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Malignant infantile osteopetrosis is a rare genetic disease characterized by increased bone density due to osteoclastic dysfunction. We report on the case of a 3-month-old girl who was referred to our hospital by the ENT department for severe anemia in the context of bilateral choanal atresia. Clinical examination showed failure to thrive, anemia, respiratory distress, bilateral choanal atresia, and chest deformation. The abdomen was soft with large hepatosplenomegaly. We noted a lack of eye tracking, no optical-visual reflexes, and left nerve facial paralysis. The blood count showed normocytic normochromic anemia with severe thrombocytopenia. The infectious work-up and blood smears were negative. The skeleton X-ray showed diffuse bone densification of the skull, long bones, pelvis, vertebrae, and ribs. The facial bone CT confirmed membranous choanal atresia. The molecular biology search for the TCIRG1 gene mutation was not available. The patient had supportive treatment (transfusion, oral steroid, vitamin D, oxygen, nutrition). Bone marrow transplantation was indicated but not available. She died at 6 months in a context of severe anemia and bleeding. Malignant infantile osteopetrosis is rare and symptoms are nonspecific. Diagnosis should be considered in young infants presenting refractory anemia, particularly in the context of choanal atresia. Bone marrow transplantation remains the only curative treatment., (Copyright © 2016 Elsevier Masson SAS. All rights reserved.)

Malignant infantile osteopetrosis is a rare congenital disease characterized by a dysfunction of osteoclasts followed by an abnormal bone densification. We report the case of a 5-month-old infant in whom this disease was suspected because of the clinical (hepatosplenomegaly, gingival hypertrophy), hematological (pancytopenia and hypocalcemia), and radiological criteria (abnormal bone density, periosteal reaction). The genetic investigation confirmed the diagnosis. Compound heterozygous mutations in the CLCN7 gene were identified, including an as yet undescribed mutation. The second mutation had already been described as being responsible for severe and irreversible neurological damage in patients with osteopetrosis. Since this patient presented severely delayed development, he was not eligible for bone marrow transplantation., (Copyright © 2015 Elsevier Masson SAS. All rights reserved.)

Twenty four patients suffering from osteopetrosis caused by carbonic anhydrase II deficiency are colliged. This pathology seems to be frequent in Tunisia. Mental retardation is present in 52%, 85% of patients have short stature and 25% have optic atrophy. All affected subjects show craniofacial disproportion and dental anomalies. Twenty patients have at least one bone fracture. Metabolic acidosis is constant: it is profound during the first life decade. A severe selective reduction of carbonic anhydrase II in erythrocyte is confirmed in 18 cases. Osteosclerosis and defective skeletal modelling are constant, cerebral calcification can be seen at the scanner approximately at the age of two years and six months. All patients are homozygous for a splice junction mutation in intron 2 of the carbonic anhydrase II gene, this mutation does not seem to protect patients from bone fractures nor induce a severe metabolic acidosis.

The osteoclast is the main effector of bone resorption. Failure in osteoclast differentiation or function leads to osteopetrosis, a bone disease characterized by an impaired bone resorption. Analysis of mouse models developing osteopetrosis as a consequence of naturally occurring mutations or gene knockouts allowed to establish the osteoclast differentiation pathway. Among these models, the oc/oc, the gl/gl and the Clcn7(-/-) mice present a phenotype similar to the one displayed by patients with infantile malignant osteopetrosis, the most severe form of osteopetrosis in human. Analysis of these models led to the identification of different mutations in the corresponding human genes TCIRG1, GL and CLCN7, in osteopetrotic patients. Mutations in the TCIRG1 gene seem the most frequent cause of malignant osteopetrosis and mutations in the CLCN7 gene seem the most frequent cause of type II osteopetrosis. Therefore, these three mouse models appear to be particularly well suited for the study of the osteoclast function in order to provide new insights in the therapy of osteopetrosis.

To date, nine chloride channels belonging to the family of CLC chloride channels have been identified. They are localized either in plasma membranes or in intracellular vesicles (endosomes or lysosomes) and can have an ubiquitus or a more restrained tissue distribution. Recent studies on ClC-K1, ClC-2, ClC-3, ClC-5 and ClC-7 knockout mice and the identification of human inherited diseases caused by mutations of some of these chloride channels (myotonia congenita for ClC-1, Bartter disease for ClC-Kb, Dent's disease for ClC-5 and osteopetrose for ClC-7) have provided lines of direct evidence of the physiological relevance and importance of these chloride channels in the transport of chloride and in the endocytosis and transcytosis of proteins in specialized cells from the kidney and other tissues.

Background: Pyknodysostosis is characterized by post-natal onset of short-limbed short stature and generalized hyperostosis. It must be differentiated from osteopetrosis with precocious manifestations in which hyperostosis may crowd the marrow cavity with extramedullary hematopoiesis., Case Reports: A boy, born from consanguineous parents presented with classical features of pyknodysostosis: short-limbed stature, large skull, frontal bossing, wide anterior fontanelle and tendency to fracture. His sister had the same features at the age of 3 months; she had hepatosplenomegaly at the age of 5 months with anemia, erythroblastosis (13%), myelemia and, at 10 months, thrombocytopenia., Conclusion: Hyperosostis can be complicated by development of such severe hematological manifestations as classically seen in osteopetrosis. Differential diagnosis between both entities is based upon radioclinical investigation.

Background: Several distinct forms of osteopetrosis have been identified. Some of the autosomally recessive inherited forms are benign, much like the autosomal dominant form. Others are more malignant., Patients: The clinical data, skeletal radiographs, histological features and histories of 32 children with osteopetrosis were analyzed retrospectively., Results: The 32 patients, belonging to 20 sibships were divided into two groups. The first group included 24 patients, aged 1 day-11 months (mean 4.5 months), suffering from hepatosplenomegaly, anemia, thrombocytopenia and optic atrophy in early infancy. They also had a generalized increase in bone density, abnormal bone remodeling, rachitic lesions and a "bone-within-bone" appearance. Biopsies showed severe bone resorption and myelofibrosis. 19 of the 20 patients whose outcomes were known died during the first year of life. The second group included 8 patients, aged 40 days-3 years (mean: 11 months). Hepatosplenomegaly appeared later, anemia was less severe and thrombocytopenia occurred in only 1 patient. However, all 8 patients suffered from optic atrophy and 3 were deaf. Radiographs showed bone growth without rachitic lesions. Biopsies from 2 patients showed bone resorption, but no myelofibrosis. The outcome was less severe: 6 patients, now aged 8 months to 8 years, have survived, 3 of them for over 5 years. Genetic investigation showed patterns compatible with autosomal recessive inheritance in both groups, with similar sets of features within each sibship., Conclusion: This study reveals a new type of recessively inherited osteopetrosis. It can be classified as an intermediate form, distinct from both the malignant and the benign forms, and also distinct from osteopetrosis with carbonic anhydrase II deficiency.

Three new cases of a syndrome including osteopetrosis, tubular acidosis, mental retardation and cerebral calcifications are reported in the same sibship. This rare syndrome has an autosomal recessive inheritance and is due to carbonic anhydrase II deficiency. Fractures and mild sensorial manifestations were noticed in 2 cases. Mental deficiency and otitis were present in the 3 cases. Blood count and phosphocalcic metabolites were normal. A proximal tubular acidosis was present in each case. The radiological features were specific: cerebral calcifications were present in all cases since the age of 2 1/2 years; osteocondensation and bone modeling were predominant in long bones metaphyses. Alcalinization improved the height growth.

Three children in two unrelated families are affected by carbonic anhydrase II (CA II) deficiency. This disease has been reported in 27 other patients to date; the study of the pedigrees indicates that it is supported by autosomal recessive inheritance. All the patients have a very high CA I/CA II ratio (greater than 10(4) versus 6 to 10 in controls) and carrier detection is possible in obligate heterozygotes (CA I/CA II = 12 to 17). The clinical presentation consists in renal tubular acidosis, osteopetrosis and cerebral calcifications. The long term follow-up of these patients shows that the prognosis is mainly of neurological and mental expression.

The intraperitoneal infusion of male bone marrow cells to the "op" female Rat reverses the course of the lethal disease and initiates a repopulation of the thymus, spleen and bone marrow. The weight of the atrophic "op" thymus increases before any sign of recovery becomes apparent.

In the osteopetrotic mutant rat "op", the white pulp of the spleen is poor in T lymphocytes, while the red pulp is hyperplastic in reaction to the aplastic bone marrow. Grafting of normal thymus into the mutant corrects these anomalies.

Six cases of a new hereditary chondrodyplasia are reported. The features are severe dwarfism, generalized hypotonia, frequent and considerable desaxations of fingers and toes. Slight facial dysmorphism with evolutive scoliosis is often associated. Osteopetrosis is diffuse and is associated with important metaphyseal widening as well as epiphyseal irregularities and often carpal and tarsal supernumerary bones. No metabolic or chromosomal abnormality was found. The relations of the disease with related types described in Larsen's syndrome are considered.

A graft of normal thymus performed after thymectomy can cure the lethal osteopetrotic condition of the "op" Rat. The beneficial effect of normal bone marrow injection can be suppressed by prior thymectomy of the "op" Rat. Thymus is likely to play a role in the pathogenesis of osteopetrosis.

It is possible to make an early diagnosis of rat " op " osteopetrosis. The growth of the mandibular incisor is stopped at birth by failure of bone resorption around the dental root. The primary trabeculae of the long bones fail to undergo resorption: osteoblasts differentiate along them, but osteoclasts are missing and reticular cells are not distinguishable. When 2 and 3 days old, the medullary cavity is obstructed by osseous trabeculae, vascular system is lacking, hemopoietic cells no longer differentiate, osteoclasts are scarce and degenerative; medullary tissue is compact, including numerous osteoblastic cells. Bone marrow smears clearly show medullary cell deficiency, weakening hemopoiesis, prevalent osteoblasts and a lack of osteoclasts. Marrow is taken out "in vivo" from an excised metatarsal bone, at birth and over the next few days. Osteopetrotic rats identified in this way in litters issued from heterozygote pair can be treated from the first week.

On the basis of one case, the diagnostic features of Pycnodysostosis, a constitutional bone disease with autosomal recessive transmission, are reviewed: Clinically: stunted growth and a special type of craniofacial dysmorphism. Radiologically: overall density of the skeleton. It is pointed out that repositioning in situ of dental germs in malposition usually gives good results, but that more reservations must be expressed when dealing with pathological bone as is the case in Pycnodysostosis.