occipital encephalocele

Knobloch Syndrome 2

Clinical Characteristics
Ocular Features: 

In an 18 month infant, ectopia lentis, cataract, and myopia with poor vision were noted.  This individual subsequently developed retinal degeneration and a serous retinal detachment.

Systemic Features: 

Only one patient has been reported.  While the clinical signs resemble Knobloch 1 syndrome, brain imaging does not reveal malformations in this syndrome.  The only systemic sign, in addition to an occipital encephalocele, is a minor delay in fine motor skills.

Genetics

This autosomal recessive disorder results from homozygous loss of function mutations in the ADAMTS18 gene (16q23.1).  The gene product has been found in the lens and retina in the murine eye.

Mutations in ADAMTS18 have also been found in the syndrome of Micorcornea, Myopia, Chorioretinal atrophy, and Telecanthus.  It may also be responsible for a retinal dystrophy.

Knobloch 2 syndrome was identified in a single female born to consanguineous parents.

This disorder is separate to Knobloch 1 syndrome (267750) based on the causative mutations.  A third type, KNO3, has been proposed since the Knobloch clinical features were found in a 4-generation consanguineous Pakistani family but the phenotype mapped to 17q11.2.

Pedigree: 
Autosomal recessive
Treatment
Treatment Options: 

The skull defect can be closed and the lenses can be removed if indicated.

References
Article Title: 

Knobloch Syndrome 1

Clinical Characteristics
Ocular Features: 

The ocular findings include high myopia, vitreoretinal degeneration, dislocated lenses, cataracts, and retinal detachment.  Some patients have early onset (2-4 years old) night blindness and progress to total blindness before 20 years of age.  Nystagmus, strabismus, small optic discs, glaucoma, and cataracts have been reported.  Poor vision and progressive loss of acuity are common.  The vitreous appears to be condensed into sheets and there may be distortion of the vitreoretinal interface with irregular white dots and lines.  Pigmentary changes are common in the retina which some have described as consistent with choroidal sclerosis and chorioretinal atrophy.  Atrophic changes are often seen in the macula.

Systemic Features: 

The degree of skull and brain defects is variable.  Some patients have only occipital scalp defects while others have occipital encephaloceles.  The scalp defect may contain heterotopic neuronal tissue suggesting neuronal migratory defects.  Brain imaging has revealed a variety of defects and some patients have cognitive deficits and personality changes.  Cerebellar atrophy with ataxia is found in some patients.

Genetics

This is an autosomal recessive disorder secondary to homozygous mutations in the COL18A1 gene (21q22.3).  Mutated COL18A1 leads to defects in type XVIII collagen which is a component of basement membranes throughout the body, especially in the eye.

In spite of some clinical similarities, this disorder is genetically distinct from Knobloch 2 syndrome (608454).  A third type, KNO3, has been proposed since the Knobloch clinical features were found in a 4-generation consanguineous Pakistani family but the phenotype mapped to 17q11.2.

Pedigree: 
Autosomal recessive
Treatment
Treatment Options: 

Treatment is largely supportive.  Attempts at repair of retinal detachments often fail and phthisis bulbi is not uncommon.

References
Article Title: 
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