Mutations in UPF3B, a member of the nonsense-mediated mRNA decay complex, cause syndromic and nonsyndromic mental retardation.

Nonsense-mediated mRNA decay (NMD) is of universal biological significance. It has emerged as an important global RNA, DNA and translation regulatory pathway. By systematically sequencing 737 genes (annotated in the Vertebrate Genome Annotation database) on the human X chromosome in 250 families with X-linked mental retardation, we identified mutations in the UPF3 regulator of nonsense transcripts homolog B (yeast) (UPF3B) leading to protein truncations in three families: two with the Lujan-Fryns phenotype and one with the FG phenotype. We also identified a missense mutation in another family with nonsyndromic mental retardation. Three mutations lead to the introduction of a premature termination codon and subsequent NMD of mutant UPF3B mRNA. Protein blot analysis using lymphoblastoid cell lines from affected individuals showed an absence of the UPF3B protein in two families. The UPF3B protein is an important component of the NMD surveillance machinery. Our results directly implicate abnormalities of NMD in human disease and suggest at least partial redundancy of NMD pathways.

Deletion of the immunoglobulin domain of IL1RAPL1 results in nonsyndromic X-linked intellectual disability associated with behavioral problems and mild dysmorphism.

X-Linked intellectual disability accounts for a significant fraction of males with cognitive impairment. Many of these males present with a non-syndromic phenotype and presently mutations in 17 X-linked genes are associated with these patients. Mutations in IL1RAPL1 have been found in multiple families with non-syndromic X-linked intellectual disability. All of the published mutations predict loss of function of the protein. We have identified an additional two families with deletions of a portion of the gene that give rise to cognitive impairment, as well as some behavioral problems and mild dysmorphism. Our clinical findings better delineate the phenotypic spectrum associated with IL1RAPL1 mutations.

Autistic Disorder: A 20 Year Chronicle.

The course of 187 individuals ages 3-21 years with Autistic Disorder was traced through a period of 20 years (enrollment: 1995-1998, follow up: 2014-2019). Specific genetic and environmental causes were identified in only a minority. Intellectual disability coexisted in 84%. Few became independent with 99% living at home with relatives, in disability group homes or in residential facilities. Seven individuals (3.7%) attained postsecondary education, two receiving baccalaureate degrees, two receiving associate degrees, and three receiving certificates from college disability programs. It may be anticipated that the long term outcome for individuals currently diagnosed with Autism Spectrum Disorder (ASD) will be substantially better than for individuals with Autistic Disorder in this cohort.

Cognitive-behavioral features of Wolf-Hirschhorn syndrome and other subtelomeric microdeletions.

Wolf-Hirschhorn syndrome (WHS) is a complex congenital malformation produced by a loss of genomic material at the locus 4p16.3. In addition to its dysmorphic features, the deletion produces a range of intellectual disability (ID). Many clinical aspects of WHS are well-characterized; however, the cognitive-behavioral characteristics have been rarely examined in a systematic fashion. The purpose of our study was to examine the cognitive-behavioral features of WHS and to compare them to children with other subtelomeric deletions that also produce ID. We recruited 45 children with subtelomeric deletions and examined their cognitive-behavioral abilities using a neuropsychological assessment battery composed of standardized instruments. Nineteen children were diagnosed with WHS and 26 children with one of three other subtelomeric deletions-11q25 (Jacobsen syndrome), deletion 2q37, and inversion duplication deletion 8p21-23. We found children with WHS to be more severely impacted cognitively than children from any of the other groups. Their overall adaptive behavior was lower as well. However, children with WHS exhibit strengths in socialization skills comparable to the levels attained by the other groups we assessed. Importantly, the proportion of children with WHS with autism or autistic-like features is significantly lower than the rates of autism found in the other subtelomeric disorders we examined.

The course of cognitive-behavioral development in children with the FMR1 mutation, Williams-Beuren syndrome, and neurofibromatosis type 1: The effect of gender.

The course of cognitive-behavioral development in children with intellectual disabilities produced by genetic disorders has only recently begun to be examined systematically. Unfortunately, these studies are few in number. Previously, we examined cognitive-behavioral development in children with the fragile X (FMR1) mutation and found longitudinal decreases in both IQ and adaptive behavior (DQ) scores in most males and females with the full mutation. In this study, we examine longitudinal changes in IQ and DQ in children with neurofibromatosis type 1 (NF1) and Williams-Beuren Syndrome (WBS) by examining differences in composite IQ and DQ scores between the first test (T1) and retest (T2), and compare their developmental trajectory to children with the FMR1 mutation. Sixty-five children with the FMR1 mutation, or NF1, or WBS, ages 4-16 years, were retested two years after initial testing with the Stanford-Binet 4th Edition (SBFE) and the Vineland Adaptive Behavior Scale (VABS). In addition to significant longitudinal declines in IQ and DQ noted previously in children with the FMR1 mutation, we found significant decreases in IQ in males compared to females in the remainder of our sample. We also observed statistically significant decreases in DQ scores among children the FMR1 mutation, as noted previously, but not among children with NF1 or WBS. Moreover, significant declines were found only among males with the FMR1 mutation. Unlike declines in IQ scores, decreases in DQ were not significantly different between males and females.

Natural history of Christianson syndrome.

Christianson syndrome is an X-linked mental retardation syndrome characterized by microcephaly, impaired ocular movement, severe global developmental delay, hypotonia which progresses to spasticity, and early onset seizures of variable types. Gilfillan et al.2008] reported mutations in SLC9A6, the gene encoding the sodium/hydrogen exchanger NHE6, in the family first reported and in three others. They also noted the clinical similarities to Angelman syndrome and found cerebellar atrophy on MRI and elevated glutamate/glutamine in the basal ganglia on MRS. Here we report on nonsense mutations in two additional families. The natural history is detailed in childhood and adult life, the similarities to Angelman syndrome confirmed, and the MRI/MRS findings documented in three affected boys.

Intellectual functioning in alpha-mannosidosis.

Alpha-mannosidosis is a rare inherited metabolic disorder (OMIM #248500) caused by mutations in the enzyme α-mannosidase encoded by the gene MAN2B1. Patients have distinct physical and developmental features, but only limited information regarding standardized cognitive functioning of patients has been published. Here we contribute intellectual ability scores (IQ) on 12 patients with alpha-mannosidosis (ages 8-59 years, 10 males, 2 females). In addition, a pooled analysis was performed with data collected from this investigation and 31 cases obtained from the literature, allowing a comprehensive analysis of intellectual functioning in this rare disease. The initial and pooled analyses show that patients with alpha-mannosidosis have variable degrees of intellectual disability but show decline in IQ with age, particularly during the first decade of life. Patients treated with hematopoietic stem cell transplantation tend to show stabilized cognitive abilities.

Cognitive-behavioral features of children with Wolf-Hirschhorn syndrome: preliminary report of 12 cases.

As a subset of genetic abnormalities, subtelomeric deletions have been found in 7-10% of individuals with mental retardation (MR). One subtelomeric deletion, Wolf-Hirschhorn syndrome (WHS), causes mild to severe MR, but the cognitive-behavioral features of individuals with WHS have not been studied systematically. To that end, we administered a comprehensive cognitive-behavioral battery to 12 children with WHS, ages 4-17 years, who also had some expressive language. Using the Stanford-Binet (4th Edition), we found cognitive deficits ranged from mild to severe, with mean IQ = 44.1. Interviewing parents with the Vineland Adaptive Behavior Scales, we found mean adaptive behavior score (DQ) = 37.3, with females exhibiting slightly higher scores than males. Cognitive profiles indicated relative strengths in Verbal and Quantitative Reasoning. Adaptive behavior profiles noted significant relative strengths in the Socialization Domain. These cognitive-behavioral profiles differed from children with other subtelomeric deletion syndromes, 2q37 or 8p23. Attention deficits and hyperactivity (ADHD) were observed in 7/12 (58%) of the children we tested. One child attained a score on the Child Autism Rating Scale (CARS) suggestive of mild autism. We conclude that different genetic disorders, which cause MR, produce diverse cognitive-behavioral profiles. Consequently, cognitive-behavioral profiles of children with MR need to be assessed more comprehensively.

Evidence that SIZN1 is a candidate X-linked mental retardation gene.

An estimated 1-3% of individuals within the United States are diagnosed with mental retardation (MR), yet the cause is unknown in nearly 50% of the patients. While several environmental, genetic and combined teratogenetic etiologies have been identified, many causative genes remain to be identified. Furthermore, the pathogenetic mechanisms underlying MR are known for very few of these genes. Males have a much higher incidence of MR implicating genes on the X-chromosome. We have recently identified a novel gene, SIZN1, on the X-chromosome and showed that it functions in modulating the BMP signaling pathway. Furthermore, we have shown this gene is necessary for basal forebrain cholinergic neuron (BFCN) specific gene expression. Given that cognitive function is impaired when BFCNs are lost or functionally disrupted, we undertook a screen of cognitively impaired males for SIZN1 mutations. We report on four different sequence variants in SIZN1 in 11 individuals with nonsyndromic X-linked mental retardation (XLMR). Our data implicate SIZN1 as a candidate gene for XLMR and/or as a neurocognitive functional modifier.

Behavior of 10 patients with FG syndrome (Opitz-Kaveggia syndrome) and the p.R961W mutation in the MED12 gene.

Opitz and Kaveggia [Opitz and Kaveggia (1974); Z Kinderheilk 117:1-18] reported on a family of five affected males with distinctive facial appearance, mental retardation, macrocephaly, imperforate anus and hypotonia. Risheg et al. [Risheg et al. (2007); Nat Genet 39:451-453] identified an identical mutation (p.R961W) in MED12 in six families with Opitz-Kaveggia syndrome, including a surviving affected man from the family reported in 1974. The previously defined behavior phenotype of hyperactivity, affability, and excessive talkativeness is very frequent in young boys with this mutation, along with socially oriented, attention-seeking behaviors. We present case studies of two older males with FG syndrome and the p.R961W mutation to illustrate how their behavior changes with age. We also characterize the behavior of eight additional individuals with FG syndrome and this recurrent mutation in MED12 using the Vineland Adaptive Behavior Scales 2nd edition, the Reiss Profile of Fundamental Goals and Motivation Sensitivities, and the Achenbach Child Behavior Checklist. Males with this MED12 mutation had deficits in communication skills compared to their socialization and daily living skills. In addition, they were at increased risk for maladaptive behavior, with a propensity towards aggression, anxiety, and inattention. Based on the behavior phenotype in 10 males with this recurrent MED12 mutation, we offer specific recommendations and interventional strategies. Our findings reinforce the importance of testing for the p.R961W MED12 mutation in males who are suspected of having developmental and behavioral problems with a clinical phenotype that is consistent with FG syndrome.

The original Lujan syndrome family has a novel missense mutation (p.N1007S) in the MED12 gene.

A novel missense mutation in the mediator of RNA polymerase II transcription subunit 12 (MED12) gene has been found in the original family with Lujan syndrome and in a second family (K9359) that was initially considered to have Opitz-Kaveggia (FG) syndrome. A different missense mutation in the MED12 gene has been reported previously in the original family with FG syndrome and in five other families with compatible clinical findings. Neither sequence alteration has been found in over 1400 control X chromosomes. Lujan (Lujan-Fryns) syndrome is characterised by tall stature with asthenic habitus, macrocephaly, a tall narrow face, maxillary hypoplasia, a high narrow palate with dental crowding, a small or receding chin, long hands with hyperextensible digits, hypernasal speech, hypotonia, mild-to-moderate mental retardation, behavioural aberrations and dysgenesis of the corpus callosum. Although Lujan syndrome has not been previously considered to be in the differential diagnosis of FG syndrome, there are some overlapping clinical manifestations. Specifically, these are dysgenesis of the corpus callosum, macrocephaly/relative macrocephaly, a tall forehead, hypotonia, mental retardation and behavioural disturbances. Thus, it seems that these two X-linked mental retardation syndromes are allelic, with mutations in the MED12 gene.

HUWE1 mutations in Juberg-Marsidi and Brooks syndromes: the results of an X-chromosome exome sequencing study.

BACKGROUND: X linked intellectual disability (XLID) syndromes account for a substantial number of males with ID. Much progress has been made in identifying the genetic cause in many of the syndromes described 20-40 years ago. Next generation sequencing (NGS) has contributed to the rapid discovery of XLID genes and identifying novel mutations in known XLID genes for many of these syndromes. METHODS: 2 NGS approaches were employed to identify mutations in X linked genes in families with XLID disorders. 1 involved exome sequencing of genes on the X chromosome using the Agilent SureSelect Human X Chromosome Kit. The second approach was to conduct targeted NGS sequencing of 90 known XLID genes. RESULTS: We identified the same mutation, a c.12928 G>C transversion in the HUWE1 gene, which gives rise to a p.G4310R missense mutation in 2 XLID disorders: Juberg-Marsidi syndrome (JMS) and Brooks syndrome. Although the original families with these disorders were considered separate entities, they indeed overlap clinically. A third family was also found to have a novel HUWE1 mutation. CONCLUSIONS: As we identified a HUWE1 mutation in an affected male from the original family reported by Juberg and Marsidi, it is evident the syndrome does not result from a mutation in ATRX as reported in the literature. Additionally, our data indicate that JMS and Brooks syndromes are allelic having the same HUWE1 mutation.

X-linked spermine synthase gene (SMS) defect: the first polyamine deficiency syndrome.

Polyamines (putrescine, spermidine, spermine) are ubiquitous, simple molecules that interact with a variety of other molecules in the cell, including nucleic acids, phospholipids and proteins. Various studies indicate that polyamines are essential for normal cell growth and differentiation. Furthermore, these molecules, especially spermine, have been shown to modulate ion channel activities of certain cells. Nonetheless, little is known about the specific cellular functions of these compounds, and extensive laboratory investigations have failed to identify a heritable condition in humans in which polyamine synthesis is perturbed. We report the first polyamine deficiency syndrome caused by a defect in spermine synthase (SMS). The defect results from a splice mutation, and is associated with the Snyder-Robinson syndrome (SRS, OMIM_309583), an X-linked mental retardation disorder. The affected males have mild-to-moderate mental retardation (MR), hypotonia, cerebellar circuitry dysfunction, facial asymmetry, thin habitus, osteoporosis, kyphoscoliosis, decreased activity of SMS, correspondingly low levels of intracellular spermine in lymphocytes and fibroblasts, and elevated spermidine/spermine ratios. The clinical features observed in SRS are consistent with cerebellar dysfunction and a defective functioning of red nucleus neurons, which, at least in rats, contain high levels of spermine. Additionally, the presence of MR reflects a role for spermine in cognitive function, possibly by spermine's ability to function as an 'intrinsic gateway' molecule for inward rectifier K(+) channels.

Longitudinal changes in cognitive and adaptive behavior scores in children and adolescents with the fragile X mutation or autism.

Studies of the relationship between the fragile X (FRAXA) mutation and autism have been controversial. Although there are differences between the two populations, individuals with FRAXA and autism exhibit remarkably similar aberrant behavior patterns. We examined comparably aged children and adolescents with FRAXA or autism to determine whether longitudinal changes in cognitive ability and adaptive behavior were similar in the two groups. We found decreases in IQ scores in young children with FRAXA as well as in those with autism. Declines in IQ scores were steeper among children with FRAXA. Older children and adolescents with autism exhibit stable test-retest scores, whereas older children with FRAXA continue to show decreases. Comparable declines in adaptive behavior composite scores were observed in both groups, at all ages tested, and across all adaptive behavior domains.

Developmental trajectories in syndromes with intellectual disability, with a focus on Wolf-Hirschhorn and its cognitive-behavioral profile.

Few studies exist of developmental trajectories in children with intellectual disability, and none for those with subtelomeric deletions. We compared developmental trajectories of children with Wolf-Hirschhorn syndrome to other genetic disorders. We recruited 106 children diagnosed with fragile X, Williams-Beuren syndrome, or Wolf-Hirschhorn syndrome, assessing their intellectual and adaptive behavior abilities. We retested 61 children 2 years later. We compared Time 1 and Time 2 difference scores related to genetic disorder, age, initial IQ, or adaptive behavior composite. Results show genetic disorder and initial IQ score were significant factors for IQ differences, but only genetic disorder affected adaptive behavior differences. Results suggest different gene-brain-behavior pathways likely exist for these genetic disorders. Different developmental trajectories will influence the type and intensity of intervention implemented by caregivers.

Finding new etiologies of mental retardation and hypotonia: X marks the spot.

Mental retardation (MR) and hypotonia occur together frequently and have a heterogeneous etiology. Molecular and clinical studies have led to the recent discovery of genes on the X chromosome that may be associated with syndromal forms of X-linked MR (XLMR). These disorders manifest additional neurological and somatic features that are helpful in establishing a specific diagnosis and etiology. This article provides an overview of MR and its association with hypotonia, with a review of five 'new' XLMR-hypotonia syndromes.

Pelizaeus-Merzbacher syndrome: neurocognitive function in a family with carrier manifestations.

A Cajun kindred with Pelizaeus-Merzbacher disease was found to have a p.Q128X mutation in exon 3B of proteolipid protein 1 (PLP1). The affected males were globally delayed in development, nonambulatory, and severely dysarthric. The heterozygous females developed progressive gait disturbances and cognitive deterioration starting in the fourth decade of life. The average IQ (Stanford-Binet Intelligence Scale: 4th Edition (SBFE)) of the carrier females was 54.2, compared to the average IQ of 97.5 in nonaffected relatives. The X-inactivation ratios in the three carrier females were not markedly skewed (55:45, 70:30, and 85:15). The presence of neurological and cognitive deterioration in the three carriers deviates from the usual expectation that carrier expression only occurs in families when males are mildly affected.