MMP13-related metaphyseal dysplasia: a differential diagnosis of rickets.

Objectives: MMP13-related metaphyseal dysplasia Spahr type, is an extremely rare skeletal disorder, and only a dozen patients with a confirmed molecular diagnosis have been reported. It is characterized by mild short stature, genu varum, and metaphyseal irregularities including fraying, splaying, and cupping of the long bones. The disorder is in the differential diagnosis of rickets, a relatively common disorder in childhood that shares similar clinical and radiological features with metaphyseal dysplasia.

Case presentation: Herein, we present a 39-month-old girl patient who was initially evaluated for rickets due to mild short stature, bowing of the lower extremities, and metaphyseal changes. Biochemical tests including calcium, phosphate, alkaline phosphatase, and vitamin D levels were all within normal ranges. Radiographies revealed advanced bone age, mildly enlarged epiphyses, wide and irregular metaphyses of the long tubular bones, mildly thickened long tubular bones, and coxa vara. Clinical exome sequencing identified a homozygous variant in the MMP13 gene, confirming the diagnosis of metaphyseal dysplasia Spahr type.

Conclusions: We emphasize that metaphyseal dysplasias mimic the clinical and radiographic features of rickets and play a significant role in the differential diagnoses, particularly in patients presenting with short stature, genu varum, and metaphyseal irregularities, despite the absence of biochemical abnormalities. In accordance with the Nosology of Genetic Skeletal Disorders: 2023 Revision, we reinforce the dyadic naming system for the two groups of MMP13-related metaphyseal dysplasia, differentiated solely by their inheritance patterns, which also exhibit consistency with the location of the variants.