osteoporosis

Spondyloocular Syndrome

Clinical Characteristics
Ocular Features: 

Cataracts have been noted in several patients in the first and second decades of life.  Nystagmus and ‘amblyopia’ have also been reported.  Several individuals have had retinal detachments.

Systemic Features: 

Only a small number of families have been reported.  Poor bone mineralization with frequent fractures in long bones and vertebral compression seem to be consistent features often noted in the first and second decades of life.  Moderate osteoporosis and advanced bone age with platyspondyly may be present.  The vertebral fractures lead to abnormal spinal curvature and may result in shortened stature. 

Some sensorineural hearing loss is sometimes detected in the first decade.  The ears have been described as low-set and posteriorly rotated.  A variety of cardiac defects have been reported including mitral valve prolapse, septal defects, and anomalies of the aortic valve. 

Genetics

This is an autosomal recessive disorder secondary to homozygous mutations in the XYLT2 gene located at 17q21.33. 

Pedigree: 
Autosomal recessive
Treatment
Treatment Options: 

Pamidronate given intravenously seems to have little therapeutic value.  Hearing aids can be beneficial.  Lensectomy may be of benefit although no reports of cataract surgery have been reported.  Fractures need immediate attention.  Patient may become wheelchair-bound by the second decade.  Special education may be helpful for those with learning difficulties.

References
Article Title: 

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

Peroxisome Biogenesis Disorder 3B (Infantile Refsum Disease)

Clinical Characteristics
Ocular Features: 

This peroxisomal disorder presents in the first year of life with both systemic and ocular features.  Night blindness is the major ocular feature and at least some have optic atrophy similar to the adult form.  Nystagmus may be present.  Reduction or absence of rod responses on ERG can be used in young children to document the retinopathy. Blindness and deafness commonly occur in childhood.

Systemic Features: 

This disorder is classified as a peroxisomal biogenesis disorder (PBD) associated with the breakdown of phytanic acid.  Ataxia and features of motor neuron disease are evident early.  Hepatomegaly and jaundice may also be an early diagnostic feature as bile acid metabolism is defective.  Infant hypotonia is often seen.  Nonspecific facial dysmorphism has been reported as a feature. The teeth are abnormally large and often have yellowish discoloration.  Postural unsteadiness is evident when patients begin walking.  Diagnosis can be suspected from elevated serum phytanic and pipecolic acid (in 20% of patients) or by demonstration of decreased phytanic acid oxidation in cultured fibroblasts.  Other biochemical abnormalities such as hypocholesterolemia and elevated very long chain fatty acids and trihydroxycholestanoic acid are usually present.  Anosmia and mental retardation are nearly universal features.  Early mortality in infancy or childhood is common although some survive into the 2nd and 3rd decades.

Genetics

This is an autosomal recessive peroxisomal biogenesis disorder (PBD) resulting from mutations in a number of PEX genes (PEX1, PEX2, PEX3, PEX12, PEX26).  It shares many features with other PBDs including those formerly called Zellweger syndrome (214100), rhizomelic chondrodysplasia punctata (215100), and neonatal adrenoleukodystrophy (601539).

Pedigree: 
Autosomal recessive
Treatment
Treatment Options: 

No effective treatment is known.

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: 

Dyskeratosis Congenita

Clinical Characteristics
Ocular Features: 

The conjunctiva and eyelids are prominently involved as part of the generalized mucocutaneous disease.  Keratinization of the lid margins, absent lacrimal puncta, trichiasis, cicatrizing conjunctivitis, entropion, ectropion, blepharitis, sparse eyelashes, and symblephara are important features.  The cornea is also involved with keratinization of the epithelial surface and vascularization.  The nasolacrimal duct is sometimes blocked.  At least one patient has been reported to have an exudative retinopathy. 

Systemic Features: 

Dyskeratosis congenita consists of a heterogeneous (genetic and clinical) group of inherited bone marrow failure and premature aging syndromes with the common feature of shortened telomeres.  There is considerable variability in the clinical features.  Prominent manifestations include nail dysplasia, oral leukoplakia, abnormal dentition, and reticulated skin pigmentation. Some patients have cognitive impairments.  Liver failure, testicular atrophy, pulmonary fibrosis, aplastic anemia, and osteoporosis along with features of aging such as premature grey hair and loss are typical.  There is an increased risk of malignancies, especially acute myelogenous leukemia.  Bone marrow failure is the major cause of early death.

Genetics

At least three autosomal dominant, three autosomal recessive, and one X-linked form of dyskeratosis congenita are recognized.  Mutations in at least 7 genes have been implicated.

Autosomal dominant disease can result from mutations in the TERC gene (DKCA1; 3q36.2; 127550), the TERT gene (DKCA2; 5p15.33; 613989), and the TINF2 gene (DKCA3; 14q12; 613990).  Mutations in the TINF2 gene are also responsible for Revesz syndrome (268130) with many features of DKC in addition to ocular findings of an exudative retinopathy resembling Coats disease.

Autosomal recessive disease is caused by mutations in the NOP10 (NOLA3) gene (DCKB1; 224230; 15q14-q15), the  NHP2 (NOLA2) gene (DKCB2; 5q35; 613987), and the WRAP53 gene (DKCB3; 17p13; 613988).  Mutations in the TERT gene may also cause autosomal recessive disease known as DKCB4 (613989).  

The X-linked disease (DKCX) (Zinsser-Engman-Cole syndrome) results from a mutation in the DKC1 gene (Xq28; 305000).  The same gene is mutated in Hoyeraal-Hreidarsson syndrome (300240) which some consider to be a more severe variant of dyskeratosis congenita with the added features of immunodeficiency, microcephaly, growth and mental retardation, and cerebellar hypoplasia. 

The majority of mutations occur in genes that provide instructions for making proteins involved in maintainence of telemeres located at the ends of chromosomes.  Shortened telomeres can result from maintainence deficiencies although the molecular mechanism(s) remain elusive.

Pedigree: 
Autosomal dominant
Autosomal recessive
X-linked recessive, carrier mother
X-linked recessive, father affected
Treatment
Treatment Options: 

Treatment for DKC with hematopoietic stem cell transplantation can be curative but its long-term efficacy is poor.  Some advocate androgen therapy first.  Lifelong cancer surveillance and frequent ocular and dental evaluations are important with specific treatment as indicated.

References
Article Title: 

Homocystinuria, Beta-Synthase Deficiency

Clinical Characteristics
Ocular Features: 

More than half of patients have ectopia lentis by the age of 10 years and the dislocation is progressive.  Ectopia lentis occurs in 90% of patients and 94% of these are noted by the age of 20 years.  The lenses seem to be more mobile than those in Marfan syndrome with a significantly increased risk of lens migration into the anterior chamber (19%) or complete dislocation into the posterior chamber (14%).   Lens surgery is required in homocystinuria about 7 years earlier than in Marfan syndrome with 62% of procedures necessitated by pupillary block glaucoma or displacement into the anterior chamber.  Whereas nearly 70% of lenses dislocate superiorly in Marfan syndrome, only 9% of homocystinuria lenses do so.

Other ocular features include optic atrophy (23%), iris atrophy (21%), anterior staphylomas (13%) and corneal opacities (9%).  Retinal detachments occur in 5-10%.  The majority of patients both pre- and postoperatively have vision of 20/50 or worse.

Systemic Features: 

Arachnodactyly and tall stature in some patients may suggest Marfan syndrome.  Mental deficiencies or behavioral problems are present in a majority of patients (50-60%) with mental functioning higher in the subset of patients who are B6-responsive.  Thromboembolic events (strokes, myocardial infarctions) are a significant risk at any age, especially so after age 20 years, and this is responsible for considerable morbidity and mortality.  The risk is especially high following general anesthesia unless hydration is strictly controlled.  Osteoporosis and seizures are common.  Hypopigmentation is often present but darkening of hair has been noted following pyridoxine treatment.  Serum homocysteine is generally elevated and the urine contains elevated levels of methionine.

Genetics

Classic homocystinuria is an autosomal recessive disorder that results from mutations in the CBS (21q22.3) gene encoding cystathionine beta-synthase.  It is the second most common error of amino acid metabolism.  Numerous mutations have been identified but among the most common ones are I278T which causes a pyridoxine-responsive disorder, and the G3307S mutation which leads to a variant that is not responsive to pyridoxine treatment.

Pedigree: 
Autosomal recessive
Treatment
Treatment Options: 

Patients with this disorder form two groups: those who respond to pyridoxine (vitamin B6) and those who do not.  Those who do not respond to B6 tend to have more severe disease.  Methionine restriction administered neonatally has been reported to prevent mental retardation and reduce the rate of lens dislocation.  Neonates should be treated with B6 therapy, protein and methionine restriction, betaine, and folate with vitamin B12 supplementation.  Surgical removal of lenses may be required but the rate of vitreous loss is high.

References
Article Title: 

Osteoporosis-Pseudoglioma Syndrome

Clinical Characteristics
Ocular Features: 

Retrolental masses often present at birth have been mistaken for retinoblastomas.  Hyperplasias of the vitreous, corneal opacities, and secondary glaucoma have been described.  Band keratopathy may account for some of the corneal clouding and opacities.  Most patients are blind soon after birth although some retain some vision into the second decade.

Systemic Features: 

Some patients have been described as mentally retarded but others have normal intelligence.  Hypotonia and hyperflexible joints have been noted.  Bone fractures are common sometimes resulting in scoliosis, short stature and limb deformities.  Radiography of the skeletal reveals porotic and thin bones.

Genetics

This disorder, sometimes called the ocular form of osteogenesis imperfecta, results from mutations in LRP5 (11q13.4).  The same gene is mutant in the EVR4 type of familial exudative vitreoretinopathy (601813) which has some of the same ocular and bone features.  Most descriptions of OPPG were published before the gene mutation was found and many reports do not include detailed ocular examinations.  Certainly the two disorders are allelic and likely the same condition. 

Mutations in LRP5 lead to EVR4 disease in both the heterozygous and homozygous configuration but most cases of OPPG have homozygous or compound heterozygous mutations.

Pedigree: 
Autosomal recessive
Treatment
Treatment Options: 

Bone fractures need to be repaired and glaucoma treated when present.  Bisphosphonate treatment may lead to increased bone density if initiated early.  The retrolental masses need to be carefully evaluated to rule out retinoblastoma.

References
Article Title: 

Osteoporosis-pseudoglioma syndrome, a disorder affecting skeletal strength and vision, is assigned to chromosome region 11q12-13

Gong Y, Vikkula M, Boon L, Liu J, Beighton P, Ramesar R, Peltonen L, Somer H, Hirose T, Dallapiccola B, De Paepe A, Swoboda W, Zabel B, Superti-Furga A, Steinmann B, Brunner HG, Jans A, Boles RG, Adkins W, van den Boogaard MJ, Olsen BR, Warman ML. Osteoporosis-pseudoglioma syndrome, a disorder affecting skeletal strength and vision, is assigned to chromosome region 11q12-13. Am J Hum Genet. 1996 Jul;59(1):146-51.

PubMed ID: 
8659519

Peroxisome Biogenesis Disorder 1B (neonatal adrenoleukodystrophy)

Clinical Characteristics
Ocular Features: 

This peroxisomal disorder presents in the first year of life with both systemic and ocular features.  Night blindness is the major ocular feature and at least some have optic atrophy similar to the adult form.  Central acuity is reduced secondary to macular degeneration.  A pigmentary retinopathy is frequently present and often follows the appearance of whitish retinal flecks in the midperipheray.  Nystagmus and cataracts are common features.  Reduction or absence of ERG responses can be used in young children to document the retinopathy.  Blindness and deafness commonly occur in childhood.

Systemic Features: 

This disorder is classified as a leukodystrophy, or disease of white matter of the brain, associated with the breakdown of phytanic acid.  Ataxia and features of motor neuron disease are evident early.  Hepatomegaly and jaundice may also be early diagnostic features as bile acid metabolism is defective.  Infant hypotonia is often seen.  Nonspecific facial dysmorphism has been reported.  The ears are low-set and epicanthal folds are present.  The teeth are abnormally large and often have yellowish discoloration.  Postural unsteadiness is evident when patients begin walking.  Diagnosis can be suspected from elevated serum phytanic and pipecolic acid (in 20% of patients) or by demonstration of decreased phytanic acid oxidation in cultured fibroblasts.  Other biochemical abnormalities such as hypocholesterolemia, and elevated very long chain fatty acids and trihydroxycholestanoic acid are usually present.  Anosmia, developmental delays, and mental retardation are nearly universal features.  Early mortality in infancy or childhood is common.

Genetics

This is a genetically heterogeneous disorder of peroxisome biogenesis caused by mutations in at least three genes, PEX1 (7q21-q22), PEX2 (8q21.1), and PEX6 (22q11-21).  Each is inherited in an autosomal recessive pattern.  The mechanism of disease is different from the classic or adult Refsum disorder (266500) and some have debated whether the term ‘infantile Refsum disease’ is appropriate.

This disorder shares some clinical features with other peroxisomal disorders such as Zellweger syndrome (214100) and rhizomelic chondrodysplasia punctata (215100).  Zellweger syndrome (214100), neonatal adrenoleukodystrophy and infantile Refsum disease (601539) are now considered to be peroxisomal biogenesis or Zellweger spectrum disorders.

Pedigree: 
Autosomal recessive
Treatment
Treatment Options: 

No effective treatment is known.

References
Article Title: 
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