Human ITCH E3 ubiquitin ligase deficiency causes syndromic multisystem autoimmune disease

Abstract

Ubiquitin ligases play an important role in the regulation of the immune system. Absence of Itch E3 ubiquitin ligase in mice has been shown to cause severe autoimmune disease. Using autozygosity mapping in a large Amish kindred, we identified a linkage region on chromosome 20 and selected candidate genes for screening. We describe, in ten patients, identification of a mutation resulting in truncation of ITCH. These patients represent the first reported human phenotype associated with ITCH deficiency. These patients not only have multisystem autoimmune disease but also display morphologic and developmental abnormalities. This disorder underscores the importance of ITCH ubiquitin ligase in many cellular processes.

Figure 1

Pedigree Demonstrating Autosomal-Recessive Inheritance of Traits from Several Common Ancestors Information obtained from a community genealogy book. Unaffected siblings (both carriers and noncarriers) are not displayed because of space constraints. Of the individuals tested, carriers include the parents of VII-1, the father of VII-3 (no record of testing the mother), the mother and three siblings of VII-4 and VII-5 (no record of testing the father), two brothers of VII-7 and VII-8, and one sister of VI-2.

Figure 2

The Two Index Patients Photos were used with the family's consent.

Figure 3

Histology Showing the Effects of ITCH Deficiency in Multiple Tissues (A) A mid-power view of the liver in a subject with autoimmune hepatitis shows a dense mixed inflammatory infiltrate throughout the periportal region and an accompanying cholangitis and reactive proliferation of bile ducts. (B) Mid-power view of the liver in another subject with autoimmune hepatitis shows a mixed inflammatory cell infiltrate in the periportal region. (C) Lung showing a patchy expansion of the interstitium by lymphocytes and clusters of macrophages in the alveolar airspaces. There is no fibrosis. (D) Higher magnification of the lung exhibiting a mild interstitial lymphocytic infiltrate. The central alveolar airspace contains a collection of macrophages (arrow). (E) Although liver architecture is intact in a subject with normal liver enzymes but hepatomegaly, some multinucleated hepatocytes are present, and periportal hepatocytes contain large Lafora-body-like inclusions (arrow); there is no inflammation. (F) An electron micrograph of the same specimen as in 3E reveals heterogeneous cytoplasmic material (bounded by a dotted line): small droplets of fat and endoplasmic reticulum displace mitochondria eccentrically (inset shows a normal hepatocyte for comparison).

Figure 4

Genetic Mapping and Gene Mutation in ITCH-Deficient Patients (A) Genetic mapping to chromosome 20p11.2-q12. A block of 37 contiguous SNPs on chromosome 20 provided overwhelming evidence for identity-by-descent in five affected Old Order Amish patients. (B) The ITCH sequencing trace; sequencing of the 23 coding exons of ITCH identified a single base-pair insertion in exon 6. Panel 1 shows sequence from a control sample demonstrating normal exon 6 sequence. Panel 2 depicts sequence from an obligate heterozygote showing the single base-pair insertion. Panel 3 illustrates homozygosity for the c.394_395insA mutation (the red A denotes the mutation). (C and D) The imputed effect of the insertion mutation on ITCH translation. The mutation causes a frameshift predicted to misincorporate eight amino acids in the peptide chain and cause a premature termination at codon 140. The truncated ITCH protein lacks the three WW domains as well as the HECT domain that contains the E2 interaction (active) site.