap junction channels (Rubin et al, 1996; Sundaram et al, 2003), which is often bilateral et al, 1992; White et al, 1995). Other mutations cluster in the and severe to profound (Sybert, 1997; Szymko-Bennett et al, intracellular amino terminus of this gap junction 2002). Corneal symptoms often manifest during childhood (Richard et al, 2002).

Copyright r 2004 by The Society for Investigative Dermatology, Inc. 1108 122 : 5 MAY 2004 GENETIC HETEROGENEITY OF KID SYNDROME 1109

Clouston syndrome is an autosomal dominant ectoder- At 6.5 mo of age, dermatological examination revealed mal dysplasia particularly common among the French– generalized erythema and thickened skin with a cobble- Canadian population due to a founder effect (Lamartine et al, stone appearance, sparing only the diaper area. In addition, 2000). The principal features include nail dystrophy, hair a verrucous, hyperkeratotic plaque on his left antecubital loss, and PPK. Nail abnormalities are usually present in all fossa was noted. Six years later (Fig 1), the patient’s skin patients and may range from almost normal appearing nails continued to show slight erythroderma and was covered to micro- or anonychia (Clouston, 1929). Nail plate changes with innumerable spiny papules with accentuation on the may include thickening, brittleness, discoloration, splitting, posterior neck, lower back, knees, and elbows. Only the and onycholysis (Clouston, 1929; Clouston, 1939; Rajago- glans penis and sandal strap regions of the dorsal feet were palan and Tay, 1977; Hassed et al, 1996). Paronychia and spared. He also had diffuse PPK with a cobblestone or nail infections are common (Clouston, 1929; Kibar et al, ceribriform surface. In addition, a few scattered, verrucous, 1996). Hair abnormalities manifest at birth or later as atrichia and fissured papules up to 10 mm in diameter were noted in or hypotrichosis with brittle, slow-growing hair, and may be the perineal area. The patient had complete absence of progressive. Some but not all patients develop diffuse PPK body and scalp hair, eyebrows, and eyelashes. He had mild and discrete hyperpigmentations over joints, whereas conjunctival injection and corneal neovascularization, but strabismus and cataracts are rare (Clouston, 1929; Clous- no blepharitis, ectropion, eyelid adhesions, or nystagmus. ton, 1939; Hazen, 1980). Sweat function and teeth are His primary teeth were normal in number and shape, normal (Rajagopalan and Tay, 1977; Hassed et al, 1996; although he had a few dental cavities. The oral mucosa was Sybert, 1997). Unlike in KID syndrome, patients with unremarkable. Several of his fingernails had been shed, and Clouston syndrome lack vascularizing keratitis and SNHL. the remaining ones, similar to the toenails, were thickened, The latter has only been described in families with short, and demonstrated distal onycholysis. He had mild autosomal recessive onychodystrophy (Feinmesser and heat intolerance during the summer months. The past Zelig, 1961) or autosomal dominant onychodystrophy with medical history also revealed recurrent episodes of nail additional abnormalities (conical teeth, hypodontia, syn- infections as well as an unrelated peanut allergy. dactyly, and polydactyly) without PPK and hair involvement, suggestive of a distinct syndrome (see OMIM 124480) Histology At 6.5 mo of age, a skin biopsy of the patient’s (Robinson et al, 1962). Lamartine et al (2000) identified two left posterior arm revealed an abundance of eccrine sweat different missense mutations in the Cx30 gene, G11R and glands and ducts, which could be age-related, whereas A88V, each of which segregated with Clouston syndrome in only a few small, abortive hair follicles without hair shafts 12 families of French–Canadian and other backgrounds. In were identified (Fig 1). The ostia of appendages showed addition, a de novo mutation in the first transmembrane dilatation and plugging with orthokeratotic hyperkeratosis domain of Cx30, V37E, has been detected in a patient with and a prominent granular layer. Sebaceous glands were sporadic Clouston syndrome (Smith et al, 2002). present. Here, we report a young boy with features of KID syndrome and congenital atrichia, who was found to carry a Mutation analysis reveals a heterozygous missense deleterious missense mutation in the Cx30 gene (GJB6). mutation in GJB6 (Cx30) The presence of all key features Our findings expand the phenotypic spectrum of mutations of KID-syndrome prompted initial mutation analysis of the in GJB6, and further underscore the overlapping nature of GJB2 (Cx26) gene. The proband was found to be homo- syndromes thus far attributed to the four connexins with zygous for a G to A transition at nucleotide 79 (from ATG cutaneous manifestations. start site) in codon 27, changing a hydrophobic residue, valine (GTC), with another, isoleucine (ATC) (V27I). This Results substitution, also found in unaffected controls in homo- zygous or heterozygous state, represents a common Clinical features The proband is a 6-y-old boy born to polymorphism with a frequency of the minor (A) allele of non-consanguineous, unaffected parents after an unevent- 0.005–0.52 in different populations (Kelley et al, 1998; Abe ful pregnancy. The maternal family history did not reveal et al, 2000; Kudo et al, 2000; Park et al, 2000). In our evidence for hearing impairment or ectodermal dysplasia. Northern European control cohort (156 ), the The paternal family history could not be obtained. Since allele frequency was 0.013. Since no other sequence birth, he has had dry, leathery skin; short and thickened variants were detected in GJB2, the connexin genes GJB6 dystrophic nails; no scalp hair, eyebrows and eyelashes; as well as GJB3, GJB4, GJB5, and GJA1 were scrutinized. and severe photophobia. His sweating has been impaired, The proband harbored a heterozygous 110T ! A transver- which was confirmed with a bromophenol test at 6.5 mo of sion in GJB6, which was not present in his mother’s DNA age. In early childhood, his growth and weight remained sample (Fig 2). His father was unavailable for testing. This below the 5th percentile and his motor development was point mutation is predicted to lead to a non-conservative slightly delayed. In recent years, he has caught up to the replacement of valine 37 (GTG) with a negatively charged 5th-10th percentile for these growth parameters. Audio- glutamic acid (GAG) (V37E) in the first transmembrane helix logical testing revealed prelingual bilateral mild to moderate of Cx30. The nucleotide change was not detected in a SNHL but his speech has improved significantly with the cohort of 50 unrelated individuals of Northern European use of hearing aids since the age of 5 y. Mild keratitis and origin without genodermatoses or hearing loss, nor in the corneal vascularization were evident on ophthalmologic additional 100 Northern European controls published pre- examination at the age of 5 y. viously (Smith et al, 2002), excluding the possibility that 1110 JAN ET AL THE JOURNAL OF INVESTIGATIVE DERMATOLOGY

E

A B C D F

I

G H

Figure 1 Clinical features and histopathology. Six-y–old boy with atrichia of the scalp, eyebrows and eyelashes, generalized mild erythroderma and spiculate, hyperkeratotic papules, here shown on the face (A–C). Note that each tiny white dot represents a filiform hyperkeratosis. Diffuse plantar keratoderma (D) with rough, cobblestone-like surface (D, F) and nail dystrophy with short, thickened nail plates (E). Light microscopy (H/E) of a skin biopsy at 6.5 mo of age (H) revealed paucity of hair follicles, dilatation, and orthokeratotic plugging of appendageal ostia (see close-up in (I)) in contrast to a biopsy from a 5 mo-old patient with congenital ichthyosis (G).

V37E represents a non-consequential sequence poly- 2001). Despite the apparent redundancy of the gap junction morphism. No sequence aberrations were found in four system, each connexin appears to have specific properties, other connexin genes expressed in stratifying epithelia of which is illustrated by the fact that inherited defects in ectodermal origin, including GJB3, GJB4, GJB5, and GJA1. several connexin genes result in related yet distinct skin disorders, including PPK associated with SNHL, Vohwinkel syndrome and KID syndrome (GJB2), Clouston syndrome Discussion (GJB6), and erythrokeratodermia variabilis (GJB3 and GJB4) (Richard, 2003a). Connexins are a large family of small integral membrane We report a patient with an unusual clinical presentation proteins utilized by most vertebrate tissues to establish resulting in diagnostic difficulties. He presented with a direct cell–cell communication through gap junction chan- combination of clinical features characteristic of KID nels. Similar to certain other adhesion molecules, such as syndrome, including congenital bilateral SNHL, keratitis, claudins, occludin, or PMP22, they contain four hydro- and mild erythroderma. In addition, he had congenital phobic domains transversing the plasma membrane (M1– absence of hair, PPK, and nail dystrophy, which are also M4, Fig 2). These a-helices separate 2 highly conserved seen in Clouston syndrome, and generalized spiny hyper- hydrophilic loops extending into the extracellular space keratotic papules as described in HID syndrome (Hystrix- from 3 relatively variable cytoplasmic domains. Six con- like Ichthyosis Deafness syndrome) (Traupe, 1989). In nexin molecules oligomerize into homomeric or heteromeric contrast to all other KID and HID syndrome, patients connexin hemichannels, which are integrated into the harboring pathogenic mutations in GJB2 (Richard et al, plasma membrane where they may accumulate to gap 2002; van Geel et al, 2002; van Steensel et al, 2002), our junction plaques and associate with their counterparts in molecular studies revealed a heterozygous mutation in adjacent cells to complete intercellular channels. These GJB6. The identified mutation V37E in GJB6 was recently channels permit the diffusion of small molecules (up to 1 observed in a patient with Clouston syndrome without kDa) between cells and mediate the exchange of signals evidence for abnormal sweating, hearing, photophobia, and and nutrients, thereby coordinating cellular activities and keratitis (Smith et al, 2002). These findings illustrate a response to stimuli. In the skin, up to 10 different connexin perplexing phenotypic variability of the GJB6 mutation V37E molecules have been detected, which are expressed in and underscore the profound influence of genetic and spatial and temporal overlapping patterns, and are partially epigenetic factors that modify the clinical phenotype. In shared by other stratified epithelia (Richard, 2000a; Di et al, fact, other GJB6 mutations originally described in patients 122 : 5 MAY 2004 GENETIC HETEROGENEITY OF KID SYNDROME 1111

A BC Wildtype sequence 20 18 16 37 Val 14 12 10 8 6 4 2 Human Cx26 RIMIL V VAAKE 0 3.5 4.5 5.5 6.5 Mouse Cx26 RIMIL V VAAKE Human Cx30 RVMIL V VAAQE Mouse Cx30 RVMIL V VAAQE GTG (Val37) Human Cx30.3 RVLVY V VAAEE GAG (Glu37) 12 Mouse Cx30.3 RVLVY V VAAEE 10 Human Cx31 RVLVY V VAAER 8 Mouse Cx31 RVLVY V VAAER 6 Human Cx32 RIMVL V VAAES 4 Mouse Cx32 RIMVL V VAAES 2 0 3.5 4.5 5.5 6.5

D V37E A88V G11R

NT M1E1 M2CL M3 E2 M4 CT

Figure 2 Mutation analysis. (A) Compared with the wild-type sequence (upper chromatogram), mutation analysis in the patient demonstrated a heterozygous T to A transversion, resulting in the substitution of valine with glutamic acid (V37E) (lower chromatogram). (B) dHPLC analysis of Cx30 PCR amplicons encompassing the mutation site revealed heteroduplex formation in the patient sample (double peak, lower panel), which is not present in his unaffected mother (single peak, upper panel) and unaffected controls. (C) Sequence alignment of multiple human and rodent connexins demonstrated a strong conservation of the valine residue at this position in the first transmembrane domain. (D) Schematic representation of Cx30 depicting the predicted structural motifs and the position of pathogenic mutations with cutaneous manifestation (arrows). NT: cytoplasmic amino-terminus; M1–M4: transmembrane domains; E1, E2: extracellular domains; CL: cytoplasmic loop; CT: cytoplasmic carboxy-terminus. with Clouston syndrome, such as G11R and A88V, may also type Cx30 or mutant V37E-Cx30, which could aggravate the result in forme fruste with hypertrophic nail dystrophy pathological processes. closely resembling pachyonychia congenita, alone or in Our findings demonstrate for the first time that KID combination with hypotrichosis (Van Steensel et al, 2003). In syndrome is genetically heterogeneous and caused by contrast, mutation T5M has been associated with SNHL mutations in either GJB2 or GJB6. Therefore, KID syndrome without any other associated features (Grifa et al, 1999). It is is another example of a connexin disorder attributable to tempting to speculate that the unique disorder of the patient mutations in more than one connexin gene, as are EKV studied here might be related, at least in part, to the (GJB3, GJB4), non-syndromic SNHL (GJB2, GJB6, GJB3), presence of a homozygous sequence polymorphism in or cataract (GJA3, GJA8). Although dominant Cx26 muta- GJB2 replacing valine27 with isoleucine. Despite detailed tions in KID syndrome either affect a hypermutable CpG functional analyses of numerous recessive and dominant dinucleotide in the first extracellular domain or cluster in the Cx26 mutations, the functional properties of this particular N-terminus, the mutation identified here, V37E, lies in the polymorphic variant of Cx26 remain unknown. Other Cx26 first transmembrane helix of Cx30. Based on a 3-dimen- mutations that were originally considered non-consequen- sional map of truncated Cx43 (Unger et al, 1999) as well as tial polymorphisms, such as M34T and V37I (orthologous to SCAM (scanning cysteine accessibility mutagenesis) analy- the GJB6 mutation reported here), were subsequently found sis of Cx32 (Zhou et al, 1997), this domain has been shown to represent recessive alleles with reduced or absent to line the cytoplasmic end of the channel pore and is part channel permeability (Bruzzone et al, 2003; Oshima et al, of a voltage sensing and transduction mechanism. Conse- 2003). Hence, it will be interesting to learn if V27I-Cx26 has quently, ion selectivity and other channel properties critically consequences on Cx26 function and, perhaps, on assembly depend on the sequence, charge, and side chain conserva- or channel properties of mixed channels formed with wild- tion of this domain. Replacing this hydrophobic valine in 1112 JAN ET AL THE JOURNAL OF INVESTIGATIVE DERMATOLOGY

Cx30 with a charged oglutamate acid residue can be or involvement of other ectodermal tissues, whereby muta- expected to disrupt the alpha-helical structure of this tion analysis should include all genes with potential cuta- transmembrane domain and ultimately alter the assembly neous phenotype, including Cx26, Cx30, Cx30.3, and Cx31. and function of Cx30 in our patient. This prediction is supported by an in vitro expression study of V37E-Cx30 in Materials and Methods HeLa and NEB1 keratinocytes, in which the mutant protein was synthesized but failed to be transported to the cell Patients and biological materials A 6-y-old boy and his membranes and therefore could not produce gap junction unaffected mother were ascertained and gave written informed plaques (Common et al, 2002). These results are similar to consent to participate in genetic research studies approved by the those obtained for Cx26 mutations causing PPK/SNHL institutional review board of Thomas Jefferson University, Phila- (Marziano et al, 2003) and KID syndrome (Yi, 2003) as well delphia, PA. DNA samples of both individuals were obtained from buccal mucosa cells (Richards et al, 1993). A paraffin-embedded as mutations in other connexin genes with a cutaneous 3-mm punch biopsy of lesional skin from the left arm of the 6.5-mo- phenotype (Di et al, 2002; Rouan et al, 2003). Whereas the old proband was analyzed by light microscopy (H/E). assembly and trafficking defect observed for several Cx26 mutants could be overcome by co-expression with wtCx26 DNA amplification and mutation analysis DNA samples were or wtCx30, the presence of mutant Cx26 subunits in gap amplified by PCR for direct DNA sequence analysis of the coding regions of GJB6, GJB2, GJB3, and GJB4. Primer sequences were junction plaques was shown to inhibit dominantly the derived from the genomic gene sequences (GenBank accession function of homotypic or mixed gap junction channels, thus numbers: AJ005585; NT_009799 [GJB6]; U43932; M86849; disturbing normal intercellular communication (Marziano NT_009799 [GJB2]; AF099730; AL121988 [GJB3]; AL121988 et al, 2003). These data have important implications for [GJB4]; AF099731 [GJB5]; NT_033944.2 [GJA1]) and are listed as understanding the pathomechanisms of KID syndrome and follows: [GJB6]: (sense) 50-AGAATGCTTTCAGGGTGGG-30 (nu- provide strong experimental evidence for the existence of cleotides –196 to –178 from ATG translation start site) and (anti- sense) 50-GATTCGGAAAAAGATGCTGC-30 (nucleotides 413 to mixed (heterotypic/heteromeric) Cx26/Cx30 gap junctions 432) as well as (sense) 50-GGCCTACTACAGGCACGAAA- 0(nucleo- in the non-sensory epithelia of the inner ear, where loss of 85 to 304) and (antisense) 50-GGTTGGTATTGCCTTCTGGA-30 either protein results in SNHL (Cohen-Salmon et al, 2002; (nucleotides 835-854); [GJB2]: (sense) 50-GTTCTGTCTTCACCTG- Kudo et al, 2003; Teubner et al, 2003). Both Cx26 and Cx30 30 (nucleotides 172 to 157) and (antisense) 50-GGTTGGTAT are closely related proteins with 76% amino acid identity TGCCTTCTGG-30(nucleotides 835 to 853), and [GJB5]: (sense) 50- 0 and are also co-expressed in human corneal epithelium as TCAGCTCCC TCCCTCTACAA-3 (nucleotides 177 to 153) and 0 0 well as in sweat glands, sweat ducts, and hair follicles (antisense) 5 -ATGGCTTAGCTCCCCACTCT-3 (nucleotides 896 to 917). PCR reactions were performed using 200 ng genomic DNA, (Richard et al, 2002; Coutinho et al, 2003). In contrast to 2.5 IU Taq DNA polymerase, 10% Q-solution (Qiagen, Valencia, Cx30, which is prevalent in the upper differentiated layers of CA), and standard PCR conditions for 60 mL total volume. PCR interfollicular epidermis, Cx26 is only expressed at low cycling conditions were 941C for 2 min; 36 cycles of 941C for 30 s; levels in palmoplantar epidermis but is strongly induced in 571C[GJB6]/561C[GJB2; GJB5] for 45 s; 721C for 60 s; and finally response to wounding or other trauma (Lucke et al, 1999; 721C for 7 min. Amplicons were gel purified (QIAquick gel Coutinho et al, 2003). Together with our molecular findings, extraction kit, Qiagen) and directly sequenced using the BigDye this overlapping but not identical tissue expression of Cx26 terminator sequencing system on an ABI Prism 377 sequencer (PE Applied Biosystems, Foster City, CA). Primers and PCR conditions and Cx30 implies some common functions and perhaps for amplification and sequencing of GJB3, GJB4, and GJA1 were direct interaction of both proteins in many ectodermal used as previously published (Richard et al, 2000b; Paznekas et al, epithelia, and may form the basis for the observed 2002; Richard et al, 2003b). Sequence variants were confirmed by pleiotropism of GJB2 and GJB6 mutations, which can bi-directional DNA sequencing and in case of mutation 110T ! A result in SNHL, skin, hair, nail, or corneal pathology alone or by denaturing high performance liquid chromatography (dHPLC). in combination (Richard, 2003a). The prominent hair This method was also used to exclude the mutation from 100 population-matched control chromosomes. For dHPLC analysis, a phenotype of GJB6 mutations points to a hitherto unex- 321 bp fragment of GJB6 was PCR-amplified from genomic DNA plored role of Cx30 in keratinization of hair follicles. with primers (sense) 50-GACGCTGCACACTTTCATC-30 and (anti- In summary, our data illustrate the increasing complexity sense) 50- AGTTCAGGCGAGGAGAGAA-30. Each sample was and overlap between cutaneous connexin disorders. The denatured at 941C for 10 min, cooled to 651C for 10 min to allow same Cx30 gene mutation may account for Clouston heteroduplex formation, and maintained on ice until loading. Ten syndrome or KID syndrome, which makes it difficult to micro liter of each sample was separately injected and analyzed on t draw clinical and prognostic predictions, such as ocular or aWAVE DNA fragment analysis system (Transgenomic, Omaha, NE), over 7.5 min at a temperature gradient of 621C that was audiologic involvement, based on the underlying mutation established with the WAVE Maker program 3.4 (Transgenomic). alone. Moreover, KID syndrome results from pleiotropic mutations in 2 different yet closely related connexin genes that impair the function of the inner ear, cornea, skin, and appendages with significant variability of the resulting The authors are grateful to the family who participated in our study. We phenotype. The shared tissue expression and function of thank F. Ringpfeil and J. Lee for providing the histopathological control image. This work was supported by the National Foundation for cutaneous connexins may serve as a basis for the broad Ectodermal Dysplasias and NIH/NIAMS grants K08-AR02141 (GR), clinical overlap observed among the genetic disorders and P01-AR38923 (JU, GR). resulting from alterations in these gap junction proteins. Based on our results, we suggest considering connexin DOI: 10.1111/j.0022-202X.2004.22518.x gene mutations in any patient with a congenital disorder of Manuscript received October 12, 2003; revised December 11, 2003; cornification with or without erythema associated with SNHL accepted for publication December 27, 2003 122 : 5 MAY 2004 GENETIC HETEROGENEITY OF KID SYNDROME 1113

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