# Adenosine Deaminase (ADA)-Deficient Severe Combined Immunodeficiency Unmasked by Persistent Lymphopenia and Prolonged Severe SARS-CoV-2 Infection in a Three-Week-Old Neonate

## TL;DR

A three-week-old neonate with a severe and prolonged SARS-CoV-2 infection was diagnosed with ADA-deficient SCID, highlighting the importance of recognizing immunodeficiencies in infants with persistent lymphopenia.

## Contribution

This case report emphasizes the diagnostic value of persistent lymphopenia in identifying ADA-deficient SCID in regions without newborn TREC screening.

## Key findings

- A neonate with prolonged SARS-CoV-2 infection and lymphopenia was diagnosed with ADA-deficient SCID.
- Lymphopenia can serve as a cost-effective screening marker for SCID in regions without TREC newborn screening.
- Early recognition of primary immunodeficiencies is critical to prevent severe infections and complications.

## Abstract

Adenosine deaminase (ADA) deficiency, an autosomal recessive variant, is the second most common form of severe combined immunodeficiency (SCID). We report a unique case of a three-week-old neonate who presented with prolonged and severe SARS-CoV-2 infection associated with persistent lymphopenia, subsequently revealing ADA-deficient SCID. He presented with mild and insidious symptoms, and then his clinical condition rapidly deteriorated. He required ICU admission and mechanical ventilation and developed multiple co-infections including opportunistic pathogens. Flow cytometry and whole exome sequencing diagnosed ADA-deficient SCID.

This case highlights the importance of recognizing primary immunodeficiency disorders in children who consistently display lymphopenia and experience prolonged opportunistic and viral infections. Detecting lymphopenia should prompt consideration of SCID, serving as a straightforward and cost-effective screening approach, particularly in nations such as the United Arab Emirates where T-cell receptor excision circles (TRECs) are not part of newborn screening protocols.