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Ectodermal Dysplasias

 Ectodermal Dysplasias



Overview

The ectodermal dysplasias (EDs) are a heterogeneous group of nearly 100 inherited disorders characterized by anomalies in at least two of the structures derived from the embryonic ectoderm, with at least one involving the skin appendages (hair, nails, sweat glands) or teeth. Other tissues derived from the primitive ectoderm that can be involved in EDs include the mammary glands, adrenal medulla, central nervous system, inner ear, retina, optic lens, pigment cells and branchial arch cartilages. Advances in molecular genetics and developmental biology have led to the identification of the causative genes and developmental pathways in at least 80 of the EDs.

Symptoms

Each of the nearly 100 EDs has its own set of clinical signs and symptoms. Commonly, the conditions will have one or more of the following associated findings:

Teeth: reduced number, abnormal shape or size

Hair: abnormal structure, sparse, slow-growing, often light-colored

Sweat glands: often reduced number and abnormal structure, leading to decreased sweat production and risk of elevated body temperature (hyperthermia)

Nails: toenails and fingernails can be absent, thin, thick, grooved

Cleft lip and/or palate, particularly in the TP63-related disorders

Limbs: split hand/foot, oligodactyly, syndactyly, digital duplication

Skin: spotty hypoplasia with fat herniation, severe skin erosions, pigmentary abnormalities, etc

Eyes: dry eye, corneal erosions/opacification, eyelid fusion, micropthalmia

Genitourinary system:  hydroureter, hydronephrosis, renal agenesis, micropenis, cryptorchidism, hypospadias

Growth failure (height and/or weight)

Causes

The molecular causes of these diverse conditions involve many genes and multiple developmental pathways that are necessary for normal formation, structure and function of the ectodermal derivatives. This classification scheme does not include all disorders that affect two or more ectodermal derivatives. Genetic alterations of ED-associated genes that affect only one derivative of the ectoderm would be considered non-syndromic traits of the causative gene. Conditions already included as part of other classifications or groups of diseases (vesiculobullous disorders, palmoplantar keratodermas, etc.) are not included in the ED classification. Complex syndromes that have ED signs, but also major non-ED signs, such as trisomy 21, are also excluded from the ED classification scheme.

The genetic causes of greater than 50% of the ED’s have been determined. The classification scheme clusters the disorders based on genotype, molecular pathway and physical characteristics (phenotype). Categories are:

EDA/NF KappaB Pathway

WNT Pathway

TP63 Pathway

Structure Group (Proteins important for the structure or function of the cell)

Other/Unknown

Conditions that meet the definition of ED but of unknown cause are grouped with other EDs that share the most similar phenotype. Once their genetic cause is identified, they can be classified with the appropriate category or become the anchor of a new cluster, depending on molecular etiology.

The reference listed below from Wright, et al provides a full listing of know ED conditions.

Affected populations

ED’s have been reported from essentially all races, ethnic groups and geographic regions.

Standard Therapies

Treatment depends upon the specific disease manifestations in the affected individual, and is largely aimed at minimizing symptoms. For most of the ED’s, multidisciplinary management is required, with involvement of primary care physicians, geneticists, dermatologists, multiple dental specialists, nutritionists, speech therapists, otolaryngologists, ophthalmologists, orthopedic surgeons and/or plastic surgeons.

Type of Doctor Department : A dermatologist, geneticist, dentist, and potentially a plastic surgeon or speech therapist

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