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

2. 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).

3. Comparison of incidence and mutation types of epidermolysis bullosa genes from HGMD database ( )

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

5. 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 ( )
GeneTests ( )
Online Mendelian Inheritance In Man ( )

6. 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.

7. Neurofibromatosis

8. 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

9. 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

10. 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.

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

12. 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

13. 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

14. 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

15. 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

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

17. Genetic disease with ichthyosis
Non-genetic ichthyosis: Ichthyosis acquisita

18. 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

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

20. 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

21. 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

22. 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

23. Dystrophic epidermolysis bullosa

25. 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

26. 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)

27. 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

28. 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

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

30. PCR and Sanger sequencing

31. MLPA

32. Whole exome sequencing (NGS)

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