18q-deletion syndrome

18q-deletion syndrome is a rare chromosomal anomaly where there is a deletion of part of the long arm of chromosome 18. Associated symptoms and findings vary widely, as do their severity. Characteristic clinical features include short stature, intellectual disability, hypotonia, facial, and distal skeletal abnormalities.

Clinical presentation

The presence of the syndrome is usually evident at or soon after birth. Although there is significant phenotypic variation, some features are relatively constant and include ¹:

• decreased growth
• craniofacial dysmorphism
  • midface hypoplasia
  • frontal bossing
  • "carp-like" mouth
• genital hypoplasia
• limb abnormalities
  • clubfoot
  • syndactyly
  • short thumbs
• neurological abnormalities
  • developmental delay and intellectual disability
  • ocular movement disorders
  • seizures
  • autism

Pathology

Chromosome 18q syndrome appears to result from a spontaneous, sporadic chromosomal error during very early embryonic development.

Radiographic features

MRI

The appearance of the brain on MRI is dominated by abnormal white matter, particularly posteriorly and in the periventricular region. It is characterized by bilateral symmetric deep white matter hyperintensity on T2-weighted images, with associated involvement of the subcortical white matter also frequently encountered ^1,2. The brainstem and cerebellum are usually spared.

A previous hypothesis supposed that these changes are owing to hypomyelination or dysmyelination considering that myelin basic protein gene is deleted in this syndrome. However, some pathological studies demonstrated normal brain myelination in this syndrome and suggested that white matter gliosis is probably the cause of abnormal MRI signal ^6_.

MR spectroscopy

MRS demonstrates elevated white matter choline and alpha-glutamate concentrations (resonates at 3.75 ppm) ³.