ØIncontinentia pigmenti incontinentia_pigmenti3_1a Incontinentia_pigmenti diagnosis: Incontinentia Pigmenti localisation: fingernail diagnosis: Incontinentia Pigmenti ni06 •X-linked genodermatosis, associated with mutations in the NEMO gene (NFkB essential modulator, Xq28) •Affects almost exclusively females (males die in utero before the second trimester) •Highly variable in clinical manifestations but always associated with skin defects •Incontinentia pigmenti (IP) •- characterized by four distinct dermatological stages that begin within 2 weeks after birth with blisters and inflammatory response (Stage I/Vesicular Stage, Fig. 1). Subsequently, verrucous hyperkeratotic lesions develop (Stage II/Verrucous Stage, Fig. 2) and disappear over time, leaving areas of hyperpigmentation due to melanin accumulation (Stage III/Hyperpigmented Stage, Fig. 3). These areas generally disappear by the second decade, but adults may still show areas of dermal scarring. •Fig. 1 •Fig. 2 •Fig. 3 •Incontinentia pigmenti (IP) •Every IP patient exhibits skin abnormalities, blindness and central nervous system anomalies are occurring in about 40% and 30% of patients, resp. •Eye manifestations in IP patients (retinal detachment and consequent blindness) ← deficient vascularization of retina. •CNS manifestations in IP patients (ischemia, atrophy, seizures, paralysis, mental retardation) ← deficient vascularization of brain. •In addition to the dermal, visual and brain defects, IP patients exhibit some less medically significant problems, including hair loss (alopecia); conical, peg-shaped or absent teeth (anodontia), and nail dystrophy. Retina localisation: fingernail diagnosis: Incontinentia Pigmenti •Incontinentia pigmenti (IP) •Genomic rearrangement of NEMO •Xq28, the NEMO gene. •IP rearrangement - excision of the region between two MER67B repeats located upstream of exon 4 and downstream of exon 10. •G Courtois, Cell Death and Differentiation (2006) Figure 2: Multiplex PCR products in IP patients and controls. Presence of 1045 bp band indicates the presence of the common rearrangement in IP patients only. 733 bp product serves as internal amplification control. Lane 1: ΦX174 DNA/ (HaeIII digested) DNA marker; Lane 2: Mother of case 2; Lane 3: Father of case 2; Lane 4: Case 2, Positive for deletion; Lane 5: Case 3, Positive for deletion; Lane 6: Mother of case 3; Lane 7: Father of case 3; Lane 8 & 9: Normal control (As this is a representative picture and the cases were analyzed at different times, the mothers of other cases are not shown). •Multiplex PCR products in IP patients and controls. Presence of 1045 bp band indicates the presence of the common rearrangement in IP patients. 733 bp product serves as internal amplification control. •Incontinentia pigmenti (IP), NEMO •Resting cells: NFkB is kept inactive in cytoplasm through interaction with IkB inhibitory molecules. •In response to multiple stimuli (cytokines, ....) IkBs are phosphorylated, ubiquitinated, and destructed via the proteasome. As a consequence, NFkB enters the nucleus and activates transcription of genes participating in immune and inflammatory response, and protection against apoptosis. •The kinase that phosphorylates IkB, IKK (IkB kinase), is a high-molecular-weight complex. It contains two catalytic subunits and one regulatory subunit (NEMO). •DL Nelson, Current Opinion in Genetics & Development 2006 •NEMO, NFkB •XCI (the transcriptional silencing of one X chromosome in females) is the means for attainment of gene dosage parity between XX female and XY male. •Two steps of XCI: initiation and maintenance. •The initiation phase - the chromosome X undergoes specific epigenetic modifications. •The maintenance phase - replicated copies of the inactive X-chromosome are maintained inactive through multiple rounds of cell division. Epigenetic mechanisms •X chromosome inactivation (XCI) •A model illustrating the XCI process starting with the regulated expression of Xist (X-inactive specific transcript, red) from the X inactivation centre (Xic). Subsequently, Xist RNA coats the entire chromosome in cis thus facilitating gene silencing through the recruitment of repressive factors (polycomb repressor proteins, specific histone variants, CpG island methylation of promoter regions, …) that modify the chromatin structure. These multiple modifications ensure the stabilization and maintenance of the inactive state throughout subsequent mitotic divisions. •A Tattermusch, Hum Genet (2011) •X chromosome inactivation (XCI) Co-evolution of X-chromosome inactivation and imprinting in mammals •Red rectangles - X chromosome of maternal origin (M), blue rectangles - X chromosome of paternal origin (P). The active and inactive X chromosomes are indicated by Xa and Xi, respectively. The zygote (a) – both X chromosomes are potentially active. The blastocyt (b) – inactivation of imprinted paternal X chromosome is established (red crosses). The placenta and other extra-embryonic tissues (c) – inactivation of imprinted paternal X chromosome is maintained. The embryonic tissues (d) – inactivation of imprinted paternal X chromosome is erased and random X-chromosome inactivation is then established (e) and maintained throughout adult life. •X chromosome inactivation (XCI) •IP patients present at birth with mosaic skin composed of cells expressing either wild-type or mutated NEMO. •In response to some signals mutated cells start to produce cytokines such as IL-1 (a well-known stress-response molecule of epidermis). •This, in turn, appears to induce the release of TNFa by wild-type cells, which acts back by inducing hyperproliferation and inflammation of wild-type cells and apoptosis of mutated cells. •The whole process results in elimination of the mutated cells and, consequently, disappearance over time of the skin lesions. •In this model, the mutated cells initiating the process indirectly responsible for their own elimination. •Incontinentia pigmenti (IP) •G Courtois, Cell Death and Differentiation (2006) •IP manifests typically as a male-lethal disorder, whereas most female patients survive because of selective elimination of cells expressing the mutant X chromosome. •Some tissues undergo this selection early in development and are therefore spared any apparent phenotype at the time of birth (leukocytes and hepatocytes). •Epidermis undergo this selection within 2 weeks after birth causing IP associated dermatosis. •Incontinentia pigmenti (IP) •G Courtois, Cell Death and Differentiation (2006) •IP is an X-linked, dominant genodermatosis usually fatal in utero in males. •The three mechanisms for survival of IP males are hypomorphic alleles; the 47, XXY karyotype (Klinefelter syndrome); and somatic mosaicism. •IP in male •A male patient is reported. A nonsense variant, c.937C>T (p.Gln313*) in NEMO was identified at level of 15% in blood taken at 10 days of age, but was undetectable in a sample taken at 3 years most likely due to selective apoptosis of mutant cells. Samples taken from the patient when he was 5 years of age identified the mutation at low level in hair roots and urine but not in blood or buccal cells. The detection of the mutation in different cells indicates a de novo event at an early stage of embryogenesis (somatic mosaicism). •D: photograph of lower limbs age 2 weeks demonstrating widespread vesicularrash; e: photograph of left hand age 6 months demonstrating verrucous lesions; f: photograph of left knee age 6 months with subtle hypopigmented streaks; g: photograph of right groin age 8 months with hyperpigmented streak. •S. Hull, Am J Med Genet Part A. 167A:1601–1604 •Clinical features (a) Blaschkoid distribution of hyperpigmentation with hyperkeratotic plaques, with some pallor and atrophy, affecting the abdomen in the father. (b) Similar Blaschko-linear changes are evident on his right leg. (c) Lower limbs of his daughter showing Blaschko-linear vesicles and early verrucous inflammatory plaques. •PCR identifies the intragenic deletion of NEMO in the DNA samples from the affected skin of the father and the dauther’s blood, but not from the father’s blood. Only a very faint band was detected in the DNA from the father’s unaffected skin. •For these specific PCR conditions, the upper 1045-bp band indicates the presence of the deletion, whereas •the 733-bp band is wild-type. •IP in father and his dauther E. Rashidghamat, British Journal of Dermatology (2016) •C, control DNA; MW, molecular weight ladder. •The detection of the mutation in different cells indicates a de novo event at an early stage of embryogenesis (somatic mosaicism) that unexpectedly also affected the gonads and has hence been transmitted to his daughter as a germline abnormality. •In 1993, Coleman et al. described a female infant that had hemophilia caused by inheritance of a maternally contributed IP mutation and a paternally contributed mutation in factor VIII. •Her two sisters had normal clotting despite inheriting the same paternal X-chromosome. •In the proband’s case, the presence of the IP mutation unmasked the hemophilia mutation by X inactivation selection. This case is a favorite one for teaching principles of X inactivation and X-linked disease. •IP, hemophilia •Inheritance of IP