A report of novel STIM1 deficiency and 6 year follow up of two previous cases associated with mild immunological phenotype Laura Rice1*, Claire Stockdale2*, Ian Berry3, Sean O’Riordan4, Karen Pysden5, Rashida Anwar1, Roger Rushambuza6, Moira Blyth3, Sonal Srikanth7, Yousang Gwack7, Yasser M. El-Sherbiny8,9,10 Clive Carter2, Sinisa Savic2,10 1 Leeds Institute of Biomedical and Clinical Sciences, University of Leeds, Wellcome Trust Brenner Building, St James’s University Hospital, Beckett Street, Leeds, UK 2 Department of Clinical Immunology and Allergy, St James’s University Hospital, Beckett Street, Leeds, UK 3 Yorkshire Regional Genetics Service, Chapel Alleron Hospital, Leeds, UK 4 Department of Paediatric Immunology, Leeds General Infirmary, Leeds, UK 5 Department of Paediatric Neurology, Leeds General Infirmary, Leeds, UK 6 Department of Radiology, Calderdale and Huddersfield NHS Foundation Trust, UK 7 Department of Physiology, David Geffen School of Medicine, UCLA, Los Angeles, CA 90095, USA 8 Department of Biosciences, School of Science and Technology, Nottingham Trent University, Nottingham, UK. 9 Clinical Pathology Department, Faculty of Medicine, Mansoura University, Egypt. 10 National Institute for Health Research—Leeds Biomedical Research Centre and Leeds Institute of Rheumatic and Musculoskeletal Medicine (LIRMM), Wellcome Trust Brenner Building, St James’s University Hospital, Beckett Street, Leeds, UK * Equal contribution Correspondence to: Dr Sinisa Savic, [email protected] To the Editor, Loss of function or null mutations of Stromal interaction molecule 1 (STIM1) are known to cause early-onset combined immunodeficiency (CID) disease with recurrent and chronic infections, autoimmunity, haemolytic anaemia, ectodermal dysplasia, muscular weakness and myalgia (1). STIM1 and ORAI1 form the calcium release-activated calcium (CRAC) channels and are involved in calcium signalling, which is especially important in T cells for activation, proliferation and cytokine production (2). ORAI1 forms the pore in the plasma membrane and STIM1 is a calcium sensor protein that activates the ORAI1 when the endoplasmic reticulum (ER) Ca2+ stores are depleted. STIM1-deficient patients have impaired T cells and NK cell function, but usually a normal distribution of the major immune cell types, including T cells, B cells and natural killer (NK) cells with the T cell repertoire that is normally comparable to healthy individuals (3). STIM1 deficiency results in no store-operated calcium entry (SOCE) in T cells and as a result the patient’s cells cannot respond appropriately to T cell receptor (TCR) activation or pharmacological agents such as ionomycin, thapsigargin (TG), which typically trigger Ca2+ influx (1). Recently a new biological role for STIM1 has been identified. STIM1 was found to act as a negative regulator for STimulator of INterferon Genes (STING). STIM1 was shown to inhibit STING trafficking by physically interacting with STING and retaining it at the ER membrane. This interaction is important in maintaining STING in an inactive state (4). Several STING mutations which have previously shown to cause an autoinflammatory condition named STING-associated vasculopathy with onset in infancy (SAVI), appear to exert their dominant effects by weakening the interaction between STIM1 and STING (4). Here we describe a 5-year-old boy of consanguineous Pakistani background with overlapping clinical features of CID and autoinflammatory disorder. The boy was initially referred to pediatric immunology services with a history of recurrent sinopulmonary infections. The patient was born at full term by normal vaginal delivery following a normal pregnancy. An inguinal hernia was noted when six days old and was repaired the same day. He initially fed well. At six months of age it was noted that he was quieter and delayed in his development. He sat at 18 months and walked at 3 years and crawls upstairs using his head as support. Currently, at 5 years he is alert and engaging but has speech delay putting 2-3 words together. He can scribble and draw circles. He was fully toilet-trained at 3 years. He is in mainstream education but requires additional support. When examined at 5 years, he weighed 11.5kg (-5SD), with a height of 94.2cm (-4SD) and head circumference of 46.1cm (-4SD). He is slim, with reduced proximal upper limb muscle bulk and globally in his lower limbs, lordosis and is hypermobile across all his joints. He has proximal weakness leading to a waddling gait, and uses a Gowers manoeuvre to stand. He has no facial weakness, no opthalmoparesis but has fixed dilated pupils. The patient infection history included recurrent sinopulmonary infections with one episode of pneumonia requiring hospital admission and intravenous antibiotics. He had received all his primary vaccinations, including MMR, without significant complications. He was hospitalized for a complicated primary varicella zoster infection due to bacterial suprainfection requiring antibiotic treatment. In addition, he had several hospitalizations with suspected infections, but despite having documented fevers, no apparent infective cause was found and on several occasions, he recovered without receiving antibiotics. A full dental clearance was performed due to recurrent tooth infections and tooth enamel deficiency. Other characteristics include, ichthyosis, anhidrosis and low zinc levels [7.8 mol/l (reference range 10.3-18.1)]. Although he was described to have severe eczema his skin eruptions mainly affected the palms, soles of the feet and cheeks, (cold exposed areas), and would start with blistering sterile pustular psoriasiform rash, eventually resulting in skin desquamation. Zinc replacement did not lead to improvement, and there was minimal benefit from application of topical steroid. The patient also had pronounced nail dystrophy (Figure 1). There was no history of Raynaud’s phenomena. He has two other siblings who are fit and healthy. The pedigree is shown in Figure 2A. The initial investigations including full blood count, creatinine kinase, screen for inherited metabolic diseases and MRI scan of the head were all normal. The immunological work up showed essentially normal numbers of T, B and NK cells. More detailed phenotyping revealed, detectable regulatory T cells and unremarkable memory B cell profile. Immunoglobulin profile (IgG, IgA, IgM and IgG subclasses) was normal with marginally elevated total IgE. The levels of specific antibodies to tetanus and Haemophilus influenzae type b (Hib) were adequate and showing a good response to previous vaccination. Interestingly, the total anti-pneumococcal antibody levels were reduced, however, following a challenge vaccination with pneumovax, the levels increased well above the protective titre (from 6.2 to 120.7 g/ml) Considering some of the clinical features, diagnosis of STIM1 or ORAI1 deficiency was suspected. The parents consented for genetic testing. A modified exome sequencing approach was performed using Agilent SureSelectXT with All Exon v5 capture library and sequenced on Illumina HiSeq 3000 for 2x150-bp paired- end sequencing. Genetic testing identified a homozygous deletion in STIM1 NM_003156.3:c.478del, p.(Ser160ValfsTer15), and a homozygous CANT1 mutation NM_001159772.1:c.676G>A, p.(Val226Met) (Figure 2A). This known pathogenic CANT1 mutation has previously been described in multiple patients with “Kim- variant” Desbuquois dysplasia, usually in compound heterozygosity with another mutation (5,6). These patients have normal hands on clinical examination but advanced carpal age, elongated phalanges and short metacarpals on radiological examination. Only one patient reported to have “Kim-variant” Desbuquois dysplasia was homozygous for the CANT1 c.676G>A mutation but little phenotypic information is provided (5,6). The same homozygous mutation has also been described in a single patient with autosomal recessive multiple epiphyseal dysplasia (7). That patient did not have many of the features of “Kim-variant” Desbuquois dysplasia but had developed the degenerative arthrosis of the hands and spine by the age of 25 years. The novel single nucleotide deletion at c.478 in STIM1 results in a frameshift such that translation terminates prematurely within the sterile alpha motif (SAM), the region regulating stability within STIM proteins. The truncated polypeptide of 173 amino acids (wild type STIM1 polypeptide has several splice variants, one of which is 791 amino acids, another form is 685) lacks important functional domains of STIM1, including the transmembrane region and the CRAC activation domain (CAD). We used western blot to investigate the expression of STIM1 in the patient’s (P1) PBMCs, and failed to detect either the full length or the truncated variant of STIM1 (Figure 1B). The functional impact of these mutations was investigated further. Regarding the STIM1 variant we performed flow cytometry T receptor spectraphenotyping and showed essentially normal TCR repertoire (Figure 1 Suppl). A single Vb region (Vb7.2) was missing from patient’s T cells, however the clinical significance of this is unknown. Proliferative responses to Phytohaemagglutinin (PHA) were adequate (although reduced at high concentrations) and the response to anti-CD3 was preserved (Figure 2A Suppl). There was significantly reduced upregulation of CD25 following anti-CD3 in-vitro stimulation whilst upregulation of HLA-DR and CD69 was normal (Figure2B suppl). Measurement of store-operated Ca2+ entry in patient T cells revealed a complete