Monday, September 12, 2022

DDX3X-related neurodevelopmental disorder

Inspired by a patient

Johnson-Kerner B, Snijders Blok L, Suit L, Thomas J, Kleefstra T, Sherr EH. DDX3X-Related Neurodevelopmental Disorder. 2020 Aug 27. In: Adam MP, Everman DB, Mirzaa GM, Pagon RA, Wallace SE, Bean LJH, Gripp KW, Amemiya A, editors. GeneReviews® [Internet]. Seattle (WA): University of Washington, Seattle; 1993–2022. PMID: 32852922.


Clinical characteristics: DDX3X-related neurodevelopmental disorder (DDX3X-NDD) typically occurs in females and very rarely in males. All affected individuals reported to date have developmental delay / intellectual disability (ID) ranging from mild to severe; about 50% of affected girls remain nonverbal after age five years. Hypotonia, a common finding, can be associated with feeding difficulty in infancy. Behavioral issues can include autism spectrum disorder, attention-deficit/hyperactivity disorder and hyperactivity, self-injurious behavior, poor impulse control, and aggression. Other findings can include seizures, movement disorders (dyskinesia, spasticity, abnormal gait), vision and hearing impairment, congenital heart defects, respiratory difficulties, joint laxity, and scoliosis. Neuroblastoma has been observed in three individuals.

Diagnosis/testing: The diagnosis of DDX3X-NDD is established in a female proband with suggestive findings and a heterozygous de novo DDX3X pathogenic variant identified by molecular genetic testing and in a male proband with suggestive findings and a hemizygous DDX3X pathogenic variant.

Management: Treatment of manifestations: Treatment is symptomatic and focuses on optimizing the individual's abilities using a multidisciplinary approach that should also include psychosocial support for family members. Management of feeding difficulty, ID, behavioral issues, seizures, spasticity and other movement disorders, vision and hearing impairment, congenital heart defects, respiratory difficulties, joint laxity, and scoliosis as per standard care.

Surveillance: Periodic evaluation by the multidisciplinary team regarding growth, developmental progress and educational needs, and psychiatric/behavioral issues; regular assessment of vision and hearing, of the spine for scoliosis, for seizure control (when relevant), and for cardiac and respiratory issues. Starting at age eight years, assess girls for evidence of precocious puberty.

Genetic counseling: DDX3X-NDD is an X-linked disorder.

  1. Females. Most female probands represent simplex cases (i.e., a single occurrence in a family) and have the disorder as the result of a de novo pathogenic variant.

  2. Males. DDX3X-NDD in males is caused by either a pathogenic variant inherited from an unaffected heterozygous mother or a de novo pathogenic variant. If the mother of an affected male has a DDX3X pathogenic variant, the chance of transmitting it in each pregnancy is 50%. Males who inherit the pathogenic variant will be affected; females who inherit the pathogenic variant will be heterozygotes and are not expected to manifest a neurodevelopmental phenotype.

If the proband is female and represents a simplex case and if the DDX3X pathogenic variant cannot be detected in the leukocyte DNA of either parent – or the proband is male and the DDX3X pathogenic variant cannot be detected in the leukocyte DNA of the mother – the risk to sibs is slightly greater than that of the general population (though still <1%) because of the possibility of parental germline mosaicism.

Once the DDX3X pathogenic variant has been identified in an affected family member, prenatal testing for a pregnancy at increased risk and preimplantation genetic testing are possible.

Snijders Blok L, Madsen E, Juusola J, Gilissen C, Baralle D, Reijnders MR, Venselaar H, Helsmoortel C, Cho MT, Hoischen A, Vissers LE, Koemans TS, Wissink-Lindhout W, Eichler EE, Romano C, Van Esch H, Stumpel C, Vreeburg M, Smeets E, Oberndorff K, van Bon BW, Shaw M, Gecz J, Haan E, Bienek M, Jensen C, Loeys BL, Van Dijck A, Innes AM, Racher H, Vermeer S, Di Donato N, Rump A, Tatton-Brown K, Parker MJ, Henderson A, Lynch SA, Fryer A, Ross A, Vasudevan P, Kini U, Newbury-Ecob R, Chandler K, Male A; DDD Study, Dijkstra S, Schieving J, Giltay J, van Gassen KL, Schuurs-Hoeijmakers J, Tan PL, Pediaditakis I, Haas SA, Retterer K, Reed P, Monaghan KG, Haverfield E, Natowicz M, Myers A, Kruer MC, Stein Q, Strauss KA, Brigatti KW, Keating K, Burton BK, Kim KH, Charrow J, Norman J, Foster-Barber A, Kline AD, Kimball A, Zackai E, Harr M, Fox J, McLaughlin J, Lindstrom K, Haude KM, van Roozendaal K, Brunner H, Chung WK, Kooy RF, Pfundt R, Kalscheuer V, Mehta SG, Katsanis N, Kleefstra T. Mutations in DDX3X Are a Common Cause of Unexplained Intellectual Disability with Gender-Specific Effects on Wnt Signaling. Am J Hum Genet. 2015 Aug 6;97(2):343-52. doi: 10.1016/j.ajhg.2015.07.004. Epub 2015 Jul 30. PMID: 26235985; PMCID: PMC4573244.


Intellectual disability (ID) affects approximately 1%-3% of humans with a gender bias toward males. Previous studies have identified mutations in more than 100 genes on the X chromosome in males with ID, but there is less evidence for de novo mutations on the X chromosome causing ID in females. In this study we present 35 unique deleterious de novo mutations in DDX3X identified by whole exome sequencing in 38 females with ID and various other features including hypotonia, movement disorders, behavior problems, corpus callosum hypoplasia, and epilepsy. Based on our findings, mutations in DDX3X are one of the more common causes of ID, accounting for 1%-3% of unexplained ID in females. Although no de novo DDX3X mutations were identified in males, we present three families with segregating missense mutations in DDX3X, suggestive of an X-linked recessive inheritance pattern. In these families, all males with the DDX3X variant had ID, whereas carrier females were unaffected. To explore the pathogenic mechanisms accounting for the differences in disease transmission and phenotype between affected females and affected males with DDX3X missense variants, we used canonical Wnt defects in zebrafish as a surrogate measure of DDX3X function in vivo. We demonstrate a consistent loss-of-function effect of all tested de novo mutations on the Wnt pathway, and we further show a differential effect by gender. The differential activity possibly reflects a dose-dependent effect of DDX3X expression in the context of functional mosaic females versus one-copy males, which reflects the complex biological nature of DDX3X mutations.

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