Swaroop Aradhya

Genomic rearrangement in NEMO impairs NF-κB activation and is a cause of incontinentia pigmenti: The International Incontinentia Pigmenti (IP) Consortium

Familial incontinentia pigmenti (IP; MIM 308310) is a genodermatosis that segregates as an X-linked dominant disorder and is usually lethal prenatally in males. In affected females it causes highly variable abnormalities of the skin, hair, nails, teeth, eyes and central nervous system. The prominent skin signs occur in four classic cutaneous stages: perinatal inflammatory vesicles, verrucous patches, a distinctive pattern of hyperpigmentation and dermal scarring1. Cells expressing the mutated X chromosome are eliminated selectively around the time of birth, so females with IP exhibit extremely skewed X-inactivation2. The reasons for cell death in females and in utero lethality in males are unknown. The locus for IP has been linked genetically to the factor VIII gene in Xq28 (ref. 3). The gene for NEMO (NF-κB essential modulator)/IKKγ (IκB kinase-γ) has been mapped to a position 200 kilobases proximal to the factor VIII locus4. NEMO is required for the activation of the transcription factor NF-κB and is therefore central to many immune, inflammatory and apoptotic pathways5,6,7,8,9. Here we show that most cases of IP are due to mutations of this locus and that a new genomic rearrangement accounts for 80% of new mutations. As a consequence, NF-κB activation is defective in IP cells.Familial incontinentia pigmenti (IP; MIM 308310) is a genodermatosis that segregates as an X-linked dominant disorder and is usually lethal prenatally in males. In affected females it causes highly variable abnormalities of the skin, hair, nails, teeth, eyes and central nervous system. The prominent skin signs occur in four classic cutaneous stages: perinatal inflammatory vesicles, verrucous patches, a distinctive pattern of hyperpigmentation and dermal scarring. Cells expressing the mutated X chromosome are eliminated selectively around the time of birth, so females with IP exhibit extremely skewed X-inactivation. The reasons for cell death in females and in utero lethality in males are unknown. The locus for IP has been linked genetically to the factor VIII gene in Xq28 (ref. 3). The gene for NEMO (NF-κB essential modulator)/IKKγ (IκB kinase-γ) has been mapped to a position 200 kilobases proximal to the factor VIII locus. NEMO is required for the activation of the transcription factor NF-κB and is therefore central to many immune, inflammatory and apoptotic pathways. Here we show that most cases of IP are due to mutations of this locus and that a new genomic rearrangement accounts for 80% of new mutations. As a consequence, NF-κB activation is defective in IP cells.

Atypical Forms of Incontinentia Pigmenti in Male Individuals Result from Mutations of a Cytosine Tract in Exon 10 of NEMO (IKK-γ)

Familial incontinentia pigmenti (IP [MIM 308310]), or Bloch-Sulzberger syndrome, is an X-linked dominant and male-lethal disorder. We recently demonstrated that mutations in NEMO (IKK-gamma), which encodes a critical component of the NF-kappaB signaling pathway, were responsible for IP. Virtually all mutations eliminate the production of NEMO, causing the typical skewing of X inactivation in female individuals and lethality in male individuals, possibly through enhanced sensitivity to apoptosis. Most mutations also give rise to classic signs of IP, but, in this report, we describe two mutations in families with atypical phenotypes. Remarkably, each family included a male individual with unusual signs, including postnatal survival and either immune dysfunction or hematopoietic disturbance. We found two duplication mutations in these families, at a cytosine tract in exon 10 of NEMO, both of which remove the zinc (Zn) finger at the C-terminus of the protein. Two deletion mutations were also identified in the same tract in additional families. However, only the duplication mutations allowed male individuals to survive, and affected female individuals with duplication mutations demonstrated random or slight skewing of X inactivation. Similarly, NF-kappaB activation was diminished in the presence of duplication mutations and was completely absent in cells with deletion mutations. These results strongly indicate that male individuals can also suffer from IP caused by NEMO mutations, and we therefore urge a reevaluation of the diagnostic criteria.

Validation studies of SNRPN methylation as a diagnostic test for Prader-Willi syndrome

Prader-Willi syndrome (PWS) is caused by absence of a paternal contribution of the chromosome region 15q11-q13, resulting from paternal deletions, maternal uniparental disomy, or rare imprinting mutations. Laboratory diagnosis is currently performed using fluorescence in situ hybridization (FISH), DNA polymorphism (microsatellite) analysis, or DNA methylation analysis at locus PW71 (D15S63). We examined another parent-of-origin-specific DNA methylation assay at exon alpha of the small nuclear ribonucleoprotein-associated polypeptide N gene (SNRPN) in patients referred with clinical suspicion of PWS or Angelman syndrome (AS). These included 30 PWS and 17 AS patients with known deletion or uniparental disomy status, and a larger cohort of patients (n = 512) suspected of PWS who had been analyzed previously for their methylation status at the PW71 locus. Results of SNRPN methylation were consistent with known deletion or uniparental disomy (UPD) status as determined by other molecular methods in all 47 cases of PWS and AS. In the larger cohort of possible PWS patients, SNRPN results were consistent with clinical diagnosis by examination and with PW71 methylation results in all cases. These data provide support for the use of SNRPN methylation as a diagnostic method. Because methylation analysis can detect all three major classes of genetic defects associated with PWS (deletion, UPD, or imprinting mutations), methylation analysis with either PW71 or SNRPN is an efficient primary screening test to rule out a diagnosis of PWS. Only patients with an abnormal methylation result require further diagnostic investigation by FISH or DNA polymorphism analysis to distinguish among the three classes for accurate genetic counseling and recurrence-risk assessment.

NF-κB signaling and human disease

Despite substantial progress in understanding the NF-kappaB signaling pathway, the connections between this pathway and human disease are only now being elucidated. Genes that function within or upstream of the NF-kappaB pathway have been found to cause four distinct disorders and two allelic conditions. Investigation of these genes and disorders has brought significant insight into the role of NF-kappaB in various aspects of physiological development.