Malignant infantile osteopetrosis and primary pulmonary hypertension: a new combination?

Phenotype-autosomal recessive osteopetrosis

Osteopetrosis (OPT) is a life-threatening disease characterized by increased bone mass caused by diminished osteoclast function/differentiation. The autosomal recessive forms, caused by biallelic variants in implicated genes, usually present in infancy. Without treatment, autosomal recessive OPTs are usually fatal within the first 10 years of life [1]. Here, we review the clinical features and associated pathophysiology of the autosomal recessive OPT. A greater understanding of these rare disorders will advance early diagnosis and optimal management.

Loss of PPARγ in endothelial cells leads to impaired angiogenesis

Tie2-promoter-mediated loss of peroxisome proliferator-activated receptor gamma (PPARγ, also known as PPARG) in mice leads to osteopetrosis and pulmonary arterial hypertension. Vascular disease is associated with loss of PPARγ in pulmonary microvascular endothelial cells (PMVEC); we evaluated the role of PPARγ in PMVEC functions, such as angiogenesis and migration. The role of PPARγ in angiogenesis was evaluated in Tie2CrePPARγ(flox/flox) and wild-type mice, and in mouse and human PMVECs. RNA sequencing and bioinformatic approaches were utilized to reveal angiogenesis-associated targets for PPARγ. Tie2CrePPARγ(flox/flox) mice showed an impaired angiogenic capacity. Analysis of endothelial progenitor-like cells using bone marrow transplantation combined with evaluation of isolated PMVECs revealed that loss of PPARγ attenuates the migration and angiogenic capacity of mature PMVECs. PPARγ-deficient human PMVECs showed a similar migration defect in culture. Bioinformatic and experimental analyses newly revealed E2F1 as a target of PPARγ in the regulation of PMVEC migration. Disruption of the PPARγ-E2F1 axis was associated with a dysregulated Wnt pathway related to the GSK3B interacting protein (GSKIP). In conclusion, PPARγ plays an important role in sustaining angiogenic potential in mature PMVECs through E2F1-mediated gene regulation.

A fatal case of infantile malignant osteopetrosis complicated by pulmonary arterial hypertension after hematopoietic stem cell transplantation

Infantile malignant osteopetrosis (IMO) is a rare and fatal autosomal recessive condition characterized by a generalized increased in bone density. Hematopoietic stem cell transplantation (HSCT) is the only effective and rational therapy with achieving long-term disease-free survival. However, complications with HSCT for IMO remain unclear. Here we describe a male infant with IMO, carrying two novel mutations in the T-cell immune regulator 1 (TCIRG1) gene. The TCIRG1 gene encodes the a3 subunit of vacuolar H(+)-ATPase that plays an essential role in the resorptive function of osteoclasts. Direct sequencing of all 20 exons of the TCIRG1 gene revealed a single nucleotide change in exon 11 (c1305 G > T), which causes the substitution of Asp (GAT) for Glu (GAG) at position 435, and a two-nucleotide deletion in exon 16 (c1952-1953 del CA), causing a frame-shift mutation. However, the functional consequence of each mutation remains to be determined. Allogeneic HSCT was performed in the patient at the age of nine months. Donor engraftment was achieved, and abnormal bone metabolism and extramedullary hematopoiesis were corrected. Graft-versus-host disease was mild (grade I). However, the patient died of complication of pulmonary arterial hypertension at seven months after the HSCT. Postmortem examination revealed prominent vascular wall thickening of the pulmonary artery and macrophage infiltration to alveoli. It should be noted that a patient with IMO has a risk for pulmonary arterial hypertension, and the evaluation of pulmonary arterial flow should be included in the assessment of each patient with IMO even after HSCT.

Hematopoietic stem cell transplantation for infantile osteopetrosis

We report the international experience in outcomes after related and unrelated hematopoietic transplantation for infantile osteopetrosis in 193 patients. Thirty-four percent of transplants used grafts from HLA-matched siblings, 13% from HLA-mismatched relatives, 12% from HLA-matched, and 41% from HLA-mismatched unrelated donors. The median age at transplantation was 12 months. Busulfan and cyclophosphamide was the most common conditioning regimen. Long-term survival was higher after HLA-matched sibling compared to alternative donor transplantation. There were no differences in survival after HLA-mismatched related, HLA-matched unrelated, or mismatched unrelated donor transplantation. The 5- and 10-year probabilities of survival were 62% and 62% after HLA-matched sibling and 42% and 39% after alternative donor transplantation (P = .01 and P = .002, respectively). Graft failure was the most common cause of death, accounting for 50% of deaths after HLA-matched sibling and 43% of deaths after alternative donor transplantation. The day-28 incidence of neutrophil recovery was 66% after HLA-matched sibling and 61% after alternative donor transplantation (P = .49). The median age of surviving patients is 7 years. Of evaluable surviving patients, 70% are visually impaired; 10% have impaired hearing and gross motor delay. Nevertheless, 65% reported performance scores of 90 or 100, and in 17%, a score of 80 at last contact. Most survivors >5 years are attending mainstream or specialized schools. Rates of veno-occlusive disease and interstitial pneumonitis were high at 20%. Though allogeneic transplantation results in long-term survival with acceptable social function, strategies to lower graft failure and hepatic and pulmonary toxicity are urgently needed.

An Adolescent Case of Osteopetrosis with Portal Hypertension as well as Mandibula Osteomyelitis

Osteopetrosis is a clinical syndrome characterized by the failure of osteoclasts to resorb bone. Excessive bone density can interfere with vital tissues and structures, causing serious problems of the body. Hematopoietic insufficiency, disturbed tooth eruption, nerve entrapment syndromes, and growth impairment may develop in a patient with osteopetrosis. Herein, we present an adolescent girl diagnosed with non-infantile type of osteopetrosis with rare complications of the disease like mandibular osteomyelitis and portal hypertension (PHT) without liver cirrhosis. To our knowledge, this is the first pediatric case with osteopetrosis related PHT.

Complications of anesthesia for children with malignant infantile osteopetrosis before and after hematopoietic stem cell transplantation

OBJECTIVES AND AIMS

The primary aim was to determine the frequency of anesthetic-related complications for patients with malignant infantile osteopetrosis (MIOP) before and after hematopoietic stem cell transplant (HSCT). The secondary aims were to describe the types of complications that occurred, to determine whether the risk of anesthetic complications was altered by HSCT, and to determine the frequency of difficult intubation.

BACKGROUND

Patients with MIOP undergo HSCT, often in infancy, and anesthesia is frequently required for investigations and procedures associated with transplantation. Although MIOP has adverse implications for anesthetic management, the literature describing the anesthetic management of MIOP patients is limited.

METHODS

A retrospective review of medical and anesthetic records was undertaken between November 2000 and March 2008.

RESULTS

Eleven patients underwent 127 anesthetics. The overall complication rate was 11%. Before HSCT, there were 12 complications in 62 anesthetics (19.3%). After HSCT, there were two complications in 65 anesthetics (3.2%). This difference was not statistically significant. All of the complications were airway or respiratory events. Of the 26 intubations associated with anesthesia, 23 (88.5%) were easy, 1 (3.8%) was moderately difficult, and 2 (7.7%) were difficult.

CONCLUSION

Complications associated with anesthesia for infants and children with MIOP having HSCT are fairly common and are usually airway or respiratory related. Difficult endotracheal intubation is also common.

Hematopoietic stem cell transplantation for osteopetrosis

Osteopetrosis is the generic name for a group of diseases caused by deficient formation or function of osteoclasts, inherited in either autosomal recessive or dominant fashion. Osteopetrosis varies in severity from a disease that may kill infants to an incidental radiological finding in adults. It is increasingly clear that prognosis is governed by which gene is affected, making detailed elucidation of the cause of the disease a critical component of optimal care, including the decision on whether hematopoietic stem cell transplantation is appropriate. This article reviews the characteristics and management of osteopetrosis.

A single-center experience in 20 patients with infantile malignant osteopetrosis

Infantile malignant osteopetrosis (IMO) includes various genetic disorders that affect osteoclast development and/or function. Genotype-phenotype correlation studies in IMO have been hampered by the rarity and heterogeneity of the disease and by the severity of the clinical course, which often leads to death early in life. We report on the clinical and molecular findings and treatment in 20 consecutive patients (11 males, nine females) with IMO, diagnosed at a single center in the period 1991-2008. Mean age at diagnosis was 3.9 months, and mean follow-up was 66.75 months. Mutations in TCIRG1, OSTM1, ClCN7, and TNFRSF11A genes were detected in nine, three, one, and one patients, respectively. Six patients remain genetically undefined. OSTM1 and ClCN7 mutations were associated with poor neurologic outcome. Among nine patients with TCIRG1 defects, six presented with hypogammaglobulinemia, and one showed primary pulmonary hypertension. Fourteen patients received hematopoietic cell transplantation; of these, nine are alive and eight of them have evidence of osteoclast function. These data may provide a basis for informed decisions regarding the care of patients with IMO.

Airway evaluation and management in 7 children with malignant infantile osteopetrosis before hematopoietic stem cell transplantation

Malignant infantile osteopetrosis (MIOP) is a rare disorder caused by dysfunctional osteoclasts. The classic MIOP features, such as frontal bossing, micrognathia, and small thorax, may place these children at risk for developing obstructive sleep apnea (OSA) and chronic hypoxemia. To objectively document OSA, airway evaluations were performed; results impacted management. We reviewed the records of 7 MIOP patients treated at St Jude. Six underwent polysomnograms during prehematopoietic stem cell transplantation (HSCT) evaluation. To determine the existence of a relationship between OSA and radiologic imaging, initial chest radiographs and bone mineral density studies were reviewed. Pre-HSCT patients had a median apnea-hypopnea index of 17.51 (normal, 0 to 2), with <25% being central events, thus indicating OSA. The median minimal oxygen saturation was 79%, indicating intermittent hypoxemia. Neither chest radiographs nor bone mineral density correlated with severity of OSA. Four patients received tracheostomies before or during HSCT. Three surviving children underwent polysomnograms 1 year after HSCT, and median apnea-hypopnea index was 1.3, indicating near to complete resolution of OSA. Resolution of OSA may have been multifactorial. Using a quantitative approach, we demonstrate that MIOP children have OSA and hypoxemia; thus, these children should have airway evaluations and treatments to potentially reduce the risk of life-threatening pulmonary complications.

Clinical and molecular findings in a family with the carbonic anhydrase II deficiency syndrome

Carbonic anhydrase II (CA2) deficiency syndrome is an autosomal recessive disorder leading to osteopetrosis, renal tubular acidosis, and cerebral calcifications. Affected members of an Arab family with the CA2 deficiency syndrome carried the "Egyptian mutation" in CA2, i.e., c.191 del A, H64fsX90. One affected member, homozygote for the mutation, developed primary pulmonary hypertension. Primary pulmonary hypertension was never described before in patients with this unique syndrome. The likelihood of both occurring randomly in a single individual is very low. We therefore speculate that there might be a possibility of an etiologic link between these entities.

High peripheral blood progenitor cell counts enable autologous backup before stem cell transplantation for malignant infantile osteopetrosis

Autosomal recessive osteopetrosis (OP) is a rare, lethal disorder in which osteoclasts are absent or nonfunctional, resulting in a bone marrow cavity insufficient to support hematopoiesis. Because osteoclasts are derived from hematopoietic precursors, allogeneic hematopoietic cell transplantation can cure the bony manifestations of the disorder. However, high rates of graft failure have been observed in this population. It is not possible to harvest bone marrow from these patients for reinfusion should graft failure be observed. We report that 8 of 10 patients with OP had high numbers of circulating CD34(+) cells (3% +/- 0.9%). This increased proportion of peripheral CD34(+) cells made it possible to harvest 2 x 10(6) CD34(+) cells per kilogram with a total volume of blood ranging from 8.3 to 83.7 mL (1.3-11.6 mL/kg). In addition, colony-forming assays documented significantly more colony-forming unit-granulocyte-macrophage and burst-forming unit-erythroid in the blood of osteopetrotic patients compared with controls; the numbers of colony-forming units approximated those found in control marrow. We conclude that OP patients with high levels of circulating CD34(+) are candidates for peripheral blood autologous harvest by limited exchange transfusion. These cells are then available for reinfusion should graft failure be observed in patients for whom retransplantation is impractical.