Neonatal erythroderma and immunodysplasia: Overlap of cartilage-hair hypoplasia and Omenn syndrome

Cartilage hair hypoplasia (CHH) syndrome (OMIM #250250) is a rare autosomal recessive metaphyseal dysplasia, characterized by disproportionate short stature, hypotrichosis and variable extra-skeletal manifestations, including immunodeficiency, anemia, intestinal diseases, and predisposition to malignancies. CHH results from homozygous or compound heterozygous mutations in the RMRP gene on chromosome 9p13, which encodes an untranslated RNA component of mitochondrial RNA-processing endoribonuclease. RMRP pathogenic variants can also lead to Omenn Syndrome (OS) (OMIM #603554), a systemic inflammatory condition displaying neonatal erythroderma and immunodeficiency. This report highlights the genotypic and phenotypic overlap between CHH and OS, by presenting a newborn with skeletal dysplasia, immunodeficiency and neonatal onset erythroderma, carrying the homozygous NR₀03051: n. 35C > A variant in the RMRP gene.