Knobloch syndrome is a rare genetic disorder presenting severe eyesight problems and often a defect in the skull. It was named after W.H. Knobloch, who first described the syndrome in 1971. A usual occurrence is a degeneration of the vitreous humour and the retina, two components of the eye. This breakdown often results in the separation of the retina (the light-sensitive tissue at the back of the eye) from the eye, called retinal detachment, which can be recurrent. Extreme myopia (near-sightedness) is a common feature. The limited evidence available from electroretinography suggests a cone-rod pattern of dysfunction is also a feature.

Knobloch syndrome is caused by mutations in an autosomal recessive inherited gene. These mutations have been found in the COL18A1 gene that instructs for the formation of a protein that builds collagen XVIII. This type of collagen is found in the basement membranes of various body tissues. Its deficiency in the eye is thought to be responsible for affecting normal eye development. There are two types of Knobloch syndrome and the case has been made for a third.

When caused by mutations in the COL18A1 gene it is called Knobloch syndrome type 1. The genes causing types II and III have yet to be identified.

Knobloch syndrome is also characterised by cataracts, dislocated lens with skull defects such as occipital encephalocele and occipital aplasia. Encephalocele is a neural tube defect where the skull has not completely closed and sac-like protrusions of the brain can push through the skull; (it can also result from other causes).

In Knobloch’s syndrome this is usually seen in the occipital region, and aplasia is the underdevelopment of tissue again in this reference in the occipital area.

Weill–Marchesani syndrome is a rare genetic disorder characterized by short stature; an unusually short, broad head (brachycephaly) and other facial abnormalities; hand defects, including unusually short fingers (brachydactyly); and distinctive eye (ocular) abnormalities. It was named after ophthalmologists Georges Weill (1866-1952) and Oswald Marchesani (1900-1952) who first described it in 1932 and 1939, respectively.

The eye manifestations typically include unusually small, round lenses of the eyes (spherophakia), which may be prone to dislocating (ectopia lentis), as well as other ocular defects. Due to such abnormalities, affected individuals may have varying degrees of visual impairment, ranging from nearsightedness myopia to blindness. Researchers suggest that Weill–Marchesani syndrome may have autosomal recessive or autosomal dominant inheritance.

No specific treatment is available. Management is only supportive and preventive.

Those who are diagnosed with the disease often die within the first few months of life. Almost all children with the disease die by the age of three.

Eye surgery has been documented to help those with ocular diseases, such as some forms of glaucoma.

However, long term medical management of glaucoma has not proven to be successful for patients with Weill–Marchesani syndrome. Physical therapy and orthopedic treatments are generally prescribed for problems stemming from mobility from this connective tissue disorder. However, this disorder has no cure, and generally, treatments are given to improve quality of life.

Stickler syndrome and Marshall syndrome have an autosomal dominant pattern of inheritance. However, there is a great deal of variation within and among families with regard to gene expression. Some may be more severely affected and others may be very mildly affected. Often these syndromes are not recognized in a family until a baby is born with Pierre Robin syndrome or some members have detached retinas or cataracts at a young age.

Both syndromes where correlated with mutations in the COL11A1 gene.

The Jalili syndrome is caused by different mutations all with a linkage at the achromatopsia locus 2q11 on the metal transporter gene, CNNM4. Sequence analysis of this gene within Jalili syndrome sufferers has identified homozygosity or compound heterozygosity for several different mutations in the CNNM4 gene.

Walker–Warburg syndrome (WWS), also called Warburg syndrome, Chemke syndrome, HARD syndrome (Hydrocephalus, Agyria and Retinal Dysplasia), Pagon syndrome, cerebroocular dysgenesis (COD) or cerebroocular dysplasia-muscular dystrophy syndrome (COD-MD), is a rare form of autosomal recessive congenital muscular dystrophy. It is associated with brain (lissencephaly, hydrocephalus, cerebellar malformations) and eye abnormalities. This condition has a worldwide distribution. The overall incidence is unknown but a survey in North-eastern Italy has reported an incidence rate of 1.2 per 100,000 live births. It is the most severe form of congenital muscular dystrophy with most children dying before the age of three years.

Corneal-cerebellar syndrome (also known as Der Kaloustian-Jarudi-Khoury syndrome) is an autosomally resessive disease that was first described in 1985. Three cases are known: all are sisters in the same family.

One case of Cohen Syndrome, in a Palestinian boy from Tul-Karem, was reported in the Israeli monthly Kol Israel BeAsakim (in Hebrew) in the December 2007 issue. Over the past several years there have been approximately 50 new cases worldwide. There are population groups with this condition in Australia, the UK and the US. It still seems to go undiagnosed leaving the number of cases less than 500.

Diagnosis is made based on features as well as by the very early onset of serious eye and ear disease. Because Marshall syndrome is an autosomal dominant hereditary disease, physicians can also note the characteristic appearance of the biological parent of the child. There are no tests for Stickler syndrome or Marshall syndrome. Some families with Stickler syndrome have been shown to have mutations in the Type II collagen gene on chromosome 1. However, other families do not show the linkage to the collagen gene. It is an area of active research, also the genetic testing being expensive supports that the diagnosis is made depending on the features.

Jalili syndrome is a genetic disorder characterized by the combination of cone-rod dystrophy of the retina and amelogenesis imperfecta. It was characterized in 1988 by Dr. I. K. Jalili and Dr. N. J. D. Smith, following the examination of 29 members of an inbred, Arab family living within the Gaza Strip.

Cohen syndrome (also known as Pepper syndrome or Cervenka syndrome, named after Michael Cohen, William Pepper and Jaroslav Cervenka, who researched the illness) is a genetic disorder.

One family of 68 individuals over 5 generations was studied and the prevalence of disease among the family members suggests that it is indicative of dominant inheritance that is not sexually linked. This is supported by the fact that the disease failed to skip generations even in the absence of intermarriages and that disease incidence was independent of sex. The current findings suggest that the cause of the disease could be narrowed down to one enzymatic defect that is involved in the development of neuroectodermal tissue, however the exact molecular mechanisms are currently unknown. The other symptoms that arise such as bone defects and diabetes may be secondary to this enzymatic defect.

Zamzam–Sheriff–Phillips syndrome is a rare autosomal recessive congenital disorder. It is characterized by aniridia, ectopia lentis, abnormal upper incisors and intellectual disability. Not a lot of research has been undertaken of this particular disease so thus far there is no known gene that affects this condition. However it has been hypothesised that the symptoms described are found at a particular gene, though intellectual disability is believed to be due to a different genetic cause.

Consanguinuity (intermarrying among relatives such as cousins), often associated with autosomal recessive inheritance, has been attributed to the inheritance of this disease.

It was concluded by Mousa-Al et al. that the disease is different from a disease known as spastic ataxia-corneal dystrophy syndrome that had been found a year later in 1986 in an inbred Bedouin family. Corneal-cerebellar syndrome differs from the spastic ataxia-corneal dystrophy syndrome by causing mental retardation. Corneal dystrophy is also epithelian instead of being stromal.

The exact pathophysiological mechanism of Flynn–Aird syndrome is unknown. However, several theories are in place with regards to the nature of this disease including the presence of a genetically defective enzyme involving a neuroectodermal tissue constituent. This explanation provides evidence for the late onset of the condition, the intricate findings, the varied nature of the disorder, as well as the genetic incidence. In addition, some aspects of the condition may be linked to a suppressing (S) gene due to the fact that only a small amount of stigmata appeared while the defects were still transmitted in the family studied. A suppressing gene down regulates the phenotypic expression of another gene, especially of a mutant gene. Other abnormalities may be due to endocrine system diseases.

Lissencephaly 2, more commonly called Norman–Roberts syndrome, is a rare form of microlissencephaly caused by a mutation in the RELN gene.A small number of cases have been described. The syndrome was first reported by Margaret Grace Norman and M. Roberts et al. in 1976.

Lack of reelin prevents normal layering of the cerebral cortex and disrupts cognitive development. Patients have cerebellar hypoplasia and suffer from congenital lymphedema and hypotonia. The disorder is also associated with myopia, nystagmus and generalized seizures.

Norman–Roberts syndrome is one of two known disorders caused by a disruption of the reelin-signaling pathway. The other is VLDLR-associated cerebellar hypoplasia, which is caused by a mutation in the gene coding for one of the reelin receptors, VLDLR.

Disruption of the RELN gene in human patients is analogous to the malfunctioning RELN gene in the reeler mouse.

Corneodermatosseous syndrome (also known as "CDO syndrome") is an autosomal dominant condition with onset in infancy, characterized by corneal dystrophy, photophobia, diffuse palmoplantar keratoderma, distal onycholysis, skeletal abnormalities, with brachydactyly, short stature, and medullary narrowing of digits.

EEM syndrome (or Ectodermal dysplasia, Ectrodactyly and Macular dystrophy syndrome) is an autosomal recessive congenital malformation disorder affecting tissues associated with the ectoderm (skin, hair, nails, teeth), and also the hands, feet and eyes.

The condition was first described in 1978 by Pitt and Hopkins in two unrelated patients.

The genetic cause of this disorder was described in 2007. This disorder is due to a haploinsufficiency of the transcription factor 4 (TCF4) gene which is located on the long arm of chromosome 18 (18q21.2) The mutational spectrum appears to be 40% point mutations, 30% small deletions/insertions and 30% deletions. All appear to be "de novo" mutations and to date no risk factors have been identified.

A Pitt–Hopkins like phenotype has been assigned to autosomal recessive mutations of the contactin associated protein like 2 (CNTNAP2) gene on the long arm of chromosome 7 (7q33-q36) and the neurexin 1 alpha (NRXN1) gene on the short arm of chromosome 2 (2p16.3).

EEM syndrome is caused by mutations in the "P-cadherin" gene ("CDH3"). Distinct mutations in "CDH3" (located on human chromosome 16) are responsible for the macular dystrophy and spectrum of malformations found in EEM syndrome, due in part to developmental errors caused by the resulting inability of "CDH3" to respond correctly to the "P-cadherin" transcription factor p63.

The gene for p63 ("TP73L", found on human chromosome 3) may also play a role in EEM syndrome. Mutations in this gene are associated with the symptoms of EEM and similar disorders, particularly ectrodactyly.

EEM syndrome is an autosomal recessive disorder, which means the defective gene is located on an autosome, and two copies of the defective gene - one from each parent - are required to inherit 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.

Spastic ataxia-corneal dystrophy syndrome (also known as Bedouin spastic ataxia syndrome) is an autosomally resessive disease. It has been found in an inbred Bedouin family. It was first described in 1986. A member of the family who was first diagnosed with this disease also had Bartter syndrome. It was concluded by its first descriptors Mousa-Al et al. that the disease is different from a disease known as corneal-cerebellar syndrome that had been found in 1985.

Symptoms include spastic ataxia, cataracts, macular corneal dystrophy and nonaxial myopia. Mental development is normal.

A contiguous gene syndrome (CGS), also known as a contiguous gene deletion syndrome is a clinical phenotype caused by a chromosomal abnormality, such as a deletion or duplication that removes several genes lying in close proximity to one another on the chromosome. The combined phenotype of the patient is a combination of what is seen when any individual has disease-causing mutations in any of the individual genes involved in the deletion. While it can be caused by deleted material on a chromosome, it is not, strictly speaking, the same entity as a segmental aneuploidy syndrome. A segmental aneuploidy syndrome is a subtype of CGS that regularly recur, usually due to non-allelic homologous recombination between low copy repeats in the region. Most CGS involve the X chromosome and affect male individuals.

One of the earliest and most famous examples of a CGS involves a male patient with Duchenne muscular dystrophy (DMD), chronic granulomatous disease (CGD), retinitis pigmentosa and intellectual disability. When it was discovered that an X chromosome deletion (specifically Xp21) was the underlying cause of all of these features, researchers were able to use this information to clone the genes responsible for DMD and CGD.

One of those more common CGS involves a deletion on the X chromosome (near Xp21) that encompasses "DMD" (causing Duchenne muscular dystrophy), "NROB1" (causing X-linked adrenal hypoplasia congenita) and "GK" (causing glycerol kinase deficiency). These patients will have all the common features of each individual disease, resulting in a very complex phenotype. Deletions near the distal tip of the p arm of the X chromosome are also a frequent cause of CGS. In addition to the previously described CGS that occur on the X chromosome, two other common syndromes are Langer-Giedion syndrome (caused by deletions of "TRPS1" and "EXT1" on 8q24 and WAGR syndrome (caused by deletions on 11q13 encompassing "PAX6" and "WT1".)

Persistent hyperplastic primary vitreous (PHPV), also known as Persistent Fetal Vasculature (PFV), is a rare congenital developmental anomaly of the eye that results

following failure of the embryological, primary vitreous and hyaloid vasculature to regress. It can be present in three forms: purely anterior (persistent tunica vasculosa lentis and persistent posterior fetal fibrovascular sheath of the lens), purely posterior (falciform retinal septum and ablatio falcicormis congenita) and a combination of both. Most examples of PHPV are unilateral and non-hereditary. When bilateral, PHPV may follow an autosomal recessive or autosomal dominant inheritance pattern.

Causes a ‘white reflex’ in the affected eye (leukocoria), prompting further investigation.