A diagnosis of Birt-Hogg-Dubé syndrome in individuals with Smith-Magenis syndrome: Recommendation for cancer screening.

We report a series of four unrelated adults with Smith-Magenis syndrome (SMS) and concomitant features of Birt-Hogg-Dubé (BHD) syndrome based upon haploinsufficiency for FLCN and characteristic renal cell carcinomas and/or evidence of cutaneous fibrofolliculomas. Three of the cases constitute the first known association of histopathologically verified characteristic BHD-associated renal tumors in adults with SMS; the fourth was identified to have histologically confirmed skin fibrofolliculomas. Molecular analysis documented second-hit FLCN mutations in two of the three cases with confirmed BHD renal pathology. These cases suggest the need to expand management recommendations for SMS to include kidney cancer surveillance starting at 20 years of age, as per the screening recommendations for BHD syndrome.

Variegation of autism related traits across seven neurogenetic disorders.

Gene dosage disorders (GDDs) constitute a major class of genetic risks for psychopathology, but there is considerable debate regarding the extent to which different GDDs induce different psychopathology profiles. The current research speaks to this debate by compiling and analyzing dimensional measures of several autism-related traits (ARTs) across seven diverse GDDs. The sample included 350 individuals with one of 7 GDDs, as well as reference idiopathic autism spectrum disorder (ASD; n = 74) and typically developing control (TD; n = 171) groups. The GDDs were: Down, Williams-Beuren, and Smith-Magenis (DS, WS, SMS) syndromes, and varying sex chromosome aneuploidies ("plusX", "plusXX", "plusY", "plusXY"). The Social Responsiveness Scale (SRS-2) was used to measure ARTs at different levels of granularity-item, subscale, and total. General linear models were used to examine ART profiles in GDDs, and machine learning was used to predict genotype from SRS-2 subscales and items. These analyses were completed with and without covariation for cognitive impairment. Twelve of all possible 21 pairwise GDD group contrasts showed significantly different ART profiles (7/21 when co-varying for IQ, all Bonferroni-corrected). Prominent GDD-ART associations in post hoc analyses included relatively preserved social motivation in WS and relatively low levels of repetitive behaviors in plusX. Machine learning revealed that GDD group could be predicted with plausible accuracy (~60-80%) even after controlling for IQ. GDD effects on ARTs are influenced by GDD subtype and ART dimension. This observation has consequences for mechanistic, clinical, and translational aspects of psychiatric neurogenetics.

Rare germline heterozygous missense variants in BRCA1-associated protein 1, BAP1, cause a syndromic neurodevelopmental disorder.

Nuclear deubiquitinase BAP1 (BRCA1-associated protein 1) is a core component of multiprotein complexes that promote transcription by reversing the ubiquitination of histone 2A (H2A). BAP1 is a tumor suppressor whose germline loss-of-function variants predispose to cancer. To our knowledge, there are very rare examples of different germline variants in the same gene causing either a neurodevelopmental disorder (NDD) or a tumor predisposition syndrome. Here, we report a series of 11 de novo germline heterozygous missense BAP1 variants associated with a rare syndromic NDD. Functional analysis showed that most of the variants cannot rescue the consequences of BAP1 inactivation, suggesting a loss-of-function mechanism. In T cells isolated from two affected children, H2A deubiquitination was impaired. In matching peripheral blood mononuclear cells, histone H3 K27 acetylation ChIP-seq indicated that these BAP1 variants induced genome-wide chromatin state alterations, with enrichment for regulatory regions surrounding genes of the ubiquitin-proteasome system (UPS). Altogether, these results define a clinical syndrome caused by rare germline missense BAP1 variants that alter chromatin remodeling through abnormal histone ubiquitination and lead to transcriptional dysregulation of developmental genes.

De Novo KAT5 Variants Cause a Syndrome with Recognizable Facial Dysmorphisms, Cerebellar Atrophy, Sleep Disturbance, and Epilepsy.

KAT5 encodes an essential lysine acetyltransferase, previously called TIP60, which is involved in regulating gene expression, DNA repair, chromatin remodeling, apoptosis, and cell proliferation; but it remains unclear whether variants in this gene cause a genetic disease. Here, we study three individuals with heterozygous de novo missense variants in KAT5 that affect normally invariant residues, with one at the chromodomain (p.Arg53His) and two at or near the acetyl-CoA binding site (p.Cys369Ser and p.Ser413Ala). All three individuals have cerebral malformations, seizures, global developmental delay or intellectual disability, and severe sleep disturbance. Progressive cerebellar atrophy was also noted. Histone acetylation assays with purified variant KAT5 demonstrated that the variants decrease or abolish the ability of the resulting NuA4/TIP60 multi-subunit complexes to acetylate the histone H4 tail in chromatin. Transcriptomic analysis in affected individual fibroblasts showed deregulation of multiple genes that control development. Moreover, there was also upregulated expression of PER1 (a key gene involved in circadian control) in agreement with sleep anomalies in all of the individuals. In conclusion, dominant missense KAT5 variants cause histone acetylation deficiency with transcriptional dysregulation of multiples genes, thereby leading to a neurodevelopmental syndrome with sleep disturbance, cerebellar atrophy, and facial dysmorphisms, and suggesting a recognizable syndrome.

Twenty-four-hour motor activity and body temperature patterns suggest altered central circadian timekeeping in Smith-Magenis syndrome, a neurodevelopmental disorder.

Smith-Magenis syndrome (SMS) is a contiguous gene syndrome linked to interstitial microdeletion, or mutation of RAI1, within chromosome 17p11.2. Key behavioral features of SMS include intellectual disability, sleep-disturbances, maladaptive, aggressive and self-injurious behaviors, hyperactivity, and sudden changes in mood. A distinguishing feature of this syndrome is an inverted pattern of melatonin characterized by elevated daytime and low nighttime melatonin levels. As the central circadian clock controls the 24-hr rhythm of melatonin, we hypothesized that the clock itself may contribute to the disrupted pattern of melatonin and sleep. In this report, 24-hr patterns of body temperature, a surrogate marker of clock-timing, and continuous wrist activity were collected to examine the links between body temperature, sleep behavior, and the circadian clock. In addition, age-dependent changes in sleep behavior were explored. Actigraphy-estimated sleep time for SMS was 1 hr less than expected across all ages studied. The timing of the 24-hr body temperature (Tb-24) rhythm was phase advanced, but not inverted. Compared to sibling (SIB) controls, the SMS group had less total night sleep, lower sleep efficiency, earlier sleep onset, earlier final awake times, increased waking after sleep onset (WASO), and increased daytime nap duration. The timing of wake onset varied with age, providing evidence of ongoing developmental sleep changes from childhood through adolescence. Clarification of the circadian and developmental factors that contribute to the disrupted and variable sleep patterns in this syndrome will be helpful in identifying more effective individualized treatments.

Functional analysis of novel DEAF1 variants identified through clinical exome sequencing expands DEAF1-associated neurodevelopmental disorder (DAND) phenotype.

Deformed epidermal autoregulatory factor-1 (DEAF1), a transcription factor essential for central nervous system and early embryonic development, has recently been implicated in a series of intellectual disability-related neurodevelopmental anomalies termed, in this study, as DEAF1-associated neurodevelopmental disorder (DAND). We identified six potentially deleterious DEAF1 variants in a cohort of individuals with DAND via clinical exome sequencing (CES) and in silico analysis, including two novel de novo variants: missense variant c.634G > A p.Gly212Ser in the SAND domain and deletion variant c.913_915del p.Lys305del in the NLS domain, as well as c.676C > T p.Arg226Trp, c.700T > A p.Trp234Arg, c.737G > C p.Arg246Thr, and c.791A > C p.Gln264Pro. Luciferase reporter, immunofluorescence staining, and electrophoretic mobility shift assays revealed that these variants had decreased transcriptional repression activity at the DEAF1 promoter and reduced affinity to consensus DEAF1 DNA binding sequences. In addition, c.913_915del p.K305del localized primarily to the cytoplasm and interacted with wild-type DEAF1. Our results demonstrate that variants located within the SAND or NLS domains significantly reduce DEAF1 transcriptional regulatory activities and are thus, likely to contribute to the underlying clinical concerns in DAND patients. These findings illustrate the importance of experimental characterization of variants with uncertain significance identified by CES to assess their potential clinical significance and possible use in diagnosis.

Auditory Phenotype of Smith-Magenis Syndrome.

Purpose: The purpose of this study was to describe the auditory phenotype of a large cohort with Smith-Magenis syndrome (SMS), a rare disorder including physical anomalies, cognitive deficits, sleep disturbances, and a distinct behavioral phenotype. Method: Hearing-related data were collected for 133 individuals with SMS aged 1-49 years. Audiogram data (97 participants) were used for cross-sectional and longitudinal analyses. Caregivers completed a sound sensitivity survey for 98 individuals with SMS and a control group of 24 unaffected siblings. Results: Nearly 80% of participants with interpretable audiograms (n = 76) had hearing loss, which was typically slight to mild in degree. When hearing loss type could be determined (40 participants), sensorineural hearing loss (48.1%) occurred most often in participants aged 11-49 years. Conductive hearing loss (35.2%) was typically observed in children aged 1-10 years. A pattern of fluctuating and progressive hearing decline was documented. Hyperacusis was reported in 73.5% of participants with SMS compared with 12.5% of unaffected siblings. Conclusions: This study offers the most comprehensive characterization of the auditory phenotype of SMS to date. The auditory profile in SMS is multifaceted and can include a previously unreported manifestation of hyperacusis. Routine audiologic surveillance is recommended as part of standard clinical care.

Exome analysis of Smith-Magenis-like syndrome cohort identifies de novo likely pathogenic variants.

Smith-Magenis syndrome (SMS), a neurodevelopmental disorder characterized by dysmorphic features, intellectual disability (ID), and sleep disturbances, results from a 17p11.2 microdeletion or a mutation in the RAI1 gene. We performed exome sequencing on 6 patients with SMS-like phenotypes but without chromosomal abnormalities or RAI1 variants. We identified pathogenic de novo variants in two cases, a nonsense variant in IQSEC2 and a missense variant in the SAND domain of DEAF1, and candidate de novo missense variants in an additional two cases. One candidate variant was located in an alpha helix of Necdin (NDN), phased to the paternally inherited allele. NDN is maternally imprinted within the 15q11.2 Prader-Willi Syndrome (PWS) region. This can help clarify NDN's role in the PWS phenotype. No definitive pathogenic gene variants were detected in the remaining SMS-like cases, but we report our findings for future comparison. This study provides information about the inheritance pattern and recurrence risk for patients with identified variants and demonstrates clinical and genetic overlap of neurodevelopmental disorders. Identification and characterization of ID-related genes that assist in development of common developmental pathways and/or gene-networks, may inform disease mechanism and treatment strategies.

Delayed diagnosis in a house of correction: Smith-Magenis syndrome due to a de novo nonsense RAI1 variant.

We report a 25-year-old female confirmed to have Smith-Magenis syndrome (SMS) due to a de novo RAI1 variant. Her past history is significant for developmental and intellectual delay, early and escalating maladaptive behaviors, and features consistent with significant sleep disturbance, the etiology of which was not confirmed for over two decades. The diagnosis of SMS was initially suspected in 1998 (at age 12 years), but that was 5 years before the initial report of RAI1 variants as causative of the SMS phenotype; cytogenetic fluorescence in situ hybridization studies failed to confirm an interstitial deletion of 17p11.2. Re-evaluation for suspected SMS was pursued with RAI1 sequencing analysis in response to urgent parental concerns of escalating behaviors and aggression with subsequent incarceration of the subject for assault of a health professional. Genetic analysis revealed a de novo RAI1 (NM_030665.3) nonsense variant, c.5536C>T; p.Q1846X. This case illustrates the importance of confirming the SMS diagnosis, which is associated with cognitive and functional impairment, as well as significant psychiatric co-morbidities and behavioral problems. The diagnosis was particularly relevant to the legal discussion and determination of her competence to stand trial. As other similar cases may exist, this report will help to increase awareness of the possibility of a very late diagnosis of SMS, with the need for re-evaluation of individuals suspected to have SMS who were initially evaluated prior to the identification of the RAI1 gene. © 2016 Wiley Periodicals, Inc.

Immune complex-mediated autoimmunity in a patient With Smith-Magenis syndrome (del 17p11.2).

Smith-Magenis syndrome (SMS) is a sporadic congenital disorder involving multiple organ systems caused by chromosome 17p11.2 deletions. Smith-Magenis syndrome features craniofacial and skeletal anomalies, cognitive impairment, and neurobehavioral abnormalities. In addition, some SMS patients may exhibit hypogammaglobulinemia. We report the first case of SMS-associated autoimmunity in a woman who presented with adult onset of multiple autoimmune disorders, including systemic lupus erythematosus, antiphospholipid antibody syndrome, and autoimmune hepatitis. Molecular analysis using single-nucleotide polymorphism array confirmed a de novo 3.8-Mb deletion (breakpoints, chr17: 16,660,721-20,417,975), resulting in haploinsufficiency for TACI (transmembrane activator and CAML interactor). Our data are consistent with potential loss of function for the BAFF (B cell-activating factor) receptor TACI as a contributing factor to human autoimmune phenomena.

Opposite effects on facial morphology due to gene dosage sensitivity.

Sequencing technology is increasingly demonstrating the impact of genomic copy number variation (CNV) on phenotypes. Opposing variation in growth, head size, cognition and behaviour is known to result from deletions and reciprocal duplications of some genomic regions. We propose normative inversion of face shape, opposing difference from a matched norm, as a basis for investigating the effects of gene dosage on craniofacial development. We use dense surface modelling techniques to match any face (or part of a face) to a facial norm of unaffected individuals of matched age, sex and ethnicity and then we reverse the individual's face shape differences from the matched norm to produce the normative inversion. We demonstrate for five genomic regions, 4p16.3, 7q11.23, 11p15, 16p13.3 and 17p11.2, that such inversion for individuals with a duplication or (epi)-mutation produces facial forms remarkably similar to those associated with a deletion or opposite (epi-)mutation of the same region, and vice versa. The ability to visualise and quantify face shape effects of gene dosage is of major benefit for determining whether a CNV is the cause of the phenotype of an individual and for predicting reciprocal consequences. It enables face shape to be used as a relatively simple and inexpensive functional analysis of the gene(s) involved.

Three rare diseases in one Sib pair: RAI1, PCK1, GRIN2B mutations associated with Smith-Magenis Syndrome, cytosolic PEPCK deficiency and NMDA receptor glutamate insensitivity.

The National Institutes of Health Undiagnosed Diseases Program evaluates patients for whom no diagnosis has been discovered despite a comprehensive diagnostic workup. Failure to diagnose a condition may arise from the mutation of genes previously unassociated with disease. However, we hypothesized that this could also co-occur with multiple genetic disorders. Demonstrating a complex syndrome caused by multiple disorders, we report two siblings manifesting both similar and disparate signs and symptoms. They shared a history of episodes of hypoglycemia and lactic acidosis, but had differing exam findings and developmental courses. Clinical acumen and exome sequencing combined with biochemical and functional studies identified three genetic conditions. One sibling had Smith-Magenis Syndrome and a nonsense mutation in the RAI1 gene. The second sibling had a de novo mutation in GRIN2B, which resulted in markedly reduced glutamate potency of the encoded receptor. Both siblings had a protein-destabilizing homozygous mutation in PCK1, which encodes the cytosolic isoform of phosphoenolpyruvate carboxykinase (PEPCK-C). In summary, we present the first clinically-characterized mutation of PCK1 and demonstrate that complex medical disorders can represent the co-occurrence of multiple diseases.

Analysis of the sensory profile in children with Smith-Magenis syndrome.

This study systematically assessed sensory processing in 34 children, aged 3-14 years, with Smith-Magenis syndrome (SMS) using the Sensory Profile Caregiver Questionnaire. Scores for the SMS cohort were significantly different from scores of the national sample of children with and without disabilities in all Sensory Profile categories and quadrants (p < .001). No main effects of age or gender were found, but an interaction effect of age by gender was found in Modulation of Sensory Input Affecting Emotional Responses, in which older females presented with the lowest scores. A significant decline over time was found in the Seeking pattern, reflecting increased vulnerability (p < .05). Nonsignificant trends suggest more vulnerabilities for older versus younger children, especially older females. The neurobehavioral phenotype in children with SMS is expanded by this description of sensory processing. How children with SMS experience and respond to everyday sensations informs multidisciplinary team decisions.

Otologic and audiologic manifestations of Hutchinson-Gilford progeria syndrome.

OBJECTIVES/HYPOTHESIS: To define the audiologic and otologic phenotype of Hutchinson-Gilford progeria syndrome (HGPS). STUDY DESIGN: Prospective case series. METHODS: Fifteen patients with HGPS were enrolled in a prospective natural history study; 14 were evaluated in the neurotology clinic, and 11 received audiologic evaluations. The physical exam and audiologic findings of these patients were reviewed to define an otologic and audiologic phenotype for HGPS in the largest series of subjects in the literature. RESULTS: All patients were noted to have stiff auricular cartilages, small or absent lobules, and hypoplasia of the lateral soft-tissue portion of the external ear canal leading to a shortened canal. Ten of 14 patients (71%) had dry cerumen impaction, and four of 14 patients (29%) reported a history of recurrent otitis media. Nineteen of 22 ears (86.4%) demonstrated low-frequency conductive hearing loss in the 250 to 500 Hz range. Sixteen of 22 ears (73%) had type A tympanograms; three of 22 ears (14%) displayed bimodal or "W" peaked tympanograms; two of 22 ears (9%) had type B tympanograms; one of 22 ears (4%) had a type C tympanogram. Nine of 10 patients had distortion product otoacoustic emissions consistent with normal peripheral hearing sensitivity. CONCLUSIONS: HGPS is caused by a mutation in the LMNA gene resulting in the production of an abnormal nuclear protein; this in turn affects nuclear structure and function. Patients with HGPS have characteristic otologic features due to cartilaginous and subcutaneous tissue abnormalities and typically demonstrate low-frequency conductive hearing loss despite largely normal tympanometry. It is important to be aware of these conditions in managing these patients.

Molecular analysis of the Retinoic Acid Induced 1 gene (RAI1) in patients with suspected Smith-Magenis syndrome without the 17p11.2 deletion.

Smith-Magenis syndrome (SMS) is a complex neurobehavioral disorder characterized by multiple congenital anomalies. The syndrome is primarily ascribed to a ∼3.7 Mb de novo deletion on chromosome 17p11.2. Haploinsufficiency of multiple genes likely underlies the complex clinical phenotype. RAI1 (Retinoic Acid Induced 1) is recognized as a major gene involved in the SMS phenotype. Extensive genetic and clinical analyses of 36 patients with SMS-like features, but without the 17p11.2 microdeletion, yielded 10 patients with RAI1 variants, including 4 with de novo deleterious mutations, and 6 with novel missense variants, 5 of which were familial. Haplotype analysis showed two major RAI1 haplotypes in our primarily Caucasian cohort; the novel RAI1 variants did not occur in a preferred haplotype. RNA analysis revealed that RAI1 mRNA expression was significantly decreased in cells of patients with the common 17p11.2 deletion, as well as in those with de novo RAI1 variants. Expression levels varied in patients with familial RAI1 variants and in non-17p11.2 deleted patients without identified RAI1 defects. No correlation between SNP haplotype and RAI1 expression was found. Two clinical features, ocular abnormalities and polyembolokoilomania (object insertion), were significantly correlated with decreased RAI1 expression. While not significantly correlated, the presence of hearing loss, seizures, hoarse voice, childhood onset of obesity and specific behavioral aspects and the absence of immunologic abnormalities and cardiovascular or renal structural anomalies, appeared to be specific for the de novo RAI1 subgroup. Recognition of the combination of these features will assist in referral for RAI1 analysis of patients with SMS-like features without detectable microdeletion of 17p11.2. Moreover, RAI1 expression emerged as a genetic target for development of therapeutic interventions for SMS.

Autism spectrum features in Smith-Magenis syndrome.

Smith-Magenis syndrome (SMS; OMIM 182290) is a neurodevelopmental disorder characterized by a well-defined pattern of anomalies. The majority of cases are due to a common deletion in chromosome 17p11.2 that includes the RAI1 gene. In children with SMS, autistic-like behaviors and symptoms start to emerge around 18 months of age. This study included 26 individuals (15 females and 11 males), with a confirmed deletion (del 17p11.2). Parents/caregivers were asked to complete the Social Responsiveness Scale (SRS) and the Social Communication Questionnaire (SCQ) both current and lifetime versions. The results suggest that 90% of the sample had SRS scores consistent with autism spectrum disorders. Moreover, females showed more impairment in total T-scores (P = 0.02), in the social cognition (P = 0.01) and autistic mannerisms (P = 0.002) subscales. The SCQ scores are consistent to show that a majority of individuals may meet criteria for autism spectrum disorders at some point in their lifetime. These results suggest that SMS needs to be considered in the differential diagnosis of autism spectrum disorders but also that therapeutic interventions for autism are likely to benefit individuals with SMS. The mechanisms by which the deletion of RAI1 and contiguous genes cause psychopathology remain unknown but they provide a solid starting point for further studies of gene-brain-behavior interactions in SMS and autism spectrum disorders.

Pharmacological treatment of disruptive behavior in Smith-Magenis syndrome.

Smith-Magenis syndrome (SMS) is a complex genetic syndrome caused by an interstitial deletion of chromosome 17p11.2. Children and adults with SMS appear to have unique neurobehavioral problems that include: sleep disturbance, self-injurious and maladaptive behaviors, stereotypies, and sensory integration disorders. We gathered retrospective psychotropic use information from parents or other caregivers of 62 individuals with SMS who were asked about use of psychotropic medication from a list of commonly used psychiatric medications. For those drugs identified, respondents were asked to rate the experience with the particular medication using a likert-type scale. Drugs were grouped into seven main categories: (1) stimulants; (2) antidepressants; (3) antipsychotics; (4) sleep aides; (5) mood stabilizers; (6) alpha 2 agonists; and (7) benzodiazepines. Relative frequencies, means and standard deviations pertaining to age and medication effect were derived for each medication category. Six of the seven medication categories examined showed no meaningful deviations from the "no change" score. The benzodiazepine group showed a mild detrimental effect. There were no gender differences in efficacy. Use of psychotropic medication started early in life (mean age 5 years), particularly with sleep aides. Although no medication category was identified as efficacious in SMS, all the categories reported herein may be considered as an option for brief symptomatic relief.

Diagnostic utility of daytime salivary melatonin levels in Smith-Magenis syndrome.

An inverted circadian rhythm of melatonin (MT) likely contributes to the sleep disturbance in patients with Smith-Magenis syndrome (SMS). Plasma MT levels have documented this altered rhythm, but daytime levels of salivary MT has not been determined. Daytime measures of salivary MT might have utility in home/outpatient settings for assessing MT levels in undiagnosed patients with clinical features of SMS. The objective of this study was to determine the utility of daytime salivary MT as a diagnostic test in SMS. Thirty individuals with confirmed SMS [28 with del 17p11.2 and 2 with the retinoic acid induced 1 (RAI1) gene mutation] and five controls were studied. Single or serial daytime salivary MT levels were measured. The mean midday salivary MT level was 79.0 pg/ml in SMS patients, compared with 16.3 pg/ml in controls, with nine patients having values similar to controls. The median MT level in SMS patients was 49.0 pg/ml (first and third quartile values = 15.5 and 106.8 pg/ml). Twenty-six (90%) of 29 patients had at least one MT value >15.5 pg/ml, including 70 (78%) of 90 samples from patients with del 17p11.2 and one (20%) of five samples from the two patients with the RAI1 mutation. Neither the pattern of medication use nor age had an effect on daytime salivary MT levels. Although most SMS patients had elevated daytime salivary MT levels, multiple sampling appears necessary to distinguish patients with SMS from other conditions.

Sensory motor and functional skills of dizygotic twins: one with Smith-Magenis syndrome and a twin control.

Smith-Magenis syndrome (SMS), the result of an interstitial deletion within chromosome 17p11.2, is a disorder that may include minor dysmorphic features, brachydactyly, short stature, hypotonia, speech delays, cognitive deficits, signs of peripheral neuropathy, scoliosis, and neurobehavioral problems including sleep disturbances and maladaptive repetitive and self-injurious behaviors. Physical and occupational therapists provide services for children who have the syndrome, whose genetic disorder is frequently not identified or diagnosed before 1 year of age. A comprehensive physical and occupational therapy evaluation was completed in nonidentical twins with one having SMS, using the Sensory Profile; Brief Assessment of Motor Function (BAMF); Peabody Developmental Motor Scales, Second Edition (PDMS-2); and Pediatric Evaluation of Disability Inventory (PEDI). This provides a framework for conducting assessments to enhance early detection and interdisciplinary management with this specialized population.

Neurodevelopment of children under 3 years of age with Smith-Magenis syndrome.

Systematic data regarding early neurodevelopmental functioning in Smith-Magenis syndrome are limited. Eleven children with Smith-Magenis syndrome less than 3 years of age (mean, 19 months; range, 5-34 months) received prospective multidisciplinary assessments using standardized measures. The total sample scored in the moderately to severely delayed range in cognitive functioning, expressive language, and motor skills and exhibited generalized hypotonia, oral-motor abnormalities, and middle ear dysfunction. Socialization skills were average, and significantly higher than daily living, communication, and motor abilities, which were below average. Mean behavior ratings were in the nonautistic range. According to exploratory analyses, the toddler subgroup scored significantly lower than the infant subgroup in cognition, expressive language, and adaptive behavior, suggesting that the toddlers were more delayed than the infants relative to their respective peers. Infants aged approximately 1 year or younger exhibited cognitive, language, and motor skills that ranged from average to delayed, but with age-appropriate social skills and minimal maladaptive behaviors. At ages 2 to 3 years, the toddlers consistently exhibited cognitive, expressive language, adaptive behavior, and motor delays and mildly to moderately autistic behaviors. Combining age groups in studies may mask developmental and behavioral differences. Increased knowledge of these early neurodevelopmental characteristics should facilitate diagnosis and appropriate intervention.