1. In the lumbar spinal canal of the achondroplast there is decreased cross-sectional area. In addition the intervertebral foramina are narrow. These changes result in reduced area for the dural sac and exiting spinal nerves. 2. There is associated thoracolumbar kyphosis and a lumbosacral hyperlordosis. These sagittal plane changes result in increased tension on the dural sac and nerves. 3. With aging there is disc degeneration with disc space narrowing and osteophyte formation. In addition facet hypertrophy with osteophyte formation are common. These degenerative changes further reduce the size of an already compromised spinal canal and intervertebral foramina. The above understanding of the normal spinal and anatomy in the achondroplast, and the added effects of aging allow the surgeon to plan a logical treatment regimen for neurological problems in the achondroplast. Fig. 6. Cross-section at the di sc level of an achondroplast (A) and an age matched non-achondroplast (B). The cross-sectional area of the spinal canal is reduced in the achondroplast, with a reduction in the antero- posterior canal (C vs. C 1 ). There is facet hyper- trophy extending into the nerve root canal and into the spinal canal lateral recess (B vs. B 1 ). In ad- dition the nerve root canal is markedly reduced in-the achondroplast (D vs. D1 ). (Reprinted with permis- sion, as of Fig. 5). 225 REFERENCES 1. R. J. Eulert, Scoliosis and kyphosis in dwarfing conditions, Arch. Orthop.Traum. Surg.102:45 (1983).

The twelfth edition of this classic reference work includes:

- More than 2,000 new entries

- A total of more than 9,000 entries

- New features and enhancement of the familiar old features

- Mapping information on more than 4,000 genes of known function

- Information on specific point mutations responsible for more than 700 genetic disorders or neoplasms

"Mendelian Inheritance in Man" (MIM) is a genetic knowledgebase that serves clinical medicine and biomedical research, including the Human Genome Project. It aims to be comprehensive (not only complete, but also collated, integrated, and interpreted), authoritative (not only accurate but also sound in its interpretations and judgements), and timely (not only up-to-date but also historically dimensioned).

"From a review of the eleventh edition, "Reproductive Toxicology: "Even the convenience of computer-based forms of "MIM" cannot eliminate the need for "MIM" in book form. The preface provides a wonderful synopsis of human genetics. The information contained in this text serves as a concise review for those with a genetics background."

"From a review of the tenth edition, "New England Journal of Medicine: " Victor McKusick] has been for all these years the shepherd of the development of the field of clinical genetics]. Perhaps his most important pragmatic achievement has been the 10 editions of "Mendelian Inheritance in Man, " which rapidly became and has remained the principal source of information on inherited diseases for all clinical geneticists.

"In addition to the erudite entries in the books, the references given with each description represent a magnificent bibliography of clinical genetics. With McKusick's leadership and continued interest in gene mapping, the book also rep-resents an important compen-dium of the location of genes on specific chromosomes.

"The book is a magnificent security blanket for the clinical geneticist and should be in the libraries not only of these specialists, but also of all others who see patients with diseases that have genetic components."