Quantitative hypermorphic FAM111A alleles cause autosomal recessive Kenny-Caffey syndrome type 2 and osteocraniostenosis

• Text
• PDF

Abstract

Kenny-Caffey syndrome (KCS) is a rare genetic disorder characterized by extreme short stature, cortical thickening and medullary stenosis of tubular bones, facial dysmorphism, abnormal T cell function, and hypoparathyroidism. Biallelic loss-of-function variants in TBCE cause autosomal recessive type 1 KCS (KCS1). By contrast, heterozygous missense variants in a restricted region of the FAM111A gene have been identified in autosomal dominant type 2 KCS (KCS2) and a more severe lethal phenotype, osteocraniostenosis (OCS); these variants have recently been shown to confer a gain of function. In this study, we describe 2 unrelated children with KCS and OCS who were homozygous for different FAM111A variant alleles that result in replacement of the same residue, Tyr414 (c.1241A>G, p.Y414C and c.1240T>A, p.Y414N), in the mature FAM111A protein. Their heterozygous relatives are asymptomatic. Functional studies of recombinant FAM111AY414C demonstrated normal dimerization and a mild gain-of-function effect. This study provides evidence that both biallelic and monoallelic variants of FAM111A with varying degrees of activation can lead to dominant or recessive KCS2 and OCS.

Authors

Dong Li, Niels Mailand, Emma Ewing, Saskia Hoffmann, Richard C. Caswell, Lewis Pang, Jacqueline Eason, Ying Dou, Kathleen E. Sullivan, Hakon Hakonarson, Michael A. Levine