intellectual disabilities

Retinitis Pigmentosa With or Without Skeletal Anomalies

Clinical Characteristics
Ocular Features: 

Downward slanting lid fissures may be detectable at birth as part of the general craniofacial dysmorphism.  Some degree of night blindness causes symptoms by the second decade of life and constricted visual fields with pigmented retinopathy and vessel narrowing can be detected.  The ERG shows reduced or absent responses.  The retinal phenotype is progressive.   

Systemic Features: 

Most but not all patients have skeletal anomalies.  Nonspecific craniofacial dysmorphology features are frequently present including frontal bossing, macrocephaly, low-set ears, large columella, hypoplastic nares, and malar hypoplasia.  A short neck, brachydactyly, and overall shortness of stature are often present.  Some individuals have nail dysplasia.  The proximal femoral metaphyses sometimes show chondrodysplasia.

There is often some degree of intellectual disability and there may be delays in speech, feeding, and walking.

Genetics

This disorder results from homozygous or compound heterozygous mutations in the CWC27 gene (5q12.3).

Pedigree: 
Autosomal recessive
Treatment
Treatment Options: 

No general treatment has been reported.  Low vision aids and night vision devices may be helpful, especially for educational activities.

References
Article Title: 

Mutations in the Spliceosome Component CWC27 Cause Retinal Degeneration with or without Additional Developmental Anomalies

Xu M, Xie YA, Abouzeid H, Gordon CT, Fiorentino A, Sun Z, Lehman A, Osman IS, Dharmat R, Riveiro-Alvarez R, Bapst-Wicht L, Babino D, Arno G, Busetto V, Zhao L, Li H, Lopez-Martinez MA, Azevedo LF, Hubert L, Pontikos N, Eblimit A, Lorda-Sanchez I, Kheir V, Plagnol V, Oufadem M, Soens ZT, Yang L, Bole-Feysot C, Pfundt R, Allaman-Pillet N, Nitschke P, Cheetham ME, Lyonnet S, Agrawal SA, Li H, Pinton G, Michaelides M, Besmond C, Li Y, Yuan Z, von Lintig J, Webster AR, Le Hir H, Stoilov P; UK Inherited Retinal Dystrophy Consortium., Amiel J, Hardcastle AJ, Ayuso C, Sui R, Chen R, Allikmets R, Schorderet DF. Mutations in the Spliceosome Component CWC27 Cause Retinal Degeneration with or without Additional Developmental Anomalies. Am J Hum Genet. 2017 Apr 6;100(4):592-604.

PubMed ID: 
28285769

ZTTK Syndrome

Clinical Characteristics
Ocular Features: 

The eyes are deep-set and the palpebral fissures slant downward.  Optic atrophy is often present.  The majority of individuals have poor visual responses which may also be attributed to central or cortical impairment.  Strabismus and nystagmus are frequently present.

Systemic Features: 

ZTTK syndrome is multisystem malformation and developmental disorder with a heterogeneous clinical presentation.  The facial features might suggest the diagnosis at birth but most of the signs are nonspecific including frontal bossing, underdevelopment of the midface, facial asymmetry, low-set ears, broad and/or depressed nasal bridge, and a short philtrum.  Poor feeding and hypotonia in the neonatal period are usually present and physical growth is subnormal resulting in short stature.

Brain imaging may show abnormal gyral patterns, ventriculomegaly, hypoplasia of the corpus callosum, cerebellar hypoplasia, arachnoid cysts, and loss of periventricular white matter.  About half of patients develop seizures and many have intellectual disabilities.  Spinal anomalies include hemivertebrae with scoliosis and/or kyphosis.  Other skeletal features include joint laxity in some patients and contractures in others.  Arachnodactyly, craniosynostosis, and rib anomalies have been reported.  There may be malformations in the GI, GU, and cardiac systems while immune and coagulation abnormalities have also been reported.

Genetics

Heterozygous mutations in the SON gene (21q22.11) have been identified in patients with this condition.  They may cause truncation of the gene product with haploinsufficiency or, in other patients, a frameshift in the reading.  The SON gene is a master RNA splicing regulator that impacts neurodevelopment.

Virtually all cases are the result of de novo mutations.

Pedigree: 
Autosomal dominant
Treatment
Treatment Options: 

No effective treatment has been reported.  Physical therapy and assistive devices may be helpful.

References
Article Title: 

De Novo Truncating Variants in SON Cause Intellectual Disability, Congenital Malformations, and Failure to Thrive

Tokita MJ, Braxton AA, Shao Y, Lewis AM, Vincent M, Kury S, Besnard T, Isidor B, Latypova X, Bezieau S, Liu P, Motter CS, Melver CW, Robin NH, Infante EM, McGuire M, El-Gharbawy A, Littlejohn RO, McLean SD, Bi W, Bacino CA, Lalani SR, Scott DA, Eng CM, Yang Y, Schaaf CP, Walkiewicz MA. De Novo Truncating Variants in SON Cause Intellectual Disability, Congenital Malformations, and Failure to Thrive. Am J Hum Genet. 2016 Sep 1;99(3):720-7.

PubMed ID: 
27545676

De Novo Mutations in SON Disrupt RNA Splicing of Genes Essential for Brain Development and Metabolism, Causing an Intellectual-Disability Syndrome

Kim JH, Shinde DN, Reijnders MR, Hauser NS, Belmonte RL, Wilson GR, Bosch DG, Bubulya PA, Shashi V, Petrovski S, Stone JK, Park EY, Veltman JA, Sinnema M, Stumpel CT, Draaisma JM, Nicolai J; University of Washington Center for Mendelian Genomics, Yntema HG, Lindstrom K, de Vries BB, Jewett T, Santoro SL, Vogt J; Deciphering Developmental Disorders Study, Bachman KK, Seeley AH, Krokosky A, Turner C, Rohena L, Hempel M, Kortum F, Lessel D, Neu A, Strom TM, Wieczorek D, Bramswig N, Laccone FA, Behunova J, Rehder H, Gordon CT, Rio M, Romana S, Tang S, El-Khechen D, Cho MT, McWalter K, Douglas G, Baskin B, Begtrup A, Funari T, Schoch K, Stegmann AP, Stevens SJ, Zhang DE, Traver D, Yao X, MacArthur DG, Brunner HG, Mancini GM, Myers RM, Owen LB, Lim ST, Stachura DL, Vissers LE, Ahn EY. De Novo Mutations in SON Disrupt RNA Splicing of Genes Essential for Brain Development and Metabolism, Causing an Intellectual-Disability Syndrome. Am J Hum Genet. 2016 Sep 1;99(3):711-9.

PubMed ID: 
27545680
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