Developmental Spectrum of Children With Congenital Osteopetrosis, by J.M. Charles and L.L. Key, Journal of Pediatrics, 1998,132,371–374.
Osteopetrosis is a disease process characterized by defects in osteoclastic function and in superoxide production by leukocytes. The defects caused by the disease result in narrowing of cranial nerve foramina and a decrease in bone marrow space, which leads to abnormal bone remodeling, leukoerythroblastic anemia, immune dysfunction, impaired vision and hearing, fractures, growth failure, and neurologic impairment. The purpose of this descriptive study was to outline the developmental process of children with the severe recessive form of osteopetrosis. The authors report that improved treatment has expanded the lifespan of those with this form of osteopetrosis, and thus, unanswered questions are surfacing regarding the growth and development of these children. Although a poor prognosis is usually predicted, nothing has been done formally to prove this.
Twenty-three children admitted to the hospital for an evaluation of interferon-gamma, which is a medication prescribed to treat osteopetrosis, served as subjects. The ages of these children ranged from two weeks to 11 years, seven months with an average of 4.25 years. Between October 1992 and July 1996, these children were seen once or twice a year at which time a developmental evaluation was done by a developmental pediatrician. Various testing instruments were used depending on the age and visual status of the subject. The Clinical Assessment Test/Clinical Linguistic Auditory Milestones were administered to children younger than three years of age with normal or mild visual impairment to determine a cognitive and language developmental quotient. The Clinical Linguistic Auditory Milestone was administered to determine the language quotient of those who had more than a mild visual impairment. The Slossom Intelligence Test was given to children older than three years of age, regardless of their visual impairment, to assess their verbal ability. The Maxfield-Bucholz Scale of Social Maturity for Preschool Blind Children (M-B) was given to the children who were blind or those with partial visual loss with a chronological age of less than seven years to obtain a social quotient. It was also used with children whose mental age was less than seven years of age, although they were older chronologically, to determine their adaptive abilities. For children five years of age and younger, an unpublished gross motor milestone test was used to determine gross motor quotient. The subjects older than five years of age were noted as ambulatory or nonambulatory.
The results of this study revealed that the language quotients for the visually impaired children three years and younger ranged from average to moderately handicapped. For the children without visual impairment, language quotients ranged from average to low average with problem-solving skills spanning from average to mildly handicapped. The verbal abilities of the children with visual impairments who were older than three years of age ranged from average to moderately handicapped. The verbal abilities of the older children without any visual impairment ranged from average to mildly handicapped. The Slossom Intelligence Test was not given to four subjects because of either noncompliance or severe language deficit. The social quotient for three of the four subjects not given the Slossom spanned from moderate to profound retardation. The M-B estimated social quotient ranged from average to profoundly mentally handicapped. Gross motor skills showed a slight delay initially, which declined to a more severe level and then improved gradually. Therefore, by four years of age, all the subjects with the exception of two were ambulatory.
The authors found a variety of cognitive and adaptive abilities among the 23 subjects. However, the study, which is the most comprehensive report of the developmental spectrum of children with congenital osteopetrosis, had some limitations. There seems to be a lack of reliable and valid standardized tests for individuals with visual impairments. The tests administered do not consider motor deficits and are not designed specifically for the child with multiple handicaps. In addition, other factors besides visual impairment such as bony overgrowth, hearing loss, poor nutrition, chronic hypoxia, and frequent fractures may lead to developmental delays. The authors suggest the long-term impact of caring for a child with osteopetrosis be included in future studies as well as the psychological stresses on families of such children and their longitudinal outcome.
Limitations and Implications
The authors had good intentions to study the developmental progress of children with the recessive form of osteopetrosis, especially because their lifespan had been increased because of better and more effective treatment. However, the study had some major limitations, and the authors did not address many important questions. More background information should have been provided regarding the tests administered in the study such as the reliability and validity of the tests, an explanation of the testing procedure, and the rating scales used. The tables included with the report were somewhat difficult to understand because the legends did not define all the symbols used in the tables.
The sample size was small and included children with a wide range of ages and medical complications, which can lead to questionable validity and reliability of the results of the study. Only data ranges were given in the report. Means for the data for subjects under the age of three or over the age of three could have been provided. The results as stated were difficult to interpret. The authors should have used more consistent testing procedures. For example, one test, if possible should have been given to the children three years of age and younger regardless of visual impairment. The researchers did not explain the rationale and the appropriateness for administering the M-B test to children whose chronological age was older than seven years of age. Also, they did not discuss thoroughly the significance of the findings of the study.
Regardless of the limitations, the authors have provided a foundation for other studies to follow. They were successful in proving the importance and relevance of such a study. Perhaps in the future, a study with more subjects and more reliable and valid testing methods would provide more information about the development of children with osteopetrosis.