Bone Abstracts

Background: Trisomy 9p is a rare abnormality caused by duplication of the short arm of chromosome 9. Translocation t(9;11) is a rarer variant. Both anomalies are compatible with long survival. Clinical manifestations are very variable, and include short height, mental retardation, hypertelorism, strabismus, foot/hand anomalies, delayed bone maturation. Low bone mineral density (BMD) or fragility fractures have never been reported.

Presenting problem: A 12-year-old boy and a 9-year-old girl with unbalanced translocation t(9;11) were referred to our Center: the boy for two forearm fractures after minimal trauma, the girl for kyphosis. Blood exams, including calcium, phosphorus and magnesium, were normal for age in both subjects. The 24-hour urine collection revealed much reduced calciuria (boy: 56 mg/24 h; girl: 58 mg/24 h; normal range 100–250 mg/24 h) with normal phosphaturia. 25OH-vitamin D levels were normal in both children, but the boy had moderately elevated parathyroid hormone levels (77 pg/ml). In both children, bone resorption turnover markers were moderately increased for age. Other metabolism studies (including thyroid activity, intestinal malabsorption, liver and kidney function, inflammatory markers, electrolytes and urine analysis) revealed no abnormalities, thus excluding other causes of low bone density. Dual energy X-ray absorptiometry (DXA; by Hologic Discovery) was performed at lumbar spine (LS) and on total body less head (TBLH). In both cases, at both sites, BMD was severely reduced (LS BMD Z-score: boy −3.8, girl −4.2; TBLH BMD Z-score boy −3.2, girl −3.4).

Clinical management: In the girl only, spine X-rays revealed fractures of 5 thoracic vertebrae. For this reason, she was put on treatment with i.v. pamidronate (0.5 mg/kg per day for 3 consecutive days every 4 months). After 3 years of treatment no new vertebral or peripheral fractures were observed. DXA revealed a significant increase in BMD (spine Z-score −1.9).

Discussion: The rarity of this genetic alteration does not allow controlled studies. Our finding of reduced BMD and fractures in two cases of unbalanced translocation t(9;14) justifies DXA BMD evaluation, search for undiagnosed vertebral fractures, and adequate therapeutic measures as necessary, in similar cases.

Disclosure: The authors declared no competing interests.