Clinical and Genetic Characteristics of Ectodermal Dysplasia in Four Indian Children.

Introduction: Ectodermal dysplasias (EDs) affect structures derived from the ectoderm such as skin, its appendages, nail, and teeth. In this series, we describe four patients presenting with a clinical phenotype of dysplasia of one or more ectodermal structures who underwent next-generation sequencing for mutational analysis. Case Series: The clinical phenotype of three patients was hypohidrotic ectodermal dysplasia (HED) and one patient was diagnosed with autoimmune polyglandular syndrome (APS) type 1. Two patients with classical clinical features of X-linked HED (XLHED) had mutations in EDA gene; variant c.924+ 8C>G (5' proximal splice site) and c.760C>T (p.Gln254Ter). Case 3 had clinical phenotype of HED with urticaria pigmentosa, which was confirmed on skin biopsy and immunohistochemistry. This patient was found to have mutation in C1orf172; c.449G>A (p.Arg150Gln) which has not been reported previously. Case 4 was diagnosed to have APS type 1 with cutaneous features of discoloration of teeth and chronic mucocutaneous candidiasis. This patient had a compound heterozygous mutation of AIRE gene. The two variants detected were c.169C>T (p.Gln57Ter) and c.47C>T (p.Thr16Met).
Conclusion: The present series highlights the clinic-genetic correlation in four patients with features of ED. Two variants of uncertain significance and two previously unreported variants were also found in this study. Copyright:

Introduction

Ectodermal dysplasias (EDs) are a large and complex group of genodermatoses, which affect ectodermal structures such as the skin and its appendages, but are typically characterized by wide heterogeneity in both genotype and clinical phenotype. The common underlying feature is the development defect of structures derived from the ectoderm. With newer advancing molecular diagnostic methods, the genetic basis of several phenotypic variants has been elucidated.[12] The most common form is the X-linked hypohidrotic ectodermal dysplasia (XLHED) which is characterized by decreased sweat and sebaceous glands, dry skin, sparse hair over scalp and eyebrows, teeth dystrophy. Numerous mutations in the gene EDA (ectodysplasin-A) have been identified as causes of XLHED. Autosomal recessive variants are associated with mutation in ectodysplasin A-receptor (EDAR) and EDAR-associated death domain (EDARADD) genes.[3]

In this series, we describe four patients presenting to our out-patient with clinical features of ED (phenotype of dysplasia of one or more ectodermal structures) who underwent next-generation sequencing (NGS) for mutational analysis.

Case Series

Table 1 details the clinical and genotypic characteristics of the study population [Figures 1-5].

Table 1

Clinical phenotype and details of genetic analysis of the study population

	Proband 1	Proband 2	Proband 3	Proband 4
Age	1 yr	6 months	3 yr	12 yr
Gender	Male	Male	Male	Female
Clinical diagnosis	Hypohidrotic ectodermal dysplasia	Hypohidrotic ectodermal dysplasia	Hypohidrotic ectodermal dysplasia	Autoimmune polyendocrinopathy- candidiasis-ectodermal dystrophy
Hypohidrosis	No	Yes	Yes	No
Intolerance to heat	Yes	Yes	Yes	No
Sparse/brittle hair	Yes	Yes	Yes	No
Teeth	Edentulous	Edentulous	Peg shaped	Dystrophic with yellowish discoloration [Figure 3a]
Nails	Normal	Normal	Normal	Onychomycosis [Figure 3b]
Other findings	Seborrheic Dermatitis, frontal bossing, depressed nasal bridge, Periorbital and perioral wrinkling [Figure 1]	Seborrheic Dermatitis, Periorbital and perioral wrinkling	Cutaneous mastocytosis [Figure 2a]; Darrier sign was positive; confirmed on Skin biopsy [Figure 2b]	Chronic mucocutaneous candidiasis, seizures, Addison’s disease and hypoparathyroidism; Alopecia areata
Family history	No	No	No	No
Consanguinity	No	No	No	No
Neurodevelopmental delay	No	No	No	No
NGS findings
Gene	EDA	EDA	C1orf172	AIRE
Location	Intron 7	Exon 6	Exon 2	Exon 2	Exon 1
Nucleotide change	chrX: g. 69253386C>G	chrX: g. 69250337C>T	chr1:g. 27278423C>T	chr21:g. 45706476C>T	chr21:g. 45705936C>T
Protein change	-	p.Gln254Ter	p.Arg150Gln	p.Gln57Ter	p.Thr16Met
Mutation type	Splice	Nonsense	Missense	Nonsense	Missense
Variant	c. 924 + 8C > G (5’ proximal splice site)	c. 760C>T (p.Gln254Ter)	c. 449G>A (p.Arg150Gln)	c. 169C > T (p.Gln57Ter)	c. 47C>T (p.Thr16Met)
Zygosity	Hemizygous	Hemizygous	Heterozygous	Compound Heterozygous
				Heterozygous	Heterozygous
Inheritance	X-linked recessive	X-linked recessive	Autosomal dominant	Autosomal recessive
OMIM disease	Hypohidrotic ectodermal dysplasia-1	Hypohidrotic ectodermal dysplasia-1	Ectodermal dysplasia 12	Autoimmune polyendocrinopathy syndrome type I
Classification	Variant of Uncertain significance*	Pathogenic	Variant of Uncertain significance	Pathogenic*	Likely Pathogenic

*Previously unreported variant

Figure 1

Proband 1 – XLHED with cutaneous features of sparse hair, periorbital wrinkling, frontal bossing, and depressed nasal bridge

Figure 5

Integrative Genomic Data (IGV) images of the genomic data of the variants in all 4 probands

(a) Proband 3 – Autosomal dominant ectodermal dysplasia – multiple elongated oval brownish macules over the buttocks and trunk. (b) Skin biopsy showing band-like infiltrate by mast cells in the upper dermis (hematoxylin and eosin, ×100)

(a) Proband 4 APS type 1 – dystrophy of teeth with yellowish discoloration. (b) Yellowish discoloration and dystrophy of thumb nail, diagnosed as candidal onychomycosis based on fungal culture

The cells are strongly positive for CD117 (Magnification 20×)

Discussion

The first two infants confirmed to have XLHED had common cutaneous features in the form of sparse scalp and eyebrow hair and periorbital and perioral wrinkling. The complaints of recurrent hyperthermia were also reported in both patients although severity was more in the second child. In Proband 1, the observed variant – c.924+8C> G(5′ proximal splice site) has been previously reported in a child with ED but has not been reported in the 1000 genomes, and ExAC databases.[4] Notably, this child did not have a significant history of recurrent fever and infections but further follow-up is required to understand the effect on the development of teeth. In contrast, in Proband 2, the child had more severe complaints of hyperthermia and reduced sweating. A known pathogenic variant of EDA gene was detected: the presence of a truncated mutation (c.760C>T (p.Gln254Ter)) could possibly explain the severity of the disease.[5] This is in contrast with autosomal dominant ED with immunodeficiency where IκBα point mutations were associated with more severe disease compared with truncation mutants.[6] In an Indian study, Bashayam et al. found that 90% of the cases of HED had mutations in EDA-A1 and EDAR genes.[78] In the cases of XLHED, five of six of the confirmed maternal carriers had mild symptoms. Mothers of both probands 1 and 2 did not have any features of ED.

C1orf172, also known as KDF1 gene (keratinocyte differentiating factor) is involved in the formation of the epidermis and differentiation of the basal cell progeny.[8] Heterozygous mutation in the KDF1 gene on chromosome 1p36 has been reported to be causative for ED 12 (ECTD12). Shamseldin et al.[10] described a third-generation nonconsanguineous family from Saudi Arabia presenting with an autosomal dominant form of HED with involvement of hair, teeth, and nails. Other cutaneous features described were short philtrum, accentuated palmar creases, natal teeth, and keratosis pilaris.[9] Similarly, in the present series, the child (Proband 3) had a previously unreported variant (VUS) with an autosomal dominant inheritance. The pathogenic role of KDF1 gene in ED is still being explored as it is one of the five genes that regulate TP63 gene expression. Another interesting aspect was the association with cutaneous mastocytosis, which has not been previously reported. Whether this was a chance association or whether the two diseases are related by some common pathomechanism is not known. The pigmented macules started appearing at the age of 6 months, which occasionally showed urticarial reaction on rubbing (Darrier sign positive) but were otherwise asymptomatic. The child responded well to nonsedating oral anti-histamines (syrup levocetirizine 2.5 mg/day).

Autoimmune polyglandular syndrome (APS) type 1 is a rare autosomal in which patients have two out of the three major manifestations – Addison's disease, hypoparathyroidism, and chronic mucocutaneous candidiasis. Among the other cutaneous manifestations' ectodermal dystrophy, alopecia and vitiligo may also be seen. The disease presents in early childhood but tissue-specific manifestations may continue to appear through adulthood as well.[1011] Around 115 mutations of the AIRE gene have been described to cause APS.[12] These are mostly frameshift or nonsense mutations that lead to truncation of protein sequences. Because of the complex structure of the AIRE gene, different mutations are associated with variable phenotypic manifestations. Because of the absence of strong genotype–phenotype correlation, it is thought that factors other than AIRE gene mutation, such as environmental and immunological factors may play a role in disease pathogenesis.[10] In a cohort from India, the most common mutation detected in AIRE gene was p.C322fsX372.[13] The median age of onset was reported to be 3.5 years and the most common initial manifestation was chronic mucocutaneous candidiasis.[12] We noted a compound heterozygous mutation in our patient (proband 4). The first variant was previously unreported and the second variant was a heterozygous missense variant in exon 1 of the AIRE gene that results in the amino acid substitution of methionine for threonine at codon 16, which lies in the homogenously staining region domain of the AIRE protein.

Conclusions

The present series provides an interesting peek into the genotype–phenotype correlation in a small cohort of Indian patients with ED. Although XLHED may show variation in clinical severity depending on the type of mutation, rarely KDF1 gene involvement, and rare associations such as cutaneous mastocytosis may be seen. The present series also found two variants of uncertain significance and two previously unreported variants were also found in this study.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.