skeletal dysplasia

Spondylometaphyseal Dysplasia, Axial

Clinical Characteristics
Ocular Features: 

Due to the small number of individuals reported, the ocular phenotype is variable and likely incompletely described.  Optic atrophy and pigmentary retinopathy are the most consistent findings.  The most completely studied individual had evidence of slight bilateral optic nerve atrophy on cerebral MRI imaging as well.  There may be extensive RPE atrophy but the fundus pigmentation is usually described as resembling retinitis pigmentosa.  The ERG in several patients during the second decade of life already shows severe dysfunction of the photoreceptors, with cones the most severely impacted.  In spite of this Goldmann visual fields have been reported to be normal.  The macula and OCT have been reported as normal.  Telecanthus, nystagmus, hypertelorism, proptosis, and photophobia have been reported.  Early onset and progressive visual impairment are characteristic.

Systemic Features: 

Only 5 patients with this condition have been reported most of whom were short in stature.  There may be frontal bossing and the chest is narrow and flattened.  Moderate platyspondyly has been described with enlarged but shortened ribs and an irregular iliac crest.  Rhizomelic shortening of the limbs is common.  The femoral metaphyses are abnormal with their necks shortened and enlarged.  The ribs are enlarged but shortened as well and are flared at the ends.  Mental development and function are normal.

Genetics

This is an autosomal recessive condition due to homozygous or compound heterozygous mutations in C21orf2.

Treatment
Treatment Options: 

No effective treatment is known.

References
Article Title: 

Axial Spondylometaphyseal Dysplasia Is Caused by C21orf2 Mutations

Wang Z, Iida A, Miyake N, Nishiguchi KM, Fujita K, Nakazawa T, Alswaid A, Albalwi MA, Kim OH, Cho TJ, Lim GY, Isidor B, David A, Rustad CF, Merckoll E, Westvik J, Stattin EL, Grigelioniene G, Kou I, Nakajima M, Ohashi H, Smithson S, Matsumoto N, Nishimura G, Ikegawa S. Axial Spondylometaphyseal Dysplasia Is Caused by C21orf2 Mutations. PLoS One. 2016 Mar 14;11(13).

PubMed ID: 
26974433

Axial spondylometaphysealdysplasia

Ehara S, Kim OH, Maisawa S, Takasago Y, Nishimura G. Axial spondylometaphysealdysplasia. Eur J Pediatr. 1997 Aug;156(8):627-30.

PubMed ID: 
9266195

CHOPS Syndrome

Clinical Characteristics
Ocular Features: 

There is usually some degree of proptosis and apparent hypertelorism.  The eyebrows are bushy and the eyelashes are luxurious.  One of three patients had cataracts and another had mild optic atrophy.

Systemic Features: 

The overall facial appearance may resemble Cornelia de Lange syndrome with hypertrichosis and a coarse, round facies.  Head circumference is low normal.  Septal defects and a patent ductus arteriosus are often present.  Laryngeal and tracheal malacia predispose to recurrent pulmonary infections and chronic lung disease.  Skeletal dysplasia includes brachydactyly and anomalous vertebral bodies resulting in short stature (3rd percentile).  Genitourinary abnormalities include cryptorchidism, horseshoe kidney, and vesiculoureteral reflux.  Delayed gastric emptying and reflux have been reported.

Genetics

Heterozygous mutations in the AFF4 gene (5q31.1) have been identified in 3 unrelated individuals with this condition.  No familial cases have been identified.  The gene is a core component of the super elongation complex that is critical to transcriptional elongation during embryogenesis.

Pedigree: 
Autosomal dominant
Treatment
Treatment Options: 

There is no treatment for the general disorder.  Tracheostomy was required in 2 of three reported patients. 

References
Article Title: 

Germline gain-of-function mutations in AFF4 cause a developmental syndrome functionally linking the super elongation complex and cohesin

Izumi K, Nakato R, Zhang Z, Edmondson AC, Noon S, Dulik MC, Rajagopalan R, Venditti CP, Gripp K, Samanich J, Zackai EH, Deardorff MA, Clark D, Allen JL, Dorsett D, Misulovin Z, Komata M, Bando M, Kaur M, Katou Y, Shirahige K, Krantz ID. Germline gain-of-function mutations in AFF4 cause a developmental syndrome functionally linking the super elongation complex and cohesin. Nat Genet. 2015 Apr;47(4):338-44.

PubMed ID: 
25730767

Gracile Bone Dysplasia

Clinical Characteristics
Ocular Features: 

The eyes have been described as small.  Aniridia may be present.

Systemic Features: 

This is a usually fatal form of skeletal dysplasia with splenic and ocular features as well.  In utero death is not uncommon while newborns may not survive the neonatal period.  The face has been described as dysmorphic with a high forehead, flat nasal bridge, a cloverleaf-shaped skull, and hypoplastic cranial bones with premature suture closure.  The long bones are dysplastic as well with thinned diaphyses (sometimes fractured in utero), growth plate disorganization, excessive remodeling, and signs of arrested growth.  The ribs share in the dysplasia but pulmonary hypoplasia has also been described.  Most individuals have short limbs.

The spleen can be hypoplastic or aplastic and ascites has been noted in several infants.  Failure to thrive is common and seizures have been reported.  Males may have micropenis and hypospadias while females have been described with labial fusion.  

Low parathyroid hormone levels and hypocalcemia has been reported in most individuals.

Genetics

Heterozygous mutations in the FAM111A gene (11q12.1) have been associated with this disorder.  The functional role of FAM111A products is unknown but likely play a role in calcium metabolism, parathyroid hormone secretion, and osseous development.

Mutations in the same gene can be responsible for the allelic autosomal dominant Kenny-Caffey syndrome (127000) with some similar features.

Pedigree: 
Autosomal dominant
Treatment
Treatment Options: 

No treatment has been reported.

References
Article Title: 

FAM111A mutations result in hypoparathyroidism and impaired skeletal development

Unger S, Gorna MW, Le Bechec A, Do Vale-Pereira S, Bedeschi MF, Geiberger S, Grigelioniene G, Horemuzova E, Lalatta F, Lausch E, Magnani C, Nampoothiri S, Nishimura G, Petrella D, Rojas-Ringeling F, Utsunomiya A, Zabel B, Pradervand S, Harshman K, Campos-Xavier B, Bonafe L, Superti-Furga G, Stevenson B, Superti-Furga A. FAM111A mutations result in hypoparathyroidism and impaired skeletal development. Am J Hum Genet. 2013 Jun 6;92(6):990-5.

PubMed ID: 
23684011

Morquio Syndrome (MPS IVB)

Clinical Characteristics
Ocular Features: 

Corneal clouding may not be seen until 10 years of age and is sometimes associated with photophobia.  The stroma has fine dust-like particles most dense centrally.  Penetrating keratoplasty is rarely indicated. There is little retinal degeneration unlike that often seen in other mucopolysaccharidoses but the corneal clouding often precludes detailed examination.

Systemic Features: 

This form of mucopolysaccharidosis is characterized by the urinary excretion of keratin sulfate.  Age of onset is highly variable but most children are diagnosed by 6 years of age.  It is a milder disease than the somewhat similar but genetically distinct Morquio type A (253000)  disorder.  Intelligence is normal and there is no central nervous system involvement.  Hip joints are dysplastic and frequently painful.  Vertebral malformations lead to kyphoscoliosis and short trunk dwarfism.  Odontoid hypoplasia can cause cervical instability and increases the risk of myelopathy with secondary bowel and bladder dysfunction.  Coxa valgum, and narrow phalanges are common.  Many individuals have a characteristic gait secondary to genu valgum.  Patients with MPS IVB initially do not have the coarse facies seen in some other forms of MPS.  Further accumulation of cellular keratin sulfate may lead to some coarsening of facial features, increased corneal clouding, and hepatomegaly.  Some form of hearing loss is common.

Genetics

This is an autosomal recessive lysosomal storage disease caused by a mutation in the GLB1 gene (3p21.33) encoding beta-galactosidase.  It is allelic to GM1 gangliosidosis (230500).  Type A Morquio syndrome (253000) is a separate disorder secondary to a mutation in a different gene.

Pedigree: 
Autosomal recessive
Treatment
Treatment Options: 

A variety of treatments are under investigation including enzyme replacement, gene therapy, and bone marrow transplantation.  Supportive and palliative measures for respiratory difficulties and skeletal deformities can be used.  Atlantoaxial subluxation is a constant risk and some physicians recommend prophylactic vertebral fusion.  Intubation for general anesthesia carries special risks.

References
Article Title: 

Mucopolysaccharidoses and the eye

Ashworth JL, Biswas S, Wraith E, Lloyd IC. Mucopolysaccharidoses and the eye. Surv Ophthalmol. 2006 Jan-Feb;51(1):1-17. Review.

PubMed ID: 
16414358

Mutation analyses in 17 patients with deficiency in acid beta-galactosidase: three novel point mutations and high correlation of mutation W273L with Morquio disease type B

Paschke E, Milos I, Kreimer-Erlacher H, Hoefler G, Beck M, Hoeltzenbein M, Kleijer W, Levade T, Michelakakis H, Radeva B. Mutation analyses in 17 patients with deficiency in acid beta-galactosidase: three novel point mutations and high correlation of mutation W273L with Morquio disease type B. Hum Genet. 2001 Aug;109(2):159-66.

PubMed ID: 
11511921

Morquio Syndrome (MPS IVA)

Clinical Characteristics
Ocular Features: 

Corneal clouding in the form of fine deposits in the stroma is the major ocular manifestation but it may not be noted for several years after birth.  Penetrating keratoplasty is rarely needed.  Glaucoma occurs rarely.

Systemic Features: 

There is wide variation in the clinical disease in this disorder and some have grouped cases into severe, intermediate and mild categories.   Onset is about 2 years of age and three-quarters of patients are diagnosed by the age of 6 years.  Intelligence is usually normal and the central nervous system is spared similar to MPS IVB. However, the skeletal dysplasia can lead to neurologic complications.  In particular, odontoid hypoplasia raises the risk of atlantoaxial dislocation and spinal cord damage. The maxillary teeth are often abnormal with wide spacing and a flared appearance.  Truncal dwarfism is characteristic but the facies are often more fine-featured than in other mucopolysaccharidoses.  Lifespan is shortened in most patients.

Genetics

This is an autosomal recessive disorder resulting from mutations in the GALNS gene (16q24.3) encoding galactosamine-6-sulfate sulfatase.  Keratan sulfate and chondroitin-5-sulfate accumulates in lysosomes.  Urinary keratin sulfate excretion is increased.

A clinically similar disease, Morquio syndrome B (253010), is caused by a different mutation.

Pedigree: 
Autosomal recessive
Treatment
Treatment Options: 

No specific treatment is available for this disease.  Some have recommended cervical spine fusion to stabilize the atlantoaxial joint. Orthopedic surgery may be indicated for joint and spine deformities.  Special precautions should be taken during intubation for general anesthesia.

Enzyme replacement therapies and hematopoietic stem cell transplantation techniques now being developed hold promise for more specific treatment for the underlying enzyme deficiencies in mucopolysaccharidoses.

References
Article Title: 

Mucopolysaccharidoses and the eye

Ashworth JL, Biswas S, Wraith E, Lloyd IC. Mucopolysaccharidoses and the eye. Surv Ophthalmol. 2006 Jan-Feb;51(1):1-17. Review.

PubMed ID: 
16414358
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