A homozygous missense variant in PTPN2 with early-onset Crohn's disease, growth failure and dysmorphic features in an infant: a case report

Crohn's disease (CD) is a chronic idiopathic inflammatory bowel condition that can affect any part of the gastrointestinal tract. Several hundred candidate loci or genes including PTPN2 have been reportedly associated with CD. A whole-exome sequencing (WES) was conducted in a 9-year-old Lebanese girl with a CD onset at 13 months and in both her asymptomatic parents. The analysis detected an extremely rare homozygous variant in PTPN2: c.359C>T, p.(Ser120Leu) in the patient, while both her parents were heterozygous. This variant, located in the protein tyrosine phosphatase (PTP) domain within a highly conserved amino acid, is classified as VUS according to the American College of Medical Genetics (ACMG) criteria. To evaluate the hypothetical functional consequences of the identified variant, a quantitative expression analysis of PTPN2 was performed in blood tissues of the patient, her parents, and two healthy controls. PTPN2 expression was not noted in the patient compared to her parents and the normal controls, suggesting a functional PTPN2 impairment caused by c.359C>T. This variant c.359C>T, p.(Ser120Leu) in PTPN2 has never been previously described in the literature. Our report suggests an association of PTPN2: c.359C>T with early-onset CD.