Genetics and Molecular diagnosis of Genodermatosis Dr. Majid Kheirollahi Associate professor of Medical Genetics ISFAHAN UNIVERSITY OF MEDICAL SCIENCES

Clinical Diagnosis of Genodermatoses and How Molecular Diagnosis Helps molecular diagnosis helps to: differentiate confirm the diagnosis A condition may have a wide clinical spectrum (allelic heterogeneity) and at the same time defects in many different genes can have very similar appearance (locus heterogeneity).

Comparison of incidence and mutation types of epidermolysis bullosa genes from HGMD database ( http://hgmd.org )

Chalenges in diagnosis of Genodermatoses Phenocopy Late Onset and Low Penetrance Mitochondrial Inheritance Pigmentary Mosaicism and Chimerism

Methods in Molecular Diagnosis of Some Genodermatoses Molecular diagnosis for genodermatoses is usually straightforward Many database of genodermatosis and other inherited diseases The Human Gene Mutation Database ( http://hgmd.org ) GeneTests ( http://www.ncbi.nlm.nih.gov/sites/GeneTests/ ) Online Mendelian Inheritance In Man ( http://www.ncbi.nlm.nih.gov/omim )

Providing of information These web sites provide invaluable information about: the genes Diseases Mutations diagnostic clinical and research laboratories that provide genetic testings and other pertinent data for scientists and clinicians interested in the field and are regularly updated.

Neurofibromatosis

Neurofibromatosis Relatively common, 1 in 3000 Autosomal dominant There are two types: NF-1 (85% of all cases) VON RECKLINGHAUSEN DISEASE a gene located on chromosomal segment 17q11.2 NF-2 known as MISSME syndrome - multiple inherited schwannomas, meningiomas, and ependymomas

NF-1 NF-1 is a microdeletion syndrome by a mutation of a gene located on chromosomal segment 17q11.2 encodes a protein known as neurofibromin (plays a role in cell signaling) a negative regulator of the Ras oncogene signal transduction pathway stimulates the GTPase activity of Ras

mutation types in neurofibromatosis Different mutation types are found in neurofibromatosis patients, with the frequent categories including small deletions missense/nonsense Splicing small insertions and gross deletions 90% of mutations are small changes detectable by molecular genetic techniques.

Comparison of incidence and mutation types of NF1 gene from HGMD database ( http://hgmd.org )

NF-1 up to 50% of NF-1 cases arise due to spontaneous mutation spontaneous change in the genes during pregnancy The neurofibromin gene found to be 350,000 base pairs in length a 50% percent chance of passing the disorder on to their kids

NF-2 type of mutations include inactivating mutations in the NF2 gene located at 22q12.2 type of mutations include protein-truncating alterations (frameshift deletions/insertions and nonsense mutations) splice-site mutations missense mutations and others

NF-2 mutations Deletions in the NH2-terminal domain of merlin proteins associated with early tumor onset and poor prognosis in people with NF II Protein truncating mutations correlate with more severe phenotype one-half of cases are inherited, and one-half are the result of new, de novo mutations

Ichthyosis Ichthyosis is a family of rare genetic skin disorders characterized by dry, thickened, scaly skin mode of inheritance autosomal dominant autosomal recessive X-linked

Genetic simple ichthyoses Ichthyosis vulgaris (IV) is the most common type of ichthyosis with an estimated prevalence of 1 in 250 to 400 individuals.

Genetic disease with ichthyosis Non-genetic ichthyosis: Ichthyosis acquisita

Epidermolysis bullosa Epidermolysis bullosa (EB) is a group of genetic conditions result in easy blistering of the skin and mucous membranes due to a mutation in at least one of 18 different genes Some types are autosomal dominant others are autosomal recessive

Classification Epidermolysis bullosa simplex Junctional epidermolysis bullosa Dystrophic epidermolysis bullosa epidermolysis bullosa, lethal acantholytic Epidermolysis bullosa acquisita

Epidermolysis bullosa simplex is typically inherited in an autosomal dominant manner affecting the keratin genes KRT5 and KRT14 is a failure in keratinization affects the integrity and the ability of the skin to resist mechanical stresses

Junctional epidermolysis bullosa is an inherited disease affecting laminin and collagen is inherited in an autosomal recessive manner Less than one person per million people is estimated to have this form of epidemolysis bullosa

Dystrophic epidermolysis bullosa is an inherited variant affecting the skin and other organs is caused by mutations within the human COL7A1 gene encoding the protein type VII collagen autosomal dominant or autosomal recessive Epidermis bullosa pruriginosa and Albopapuloid epidermolysis bullosa (Pasini's disease) are rare subtypes of this disease

Dystrophic epidermolysis bullosa

Tuberous sclerosis is a genetic disorder with an autosomal dominant pattern of inheritance variable expressivity, and incomplete penetrance Two-thirds of TSC cases result from sporadic genetic mutations, not inheritance So far, it has been mapped to two genetic loci, TSC1 and TSC2

Tuberous sclerosis TSC1 encodes for the protein hamartin, is located on chromosome 9 q34 TSC2 encodes for the protein tuberin, is located on chromosome 16 p13.3 TSC2 is contiguous with PKD1, the gene involved in one form of polycystic kidney disease (PKD)

Tuberous sclerosis Estimates of the proportion of TSC caused by TSC2 range from 55% to 90% TSC1 and TSC2 are both tumor suppressor genes that function according to Knudson's "two hit" hypothesis That is, a second random mutation must occur before a tumor can develop This explains why, despite its high penetrance, TSC has wide expressivity

TS mutations Gross deletions affecting both genes may account for the 2% of individuals with TSC who also develop polycystic kidney disease in childhood TSC2 has been associated with a more severe form of TSC However, the difference is subtle and cannot be used to identify the mutation clinically

Lab Methods PCR/Sanger Sequencinf Deletion/Duplication Analysis MLPA Next-Gen Sequencing

PCR and Sanger sequencing

MLPA

Whole exome sequencing (NGS)

Diagnosis Prenatal testing and prenatal expectations Prenatal testing in vitro fertilisation, via preimplantation genetic diagnosis Chorionic villus sampling amniocentesis