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1.
Am J Hum Genet ; 105(4): 854-868, 2019 Oct 03.
Artigo em Inglês | MEDLINE | ID: mdl-31585109

RESUMO

Cadherins constitute a family of transmembrane proteins that mediate calcium-dependent cell-cell adhesion. The extracellular domain of cadherins consists of extracellular cadherin (EC) domains, separated by calcium binding sites. The EC interacts with other cadherin molecules in cis and in trans to mechanically hold apposing cell surfaces together. CDH2 encodes N-cadherin, whose essential roles in neural development include neuronal migration and axon pathfinding. However, CDH2 has not yet been linked to a Mendelian neurodevelopmental disorder. Here, we report de novo heterozygous pathogenic variants (seven missense, two frameshift) in CDH2 in nine individuals with a syndromic neurodevelopmental disorder characterized by global developmental delay and/or intellectual disability, variable axon pathfinding defects (corpus callosum agenesis or hypoplasia, mirror movements, Duane anomaly), and ocular, cardiac, and genital anomalies. All seven missense variants (c.1057G>A [p.Asp353Asn]; c.1789G>A [p.Asp597Asn]; c.1789G>T [p.Asp597Tyr]; c.1802A>C [p.Asn601Thr]; c.1839C>G [p.Cys613Trp]; c.1880A>G [p.Asp627Gly]; c.2027A>G [p.Tyr676Cys]) result in substitution of highly conserved residues, and six of seven cluster within EC domains 4 and 5. Four of the substitutions affect the calcium-binding site in the EC4-EC5 interdomain. We show that cells expressing these variants in the EC4-EC5 domains have a defect in cell-cell adhesion; this defect includes impaired binding in trans with N-cadherin-WT expressed on apposing cells. The two frameshift variants (c.2563_2564delCT [p.Leu855Valfs∗4]; c.2564_2567dupTGTT [p.Leu856Phefs∗5]) are predicted to lead to a truncated cytoplasmic domain. Our study demonstrates that de novo heterozygous variants in CDH2 impair the adhesive activity of N-cadherin, resulting in a multisystemic developmental disorder, that could be named ACOG syndrome (agenesis of corpus callosum, axon pathfinding, cardiac, ocular, and genital defects).

2.
Childs Nerv Syst ; 35(10): 1665-1671, 2019 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-31385087

RESUMO

PURPOSE: Chiari malformation type I (CMI), a rare disorder of the craniocerebral junction with an estimated incidence of 1 in 1280, is characterized by the downward herniation of the cerebellar tonsils of at least 5 mm through the foramen magnum, resulting in significant neurologic morbidity. Classical CMI is thought to be caused by an underdeveloped occipital bone, resulting in a posterior cranial fossa which is too small to accommodate the normal-sized cerebellum. In this review, we dissect the lines of evidence supporting a genetic contribution for this disorder. METHODS: We present the results of two types of approaches: animal models and human studies encompassing different study designs such as whole genome linkage analysis, case-control association studies, and expression studies. The update of the literature also includes the most recent findings emerged by whole exome sequencing strategy. RESULTS: Despite evidence for a genetic component, no major genes have been identified and the genetics of CMI is still very much unknown. One major challenge is the variability of clinical presentation within CMI patient population that reflects an underlying genetic heterogeneity. CONCLUSIONS: The identification of the genes that contribute to the etiology of CMI will provide an important step to the understanding of the underlying pathology. The finding of a predisposing gene may lead to the development of simple and accurate diagnostic tests for better prognosis, counseling, and clinical management of patients and their relatives.

3.
Hum Mutat ; 2019 Jul 13.
Artigo em Inglês | MEDLINE | ID: mdl-31301155

RESUMO

The wobble position in the anticodon loop of transfer ribonucleic acid (tRNA) is subject to numerous posttranscriptional modifications. In particular, thiolation of the wobble uridine has been shown to play an important role in codon-anticodon interactions. This modification is catalyzed by a highly conserved CTU1/CTU2 complex, disruption of which has been shown to cause abnormal phenotypes in yeast, worms, and plants. We have previously suggested that a single founder splicing variant in human CTU2 causes a novel multiple congenital anomalies syndrome consisting of dysmorphic facies, renal agenesis, ambiguous genitalia, microcephaly, polydactyly, and lissencephaly (DREAM-PL). In this study, we describe five new patients with DREAM-PL phenotype and whose molecular analysis expands the allelic heterogeneity of the syndrome to five different alleles; four of which predict protein truncation. Functional characterization using patient-derived cells for each of these alleles, as well as the original founder allele; revealed a specific impairment of wobble uridine thiolation in all known thiol-containing tRNAs. Our data establish a recognizable CTU2-linked autosomal recessive syndrome in humans characterized by defective thiolation of the wobble uridine. The potential deleterious consequences for the translational efficiency and fidelity during development as a mechanism for pathogenicity represent an attractive target of future investigations.

5.
Am J Hum Genet ; 104(6): 1210-1222, 2019 Jun 06.
Artigo em Inglês | MEDLINE | ID: mdl-31079897

RESUMO

We delineate a KMT2E-related neurodevelopmental disorder on the basis of 38 individuals in 36 families. This study includes 31 distinct heterozygous variants in KMT2E (28 ascertained from Matchmaker Exchange and three previously reported), and four individuals with chromosome 7q22.2-22.23 microdeletions encompassing KMT2E (one previously reported). Almost all variants occurred de novo, and most were truncating. Most affected individuals with protein-truncating variants presented with mild intellectual disability. One-quarter of individuals met criteria for autism. Additional common features include macrocephaly, hypotonia, functional gastrointestinal abnormalities, and a subtle facial gestalt. Epilepsy was present in about one-fifth of individuals with truncating variants and was responsive to treatment with anti-epileptic medications in almost all. More than 70% of the individuals were male, and expressivity was variable by sex; epilepsy was more common in females and autism more common in males. The four individuals with microdeletions encompassing KMT2E generally presented similarly to those with truncating variants, but the degree of developmental delay was greater. The group of four individuals with missense variants in KMT2E presented with the most severe developmental delays. Epilepsy was present in all individuals with missense variants, often manifesting as treatment-resistant infantile epileptic encephalopathy. Microcephaly was also common in this group. Haploinsufficiency versus gain-of-function or dominant-negative effects specific to these missense variants in KMT2E might explain this divergence in phenotype, but requires independent validation. Disruptive variants in KMT2E are an under-recognized cause of neurodevelopmental abnormalities.

6.
Eur J Hum Genet ; 27(8): 1254-1259, 2019 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-30936465

RESUMO

De novo DDX3X variants account for 1-3% of syndromic intellectual disability (ID) in females and have been occasionally reported in males. Furthermore, somatic DDX3X variants occur in several aggressive cancers, including medulloblastoma. We report three unrelated females with severe ID, dysmorphic features, and a common brain malformative pattern characterized by malformations of cortical development, callosal dysgenesis, basal ganglia anomalies, and midbrain-hindbrain malformations. A pilocytic astrocytoma was incidentally diagnosed in Patient 1 and trigonocephaly was found in Patient 2. With the use of family based whole exome sequencing (WES), we identified three distinct de novo variants in DDX3X. These findings expand the phenotypic spectrum of DDX3X-related disorders, demonstrating unique neuroradiological features resembling those of the tubulinopathies, and support a role for DDX3X in neuronal development. Our observations further suggest a possible link between germline DDX3X variants and cancer development.

7.
Neurogenetics ; 20(2): 103-108, 2019 05.
Artigo em Inglês | MEDLINE | ID: mdl-30924036

RESUMO

Aminoacyl-tRNA synthetase-interacting multifunctional protein 1 (AIMP1) is a non-catalytic component of the multi-tRNA synthetase complex which catalyzes the ligation of amino acids to the correct tRNAs. Pathogenic variants in several aminoacyl-tRNA synthetases genes have been linked to various neurological disorders, including leukodystrophies and pontocerebellar hypoplasias (PCH). To date, loss-of-function variants in AIMP1 have been associated with hypomyelinating leukodystrophy-3 (MIM 260600). Here, we report a novel frameshift AIMP1 homozygous variant (c.160delA,p.Lys54Asnfs) in a child with pontocerebellar hypoplasia and simplified gyral pattern, a phenotype not been previously described with AIMP1 variants, thus expanding the phenotypic spectrum. AIMP1 should be included in diagnostic PCH gene panels.

9.
J Neurol ; 266(5): 1167-1181, 2019 May.
Artigo em Inglês | MEDLINE | ID: mdl-30796522

RESUMO

OBJECTIVES: To describe the neurological phenotype of children with prenatal diagnosis of agenesis of corpus callosum (ACC) and interhemispheric cysts associated with malformations of cortical development (MCD). METHODS: We reviewed the neuroimaging, neurologic, EEG, and genetic data of 36 patients (21 males, mean age 7 years) with ACC and interhemispheric cysts. Associations were tested with Chi-squared and Fisher exact tests. RESULTS: According to the 2001 Barkovich classification, we found 4 type 1c (11.1%), 6 type 2a (16.6%), 18 type 2b (50%, 6/18 girls with Aicardi syndrome), and 9 type 2c cysts (22.2%). EEG showed specific epileptic activity in 27/36 patients (75%). Epilepsy was diagnosed in 16 subjects (16/36, 44.4%), including all Aicardi patients, and was associated with cognitive impairment (p = 0.032). Severe intellectual disability and epilepsy were associated with type 2b cysts, always due to Aicardi patients (p < 0.05). After excluding Aicardi patients, all subjects with type 2b cysts had mild neurological phenotype. Patients with 2a and 2c cysts more frequently had normal cognition (83.3% and 62.5% of cases, respectively). Patients with type 1c cyst mostly had mild/moderate cognitive impairment. Severe neurologic deficits were associated with 1c cysts and 2b cysts with Aicardi syndrome (p < 0.05). Multilobar and/or bilateral MCD were associated with severe neurological and epileptic phenotypes (p < 0.05). CONCLUSION: Once excluded Aicardi syndrome, most patients with ACC and interhemispheric cysts have a mild clinical phenotype characterized by borderline/normal cognition and minor neurological signs. Despite the high prevalence of EEG epileptic abnormalities, epilepsy in these cases is infrequent and usually responsive to antiepileptic drugs.


Assuntos
Agenesia do Corpo Caloso/complicações , Cistos/complicações , Malformações do Desenvolvimento Cortical/complicações , Agenesia do Corpo Caloso/diagnóstico por imagem , Encéfalo/diagnóstico por imagem , Canadá , Criança , Cistos/diagnóstico por imagem , Feminino , Seguimentos , Humanos , Imagem Tridimensional , Itália , Imagem por Ressonância Magnética , Masculino , Malformações do Desenvolvimento Cortical/diagnóstico por imagem , Entrevista Psiquiátrica Padronizada , Exame Neurológico , Estudos Retrospectivos
10.
Nat Commun ; 10(1): 707, 2019 02 12.
Artigo em Inglês | MEDLINE | ID: mdl-30755602

RESUMO

Aminoacyl-tRNA synthetases (ARSs) function to transfer amino acids to cognate tRNA molecules, which are required for protein translation. To date, biallelic mutations in 31 ARS genes are known to cause recessive, early-onset severe multi-organ diseases. VARS encodes the only known valine cytoplasmic-localized aminoacyl-tRNA synthetase. Here, we report seven patients from five unrelated families with five different biallelic missense variants in VARS. Subjects present with a range of global developmental delay, epileptic encephalopathy and primary or progressive microcephaly. Longitudinal assessment demonstrates progressive cortical atrophy and white matter volume loss. Variants map to the VARS tRNA binding domain and adjacent to the anticodon domain, and disrupt highly conserved residues. Patient primary cells show intact VARS protein but reduced enzymatic activity, suggesting partial loss of function. The implication of VARS in pediatric neurodegeneration broadens the spectrum of human diseases due to mutations in tRNA synthetase genes.


Assuntos
Epilepsia/genética , Mutação , Valina-tRNA Ligase/genética , Alelos , Anticódon , Criança , Pré-Escolar , Progressão da Doença , Epilepsia/enzimologia , Epilepsia/patologia , Feminino , Predisposição Genética para Doença , Humanos , Estudos Longitudinais , Mutação com Perda de Função , Masculino , Microcefalia/enzimologia , Microcefalia/genética , Modelos Moleculares , Transtornos do Neurodesenvolvimento/enzimologia , Transtornos do Neurodesenvolvimento/genética , Transtornos do Neurodesenvolvimento/patologia , Linhagem , Biossíntese de Proteínas , Domínios e Motivos de Interação entre Proteínas , RNA de Transferência/genética , Sequenciamento Completo do Exoma , Sequenciamento Completo do Genoma
11.
Pediatr Neurol ; 92: 32-36, 2019 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-30581057

RESUMO

BACKGROUND: Recent technological advances have improved the understanding and identification of the genetic basis of intellectual disability (ID) and global developmental delay (GDD). Next-generation sequencing panels of ID genes are now available for clinical testing; however, their overall yield in clinical practice has not yet been investigated. AIM: We determined the diagnostic yield of ID gene panels in a clinical setting and explored whether any clinical features are associated with an increased diagnostic yield. METHODS: We performed a systematic retrospective chart review of all patients with ID/GDD who underwent an ID gene panel between April 2014 and July 2017 at our institution. Chi-square analysis assessed whether any specific clinical features were significantly associated with a positive diagnostic yield. RESULTS: Forty-eight subjects (18 females, 30 males; median age: 7.5 years) were included. Consanguinity was present in 17%, autism in 38%, seizures in 42%, nonspecific dysmorphic features in 67%, and abnormalities on neurological examination in 56%; furthermore, 29% of the cohort was nonverbal and 4% was nonambulatory. Four different gene panels were used. The diagnostic yield was 21% (10/48) overall, and 38% with the more recent trio-based panel. Eight of 10 patients had de novo pathogenic dominant mutations, one had an inherited pathogenic autosomal dominant mutation, and one had compound heterozygous pathogenic recessive mutations. No clinical feature was significantly associated with an increased diagnostic yield. CONCLUSIONS: Our study suggests that ID gene panels have a high yield and are a valuable diagnostic tool in the evaluation of children with ID/GDD.

12.
J Pediatr Endocrinol Metab ; 32(1): 95-99, 2019 Jan 28.
Artigo em Inglês | MEDLINE | ID: mdl-30530901

RESUMO

Background The genetic causes of abnormal pituitary development have been extensively studied in the last few years. ROBO1 is involved in neurogenesis and axon guidance. Loss-of-function variants in ROBO1 have been associated with pituitary stalk interruption syndrome (PSIS), suggesting that its haploinsufficiency could impair the guidance of hypothalamic axons to the pituitary gland leading to developmental abnormalities. Case presentation We report a 4.5-year-old girl with anterior pituitary hypoplasia and pituitary stalk duplication in the ventral-dorsal direction. Her father had a similar pituitary phenotype, characterized by anterior pituitary hypoplasia combined with ectopic posterior pituitary. Comparative genomic hybridization (CGH) microarray analysis identified a 343.7 kb deletion of 3p12.3 encompassing ROBO1 in both individuals. Conclusions We report the first familial ROBO1 deletion in two individuals with peculiar pituitary anomalies, including the rare pituitary stalk duplication in the ventral-dorsal direction. These findings widen the spectrum of the phenotypes associated with ROBO1 haploinsufficiency and support its role in human pituitary development.


Assuntos
Deleção de Genes , Predisposição Genética para Doença , Hipopituitarismo/genética , Hipopituitarismo/patologia , Proteínas do Tecido Nervoso/genética , Doenças da Hipófise/genética , Doenças da Hipófise/patologia , Hipófise/fisiopatologia , Receptores Imunológicos/genética , Pré-Escolar , Feminino , Humanos , Prognóstico
13.
J Child Neurol ; : 883073818811223, 2018 Nov 28.
Artigo em Inglês | MEDLINE | ID: mdl-30486714

RESUMO

AIMP1/p43, is a noncatalytic component of the mammalian multi-tRNA synthetase complex that catalyzes the ligation of amino acids to their cognate tRNAs. AIMP1 is largely expressed in the central nervous system, where it is part of the regulatory machine of the neurofilament assembly, playing a crucial role in neuronal development and function. To date, nonsense mutations in AIMP1 have been associated with a primary neurodegenerative disorder consisting of cerebral atrophy, hypomyelination, microcephaly and epilepsy, whereas missense mutations have recently been linked to intellectual disability without neurodegeneration. Here, we report the first French-Canadian patient with a novel frameshift AIMP1 homozygous mutation (c.191_192delAA, p.Gln64Argfs*25), resulting in a severe neurodegenerative phenotype. We review and discuss the phenotypic spectrum associated with AIMP1 pathogenic variants.

14.
Dev Med Child Neurol ; 2018 Oct 15.
Artigo em Inglês | MEDLINE | ID: mdl-30320441

RESUMO

AIM: Neurodevelopmental outcomes in children with congenital cerebellar malformations (CCMs) remain poorly defined. We aimed to assess whether specific neuroimaging features in CCM patients correlate with neurodevelopmental outcomes. METHOD: Hospital records and neuroimaging of 67 children with CCMs were systematically reviewed. Logistic regression analyses were used to assess associations between specific imaging features and neurodevelopmental outcomes. RESULTS: CCM categories were distributed as follows: 28 percent isolated vermis hypoplasia (n=19), 28 percent global cerebellar hypoplasia (n=19), 15 percent Dandy-Walker malformation (n=10), 13 percent pontocerebellar hypoplasia (PCH, n=9), 9 percent molar tooth malformation (n=6), 3 percent rhombencephalosynapsis (n=2), and 3 percent unilateral cerebellar malformation (n=2). Overall, 85 percent (55/65) of the cohort had global developmental delay (GDD). Intellectual disability was present in 61 percent (27/43) and autism spectrum disorder (ASD) in 12 percent (6/52). Adjusting for supratentorial malformations and presence of genetic findings, severe GDD was associated with cerebellar hypoplasia (p=0.049) and PCH (p=0.030), whereas children with vermis hypoplasia were less likely to have severe GDD (p=0.003). Presence of supratentorial abnormalities was not significantly associated with worse neurodevelopmental outcome but was associated with epilepsy. INTERPRETATION: Children with CCMs have high prevalence of neurodevelopmental deficits. Specific features on imaging can aid prognostication and establish early intervention strategies. WHAT THIS PAPER ADDS: Atypical long-term neurodevelopmental outcome is very common in patients with congenital cerebellar malformations (CCMs). Involvement of the brainstem and cerebellar hemispheres predicts more severe neurodevelopmental disability. Most patients with vermis hypoplasia have language delay but are verbal. Supratentorial abnormalities are not significantly associated with worse neurodevelopmental outcome but are associated with epilepsy. Comorbidities are common in CCMs, especially ophthalmological issues in cerebellar hypoplasia and sensorineural hearing loss in pontocerebellar hypoplasia.

15.
Am J Med Genet A ; 2018 Sep 20.
Artigo em Inglês | MEDLINE | ID: mdl-30238602

RESUMO

THO/TREX (transcription/export) is a conserved eukaryotic complex that plays a crucial role in gene expression and prevents DNA damage during mitosis and meiosis. In mammals, TREX is essential during embryogenesis, determining stem cell fate specification by regulating posttranscriptional self-renewal and differentiation in several tissues. It is composed of a core called THO, consisting of THOC1, 2, 5, 6, 7, and additional proteins. Bi-allelic mutations in THOC6 have been associated to Beaulieu-Boycott-Innes syndrome (BBIS), a syndromic form of intellectual disability (ID). To date, nine patients harbouring homozygous or compound heterozygous mutations in THOC6 have been reported. Despite the clinical heterogenity and subtle dysmorphic features in some individuals, distinctive facial features are tall forehead, short and upslanting palpebral fissures, deep set eyes, flat philtrum, and malocclusion. Nonlife threatening congenital anomalies are common, including cardiac and renal malformations, anteriorly displaced anus, cryptorchidism in males, submucous cleft palate, and corpus callosum dysgenesis. Affected patients usually have short stature, mild microcephaly, and mild to moderate ID. Here, we describe an Italian patient with BBIS, carrying two compound heterozygous loss-of-function (LoF) variants in THOC6 (c.577C > T, p.R193* and c.792_793delCA, p.V264Vfs*48). In addition to the common phenotype, she displays cerebellar hypoplasia with severe vermian dysgenesis and hydrocephalus due to aqueductal stenosis, multiple skeletal anomalies and hypergonadotropic hypogonadism. Thus, we review the previous cases and discuss the phenotypic spectrum of BBIS, providing further evidence regarding the pivotal role of TREX complex in human development.

16.
Eur J Med Genet ; 2018 Jul 17.
Artigo em Inglês | MEDLINE | ID: mdl-30026055

RESUMO

Magnesium (Mg2+) plays a crucial role in many biological processes especially in the brain, heart and skeletal muscle. Mg2+ homeostasis is regulated by intestinal absorption and renal reabsorption, involving a combination of different epithelial transport pathways. Mutations in any of these transporters result in hypomagnesemia with variable clinical presentations. Among these, CNNM2 is found along the basolateral membrane of distal tubular segments where it is involved in Mg2+ reabsorption. To date, heterozygous mutations in CNNM2 have been associated with a variable phenotype, ranging from isolated hypomagnesemia to intellectual disability and epilepsy. The only homozygous mutation reported so far, is responsible for hypomagnesemia associated with a severe neurological phenotype characterized by refractory epilepsy, microcephaly, severe global developmental delay and intellectual disability. Here, we report the second homozygous CNNM2 mutation (c.1642G > A,p.Val548Met) in a Moroccan patient, presenting with hypomagnesemia and severe epileptic encephalopathy. Thus, we review and discuss the phenotypic spectrum associated with CNNM2 mutations.

17.
Neurology ; 90(20): e1832-e1833, 2018 May 15.
Artigo em Inglês | MEDLINE | ID: mdl-29760006
18.
Eur J Hum Genet ; 26(7): 1026-1037, 2018 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-29662154

RESUMO

Retinoblastoma is the most common eye cancer in children. Numerous families have been described displaying reduced penetrance and expressivity. An extensive molecular characterization of seven families led us to characterize the two main mechanisms impacting on phenotypic expression, as follows: (i) mosaicism of amorphic pathogenic variants; and (ii) parent-of-origin-effect of hypomorphic pathogenic variants. Somatic mosaicism for RB1 splicing variants (c.1960+5G>C and c.2106+2T>C), leading to a complete loss of function was demonstrated by high-depth NGS in two families. In both cases, the healthy carrier parent (one with retinoma) showed a variant frequency lower than that expected for a heterozygous individual, indicating a 56-60% mosaicism level. Previous evidences of a ~3-fold excess of RB1 maternal canonical transcript led us to hypothesize that this differential allelic expression could influence phenotypic outcome in families at risk for RB onset. Accordingly, in five families, we identified a higher tumor risk associated with paternally inherited hypomorphic pathogenic variants, namely a deletion resulting in the loss of 37 amino acids at the N-terminus (c.608-16_608del), an exonic substitution with a "leaky" splicing effect (c.1331A>G), a partially deleterious substitution (c.1981C>T) and a truncating C-terminal variant (c.2663+2T>C). The identification of these mechanisms changes the genetic/prenatal counseling and the clinical management of families, indicating a higher recurrence risk when the hypomorphic pathogenic variant is inherited from the father, and suggesting the need for second tumor surveillance in unaffected carriers at risk of developing adult-onset cancer such as osteosarcoma or leiomyosarcoma.

19.
Neuropediatrics ; 49(3): 217-221, 2018 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-29631299

RESUMO

Adams-Oliver syndrome (AOS) is characterized by a combination of congenital scalp defects (aplasia cutis congenita) and terminal transverse limb malformations of variable severity. When neurological findings are present, patients are reported as AOS variants. We describe a child with compound heterozygosity of the DOCK6 gene, aplasia cutis, terminal transverse limb defects, cardiovascular impairment, intellectual disability, and brain malformations with intracranial calcifications. He suffers from a severe refractory epileptic encephalopathy characterized by polymorphic seizures with prolonged periods of electroencephalogram (EEG), continuous epileptiform activity related to clinical inactivity, and closure of eyes with an "ON-OFF" behavior.

20.
Am J Med Genet A ; 176(4): 985-991, 2018 04.
Artigo em Inglês | MEDLINE | ID: mdl-29430868

RESUMO

Adaptor protein complex-4 (AP-4) is a heterotetrameric protein complex which plays a key role in vesicle trafficking in neurons. Mutations in genes affecting different subunits of AP-4, including AP4B1, AP4E1, AP4S1, and AP4M1, have been recently associated with an autosomal recessive phenotype, consisting of spastic tetraplegia, and intellectual disability (ID). The overlapping clinical picture among individuals carrying mutations in any of these genes has prompted the terms "AP-4 deficiency syndrome" for this clinically recognizable phenotype. Using whole-exome sequencing, we identified a novel homozygous mutation (c.991C>T, p.Q331*, NM_006594.4) in AP4B1 in two siblings from a consanguineous Pakistani couple, who presented with severe ID, progressive spastic tetraplegia, epilepsy, and microcephaly. Sanger sequencing confirmed the mutation was homozygous in the siblings and heterozygous in the parents. Similar to previously reported individuals with AP4B1 mutations, brain MRI revealed ventriculomegaly and white matter loss. Interestingly, in addition to the typical facial gestalt reported in other AP-4 deficiency cases, the older brother presented with congenital left Horner syndrome, bilateral optic nerve atrophy and cataract, which have not been previously reported in this condition. In summary, we report a novel AP4B1 homozygous mutation in two siblings and review the phenotype of AP-4 deficiency, speculating on a possible role of AP-4 complex in eye development.

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