Expanding OBSL1 Mutation Phenotype: Disproportionate Short Stature, Barrel Chest, Thoracic Kyphoscoliosis,...

We present a Pakistani kinship afflicted with a syndrome with features including short stature, reduced sitting height, orofacial symptoms including prominent forehead and thick eyebrows, short and broad thorax, and variable features such as long philtrum, short broad neck, barrel chest, thoracic kyphoscoliosis, hypogonadism, and hypospadias. Phenotypic variation even within different sibships was considerable. The unique combination of the phenotypic characteristics prompted us to determine the shared homozygosity regions in patient genomes and the pathogenic variants by next generation technologies like single nucleotide polymorphism (SNP) genotyping and whole exome sequencing (WES). Through these analyses, we detected homozygous OBSL1 c.848delG (p.Gly283AlafsTer54) as the causal variant. Biallelic variants in OBSL1 are known to cause Three M Syndrome 2 (3M2), a rare disorder of growth retardation with characteristic facial dysmorphism and musculoskeletal abnormalities. Affected members of the family do not have the 3M2 hallmark features of dolichocephaly, hypoplastic midface, anteverted nares, low nasal bridge, pectus excavatum, sacral hyperlordosis, spina bifida occulta, anterior wedging of thoracic vertebrae, prominent heels, and prominent talus. Moreover, they have some variable features not typical for the syndrome such as round face, disproportionate short stature, barrel chest, thoracic kyphoscoliosis, hypogonadism, and hypospadias. Our study facilitated genetic diagnosis in the family, expanded the clinical phenotype for 3M2, and unraveled the considerable clinical variation within the same kinship. We conclude that unbiased molecular analyses such as WES should be more integrated into healthcare, particularly in populations with high parental consanguinity, given the potential of such analyses to facilitate diagnosis.