General information
The SALSA MLPA Probemix P073 IKBKG is a research use only (RUO) assay for the detection of deletions or duplications in in the chromosome Xq28 region, including IKBKG, which is associated with Incontinentia Pigmenti (IP). Due to the high sequence homology, this assay cannot discriminate copy number status between IKBKG and its pseudogene, and the presence of e.g. the common IKBKGexon4_10del mutation always requires confirmation.
IP (OMIM #308300), or Bloch-Sulzberger Syndrome, is an X-linked dominant disorder that is primarily characterized by skin lesions. Initial clinical manifestations start at birth with a vesiculobullous eruption (Stage I), followed by a verrucous stage (Stage II), a hyperpigmentation stage (Stage III), and finally a hypopigmentation stage (Stage IV) usually continuing throughout life. Other characteristics include ocular abnormalities, central nervous system abnormalities, and teeth defects. IP is easy to diagnose when the classical features are present after birth. However, the diagnosis can be difficult in patients with partial or non-classical clinical features. The IKBKG gene is the only known gene associated with IP. The absence of a functional IKBKG gene is lethal. Therefore, as an X-linked disorder, IP occurs primarily in females. However, male patients with a 47,XXY karyotype or somatic mosaicism have been described.
The majority of patients (>65%) harbour a 11.7 kb deletion, which is generated by a recombination event between two repeats (MER67B) located in intron 3 and about 6 kb downstream of IKBKG exon 10. This results in the removal of IKBKG exon 4 to 10 (“IKBKGexon4_10del”). Additionally, other large deletions of different sizes (including parts of neighbouring genes) and single nucleotide substitutions and insertions have been reported (Conte et al., 2014). Notably, over 60% of IP patients are sporadic carrying a de novo IKBKG mutation.
Duplication of (part of) the IKBKG gene or deletion of the pseudogene IKBKGP1 are common polymorphisms throughout populations with a frequency of 1-2% and do not result in any clinical phenotype. About 10% of IP parents carry one of these common polymorphisms, making them important risk factors for IP in offspring (Fusco et al., 2009). More information is available at http://www.ncbi.nlm.nih.gov/books/NBK1472/ and https://www.omim.org/entry/308300.
Apart from IP, the IKBKG gene is also involved in X-linked hypohidrotic ectodermal dysplasia and immunodeficiency (HED-ID), which is also known as anhidrotic ectodermal dysplasia with immunodeficiency (EDA-ID; http://ghr.nlm.nih.gov/condition/anhidrotic-ectodermal-dysplasia-with-immune-deficiency), and HED-ID with osteopetrosis and lymphedema (OL-HED-ID; http://ghr.nlm.nih.gov/condition/osteopetrosis).
This SALSA MLPA probemix is not CE/FDA registered for use in diagnostic procedures. Purchase of this product includes a limited license for research purposes.

Probemix content
The SALSA MLPA Probemix P073-A1 IKBKG contains 38 MLPA probes with amplification products between 136 and 436 nucleotides (nt). This includes 13 probes for the IKBKG gene. Ten of these probes also detect sequences in IKBKGP1, hence these probes detect four copies in most healthy female individuals. The probemix further contains seven probes upstream of the IKBKG coding sequence, including six probes for the G6PD gene. Also, nine probes downstream of the IKBKG gene are included, of which four are located in the duplicated region, and therefore detect four copies in most healthy female individuals, and two of which are telomeric of IKBKGP1. In addition, nine reference probes are included that detect locations on the X-chromosome. Complete probe sequences and the identity of the genes detected by the reference probes are available online (www.mrcholland.com).
This probemix contains nine quality control fragments generating amplification products between 64 and 105 nt: four DNA Quantity fragments (Q-fragments), two DNA Denaturation fragments (D-fragments), one Benchmark fragment, and one chromosome X and one chromosome Y-specific fragment. More information on how to interpret observations on these control fragments can be found in the MLPA General Protocol and online at www.mrcholland.com.