Importance of neurological assessment before bone marrow transplantation for osteopetrosis

The clinical features of OSTM1-associated malignant infantile osteopetrosis: A retrospective, single-center experience over one decade

Mutation in OSTM1 give rise to the rarest and most lethal subtype of malignant infantile osteopetrosis (MIOP), and an improved understanding of OSTM1-associated MIOP would help with informed decision-making regarding symptom management and early palliative care referral. This retrospective study describes the clinical and laboratory features of patients with a genetic diagnosis of OSTM1 MIOP made between January 2011 and December 2021 in the Department of Pediatrics, Al-Adan Hospital, Kuwait. Twenty-two children had confirmed homozygous deletion in OSTM1 (13 females, nine males). Consanguinity was reported in almost all parents. 72.7% were diagnosed before the age of two months, most commonly incidentally with a high clinical suspicion. All 22 patients developed upper respiratory symptoms, hepatosplenomegaly, poor feeding, and had severe developmental delay. 80% of patients developed pain and/or irritability, and 40.9% were diagnosed with primary seizures. Bone fractures developed in 27% of patients, most likely iatrogenic, and some patients had hernia and gum abnormalities. The mean survival was 10.9 months. The clinical presentation, symptomatology, and mortality of our cohort were compared with other cases of OSTM1 MIOP identified through a comperhensive search of the PubMed database. The findings conclude that OSTM1 MIOP is a multi-systemic disease with distinct clinical features, of which neurological complications are the most severe and include nociplastic pain and irritability. Although orthopedic complications influence the trajectory of most patients with other forms of osteopetrosis, OSTM1 MIOP is driven by its neurological complications. Hence, OSTM1 should be regarded as a neurodegenerative disease with osteopetrosis as a comorbidity that warrants early palliative care referral.

Osteoclast-poor osteopetrosis

Osteopetrosis (OPT) is a rare inherited bone disease characterized by a bone resorption defect, due to osteoclast malfunction (in osteoclast-rich, oc-rich, OPT forms) or absence (in oc-poor OPT forms). This causes severe clinical abnormalities, including increased bone density, lack of bone marrow cavity, stunted growth, macrocephaly, progressive deafness, blindness, hepatosplenomegaly, and severe anemia. The oc-poor subtype of OPT is ultra-rare in humans. It is caused by mutations in either the tumor necrosis factor ligand superfamily member 11 (TNFSF11) gene, encoding RANKL (Receptor Activator of Nuclear factor-kappa B [NF-κB] Ligand) which is expressed on cells of mesenchymal origin and lymphocytes, or the TNFRSF member 11A (TNFRSF11A) gene, encoding the RANKL functional receptor RANK which is expressed on cells of myeloid lineage including osteoclasts. Clinical presentation is usually severe with onset in early infancy or in fetal life, although as more patients are reported, expressivity is variable. Phenotypic variability of RANK-deficient OPT sometimes includes hypogammaglobulinemia or radiological features of dysosteosclerosis. Disease progression is somewhat slower in RANKL-deficient OPT than in other 'malignant' subtypes of OPT. While both RANKL and RANK are essential for normal bone turnover, hematopoietic stem cell transplantation (HSCT) is the treatment of choice only for patients with the RANK-deficient form of oc-poor OPT. So far, there is no cure for RANKL-deficient OPT.

How we approach malignant infantile osteopetrosis

Malignant infantile osteopetrosis (MIOP) is a rare hereditary disorder characterized by excessive bone overgrowth due to a defect in bone marrow resorption by osteoclasts. In most cases, hematopoietic stem cell transplantation (HSCT) may correct bone metabolism but the rapidly progressing nature of this condition necessitates early diagnosis and prompt treatment to minimize irreversible cranial nerve damage. The management of patients with MIOP presents many unique challenges. In this review, the clinical management of patients with MIOP is discussed, including diagnosis, preparation for HSCT and special transplant considerations, management of unique HSCT complications, and long-term follow-up.

Comparison of Optic Canal Diameter in Children With Malignant Infantile Osteopetrosis and Normal Children and the Effects of Hematopoietic Stem Cell Transplantation on the Optic Canal Diameter

PURPOSE

To investigate the difference in the optic canal diameter between children with autosomal recessive malignant infantile osteopetrosis and normal children, and to assess the influence of hematopoietic stem cell transplantation on the optic canal diameter.

METHODS

Twenty pediatric patients with malignant infantile osteopetrosis and 22 normal control children were included in this study. Eleven patients with malignant infantile osteopetrosis underwent hematopoietic stem cell transplantation. The measurements included optical canal diameter and flash visual evoked potential. Comparisons of these measurements between patients with malignant infantile osteopetrosis and normal controls as well as before and after hematopoietic stem cell transplantation were performed. The correlation between age and optic canal diameter was analyzed using Pearson correlation analysis.

RESULTS

The mean optic canal diameter before hematopoietic stem cell transplantation was 1.65 ± 0.54 mm in patients with malignant infantile osteopetrosis and 3.38 ± 0.60 mm in the control group (P < .001). The mean optic canal diameter after hematopoietic stem cell transplantation was 2.72 ± 0.66 mm, which was significantly different from the pre-transplantation measurement (P < .001). The P2 latency for the flash visual evoked potential after hematopoietic stem cell transplantation (152.3 ± 36.4 ms) was significantly less than that before transplantation (165.5 ± 27.7 ms; P = .051). Pearson correlation analysis revealed a significant correlation between age and optic canal diameter (r = 0.722, P < .001).

CONCLUSIONS

The optic canal was narrower in pediatric patients with malignant infantile osteopetrosis than in age-matched normal controls. This condition can be relieved through hematopoietic stem cell transplantation and the impaired conductibility of the optic nerve can be improved in some cases. [J Pediatr Ophthalmol Strabismus. 2019;56(1):35-42.].

Impact of hematopoietic stem cell transplant on VEP and ABR values of the patients with malignant infantile osteopetrosis

OBJECTIVES

Malignant Infantile Osteopetrosis (MIOP) is a rare inherited disorder with neurological complications, notably visual impairment and decrease of hearing level. Although Hematopoietic Stem Cell Transplantation (HSCT) has been approved as the only curative treatment for these patients, the exact impact of it on visual and hearing level is still unclear.

STUDY DESIGN

We analyzed the P2 latency and amplitude from Visual Evoked Potentials (VEP) of 10 patients (20 eyes) and the threshold of wave V from Auditory Brainstem Response (ABR) of 15 patients (30 ears) with MIOP before, 6 and 12 months after HSCT.

RESULTS

Before the HSCT, 10/30 ears demonstrated some degree of hearing loss; while only 3/20 eyes had P2 wave latencies in normal range for age. Using GEE models, it was shown that 12 months after HSCT, wave V threshold of ABR of the patients was significantly lower compared to its value from before the transplant (p value: 0.04). The analysis of latency and amplitude of P2 wave of VEPs showed no significant difference between before and after the transplant.

CONCLUSION

This study clearly showed that HSCT can improve the hearing level of the patients in terms of ABR threshold. Although HSCT made no significant improvement in latency of P2 in VEP of the patients, it can be concluded that transplant can halt visual regression in these patients. Early diagnosis of MIOP with this objective tools and subsequently early HSCT in these patients can decrease the rate of neurological complications of MIOP and improve the quality of life in them.

An Exceptional Neurosurgical Presentation of a Patient with Osteopetrosis

BACKGROUND

Osteopetrosis (OP) is a varied clinical condition caused by malfunction or insufficient development of osteoclasts, or both. Neurologic findings can occur because of osteopetrotic conditions restricting neural foramina through which the spinal cord, cranial nerves, or major vascular structures traverse the skull. Renal tubular acidosis (RTA) is a well-documented condition with OP. However, Chiari I malformation is rarely reported concomitantly with OP.

CASE DESCRIPTION

We present a patient with a known RTA who was admitted with a rapid progressive tetraparesis within 24 hours. Clinical and radiologic evaluation of the patient revealed OP with RTA together with Chiari I malformation and holocord hydromyelia. Management of the patient was started with correction of severe hypokalemia (K: 1.4 mEq/L), which resulted in dramatic improvement in tetraparesis. Two days later, a posterior fossa bone decompression with ventriculoperitoneal shunt placement during the same session led to prominent decrease in size of the ventricles and the hydromyelia on long-term follow-up.

CONCLUSIONS

Patients with OP can exhibit many clinical conditions. However, our case involved an unusual and rapid progressive tetraparesis, which could confuse the management as necessitating an emergent posterior fossa decompression. Stabilizing the metabolic status of the patient facilitated elective surgery, which further improved patient's neurologic findings and diminished hydromyelia on long-term follow-up.

Hematopoietic stem cell transplantation corrects osteopetrosis in a child carrying a novel homozygous mutation in the FERMT3 gene

Osteopetrosis (OPT) is a rare skeletal disorder with phenotypic and genotypic heterogeneity: a variety of clinical features besides the bony defect may be present, and at least ten different genes are known to be involved in the disease pathogenesis. In the framework of this heterogeneity, we report the clinical description of a neonate, first child of consanguineous parents, who had osteoclast-rich osteopetrosis and bone marrow failure in early life, but no other usual classical features of infantile malignant OPT, such as visual or hearing impairments. Because of the severe presentation at birth, the patient received Hematopoietic Stem Cell Transplantation (HSCT) at 2months of age with successful outcome. Post-HSCT genetic investigation by means of exome sequencing identified a novel homozygous mutation in the Fermitin Family Member 3 (FERMT3) gene, which was predicted to disrupt the functionality of its protein product kindlin 3. Our report provides information relevant to physicians for recognizing patients with one of the rarest forms of infantile malignant OPT, and clearly demonstrates that HSCT cures kindlin 3 deficiency with severe phenotype.

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.

Osteopetrosis with Arnold Chiari malformation type I and brain stem compression

Osteopetrosis is a collective term for a range of sclerosing bone diseases resulting from an absence or defective function of osteoclasts. The clinical expression is variable and includes skeletal, hematological and neurological manifestations. The common neurological manifestation includes cranial neuropathies involving optic, cochlear, facial and trigeminal nerves. Spastic quadriplegia occurring as a result of brain stem compression in osteopetrosis is uncommon. The association of Type 1 Arnold Chiari malformation with osteopetrosis resulting in brain stem compression syndrome is an extremely rare entity.

Mutations in OSTM1 (grey lethal) define a particularly severe form of autosomal recessive osteopetrosis with neural involvement

We report three novel osteopetrosis patients with OSTM1 mutations and review two that have been previously described. Our analysis suggests that OSTM1 defines a new subset of patients with severe central nervous system involvement. This defect is also present in the gl mouse, which could represent a good model to study the role of the gene in the pathogenesis of this disease.

INTRODUCTION

Autosomal recessive osteopetrosis (ARO) is a severe hereditary bone disease whose cellular basis is in the osteoclast, but with heterogeneous molecular defects. In addition to the TCIRG1 and the ClCN7 genes, whose mutations account for approximately 55% and 10% of cases, respectively, the OSTM1 gene has been described thus far in only two ARO patients. materials and methods: We report here three novel ARO patients presenting with severe primary central nervous system involvement in addition to the classical stigmata of severe bone sclerosis, growth failure, anemia, thrombocytopenia, and visual impairment with optic atrophy. In addition we analyzed the brain morphology and histology of the grey lethal mutant mouse.

RESULTS

The analysis of the OSTM1 gene in two patients, both from Kuwait, showed homozygous two nucleotide deletion in exon 2, leading to a frameshift and premature termination. The third (Lebanese) patient showed a single point mutation in exon 1, leading to a nonsense mutation. The clinical neurological evaluation of the two Kuwaiti patients by CT and MRI scans showed a defect in the white matter, with a specific diagnosis of severe cerebral atrophy. The gl brain showed a diffuse translucent appearance with loss of the normal demarcation between the white and the grey matter, features consistent with myelin loss or hypomyelination. Histological and myelin staining analysis evidenced an atrophy of the corpus callosum with loss of myelin fibers, and in cortical areas, loss of the normal lamination consistent with multiple foci of cortical dysplasia.

CONCLUSIONS

These findings suggest that OSTM1-dependent ARO defines a new subset of patients with severe central nervous system involvement leading to a very poor prognosis. The fact that central nervous system involvement is also present in the gl mouse mutant suggests that this mouse is a good model to test possible therapies.

Allogeneic stem cell transplantation for the treatment of diseases associated with a deficiency in bone marrow products

Our understanding of the pathophysiology of hematopoietic failure associated syndromes led to the developmental of potentially curative procedures for the treatment of many diseases including Severe aplastic anemia, Fanconi's anemia, Primary immunodeficiency, Osteopetrosis, and Metabolic diseases. Although the number of patients that were transplanted for bone marrow deficiency diseases is relatively low as compared to patients with hematological malignancies, the impact on the knowledge of hematopoiesis and transplantation biology is tremendous. Moreover, the patient's average young age suffering from these diseases further encourage searching for curative approaches. Lucking a fully MHC matched donor, remained a significant obstacle in stem cell transplantation for non-malignant hematological disorders. Lessons from attempts to cure aplasic anemia with bone marrow transplantation guided us to the improvement of pretransplant conditioning regimens and prevention of graft versus host reactions after transplantation. Furthermore, in recent years optimization of disease specific protocol have been successfully designed and clinically applied.

Severe malignant osteopetrosis caused by a GL gene mutation

Infantile malignant autosomal recessive osteopetrosis is a genetically heterogeneous disease caused by the inability of OCLs to resorb and remodel bone, resulting in generalized osteosclerosis and obliteration of marrow spaces and cranial foramina. The classical clinical features are pathological fractures, visual impairment, and bone marrow failure. Two human genes have been described as the cause of this form of osteopetrosis: the T-cell immune-regulator-1 (TCIRG1) gene, which is mutated in >50% of the patients, and the chloride channel 7 (ClCN7) gene, which accounts for approximately 10% of cases. We report the clinical, radiographic, and histopathologic findings of the first human osteopetrosis case caused by a mutation in the grey-lethal (GL) gene. The patient, a 9-day-old male infant, presented with a very severe osteopetrotic phenotype including substantial hepatosplenomegaly since birth, cytopenia, and progressive major liver failure. Skeletal radiographs revealed a generalized increase in bone density with loss of corticomedullary differentiation. Histopathologic bone examination showed the typical osteopetrotic changes, with absence of resorptive activity, and osteoclasts, slightly decreased in number, with evident morphological alterations.

Long-term outcome of haematopoietic stem cell transplantation in autosomal recessive osteopetrosis: an EBMT report

A retrospective analysis was made of 122 children who had received an allogeneic haematopoietic stem cell transplantation (HSCT) for autosomal recessive osteopetrosis between 1980 and 2001. The actuarial probabilities of 5 years disease free survival were 73% for recipients of a genotype HLA-identical HSCT (n=40), 43% for recipients of a phenotype HLA-identical or one HLA-antigen mismatch graft from a related donor (n=21), 40% for recipients of a graft from a matched unrelated donor (n=20) and 24% for patients who received a graft from an HLA-haplotype-mismatch related donor (n=41). In the latter group, a trend towards improvement was achieved at the end of the study period (17% before 1994, 45% after 1994, P=0.11). Causes of death after HSCT were graft failure and early transplant-related complications. Severe visual impairment was present in 42% of the children before HSCT. Conservation of vision was better in children transplanted before the age of 3 months. Final height was related to height at the time of HSCT and better preserved in children transplanted early. Most children attended regular school or education for the visually handicapped. At present, HSCT is the only curative treatment for autosomal recessive osteopetrosis and should be offered as early as possible.

Neurological aspects of osteopetrosis

The osteopetroses are caused by reduced activity of osteoclasts which results in defective remodelling of bone and increased bone density. They range from a devastating neurometabolic disease, through severe malignant infantile osteopetrosis (OP) to two more benign conditions principally affecting adults [autosomal dominant OP (ADO I and II)]. In many patients the disease is caused by defects in either the proton pump [the a3 subunit of vacuolar-type H(+)-ATPase, encoded by the gene variously termed ATP6i or TCIRG1] or the ClC-7 chloride channel (ClCN7 gene). These pumps are responsible for acidifying the bone surface beneath the osteoclast. Although generally thought of as bone diseases, the most serious consequences of the osteopetroses are seen in the nervous system. Cranial nerves, blood vessels and the spinal cord are compressed by either gradual occlusion or lack of growth of skull foramina. Most patients with OP have some degree of optic atrophy and many children with severe forms of autosomal recessive OP are rendered blind; optic decompression is frequently attempted to prevent the latter. Auditory, facial and trigeminal nerves may also be affected, and hydrocephalus can develop. Stenosis of both arterial supply (internal carotid and vertebral arteries) and venous drainage may occur. The least understood form of the disease is neuronopathic OP [OP and infantile neuroaxonal dystrophy, MIM (Mendelian inheritance in man) 600329] which causes rapid neurodegeneration and death within the first year. Although characterized by the finding of widespread axonal spheroids and accumulation of ceroid lipofuscin, the biochemical basis of this disease remains unknown. The neurological complications of this disease and other variants are presented in the context of the latest classification of the disease.

Multiple fractures in a 3-month-old infant with severe infantile osteopetrosis

A diagnosis of severe infantile, autosomal recessive osteopetrosis (I-ARO) was made in a 3-month-old female based on characteristic radiological and histological findings. The finding of multiple fractures at presentation in this infant is highly unusual. Deficiency of carbonic-anhydrase type II was excluded.

Bone marrow transplantation corrects osteopetrosis in the carbonic anhydrase II deficiency syndrome

Carbonic anhydrase II (CAII), found in renal tubules, brain, and osteoclasts, is critical in acid-base homeostasis and bone remodeling. Deficiency of CAII gives rise to a syndrome of osteopetrosis, renal tubular acidosis (RTA), and cerebral calcification with associated developmental delay. It is inherited in an autosomal recessive fashion and found most frequently in the Mediterranean region and the Middle East. We report 2 related Irish families with clinically severe CAII deficiency in whom the gene mutation has been fully elucidated. Two children, one from each family, have undergone allogeneic bone marrow transplantation because of severe progressive visual and hearing loss. The older 2 children had already developed cerebral calcification and marked visual loss at the time of diagnosis and were treated symptomatically. Post-transplantation evaluation at 2 and 3 years demonstrates histologic and radiologic resolution of their osteopetrosis with stabilization of hearing and vision. Both children remain developmentally delayed and continue to have RTA, and the older child has now developed cerebral calcification. Allogeneic bone marrow stem cell replacement cures the osteoclast component of CAII deficiency and retards the development of cerebral calcification, but it appears to have little or no effect on the renal lesions.

Bone marrow transplantation corrects osteopetrosis in the carbonic anhydrase II deficiency syndrome

Carbonic anhydrase II (CAII), found in renal tubules, brain, and osteoclasts, is critical in acid-base homeostasis and bone remodeling. Deficiency of CAII gives rise to a syndrome of osteopetrosis, renal tubular acidosis (RTA), and cerebral calcification with associated developmental delay. It is inherited in an autosomal recessive fashion and found most frequently in the Mediterranean region and the Middle East. We report 2 related Irish families with clinically severe CAII deficiency in whom the gene mutation has been fully elucidated. Two children, one from each family, have undergone allogeneic bone marrow transplantation because of severe progressive visual and hearing loss. The older 2 children had already developed cerebral calcification and marked visual loss at the time of diagnosis and were treated symptomatically. Post-transplantation evaluation at 2 and 3 years demonstrates histologic and radiologic resolution of their osteopetrosis with stabilization of hearing and vision. Both children remain developmentally delayed and continue to have RTA, and the older child has now developed cerebral calcification. Allogeneic bone marrow stem cell replacement cures the osteoclast component of CAII deficiency and retards the development of cerebral calcification, but it appears to have little or no effect on the renal lesions. (Blood. 2001;97:1947-1950)

Osteopetrosis: a single centre experience of stem cell tranisplantation and prenatal diagnosis

Malignant osteopetrosis (MOP) is an autosomal recessive disease in which osteoclast dysfunction results in excessive bone deposition and early infant death. Thirteen children suffering from MOP from four related families all belonging to one Bedouin tribe, were studied. The disease was diagnosed as early as at a few days postnatal to 5 months. Nine children underwent BMT, four of whom are still alive; one is blind and two have markedly reduced vision. Four children who did not undergo BMT died between 4 and 6 months of age. Recently, the gene for MOP has been mapped for this Bedouin tribe allowing prenatal diagnosis. Seven pregnancies were subsequently prenatally diagnosed and two fetuses were found to be affected. Pregnancy was electively terminated in one case. In the other case the parents refused and after establishing the diagnosis, the newborn was transplanted at the age of 7 days.

Malignant infantile osteopetrosis presenting with neonatal hypocalcaemia

Presentation characteristics were reviewed in 14 children from 12 families with malignant infantile osteopetrosis seen at two large referral centres for bone marrow transplantation. Children from six of these families presented initially with symptoms of hypocalcaemia. These comprised early or late neonatal convulsions in six cases (corrected serum calcium < 1.5 mmol/l), and vomiting and irritability (serum calcium 1.68 mmol/l) in another. One other related child had severe and persistent jittering episodes almost certainly attributable to hypocalcaemia. In seven of eight cases, these symptoms developed during the first 14 days of life. Although occasionally reported previously, malignant infantile osteopetrosis remains essentially unrecognised as a cause of neonatal hypocalcaemia, often resulting in diagnostic confusion and delay. This is important in the context of curative haemopoietic stem cell transplantation where preservation of sight may depend on early intervention.