Table.

Summary of Phenotypic Differences Between the Siblings

	Male, Age 6 years		Female, Age 5 years
Phenotype	Description	Age of Onset/Progression	Description	Age of Onset/Progression
Contractures	Severe flexion contractures of knee and ankle joints, bilaterally	Birth/Persistent but less severe after multiple tenotomies	No lower extremity contractures at birth	N/A
	No upper extremity joint contractures	N/A	No upper extremity joint contractures	N/A
Fractures	More than 45 fractures	Left clavicle and multiple rib fractures at birth/Persistent in frequency; many open reductions required	Approximately 15 fractures	Rib fractures present at birth/No open reductions required
Spinal deformities	Severe cervicothoracic scoliosis, complex segmentation anomaly C6-T1	Severe status by age 3/ Spinal fusion at age 5	Moderate thoracic scoliosis, wedging of T7 and T10	Severe status by age 4/ Yet to undergo correction
Skull and facial deformities	Plagiocephaly, frontal bossing, bilateral proptosis, wormian bones	Birth/Normalized to mild deformity since birth	Midface hypoplasia, micrognathia	Birth/Persistent
Height for age, sex	Less than first percentile	Age 6 years	Between first and fifth percentiles	Age 5 years
Bone mineral density	0.459 g/cm²Age-matched Z-score of –2.3	Age 6 years	0.342 g/cm²Age-matched Z-score of –3.1	Age 5 years
Weight-bearing status	Pulls to stand, unable to walk	Persistent	Pulls to stand, walks with aid	Ability to walk decreasing with progression of scoliosis
Other	Left talipes equinovarus, right vertical talus	Birth/Only moderately improved despite serial KAFO bracing, Achilles tenotomies	No foot/ankle deformity	N/A
	No shoulder/upper extremity deformity	N/A	Misshapen and small clavicle, scapula, and proximal humerus	Birth

KAFO, knee-ankle-foot orthotic; N/A, not applicable.