Gracile bones, periostal appositions, hypomineralization of the cranial vault, and mental retardation in brothers: Milder variant of osteocraniostenosis or new syndrome?

Clinical and Molecular Diagnosis of Osteocraniostenosis in Fetuses and Newborns: Prenatal Ultrasound, Clinical, Radiological and Pathological Features

Osteocraniostenosis (OCS, OMIM #602361) is a severe, usually lethal condition characterized by gracile bones with thin diaphyses, a cloverleaf-shaped skull and splenic hypo/aplasia. The condition is caused by heterozygous mutations in the FAM111A gene and is allelic to the non-lethal, dominant disorder Kenny‐Caffey syndrome (KCS, OMIM #127000). Here we report two new cases of OCS, including one with a detailed pathological examination. We review the main diagnostic signs of OCS both before and after birth based on our observations and on the literature. We then review the current knowledge on the mutational spectrum of FAM111A associated with either OCS or KCS, including three novel variants, both from one of the OCS fetuses described here, and from further cases diagnosed at our centers. This report refines the previous knowledge on OCS and expands the mutational spectrum that results in either OCS or KCS.

Report of a novel variant in the FAM111A gene in a fetus with multiple anomalies including gracile bones, hypoplastic spleen, and hypomineralized skull

Kenny-Caffey syndrome type 2 (KCS2) and osteocraniostenosis (OCS) are allelic disorders caused by heterozygous pathogenic variants in the FAM111A gene. Both conditions are characterized by gracile bones, characteristic facial features, hypomineralized skull with delayed closure of fontanelles and hypoparathyroidism. OCS and KCS2 are often referred to as FAM111A-related syndromes as a group; although OCS presents with a more severe, perinatal lethal phenotype. We report a novel FAM111A mutation in a fetus with poorly ossified skull, proportionate long extremities with thin diaphysis, and hypoplastic spleen consistent with FAM111A-related syndromes. Trio whole exome sequencing identified a p.Y562S de novo missense variant in the FAM111A gene. The variant shows significant similarity to other reported pathogenic mutations fitting proposed pathophysiologic mechanism which provide sufficient evidence for classification as likely pathogenic. Our report contributed a novel variant to the handful of OCS and KCS2 cases reported with pathogenic variants.

Osteocraniostenosis-hypomineralized skull with gracile long bones and splenic hypoplasia. Four new cases with distinctive chondro-osseous morphology

Osteocraniostenosis is a severe skeletal dysplasia characterized by a hypomineralized skull that has been previously described as kleeblattschädel (cloverleaf skull) and overtubulated long bones. Dysmorphic facial features include a short nose, short philtrum, and a small, inverted V-shaped mouth. Splenic a/hypoplasia is a constant finding. We report four infants (two unrelated and two siblings) with osteocraniostenosis and describe the clinical, radiographic and chondro-osseous morphology findings. The two siblings lack the moderate long-bone shortening that is typically seen. The skull configuration is likely caused by severely hypoplastic cranial bones (parietal) rather than true craniosynostosis, making the term "osteocraniostenosis" misleading. Histological examination of bone in all cases showed an abnormal growth plate with short irregular columns. The resting cartilage showed pleomorphic chondrocytes with increased cellularity and unique pseudocolumn formation. There are some radiographic and chondro-osseous morphologic similarities between osteocraniostenosis and severe Hallermann-Streiff syndrome (HSS), suggesting the two disorders may be pathogenetically related.