maxillary hypoplasia

Axenfeld-Rieger Syndrome, Type 4

Clinical Characteristics
Ocular Features: 

The ocular features of this syndrome are similar to types 1-3 and primarily involve the anterior segment.  The iris stroma is hypoplastic and the pupil location may be eccentric.  Full thickness defects in the iris can lead to pseudopolycoria.   There may be anterior displacement of the angle structures with posterior embryotoxon and localized corneal opacification.    Glaucoma is a common feature and it may be present in early childhood, associated with tearing, a hazy cornea, and buphthalmos.  Vitreous condensation was noted in all 4 reported individuals.

Systemic Features: 

The midface is flat due to maxillary underdevelopment and the teeth may be abnormally small.  Micrognathia has been reported while the nasal root is abnormally broad.  The umbilical defect consists of redundant skin that failed to involute normally.  Congenital hip anomalies of undetermined nature and a hearing defect were reported in 2 of 4 individuals.

Genetics

Heterozygous mutations in the PRDM5 gene (4q25-q26) are responsible for this condition.  Mutations in CYP1b1, PITX2, and FOXC1 were not present.  One extended pedigree with 4 affected individuals from Pakistan has been reported. 

Type 1 Axenfeld-Rieger syndrome (180500) results from heterozygous mutations in PITX2RIEG2 (601499) from heterozygous mutations in 13q14, and RIEG3 (602482) from heterozygous mutations in the FOXC1 gene.  Thus in three types of Axenfeld-Rieger syndrome (1,3, and 4) the responsible mutation occurs in a transcription factor gene which may explain why the phenotype is highly variable with considerable overlap in clinical signs.

Autosomal recessive brittle cornea syndrome type 2 (614170) is also caused by mutations in the PRDM5 gene. 

Pedigree: 
Autosomal dominant
Treatment
Treatment Options: 

Treatment is directed at correction of individual problems such as glaucoma and dental anomalies.  One patient required surgery for a retinal detachment. Lifelong ocular monitoring is recommended. 

References
Article Title: 

Mandibulofacial Dysostosis with Alopecia

Clinical Characteristics
Ocular Features: 

The extensive dysplasia of the facial bones involves those of the orbital rims and zygomatic arches.  The orbital rims can be malformed and there is often a broad depression at the inferolateral region of the eyes.  Hypoplasia or even aplasia of the eyelids maybe present and some individuals have colobomas of the lower eyelids.  The lacrimal punctae may be temporally displaced.  The eyebrows and eyelashes are often sparse as part of the generalized alopecia.

Systemic Features: 

This is a disorder of craniofacial development resulting in extensive malformations of facial bones and skin.  Different rates of development among these structures leads to facial asymmetry in many patients. Maxillary, zygomatic arch, and mandibular bones are dysplastic resulting in micrognathia and a flat midface.   The temporomandibular joints are absent and the external ear canals are often incompletely formed.  Conductive hearing loss is common with hypoplastic ossicular chains while the pinnae are low-set, crumpled and abnormally cupped.  There may be preauricular tags or pits present.  Tooth eruption is often delayed and there may be agenesis of many permanent teeth.  The maxillary sinuses may be absent.  Cleft palate is often present.

Genetics

Heterozygous mutations in the EDNRA gene (4q31) are responsible for this condition.  No familial cases have been reported and it can be assumed that the mutations arise de novo. 

Pedigree: 
Autosomal dominant
Treatment
Treatment Options: 

There is no treatment for the overall condition but individual anomalies such as the colobomas, dental deformities and cleft palate may be surgically repaired.  Upper airway obstruction may require tracheostomy in infants.

References
Article Title: 

Mutations in the endothelin receptor type A cause mandibulofacial dysostosis with alopecia

Gordon CT, Weaver KN, Zechi-Ceide RM, Madsen EC, Tavares AL, Oufadem M, Kurihara Y, Adameyko I, Picard A, Breton S, Pierrot S, Biosse-Duplan M, Voisin N, Masson C, Bole-Feysot C, Nitschke P, Delrue MA, Lacombe D, Guion-Almeida ML, Moura PP, Garib DG, Munnich A, Ernfors P, Hufnagel RB, Hopkin RJ, Kurihara H, Saal HM, Weaver DD, Katsanis N, Lyonnet S, Golzio C, Clouthier DE, Amiel J. Mutations in the endothelin receptor type A cause mandibulofacial dysostosis with alopecia. Am J Hum Genet. 2015 Apr 2;96(4):519-31.

PubMed ID: 
25772936

Singleton-Merten Syndrome 1

Clinical Characteristics
Ocular Features: 

Several children have been diagnosed with glaucoma in early childhood or during puberty.  Glaucoma surgery has been beneficial in some but visual damage may be severe.

Systemic Features: 

Patients have early-onset calcifications of the aorta and of the aortic and mitral valves which may be seen in childhood and can be responsible for heart failure and early death.  Osteoporosis of the limbs and widened medullary cavities have been seen.  Abnormal bone mineralization and extends to the jaws leading to tooth loss and early-onset periodontal disease.  Eruption of both primary and permanent teeth is delayed but tooth roots can be truncated as well.  The hips dislocate easily due to shallow acetabulae and patients are susceptible to tendon tears.

Hypotonia and generalized weakness may be present which is sometimes exacerbated following a febrile illness.  The skin may be dry and scaly consistent with psoriasis and there may be photosensitivity.

The forehead is broad and prominent and the hairline is high and anterior.  The philtrum is smooth and the upper vermilion is thin.

Genetics

Heterozygous mutations in the IFIH1 gene (2q24.2) are responsible for this disorder.  Another form of Singleton-Merten Syndrome (SGMRT2; 609631) is the result of mutations in the DDX58 gene. 

Pedigree: 
Autosomal dominant
Treatment
Treatment Options: 

Treatment is directed at specific problems such as fractures, glaucoma, and periodontal disease.

References
Article Title: 

A specific IFIH1 gain-of-function mutation causes Singleton-Merten syndrome

Rutsch F, MacDougall M, Lu C, Buers I, Mamaeva O, Nitschke Y, Rice GI, Erlandsen H, Kehl HG, Thiele H, Nurnberg P, Hohne W, Crow YJ, Feigenbaum A, Hennekam RC. A specific IFIH1 gain-of-function mutation causes Singleton-Merten syndrome. Am J Hum Genet. 2015 Feb 5;96(2):275-82.

PubMed ID: 
25620204

Jackson-Weiss Syndrome

Clinical Characteristics
Ocular Features: 

The facial malformation such as the flattened midface with maxillary hypoplasia leads to shallow orbits with the result that the eyes appear proptotic.  Some but not all individuals have strabismus, usually exotropia.  Optic atrophy has not been reported. 

Systemic Features: 

Infants usually present at birth with skull deformities resembling some variant of acrocephalosyndactyly.  Some or all of the skull sutures may be fused.  In some individuals craniectomy is necessary while others have normal brain development.  Few patients have evidence of abnormal neurological development and psychometric testing reveals IQ's in the normal range.  The midface is flattened with sometimes severe maxillary hypoplasia.  No hand deformities are present. 

There may be cutaneous syndactyly of the second and third toes.  Variable tarsal fusion is often present. The great toe may be abnormally broad and deviated medially.  The first metatarsals and proximal phalanges of the great toes are generally broad.

The phenotype is highly variable and even among individuals in genetically more homogeneous populations such as the Old Order Amish the range of facial, skull, and digital anomalies include features found among all of the craniosynostosis syndromes except for Apert syndrome.

Genetics

Heterozygous mutations in the FGFR2 gene (10q26.13) are likely responsible for this autosomal dominant condition. 

Other forms of craniosynostosis in which mutations in FGFR2 have been found are: Beare-Stevenson Syndrome (123790), Crouzon Syndrome (123500), Pfeiffer Syndrome (101600), Apert Syndrome (101200), and Saethre-Chotzen Syndrome (101400).

Pedigree: 
Autosomal dominant
Treatment
Treatment Options: 

There is no treatment beyond surgical correction of selected malformations. The risk of exposure keratitis requires constant vigilance and appropriate corneal lubrication.

References
Article Title: 

Axenfeld-Rieger Syndrome, Type 2

Clinical Characteristics
Ocular Features: 

As in RIEG1 and RIEG3, glaucoma is the most serious ocular problem.  In a large family with 11 affected members, 9 had glaucoma.  All had the classic ocular signs of anterior segment dysgenesis, primarily posterior embryotoxon and iris adhesions (for a full description of the ocular features see Axenfeld-Rieger syndrome, RIEG1 [180500]).

Systemic Features: 

Oligodontia, microdontia, and premature loss of teeth are common in type 2.  Maxillary hypoplasia is less common as is hearing loss.  Umbilical anomalies were not present in any affected individuals.  Cardiac defects are rare.

Genetics

This is an autosomal dominant disorder as in the other types.  The locus is at 13q14 but no molecular defect has been defined.  At least two individuals purported to have type 2 were found to have deletions of this segment of chromosome 13.

Pedigree: 
Autosomal dominant
Treatment
Treatment Options: 

The high risk of glaucoma demands lifelong monitoring of intraocular pressure.

References
Article Title: 

Axenfeld-Rieger Syndrome, Type 1

Clinical Characteristics
Ocular Features: 

Axenfeld-Rieger syndrome consists of a heterogeneous group of disorders with overlapping features.  Common to all types are the presence of ocular, dental, facial, skeletal abnormalities and autosomal dominant inheritance.  Anterior chamber dysgenesis of some form is universally present and severe glaucoma occurs in 50% of patients.  This may have its onset in childhood with typical symptoms of congenital glaucoma such as photophobia, excessive tearing and corneal clouding.  Hypoplasia of the iris is common and when progressive may result in an ectopic pupil and/or pseudopolycoria.  Iris insertion and Schwalbe's line are often anteriorly displaced with iridocorneal adhesions, a pattern that leads to the inclusion of this disorder among those with iridogoniodysgenesis or anterior chamber dysgenesis.  Pupillary ectropion of the posterior pigmented layer of the iris may be seen.

There is considerable clinical overlap among conditions with iris dysgenesis.  Some patients with typical systemic features of Axenfeld-Rieger syndrome may even have typical anterior chamber features of Axenfeld-Rieger anomaly in one eye and severe iris hypoplasia resembling aniridia in the other.

Systemic Features: 

Dental anomalies and mid-facial hypoplasia secondary to underdeveloped maxillary sinuses are among the most common systemic features in type 1.  The nasal root often appears abnormally broad and the lower lip appears to protrude. The teeth are frequently small and conical in shape with wide spaces between them (diastema).  Some teeth may be missing.  The umbilicus may fail to involute normally and retains excessive, redundant skin that sometimes leads to the erroneous diagnosis of an umbilical hernia for which unnecessary surgery may be performed.  Hypospadius is frequently present while cardiac defects, sensorineural deafness, and anal stenosis are less common.

Genetics

There is clinical and genetic heterogeneity in this syndrome and precise classification of many families remains elusive without knowing the genotype.  Mutations in at least four genes are responsible and all are are responsible for phenotypes transmitted in autosomal dominant patterns.  Type 1 discussed here is caused by a mutation in the homeobox transcription factor gene, PITX2, located at 4q25-q26.  A type of iris hypoplasia (IH)/iridogoniodysgenesis (IGDS) (IRID2; 137600) disorder has been classified separately but is caused by a mutation in PITX2 as well and many cases have the same systemic features.  Mutations in the same gene have also been found in ring dermoid of the cornea (180550) and in some cases of Peters anomaly (604229).

RIEG2 (601499) is rare but a deletion of 13q14 has been reported in several cases.  Mapping in a large family with 11 affected individuals yielded a locus in the same region.  Clinical signs overlap types 1 and 3 with dental, craniofacial, and ocular features, but with hearing impairment and rare umbilical anomalies.

Mutations in the FOXC1 gene (6p25) may be responsible for RIEG3 (602482).  However, a family has been reported with a severe 'Axenfeld-Rieger phenotype' in which a digenic etiology may have been responsible: patients had mutations in both FOXC1 and PITX2

Heterozygous mutations in the PRDM5 gene (4q25-q26) have been identified in 4 members of a Pakistani family with typical features of the Axenfeld-Rieger syndrome. It is labeled type 4 Axenfeld-Rieger syndrome in this database. 

Pedigree: 
Autosomal dominant
Treatment
Treatment Options: 

The presence of glaucoma requires prompt and vigorous treatment but control is difficult with blindness too often the result.  Oral surgery may be beneficial for dental problems.  Low vision aids can be useful.

References
Article Title: 

The Rieger syndrome

Jorgenson RJ, Levin LS, Cross HE, Yoder F, Kelly TE. The Rieger syndrome. Am J Med Genet. 1978;2(3):307-18.

PubMed ID: 
263445
Subscribe to RSS - maxillary hypoplasia