FOXN1 compound heterozygous mutations cause selective thymic hypoplasia in humans
Qiumei Du, … , M. Teresa de la Morena, Nicolai S.C. van Oers
Qiumei Du, … , M. Teresa de la Morena, Nicolai S.C. van Oers
Published September 30, 2019
Citation Information: J Clin Invest. 2019;129(11):4724-4738. https://doi.org/10.1172/JCI127565.
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Research Article Genetics Immunology

FOXN1 compound heterozygous mutations cause selective thymic hypoplasia in humans

Abstract

We report on 2 patients with compound heterozygous mutations in forkhead box N1 (FOXN1), a transcription factor essential for thymic epithelial cell (TEC) differentiation. TECs are critical for T cell development. Both patients had a presentation consistent with T–/loB+NK+ SCID, with normal hair and nails, distinct from the classic nude/SCID phenotype in individuals with autosomal-recessive FOXN1 mutations. To understand the basis of this phenotype and the effects of the mutations on FOXN1, we generated mice using CRISPR-Cas9 technology to genocopy mutations in 1 of the patients. The mice with the Foxn1 compound heterozygous mutations had thymic hypoplasia, causing a T–B+NK+ SCID phenotype, whereas the hair and nails of these mice were normal. Characterization of the functional changes due to the Foxn1 mutations revealed a 5–amino acid segment at the end of the DNA-binding domain essential for the development of TECs but not keratinocytes. The transcriptional activity of this Foxn1 mutant was partly retained, indicating a region that specifies TEC functions. Analysis of an additional 9 FOXN1 mutations identified in multiple unrelated patients revealed distinct functional consequences contingent on the impact of the mutation on the DNA-binding and transactivation domains of FOXN1.

Authors

Qiumei Du, Larry K. Huynh, Fatma Coskun, Erika Molina, Matthew A. King, Prithvi Raj, Shaheen Khan, Igor Dozmorov, Christine M. Seroogy, Christian A. Wysocki, Grace T. Padron, Tyler R. Yates, M. Louise Markert, M. Teresa de la Morena, Nicolai S.C. van Oers

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Figure 2

Human FOXN1 compound heterozygous mutations genocopied in mice cause thymic aplasia with normal fur and nails.

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Human FOXN1 compound heterozygous mutations genocopied in mice cause thy...
(A) The human FOXN1 mutations for Pt. 1 were introduced into the murine genome by CRISPR-Cas9 technology. The DNA repair template used for each allele is shown. Silent mutations were introduced into the murine sequence to facilitate genotyping and to prevent premature stop codons. (B) Images of F2-generation mice: WT Foxn1 (Foxn1WT/WT), homozygous mutant (Foxn1933/933 and Foxn11089/1089), and compound heterozygous (Foxn1933/1089) mice, the latter genocopying Pt. 1. The genocopied mice are indicated in red font. The images are representative of 5 independently characterized mice. (C) The overall sizes of the thymi from the various mouse lines are shown for comparative purposes. (D) Thymus weights and overall thymic cellularity were calculated. Data represent the mean ± SEM. n = 22 Foxn1WT/WT, n = 6 Foxn1933/933, n = 10 Foxn11089/1089, and n = 10 Foxn1933/1089 mice. P values of less than 0.05 were considered significant. For the comparisons shown, a Brown-Forsythe and Welch’s 1-way ANOVA was applied.