Metaphyseal Dysplasia, Spahr Type; A Case Report of Variable Expressivity in Non-Consanguineous Filipino Siblings

Metaphyseal dysplasia describes a heterogenous group of skeletal dysplasias with varying inheritance patterns, which preferentially demonstrate dysplastic changes within the metaphyseal region of long bones. The clinical consequences of these dysplastic changes are highly variable, but most uniformly include decreased stature, increased upper-to-lower segment proportions, genu varus, and knee pain. Metaphyseal dysplasia, Spahr type (MDST) [MIM: 250400] is a rare primary bone dysplasia that was first clinically described in 1961 in four of five siblings with moderate short stature, metaphyseal dysplasia, mild genu vara, and no biochemical signs of rickets. For many decades, MDST was a clinical diagnosis, but the underlying genetic etiology was determined to be due to biallelic pathogenic variants in matrix metalloproteinases 13 [MIM: 600108] in 2014. Clinical case reports of this disease are limited; this paper aims to present the clinical manifestations and treatment for 3 Filipino siblings with a confirmed of MDST.

Patient 1 presented at age 8 for medial ankle pain and bilateral lower extremity bowing of several years. Radiographs showed bilateral metaphyseal irregularities, and the patient underwent bilateral lateral distal femoral and proximal tibial physeal tethering at 9 years 11 months. At 16 months post tethering, she reports reduced pain although varus deformity persists. Patient 2 presented to clinic at age 6 for concern of bilateral bowing. He has had no reported pain and demonstrates milder metaphyseal irregularities than patient 1 on radiographs. To date, patient 2 has no significant changes or gross deformity. Patient 3 examined at 19 months without observable deformity.

Suspicion for MDST should be elevated in the setting of short-stature, upper-to-lower segment disproportionality, focal metaphyseal irregularities, and normal biochemical presentation. At present, no standard of care exists for treatment of patients with these deformities. Further, identification and evaluation of impacted patients are needed to progressively optimize management.