Genetic Screening for Filaggrin Mutation in Atopic Dermatitis and Ichthyosis Vulgaris in the African American Population

• Heterozygous for Filaggrin (FLG) Null Mutations [ Time Frame: 1 month ]
  Buccal swab samples were obtained from each subject. Deoxyribonucleic acid (DNA) was purified from buccal swabs (IsoHelix Swabs, BocaScientific, Boca Raton, FL) and quantified by ultraviolet spectrophotometry. Purified genomic DNA and controls were amplified by polymerase chain reaction (PCR) from three different regions of FLG exon 3 with three primer sets. PCR products were analyzed by electrophoresis, purified (Qiaquick, Qiagen, Valencia, CA), and subjected to duplicate cycle sequencing reactions using ABI BigDye v3.1 reagents (Applied Biosystems, Carlsbad, CA). Labeled sequencing products were purified for capillary electrophoresis (ABI3730 or ABI3130 sequencer with POP7 polymer), and sequence results were examined using ABI SeqScape software. All nucleotide changes were noted, including 30 single nucleotide polymorphism (SNPs) in the population tested, the most common of which were coding changes at T454A, H2507Q, and G2545R, and silent change at nucleotide t2508c.
  
  

Genetic screening and molecular dermatology allow physicians and scientists to screen populations who manifest a specific genetic disorder of skin, hair or nails and to study animal models for experiment-induced dermatopathology, diseases, and treatments. The purpose of such screening is to identify the gene(s) involved in eliciting the phenotypic characteristics that we as clinicians identify for diagnosis and treatment of said disease(s).

The field of genetics in dermatology has progressed immensely in the last 20 years and has strongly influenced the practice of dermatology. Most known single gene disorders, such as epidermoloysis bullosa, have been mapped to a particular chromosomal region and in many cases, the causative genes have been identified. However, more common diseases that are polygenic in origin such as atopic dermatitis remain a challenge to decipher. In addition, there still remain several monogenic disorders in which the underlying genetic basis is unclear.

In some cases, genetic analysis can be performed by sequencing entire genes or gene regions, or screening for specific common mutations. In the Japanese and some of the European populations, several researchers have been able to find an association between people with atopic dermatitis and ichythosis vulgaris and the filaggrin gene. Atopic dermatitis, or ezcema, is a common, chronic, relapsing and remitting problem in many children and affects 10-20% of the pediatric population. Atopic dermatitis is often called the itch that rashes, since itch is a predominant feature of this disease and is quite disruptive to daily activities of life. In addition to itch, it is characterized by markedly dry skin, small red bumps that may have fluid. Though treatments are available to help the rash resolve and to help with itch, this disease will continue to appear when treatments are stopped and often become infected.

Ichythosis vulgaris is quite prevalent, an estimated 1 in 250 persons are affected. It is characterized by extremely dry, scaly skin with a fine white scale and increased amounts of lines noted on the palms. Ichythosis vulgaris is thought to happen due to a combination of excess production of one of the layers of the skin and abnormal skin shedding.

Filaggrin is a protein that is essential for the skin to function properly as a barrier. It was initially thought to be one of the genes responsible for causing atopic dermatitis in 2006 after it was identified as the causal mutation in ichthyosis vulgaris. This association has been extensively studied in the European population and to a lesser extent in the Japanese population; however, has not been looked at in the African American population These new insights may help lead to future targeted therapy for these two extraordinarily common skin disorders.

General clinical applications of methods for diagnosis may include histological tissue examination, laboratory-based specimen analysis, and physical examination. However, although useful, all of these methods are limited to the identification of the phenotypic expression of the genetic abnormality. Conversely, genetic screening of tissue (collected via buccal swabs) enables the clinician and scientist to have access to a more finite method of diagnosis, treatment, and prevention options. Such methods of testing are particularly appealing for use in disorders in which the exact basis of the disease is unknown, as is the case of atopic dermatitis and ichythosis vulgaris in the African American population. Thus, genetic screening in the field of dermatology remains an important research agenda and is the focus of this proposal. This study allows for the collection of genetic material from patients seen in the dermatology clinic at Ann & Robert H Lurie Children's Hospital of Chicago.