Endocrine Abstracts

Objectives: 1) When and how to investigate rarer causes of short stature. 2) Evidence for interventions to improve growth in metaphyseal chondrodysplasia, Schmid-type (MCDS).

Background: The incidence of skeletal dysplasia is one in 5000, however individually these conditions are rare and prognosis unclear. There is genotypic and phenotypic heterogeneity and no current consensus on classification, which may include clinical, radiographic, molecular or histological criteria.

Presentation may range from mild arthropathy to incompatibility with life. Here we present a case of MCDS, presenting with short stature and initial diagnostic uncertainty.

MCDS, autosomal dominant inheritance, results from mutation in COL10A1; coding collagen type X. X-ray demonstrates metaphyseal widening, coxa vara, without associated cervical spine abnormalities or extra-skeletal manifestations.

Growth hormone is only recommended in SHOX deficiency as a cause of skeletal dysplasia; otherwise it risks disproportionate limb lengthening and worsening of spinal deformities.

Case: A 15-month-old boy presented with faltering growth, bowed limbs, waddling gait, bilateral wrist swelling and height 68 cm (−3.9 S.D.). The wrist X-ray was consistent with rickets.

Normal 25-hydroxy vitamin D, calcium, phosphate, parathyroid hormone and alkaline phosphatase made vitamin D deficient and dependent rickets unlikely. A sitting height of −2 S.D. and sub-ischial leg length −4 S.D. was suspicious of skeletal dysplasia, supported by a skeletal survey demonstrating metaphysal widening, coxa varum and genu varum.

A novel heterozygous transversion 2001T>A in exon 3 of COL10A1 confirmed the diagnosis.

Learning points: 1) Consider rarer causes of rickets with clinical suspicion and normal vitamin D level. 2) Detailed auxology can guide the differential diagnosis. 3) GH is not recommended in most skeletal dysplasia.

Otherwise classified as idiopathic short stature, evidence suggests skeletal dysplasia or an underlying genetic cause may be more common than previously supposed.