LIMB LENGTH ANOMALIES ON PRENATAL ULTRASOUND; A DIAGNOSTIC CLUE FOR CARTILAGE HAIR HYPOPLASIA

Abstract

<h3>Introduction</h3> Cartilage-hair hypoplasia (CHH) is a rare autosomal recessive condition characterized by metaphyseal dysplasia, light colored hypoplastic hair, bone marrow failure and variable immunodeficiency.¹ We present a case of an infant with prenatal limb length anomalies and an abnormal TREC screen who was diagnosed with CHH. <h3>Case Description</h3> A full term African American male, born from a non-consanguineous union, presented after his newborn screen was notable for a TREC copy number of 0. Lymphocyte enumeration showed low T cell counts (CD3 600, CD4 309, CD8 221, CD45 RA 141, CD45 RO 12) with normal B cell and NK cell counts (NK 445, CD19 170), suggestive of a leaky SCID. The patient was started on Bactrim prophylaxis. His PHA was abnormal (35200) but higher than typically seen in leaky SCID. Genetic testing revealed two <i>RMRP</i> pathogenic variants in trans, consistent with diagnosis of CHH. With hindsight, his growth chart was notable for a height < 1%. Prenatal imaging was notable for in utero limb lengths below 5^th percentile at 28 weeks. A limb xray at birth was reported as normal. <h3>Discussion</h3> Cartilage hair hypoplasia is a rare disease with an immunologic phenotype ranging from no immunodeficiency to severe combined immunodeficiency² TREC screening may be useful in detecting cases of CHH with more profound T cell defects. In our patient, a combination of prenatal US and TREC screening was highly suggestive of CHH. This case highlights the importance of reviewing the prenatal course for limb length anomalies as a diagnostic clue in the differential for SCID.