Clinical manifestations associated with novel mutations in the coiled-coil domain of STAT1

Signal transducer and activator of transcription 1 (STAT1) plays a central role in signaling responses to a wide variety of cytokines including interferon (IFN)-α, -β, and -γ. Transcription 1 (STAT1) plays a central role in signaling response. Cytoplasmic STAT1 is activated by tyrosine phosphorylation, mostly by the Janus family of kinases (JAK), resulting in translocation to the nucleus and binding to specific DNA sequences (O'Shea et al. 2013).

Mutations in STAT1 have been reported in several phenotypically different immunodeficiencies such as the Mendelian susceptibility to mycobacterial diseases with susceptibility to mycobacteria as well as viral and fungal diseases (Boisson-Dupuis et al. 2012). The complete form of STAT1 deficiency is fatal in early life (Dupuis et al. 2003). Autosomal dominant gain of function mutations in the coiled-coil domain of STAT1 were recently reported, and they were associated with the clinical phenotype of chronic mucocutaneous candidiasis (CMCC), autoimmune phenomena, and central nervous system vascular events (Liu et al. 2011; van de Veerdonk et al. 2011). We recently reported an association between heterozygous STAT1 mutations, which are caused by STAT1 loss of function defects, with a phenotype of progressive severe combined immunodeficiency manifested by a decline in T and B lymphocyte numbers and function (Sharfe et al. 2014). These mutations are found in the DNA binding domain and in close proximity to that area.

We present a group of patients with novel mutations in the coiled-coil domain. These patients show severe central nervous system vascular morbidity, autoimmune manifestations, and recurrent sinopulmonary infections and autoimmunity in some patients.

All of the patients were found to have heterozygous mutations in STAT1 within the coiled domain. There were 4 new mutations in these patients (Figures 3 and 4).

Case 1 had a C to T transition at position 863, which translates into a T to I substitution at amino acid position 288. Another mutation (T288A) in this location has been previously reported (Liu et al. 2011).

Cases 2 and 3 had a C to G transition at position 820, which predicts an R to G substitution at position 274. The R274Q mutation was previously reported in this location (Liu et al. 2011).

Cases 4 and 5 had an A to C transition at position 506 predicting an E to A amino acid substitution.

Cases 6–9 (a father and 3 children) were found to have a G to A transition at the position 799, which predicts an A to T amino acid substitution at 267. A different mutation, A267V, was previously reported at the same location (Liu et al. 2011; van de Veerdonk et al. 2011).

Analysis of the sections from a brain biopsy of the case 2 patient showed several abnormalities in cerebral cortex and white matter. The pia-arachnoid showed focal dense collagenous thickening often centered around medium-sized arteries whose walls were thickened and largely acellular. Other vessels of the same size contained abundant plump fibroblasts and lymphocytes within the thickened intima and media. Interruption of the elastic lamina could occasionally be identified. Many small arteries within the cortex had thickened walls and a narrow cuff of lymphoctyes. Obliterated blood vessel lumens were rarely seen. Alongside a single pia artery were rare giant cells with several nuclei each. The cerebral cortex showed a scattered increase in the number of microglial cells and had a single microglial nodule with vague degenerative material in the center. No neurofibrillary tangles, ischemic neurons, or neuronal inclusions were seen.

In the white matter there was diffuse chronic reactive astrogliosis and several foci of demyelination with plump, reactive astroglia. The axons were relatively preserved in these foci.

Stains for fungi, acid-fast bacilli, and treponemas were unremarkable.

Electron microscopy was negative for viral inclusion bodies.

The MRI imaging demonstrated multiple infarctions involving the right basal ganglia extending to the subinsular cortex, left basal ganglia, left watershed region, and left cerebellum.

There were 2 focal areas of increased signal in the posteromedial region of the right cerebellar hemisphere measuring 1–2 cm each. There was considerable tortuosity to the basilar artery. There was a crescentic area of increased signal seen within the right lateral edge of the basilar artery, likely representing a thrombus. This study confirmed multiple infarcts and atrophy.

The characterizing features of the patients presented here with heterozygous STAT1 mutations are severe CMCC from early childhood and cerebrovascular abnormalities in the second decade of life that led to occlusive disease, hypothyroidism, malignant transformation of the skin, and in 2 patients there were recurrent sinupulmonary infections without significant detectable reduction in B- or T-cell functions.

The mutation of STAT1 in these patients resided in the coiled-coil domain, a region previously reported in the literature to harbor several mutations, all with gain of function as demonstrated in an Epstein–Barr virus cell line (Liu et al. 2011). The coiled-coil domain plays a role in STAT dimerization and later on in nuclear dephosphorylation (Chen et al. 1998; Levy and Darnell 2002). These mutations in the coiled-coil domain of STAT1 result in reduced production of IL17, IL22, and INF. Reduced production of IL17, IL22, and INF in the coiled-coil domain of STAT1 results in several gain of function mutations (Marodi et al. 2012).

In a recent study (Sharfe et al. 2014), we described a cohort of patients showing severe progressive combined immunodeficiency with some patients succumbing to disease in early adulthood or late childhood; all patients had de novo mutations in the DNA binding domain or near this area of STAT1. Our study of STAT1 activity revealed a clear loss of function (Sharfe et al. 2014). The current group of patients carry mutations in the coiled-coil domain with features resembling a previously described group of patients (Liu et al. 2011; van de Veerdonk et al. 2011) showing at least 2 generations with similar symptoms and genetic defects in an autosomal dominant inheritance fashion. This suggests either a slightly less severe effect on STAT1 activity or a different pathogenic mechanism in these 2 groups that share the hallmark of chronic candidiasis. Although they do not show significant immune compromise and fatal viral infections, the mutations in the coiled-coil domain still carry potential risk for serious morbidity. Some of the patients suffered from vascular events of the central nervous system that left them handicapped. The imaging of the central nervous system of 2 cases showed images typical of Moya–Moya disease. Vascular events occurring in early age in CMCC patients was reported first by Grouhi et al. (1998) and more recently by Liu et al. (2011). From our pathologic investigation of brain lesion sections, it appears that these are foci of ischemia that are secondary to primary vasculitis. Autoimmunity, although not varied in these patients, could be a result of a disruption of regulatory mechanisms or constant inflammation and exposure to self-antigens. The exact mechanism underlying these vascular events is yet to be elucidated.

Two of the patients showed recurrent infections, this could be due to a contribution from other genetic defects or a background attenuating disease severity. Although no major immunologic defects were found in the immune system workup, it may be that some minor functional defects contribute to this propensity.

Two patients in our group and several in Liu et al. (2011) had thyroid disease. In Park et al. (2000), it appeared that thyrotropin induced the SOCS1 protein (suppressor of cytokine signaling 1) and that this molecule affects STAT1 phosphorylation. As suggested by Park et al. (2000), it is possible that defects in STAT1 will alter thyrotropin action in the thyroid gland and lead to destruction or dysfunction of the gland.

One of our patients died of squamous cell carcinoma; from previous reports it appears that squamous cell carcinoma is prevalent in CMCC patients with STAT1 mutations (Liu et al. 2011; van de Veerdonk et al. 2011). The very same neoplastic disease was described in patients with chronic candidiasis such as those with autoimmune polyendocrinopathy–candidiasis–ectodermal dystrophy and autoimmune regulator deficiency (Perheentupa 2006; Rautemaa et al. 2007). Therefore, it is less likely that this is a direct result of STAT1 dysfunction but, rather, a compromise of immune mechanisms, such as Th17 antifungal activity, and a lack of suppression of Candida growth. Candida albicans is known to possess catalytic activity resulting in the production of nitrosamines, products that are carcinogenic and considered to be a significant risk factor for squamous cell carcinoma (Hsia 1981; Krogh 1990); therefore, it is very likely that malignant transformation occurs as a result of uncontrolled Candida proliferation and its products.

We present new mutations in the coiled-coil domain of STAT1 that are clinically different from our previously reported group of patients with mutations in the DNA binding domain (Sharfe et al. 2014). These patients appeared to have 2 severe manifestations, central nervous system vasculitis and squamous cell carcinoma; it is possible that at least the latter could be avoided by rigorous treatment with antifungals. Follow-up of these patients’ skin and mucosa conditions and vigorous treatment are crucial and life saving.