Abstract
Osteogenesis imperfecta (OI) is a skeletal dyscrasia characterized by decreased bone strength and associated fractures. Over 95% of autosomal dominant forms of this disease are associated with defects in the genes for collagen COL1A1 and COL1A2.<sup>1</sup> The lethal type II disease has been identified antenatally by symmetrically shortened long bones and micromelia. Many reports have indicated that a femur length to abdominal circumference ratio (FL:AC) of less than 0.16 is predictive of lethality associated with OI.<sup>2,3</sup> We report a case that presented at 20 weeks’ gestation with shortening of the lower limbs, specifically a lagging femur length and FL:AC of < 0.16. On subsequent ultrasound examinations, progressive shortening of the femur as well as shortening of the long bones of the upper extremities was documented. The thorax appeared normal until 31 weeks. The FL:AC remained below 0.16 throughout pregnancy. Workup in the neonatal period identified a novel mutation in COL1A1. The neonate was able to breathe spontaneously at birth requiring minimal respiratory support for the initial 2 weeks and lived for 26 days.
Highlights
Osteogenesis imperfecta (OI) is a heterogenous inheritable bone disease characterized by defects in bone matrix formation, which results in decreased bone strength and leads to bone fragility, deformity and short stature
About 95% of all cases of OI are classified into 4 subtypes (I-IV) first described by Sillence et al[4] and are associated with mutations that affect type I collagen genes, COL1A1 and COL1A2.1 Of the four main types of OI, type II is considered lethal with type III being severe
We describe a novel mutation of COL1A1 gene that was associated with lethal OI type II
Summary
Osteogenesis imperfecta (OI) is a heterogenous inheritable bone disease characterized by defects in bone matrix formation, which results in decreased bone strength and leads to bone fragility, deformity and short stature. About 95% of all cases of OI are classified into 4 subtypes (I-IV) first described by Sillence et al[4] and are associated with mutations that affect type I collagen genes, COL1A1 and COL1A2.1 Of the four main types of OI, type II is considered lethal with type III being severe. Both type II and type III OI are caused by dominant structural mutations in COL1A1 and COL1A2. The ratio of femur length to abdominal circumference has been previously shown to distinguish lethal skeletal dyscrasia including OI.[2,3] One report notes that the mean age for diagnosing lethal skeletal dyscrasias based on FL:AC was 20.4 weeks, suggesting that this ratio may be used in antenatal counseling regarding options for termination; the specific diagnosis was only correct 65% of the time.[7]
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