1. The Genetics of Ichthyosis Sherri J. Bale, PhD, FACMG Clinical Director, GeneDx FIRST Family Conference Orlando, FL - June 27, 2010

2. What we’re going to talk about A primer on how ichthyosis genetically occurs, the chances of passing it along and what genetic tests are available and how they are administered

3. How many different ichthyoses are there? > 20 disorders fit the definition of ichthyosis > 20 disorders fit the definition of ichthyosis > 10 other related disorders with more localized scaling/hyperkeratosis > 10 other related disorders with more localized scaling/hyperkeratosis

4. How are ichthyoses classified? Clinical features Clinical features Non-syndromic ichthyoses Non-syndromic ichthyoses Syndromic ichthyoses Syndromic ichthyoses Related disorders Related disorders Inheritance pattern Inheritance pattern Gene defects Gene defects Etiology Etiology Enzyme deficiencies Enzyme deficiencies Structural protein defects Structural protein defects Regulatory protein defects Regulatory protein defects Other Other

5. Genetics 101 Chromosomes – structures inside the nucleus (command center) of the cell. Chromosomes – structures inside the nucleus (command center) of the cell. On the chromosomes, we carry genes On the chromosomes, we carry genes Genes are made up of a chemical called DNA Genes are made up of a chemical called DNA Chromosomes, and thus genes, are passed from parent to child following “rules of inheritance” [Mendel’s laws ] Chromosomes, and thus genes, are passed from parent to child following “rules of inheritance” [Mendel’s laws ]

6. Genetics 101

7. Human Chromosomes

8. Types of Inheritance X-linked X-linked Recessive Recessive Dominant (rare) Dominant (rare) Autosomal Autosomal Recessive Recessive Dominant Dominant

9. Steroid-Sulfatase Deficiency X-linked recessive X-linked recessive Incidence 1:6000 males Incidence 1:6000 males Primary features Primary features Onset between 1 and 3 weeks of age Onset between 1 and 3 weeks of age Dark scale, tightly adherent Dark scale, tightly adherent Most prominent on flexure surfaces Most prominent on flexure surfaces (aka “Dirty neck” ichthyosis) (aka “Dirty neck” ichthyosis) Asymptomatic corneal opacities (10-50%) Asymptomatic corneal opacities (10-50%) Cryptorchism (12-25%), increased risk of testicular cancer Cryptorchism (12-25%), increased risk of testicular cancer The disease does not improve with age The disease does not improve with age

10. Diagnostic  plasma cholesterol sulfate levels Assay to directly measure activity of steroid sulfatase is rarely done Decreased placental sulfatase causes delayed onset/progression of labor in affected male fetuses Genetics STS gene on chromosome Xp22.32 90% of affected males have large intragenic deletions, or contiguous gene deletions Steroid-Sulfatase Deficiency

13. IchthyosisGene Epidermolytic hyperkeratosis KRT1; KRT10 Epidermolysis Bullosa Siemens KRT2e Pachyonychia congenita I,II KRT6a,b, KRT16, KRT17 Epidermolytic PPK KRT9 Non-epidermolytic PPK many genes Keratitis-Ichth-Deafness (KID)GJB2 (GJB6) Erythrokeratoderma variabilis GJB3, GJB4 Autosomal Dominant Ichthyoses

14. Epidermolytic Hyperkeratosis Autosomal Dominant Autosomal Dominant (1/2 the cases are due to new mutations) (1/2 the cases are due to new mutations) Incidence 1:200,000-1:300,000 Incidence 1:200,000-1:300,000 Primary Features Primary Features Neonatal blistering, erosions and denuded skin Neonatal blistering, erosions and denuded skin Progressive Hyperkeratosis, esp. of the flexures Progressive Hyperkeratosis, esp. of the flexures Variable palm/sole involvement Variable palm/sole involvement

15. Genetics Due to mutation in keratin-1 (KRT1) or keratin- 10 (KRT10) gene >40 different mutations, most are missense changes >80% cluster at hot spots at the beginning or end of the gene In 30% of all EHK patients mutations occur at Arg156 in KRT10 Epidermolytic Hyperkeratosis

18. ? How can you say its autosomal dominant? I’m the only person in my family with this disorder!

19. Germline Mutation Mutation Ovaries Testes Sperm Egg cell Mutation

20. Germline Mutation Mutation Conception Disease

21. ? I have a been diagnosed with an ‘Epidermal Nevus’. What is it and how does it come about?

22. Gametes Zygote Two cell lineages Cell Migration Mosaic Post-zygotic mutation Mutation ‘Epidermal Nevus’ = Skin Mosaicism for Mutation

23. Mosaicism Due to DNA Mutation that occurs during mitosis of a single cell at early stages of fetal development “post-zygotic mutation” All descendent cells will carry the mutation, other cells are normal Gives rise to two (or more) genetically distinct cell lines derived from a single zygote Mosaicism can affect somatic and/or germline tissues Generally only parts of the organism are affected

24. I have an ‘Epidermal Nevus’. Should I be worried about my children? If germline is affected, mutation can be transmitted to the offspring resulting in full-blown disease ?

25. What is my risk of having an affected child? Greater than the population risk for a new mutation Depends on what percentage of germ cells harbor mutation Rule of thumb: Small nevus-- small risk Large nevus on both sides of the body-- high risk ?

26. Ichthyosis Gene Harlequin ichthyosis ABCA12 Lamellar ichthyosis TGM1, ABCA12 CIE ALOXE3; ALOX12B Ichthyin Cytochrome P450 Sjögren-Larsson syndrome ALDH3A2 Neutral lipid storage disease CGI-58 (ABHD5) Netherton syndrome SPINK5 Refsum disease PAHX, PEX7 Trichothiodystrophy+Ichthyosis ERCC2; ERCC3 Autosomal Recessive Ichthyoses

29. Lamellar Ichthyosis Autosomal Recessive Autosomal Recessive Incidence 1:200,000 Incidence 1:200,000 Primary Features: Primary Features: Collodion baby phenotype Collodion baby phenotype Plate-like, large, dark scale Plate-like, large, dark scale Ectropion, Eclabium Ectropion, Eclabium Scarring alopecia Scarring alopecia

30. Lamellar Ichthyosis Due to mutation in the TGM1 gene in the vast majority of cases, coding for Transglutaminase-1 Due to mutation in the TGM1 gene in the vast majority of cases, coding for Transglutaminase-1 A few common mutations exist (the “German” splice-site mutation) and R141 and R142 in exon 3. A few common mutations exist (the “German” splice-site mutation) and R141 and R142 in exon 3. Few families with mutation in ABCA12, Ichthyin, and cytochrome P450 genes Few families with mutation in ABCA12, Ichthyin, and cytochrome P450 genes

31. Congenital Ichthyosiform Erythroderma Autosomal Recessive Autosomal Recessive Incidence 1:200,000-300,000 Incidence 1:200,000-300,000 Primary features Primary features Collodion baby presentation Collodion baby presentation Bright red (erythrodermic) skin Bright red (erythrodermic) skin Fine, white scale Fine, white scale

32. Due to mutation in many different genes, 5 of which are known Due to mutation in many different genes, 5 of which are known ALOX12B and ALOXE3 (in about ~10%) ALOX12B and ALOXE3 (in about ~10%) Ichthyin (in about ~10%) Ichthyin (in about ~10%) A new cytochrome P450 gene A new cytochrome P450 gene Enzymes encoded by these genes are involved in lipid metabolism Enzymes encoded by these genes are involved in lipid metabolism Operate in common membrane arachidonic acid pathway (lipoxygenase) Operate in common membrane arachidonic acid pathway (lipoxygenase) Congenital Ichthyosiform Erythroderma

33. Harlequin Ichthyosis Autosomal recessive Autosomal recessive Mutation in ABCA12 gene Mutation in ABCA12 gene (ATP-binding cassette transporter protein) (ATP-binding cassette transporter protein) Primary features: Primary features: Thick, armor-like plates of scale that fissure and crack Thick, armor-like plates of scale that fissure and crack Eclabium and Ectropion Eclabium and Ectropion Poor prognosis, although survivors have a congenital ichthyosiform erythroderma phenotype Poor prognosis, although survivors have a congenital ichthyosiform erythroderma phenotype

34. So what is a mutation, anyway?

35. How do we detect a mutation? Chromosomes DNA Metabolic Karyotype Karyotype arrayCGH arrayCGH FISH FISH Sequence analysis Sequence analysis Mutation scanning Mutation scanning Targeted mutation Targeted mutation analysis analysis Analytes Analytes Enzyme assay Enzyme assay

36. What do we need for mutation testing? Material required for testing: Material required for testing: Buccal swabs Buccal swabs Blood Blood Skin punch biopsy Skin punch biopsy

37. How is DNA Sequencing Done? Gly278Arg

38. What is the use of this mutation information ? Identification of disease-causing mutation(s) allows answers to the questions: Identification of disease-causing mutation(s) allows answers to the questions: What do I have? What do I have? Why do I have it or how did it happen? Why do I have it or how did it happen? What is the chance it will happen again? What is the chance it will happen again? What’s wrong with my skin and how best can it be treated? What’s wrong with my skin and how best can it be treated?