IL2RG and cartilage-hair hypoplasia: KREC NBS is noted for its high rate of false positives; however, its distinct sensitivity may be useful in early categorization of SCID diagnoses as subjects with T−B−SCID and Cartilage-hair hypoplasia (CHH) SCID had both abnormal TREC and KREC values while IL2RG-SCID subjects only had abnormal TREC values (32).