Chromosomal abnormalities
In those who are diagnosed with DWM before birth on ultrasound, up to half are found to have a chromosomal abnormality, with the most common being Edwards syndrome (trisomy 18), at roughly 26% of prenatal DWM cases. 6.5% of those diagnosed with DWM after birth also have Edwards syndrome. Other chromosomal abnormalities that can lead to DWM include triploidy, Patau syndrome (trisomy 13), trisomy 9 and partial 3q deletion or duplication. The 3q24 region contains the ZIC1 and ZIC4 genes, known to be associated with DWM. External toxins
Warfarin use during pregnancy has been known to lead to systemic defects in the fetus, including ocular dysgenesis, microcephaly, agenesis of the corpus callosum, skeletal abnormalities and heart defects. In 1985, it was also linked to DWM. Pathophysiology
The cerebellum begins forming at the fifth week of embryonic development. It differentiates at the top of the metencephalon, while the pons (in the brainstem) differentiates at the bottom, separated by the fourth ventricle. The cerebellar hemispheres form from the rhombic lips on the forward surface of the fourth ventricle, which expand and roll over to fuse in the midline to form the cerebellar vermis by the 15th week. If this process does not complete, the cerebellar vermis will not form fully. This long period of development of the cerebellar vermis makes it particularly vulnerable to disruptions.In DWM, the fourth ventricle opens up into and is continuous with almost the entire posterior fossa subarachnoid space. Pathophysiology of hydrocephalus
The reason why hydrocephalus occurs in DWM is not yet fully understood.
Laurence–Moon syndrome (LMS) is a rare autosomal recessive genetic disorder associated with retinitis pigmentosa, spastic paraplegia, and mental disabilities. Signs and symptoms
Intellectual disability, hexadactyly, central diabetes insipidus, blindness (usually by 30 years due to central retinal degeneration). Genetics
LMS is inherited in an autosomal recessive manner. This means the defective gene responsible for the disorder is located on an autosome, and two copies of the defective gene (one inherited from each parent) are required in order to be born with the disorder. The parents of an individual with an autosomal recessive disorder both carry one copy of the defective gene, but usually do not experience any signs or symptoms of the disorder. Diagnosis
The syndrome was originally thought to have five cardinal features (and recently a sixth was added), on the basis of which a diagnostic criterion was developed:
4 primary features or 3 primary features and 2 secondary features must be present. The primary features are:
1. Polydactyly
2. Rod-cone dystrophy
3. Learning disabilities
4. Obesity
5. Hypogonadism in males
6. Renal abnormalities
While the secondary features are stated to be as:
1. Speech disorder and/or developmental delay
2. Ophthalmic abnormalities other than rod-cone dystrophy (strabismus, cataract, astigmatism etc.) 3. Brachydactyly or Syndactyly
4. Polyuria and/or polydipsia (nephrogenic diabetes insipidus)
5. Ataxia, poor coordination, imbalance
6. Mild spasticity (especially lower limbs)
7. Diabetes mellitus
8. Dental crowding, hypodontia, small roots, high arched palate
9. Congenital heart disease
10. Hepatic fibrosis

Treatment
There is no cure to LNMS. However, symptomatic treatment is often provided. The patients with LNMS often experience ataxia, spasticity and contractures, restricting their movements and daily activities.