Date Published: January 5, 2019
Publisher: BioMed Central
Author(s): Che Kang Lim, Hassan Abolhassani, Sofia K. Appelberg, Mikael Sundin, Lennart Hammarström.
Atypical X-linked severe combined immunodeficiency (X-SCID) is a variant of cellular immunodeficiency due to hypomorphic mutations in the interleukin 2 receptor gamma (IL2RG) gene. Due to a leaky clinical phenotype, diagnosis and appropriate treatment are challenging in these patients.
We report a 16-year-old patient with a Tlow B+ NK+ cellular immunodeficiency due to a novel nonsense mutation in exon 8 (p.R328X) of the IL2RG gene. Functional impairment of the IL2RG was confirmed by IL2-Janus kinase 3-signal transducer and activator of transcription signaling pathway investigation. In addition, the characteristics of the mutations previously described in 39 patients with an atypical phenotype were reviewed and analyzed from the literature.
This is the first report of an atypical X-SCID phenotype due to an exon 8 mutation in the IL2RG gene. The variability in the phenotypic spectrum of classic X-SCID associated gene highlights the necessity of multi-disciplinary cooperation vigilance for a more accurate diagnostic workup.
The online version of this article (10.1186/s13223-018-0317-y) contains supplementary material, which is available to authorized users.
Interleukin 2 receptor gamma (IL2RG) is an important signaling component for IL2, IL4, IL7, IL9, IL15, and IL21 . The gene encodes a common gamma chain (γC) that is essential in the ontogeny and function of immune cells, in particular T and NK cells. Mutations in the gene result in X-linked severe combined immunodeficiency (X-SCID) .
The patient, a 16 years old male of Kurdish ethnicity, was admitted to the pediatric lung and allergy service of Astrid Lindgren Children’s Hospital at Karolinska University Hospital due to chronic airway hypersensitivity and recurrent sinopulmonary infections. He is the third child of consanguineous parents with a family history of several early deaths due to lung failure on the maternal side (Fig. 1). He had a normal vaccination history but a medical history of four hospitalizations due to enteroviral infection (at age 16 months presenting with skin rash and diarrhea), chronic cough and fever (at age 18 months due to Moraxella catarrhalis), otitis media, adenopathy and shingles (leading to tympanostomy at the age of 2), pneumonia and an asthmatic reaction (at the age of 6).Fig. 1a Family pedigree of the patient(s). b Sanger sequencing
Approximately 10% of the reported IL2RG mutations have been associated with atypical phenotypic variants (including Tlow/− B+ NK+ and Tlow/− Blow NK+/low/−, Table 1). The majority of the atypical patients present a “milder” form of immunodeficiency. Database summary shows that nearly half of the total IL2RG mutations are located in exon 5 (29.4%) and exon 3 (19.9%). Mutations in exon 5, which encodes the extracellular domain including the highly conserved WSXWS motif: a region essential for proper protein folding and thereby efficient intracellular transport as well as extracellular receptor binding, are expected to disrupt the γC configuration. Likewise, a similar clinically severe effect is predicted when the mutations occur in exon 3, which will modify the amino acids directly or close to the four conserved cysteine residues.