Loss of function mutation in LARP7, chaperone of 7SK ncRNA, causes a syndrome of facial dysmorphism, intellectual disability, and primordial dwarfism

Primordial dwarfism (PD) is a clinically and genetically heterogeneous condition. Various molecular mechanisms are known to underlie the disease including impaired mitotic mechanics, abnormal IGF2 expression, perturbed DNA damage response, defective spliceosomal machinery, and abnormal replication licensing. Here, we describe a syndromic form of PD associated with severe intellectual disability and distinct facial features in a large multiplex Saudi family. Analysis reveals a novel underlying mechanism for PD involving depletion of 7SK, an abundant cellular noncoding RNA (ncRNA), due to mutation of its chaperone LARP7. We show that 7SK levels are tightly linked to LARP7 expression across cell lines, and that this chaperone is ubiquitously expressed in the mouse embryo. The 7SK is known to influence the expression of a wide array of genes through its inhibitory effect on the positive transcription elongation factor b (P-TEFb) as well as its competing role in HMGA1-mediated transcriptional regulation. This study documents a critical role played by ncRNA in human development and adds to the growing list of molecular mechanisms that, when perturbed, converge on the PD phenotype.