prognathism

Elsahy-Waters Syndrome

Clinical Characteristics
Ocular Features: 

Structural anomalies of periocular tissues are common.  Hypertelorism, proptosis, and telecanthus may be striking.  Colobomas or clefts of the upper lid are frequently seen.  The eyebrows are bushy and synophyrs may be present across a broad nasal bridge.  Megalocornea, downslanting lid fissures, glaucoma and cataracts have also been reported but are uncommon.

Systemic Features: 

The skull has been described as brachycephalic.  The midface is flat due to maxillary hypoplasia. The lower jaw is prominent and some patients have mandibular prognathism.  A bifid uvula or partial clefting of the palate are common.  Low-set and posteriorly rotated ears have been reported as well.

 Both pectus excavatum and pectus carinatum have been described.  The teeth have dysplastic enamel and often have obliterated pulp chambers and dental cysts.  Their roots may be shortened and deformed and they are often lost early.  Vertebrae may have fusion of the spines, particularly in the cervical area.  A mixed type of hearing loss is common and some degree of intellectual disability is often evident, especially in older individuals.  Most males have some degree of hypospadias.  Cryptorchidism has been reported in one individual.

Brain imaging in one case revealed no abnormalities.

Genetics

This disorder results from biallelic mutations in the CDH11 gene (16q21).  The parents have been consanguineous in most reports and no vertical transmission has been documented making autosomal recessive the most likely pattern of inheritance.

Pedigree: 
Autosomal recessive
Treatment
Treatment Options: 

No treatment for the general disorder has been reported.  Eyelid and palatal defects may be surgically repaired and assistive hearing devices may be of benefit.  Special education is also likely to be helpful.

References
Article Title: 

Myasthenic Syndromes, Congenital, Including AChR Deficiency

Clinical Characteristics
Ocular Features: 

The congenital myasthenic syndromes are genetically and clinically heterogeneous.  Ptosis is the outstanding ocular sign and virtually always present.  Strabismus and ophthalmoplegia are less common.  These signs are not helpful in the differential diagnosis of the many types of congenital myasthenia.

Some degree of ptosis is usually evident during the first 6 months of life.  By about 2 years of age strabismus and ophthalmoparesis are apparent but this sequence is highly variable.

Systemic Features: 

This is a group of nonprogressive disorders most often associated with acetylcholine receptor (AChR) defects at the neuromuscular junction.  An early sign may be decreased fetal movements.  Generalized weakness, a weak cry, and hypotonia are evident at birth.  Easy fatigability and limb weakness are noted in early childhood and affected children have difficulty running. Facial weakness, dysarthria, weakness of the tongue, and dysphagia are often present and many patients have respiratory difficulties. Motor development can be delayed.  Acute illnesses may exacerbate muscle weakness.

Genetics

This is the most common form of the congenital myasthenic syndromes. It is an autosomal recessive disorder of the postsynaptic type, so called because the mutations occur in genes that encode the subunits of acetylcholine receptors: CHRNE(17P13.2), and CHRNB1(17p13.1).  A similar phenotype results from mutations in MUSK (9p31.3) which is critical for synaptic differentiation.

Mutations in RAPSN(11p11.2), whose protein product is important for stabilization of the acetylcholine receptors at the endplate, may result in a similar phenotype but may also produce the fetal akinesia deformation sequence.  This lethal condition is often associated with severe respiratory disease and dysmorphism including limb contractures, micrognathia, and feeding difficulties.  Nothing is known about the ocular signs.

Another autosomal recessive congenital myasthenic syndrome (610542), CMSTA1, has a somewhat later onset (adolescence) and weakness in a limb girdle distribution but no ptosis or oculomotor problems.  Tubular aggregates of muscle fibers can be seen on biopsy.

Presynaptic autosomal recessive forms of congenital myasthenia such as CMS20 (617143) caused by mutations in SLC5A7 (2q12) and CMS21 (617239) secondary to mutations in SLC18A3 (10q11.23) with severe episodic apnea and ocular signs of ptosis and ophthalmoparesis have been reported.

Other postsynaptic forms of congenital myasthenia are the fast-channel type (FCCNS) (608930) and the slow channel type (SCCMS) (601462).  Ophthalmoparesis occurs early in both types.

The classification of congenital myasthenia syndromes is under construction.  In the case of many types only a single or very few families have been reported.   While the clinical manifestations involve alterations in the neuromuscular junnction, some result from heterozygous mutations while others are due to homozygous changes.  The defect may reside in presynaptic, synaptic, or postsynaptic mechanisms.  For a discussion and comprehensive listing of the various types see 601462.

Pedigree: 
Autosomal recessive
Treatment
Treatment Options: 

Cholinesterase inhibitor drugs can be highly beneficial in some forms of the disease but genotyping is necessary before attempting pharmacological therapy.  Frequent ventilation and enteric feeding may be helpful for selected individuals.  Individuals should be protected from acute illnesses, especially respiratory infections.

References
Article Title: 

Impaired Presynaptic High-Affinity Choline Transporter Causes a Congenital Myasthenic Syndrome with Episodic Apnea

Bauche S, O'Regan S, Azuma Y, Laffargue F, McMacken G, Sternberg D, Brochier G, Buon C, Bouzidi N, Topf A, Lacene E, Remerand G, Beaufrere AM, Pebrel-Richard C, Thevenon J, El Chehadeh-Djebbar S, Faivre L, Duffourd Y, Ricci F, Mongini T, Fiorillo C, Astrea G, Burloiu CM, Butoianu N, Sandu C, Servais L, Bonne G, Nelson I, Desguerre I, Nougues MC, Boeuf B, Romero N, Laporte J, Boland A, Lechner D, Deleuze JF, Fontaine B, Strochlic L, Lochmuller H, Eymard B, Mayer M, Nicole S. Impaired Presynaptic High-Affinity Choline Transporter Causes a Congenital Myasthenic Syndrome with Episodic Apnea. Am J Hum Genet. 2016 Sep 1;99(3):753-61.

PubMed ID: 
27569547

Congenital myasthenic syndromes

Hanta?O D, Richard P, Koenig J, Eymard B. Congenital myasthenic syndromes. Curr Opin Neurol. 2004 Oct;17(5):539-51. Review.

PubMed ID: 
15367858

Waardenburg Syndrome, Type 3

Clinical Characteristics
Ocular Features: 

Type 3 Waardenburg syndrome has many of the features of other types but with the addition of upper limb anomalies.  Dystopia canthorum and a broad nasal root are characteristic.  Iris heterochromia is present in some patients.  Hypopigmentation may be seen in lashes and eyebrows.

Systemic Features: 

The upper limbs may appear underdeveloped with flexion contractures, fusion of the carpal bones and sometimes syndactyly.  A white forelock may or may not be present.  The cranial bones may be anomalous and rare patients can have microcephaly with significant mental retardation.  Mental function is usually normal though. Occasional patients have cleft palate and/or lip. Hearing loss is of the sensorineural type.  Hypopigmented skin patches are sometimes present but not all patients have them.

Genetics

The uniqueness of Waardenburg syndrome types 1 and 3 remains to be established.  Mutations in the PAX3 gene are responsible for both types and both have been found in the same family.  The phenotype is transmitted in an autosomal dominant pattern in either case but several families have been reported with type 1 WS in parents heterozygous for PAX3 mutations who had a homozygous child with the type 3 phenotype.  However, heterozygous individuals with type 3 have also been reported and the relationship of the two types remains unknown.

Craniofacial-deafness-hand syndrome(122880) with mutations in PAX3 has many features similar to those found in Waardenburg syndrome type 3 and may or may not be a unique disorder.

Pedigree: 
Autosomal dominant
Autosomal recessive
Treatment
Treatment Options: 

There is no treatment for the syndrome but cochlear implants might be helpful.

References
Article Title: 

Gurrieri Syndrome

Clinical Characteristics
Ocular Features: 

Tapetoretinal degeneration has been described in several patients.  Some patients have keratoconus with lens and corneal opacities.  Visual acuities have not been reported.  The full ocular phenotype must be considered unknown since most patients have not had full ophthalmic evaluations.

Systemic Features: 

Features of an osteodysplasia are among the most striking in this syndrome.  Short stature, brachydactyly, delayed bone age, osteoporosis, and hypoplasia of the acetabulae and iliac alae are usually present.  Birth weight is often low.  Joints may be hyperflexible as part of the generalized hypotonia. The eyes are deep-set, the nasal bridge is prominent, the midface is flat, and the supraorbital ridges are prominent giving the face a rather coarse look.  Prognathism with a prominent lower lip and dental malocclusion reinforce this appearance.  Seizures beginning in early childhood may be difficult to control.  Most patients have severe psychomotor retardation and never acquire speech.

Genetics

The genetics of this familial disorder remain unknown.  No locus or mutation has been identified but one patient had an absent maternal allele of the proximal 15q region as found in Angelman syndrome.

Orofaciodigital syndrome IX (258865) is another autosomal recessive syndrome sometimes called Gurrieri syndrome.  In Gurrieri’s original description of two brothers, chorioretinal lacunae, similar to those seen in Aicardi syndrome (304050), were present.  The systemic features are dissimilar, however.

Pedigree: 
Autosomal recessive
Treatment
Treatment Options: 

No treatment is known.

References
Article Title: 

Microphthalmia, Syndromic 8

Clinical Characteristics
Ocular Features: 

Microphthalmia is a consistent feature and short palpebral fissures have been described in one patient.  Microcornea has also been noted.  At least one patient was blind.

Systemic Features: 

The skull is small and mental retardation is usually a feature.  Other variable abnormalities include cardiac defects, prognathism, split-feet, cryptorchidism, and cleft lip and palate.  Few patients have been reported and the full phenotype is unknown.

Genetics

The gene remains unidentified in this rare syndrome but a locus has been identified at 6p21.  In at least one patient with a balanced translocation of t(6;13)(q21;q12) a disruption in the SNX3 gene at 6q21 was identified.  Most cases occur sporadically and have cytogenetic abnormalities.

Treatment
Treatment Options: 

No treatment is known.

References
Article Title: 

Smith-Magenis Syndrome

Clinical Characteristics
Ocular Features: 

Ocular abnormalities have been found in the majority of patients.  Microcornea, myopia, strabismus and iris dysplasia are the most common.  Rare patients have iris colobomas or correctopia.  The eyes appear deep-set and lid fissures are upward slanting.

Systemic Features: 

The facial features are considered to be distinctive, characterized by a broad, square face, prominent forehead, broad nasal bridge, and midface hypoplasia.  These and other features appear more pronounced with age as in the size of the jaw which is underdeveloped in infancy and eventually becomes prognathic.  Most patients have developmental delays, speech and motor deficits, cognitive impairments and behavioral abnormalities.  Hypotonia, hyporeflexia, failure to thrive, lethargy, and feeding difficulties are common in infants.  Older individuals have REM sleep disturbances with self-destructive behaviors, aggression, inattention, hyperactivity, and impulsivity.  Short stature, hypodontia, brachydactyly, hearing loss, laryngeal anomalies, and peripheral neuropathy are common. Seizures are uncommon.

The behavioral profile of this syndrome can resemble that of autism spectrum disorders although symptoms of compulsivity are more mild.

A related developmental disorder known as Potacki-Lupski syndrome (610883) involving the same locus on chromosome 17 has a similar behavioral profile.  Ocular and systemic malformations may be less severe though.

Genetics

Most patients (90%) with the Smith-Magenis syndrome have interstitial deletions in the short arm of chromosome 17 (17p11.2).  However, it is included here since a few have heterozygous molecular mutations in the RAI1 gene which is located in this region.  While there is considerable phenotypic overlap, individuals with chromosomal deletions have the more severe phenotype as might be expected.  For example, those with RAI1 mutations tend to be obese and are less likely to exhibit short stature, cardiac anomalies, hypotonia, hearing loss and motor delays than seen in patients with a deletion in chromosome 17.  However, the phenotype is highly variable among patients with deletions depending upon the nature and size of the deletion.

The retinoic acid induced 1 gene (RAI1) codes for a transcription factor whose activity is reduced by mutations within it.

Familial cases are rare and reproductive fitness is virtually zero.  If parental chromosomes are normal, the risk for recurrence in sibs is less than 1%.  Males and females are equally affected.

In Potocki-Lupski syndrome (610883) there is duplication of the 17p11.2 microdeletion as the reciprocal recombination product of the SMS deletion.   

Pedigree: 
Autosomal dominant
Treatment
Treatment Options: 

Medical monitoring, psychotropic medications and behavioral therapies are all useful.  Special education and vocational training may be helpful for those less severely affected.

References
Article Title: 

Characterization of Potocki-Lupski syndrome (dup(17)(p11.2p11.2)) and

Potocki L, Bi W, Treadwell-Deering D, Carvalho CM, Eifert A, Friedman EM,
Glaze D, Krull K, Lee JA, Lewis RA, Mendoza-Londono R, Robbins-Furman P, Shaw C,
Shi X, Weissenberger G, Withers M, Yatsenko SA, Zackai EH, Stankiewicz P, Lupski
JR. Characterization of Potocki-Lupski syndrome (dup(17)(p11.2p11.2)) and
delineation of a dosage-sensitive critical interval that can convey an autism
phenotype. Am J Hum Genet. 2007 Apr;80(4):633-49.

PubMed ID: 
17357070
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