HOMOZYGOUS TERT MUTATION CAUSING HOYERAAL-HREIDARSSON SYNDROME AND COMBINED IMMUNODEFICIENCY RESULTING IN FATAL, MULTI-DRUG RESISTANT CMV DISEASE Irwin AD1, Houldcroft C2, Dokal I3, Vulliamy T3, Uhlig HH4, Whittaker E1, Jones A1, Qasim W1, Breuer J5, Worth AJ1 1
Department of Immunology, Great Ormond Street Hospital for Children, London, 2 Infection, Immunity and Inflammation, University College London, 3Centre for Genomics and Child Health, Blizard Institute, Queen Mary University of London, 4Nuffield Department of Medicine, University of Oxford, 5Division of Infection and Immunity, University College London
Introduction • •
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Genetic analysis
Dyskeratosis congenita (DC) is a disorder of progressive telomere dysfunction characterised by abnormal skin pigmentation, nail dystrophy, oral leukoplakia. Eleven genes have been associated with DC, and heterozygous TERT mutations are associated with a milder, adult onset disease. A more severe form (HoyeraalHreidarsson Syndrome) presents in early life with immunodeficiency, bone marrow failure, microcephaly and cerebellar hypoplasia. We present the case of a 16 month old girl presenting with a severe clinical phenotype resulting in fatal CMV disease in association with a novel homozygous TERT mutation.
Clinical features •
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Chromosomal analysis demonstrated a normal female karyotype, and normal CGH array.
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Next generation sequencing of a targeted Primary Immunodeficiency panel identified two heterozygous sequence variants in DCLRE1C and IL10RB. No second variants were identified.
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Initial analysis of known DC genes TERC, TINF2 and CTC1 was normal. Subsequent sequencing of an extended panel revealed the patient to be homozygous for a novel TERT mutation (c.1382G>T, p.Val461Leu) predicted to be pathological with a Polyphen2 score of 0.997. The mutation was confirmed by Sanger sequencing.
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The patient’s mother was found to be heterozygous for the same mutation and is at risk of developing adult-onset disease.
A 16 month old girl of non-consanguineous Albanian parents presented with features of a severe, combined immunodeficiency, including failure to thrive, chronic diarrhoea, and recurrent respiratory infections. Examination revealed abnormal skin pigmentation and nail dystrophy. The primary acute problem was intestinal failure requiring TPN. Gut histology revealed an extensive CMV enteropathy.
Development of multi-drug resistant CMV disease •
CMV viraemia persisted despite combination antiviral therapy. No resistance mutations were detected in CMV ORFs UL27, UL54 or UL97 until day 112 of treatment.
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Sanger sequencing identified a known mutation in UL54 (D588N) associated with Ganciclovir resistance, but failed to identify multiple low level resistance mutations identified by deep sequencing.
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Maribavir resulted in a rapid increase in the frequency of the T409M mutation in UL97 known to confer cross-resistance to Ganciclovir and Maribavir.
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Resistance mutations evolved rapidly in response to treatment. Clustering of SNVs suggested the presence of parallel virus populations. The loss of multiple mutations in UL97 and UL54, alongside phylogenetic analysis of UL27 consensus sequences confirmed the impression of mixed infection
Figure 1: Histology of the colon (left) revealed oedema and loss of epithelial architecture. An inclusion body was identified on duodenal biopsy (right).
Count (x109/l) White cell count Neutrophils Lymphocytes CD3 CD19 CD16+CD56+ CD3+CD4+ CD3+CD8+ CD3+CD56+
1.92 0.73 0.7 0.67 0 0.01 0.5 0.14 0
%
96.0 0.4 2.0 71.0 20.0 0.5
Result TRECs Vbeta repertoire CD3 stimulation PHA stimulation Chromosome breakage
6644 x106 (low) Normal Normal Impaired Normal
Table 1: Initial immune investigation . The patient presented with absent B and NK cells, but subsequently evolved T cell lymphopenia. TRECs were low, and PHA impaired.
Conclusions
Figure 2: Significant telomere shortening (Image courtesy of Repeat Diagnostics, Vancouver, Canada)
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We present a case of Hoyeraal-Hreidarsson Syndrome presenting as severe combined immunodeficiency with severe enteropathy and fatal CMV disease.
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A novel TERT mutation predicted to be pathogenic was identified. Functional analysis of the gene variant would confirm its impact on telomerase activity.
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CMV viraemia persisted despite combination antiviral therapy, and multiple low-level resistance mutations were observed by deep sequencing.
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Deep sequencing identified mutations earlier and identified mutations not otherwise identified by conventional resistance testing. This approach may identify patients at high risk of treatment failure in whom adjunctive interventions may be necessary.
Correspondence:
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