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X-linked nonprogressive congenital cerebellar hypoplasia: clinical description and mapping to chromosome Xq
S N Illarioshkin1, H Tanaka, E D Markova
1Department of Neurology, Brain Research Institute, Niigata University, Japan.
Insights
This study identifies a novel X-linked recessive congenital ataxia in males, characterized by delayed motor skills and cerebellar hypoplasia. Genetic mapping located the responsible gene to chromosome Xq23, offering insights into rare cerebellar disorders.
Area of Science:
- Genetics
- Neurology
- Pediatrics
Background:
- Congenital ataxia is a group of rare neurological disorders characterized by impaired coordination present from birth.
- Familial forms of ataxia suggest a genetic basis, but novel genetic loci and distinct clinical phenotypes continue to be identified.
Observation:
- A large family presented with X-linked recessive congenital ataxia affecting 7 males across three generations.
- Affected individuals exhibited delayed motor milestones, developing cerebellar ataxia, dysarthria, and external ophthalmoplegia by age 5-7, without intellectual disability or sensory loss.
- Neuroimaging confirmed cerebellar hemispheres and vermis hypoplasia, with no disease progression after early childhood.
Findings:
- Genetic linkage analysis successfully mapped the gene responsible for this unique ataxia to a 38-cM interval on chromosome Xp11.21-q24.
- Further multipoint linkage analysis localized the disease gene to the proximal region of chromosome Xq, specifically near the DXS1059 locus (Xq23).
- This represents the first genetic mapping of a pure congenital cerebellar hypoplasia syndrome.
Implications:
- This research identifies a new genetic disorder, expanding the spectrum of known X-linked neurological conditions.
- The genetic mapping provides a crucial step towards identifying the specific gene responsible for this congenital ataxia.
- Understanding the genetic underpinnings of congenital cerebellar hypoplasia can inform future diagnostic and therapeutic strategies for similar rare diseases.
Abstract:
We examined a large family in which an X-linked recessive congenital ataxia manifested in 7 males from three generations. The affected boys first exhibited a marked delay of early developmental motor milestones. A neurological syndrome became evident by 5 to 7 years of age and included cerebellar ataxia, dysarthria, and external ophthalmoplegia; there were no symptoms of mental retardation, spastic paraparesis, or sensory loss. Neuroimaging studies revealed hypoplasia of cerebellar hemispheres and vermis. The disease showed no progression beyond early childhood. The unique heredity and clinical features clearly distinguish this new entity from a variety of previously described familial ataxias. Pairwise linkage analysis and haplotype reconstruction allowed us to map the gene responsible for this disorder to a 38-cM interval on chromosome Xp11.21-q24 flanked by the loci DXS991 and DXS1001. Upon multipoint linkage analysis, the disease gene was determined to be located most likely in the proximal part of chromosome Xq, with the maximal lod score of 4.66 at the locus DXS1059 (Xq23). This is the first example of the genetic mapping of a pure congenital cerebellar hypoplasia syndrome.