De novo variants in DENND5B cause a neurodevelopmental disorder.

The Rab family of guanosine triphosphatases (GTPases) includes key regulators of intracellular transport and membrane trafficking targeting specific steps in exocytic, endocytic, and recycling pathways. DENND5B (Rab6-interacting Protein 1B-like protein, R6IP1B) is the longest isoform of DENND5, an evolutionarily conserved DENN domain-containing guanine nucleotide exchange factor (GEF) that is highly expressed in the brain. Through exome sequencing and international matchmaking platforms, we identified five de novo variants in DENND5B in a cohort of five unrelated individuals with neurodevelopmental phenotypes featuring cognitive impairment, dysmorphism, abnormal behavior, variable epilepsy, white matter abnormalities, and cortical gyration defects. We used biochemical assays and confocal microscopy to assess the impact of DENND5B variants on protein accumulation and distribution. Then, exploiting fluorescent lipid cargoes coupled to high-content imaging and analysis in living cells, we investigated whether DENND5B variants affected the dynamics of vesicle-mediated intracellular transport of specific cargoes. We further generated an in silico model to investigate the consequences of DENND5B variants on the DENND5B-RAB39A interaction. Biochemical analysis showed decreased protein levels of DENND5B mutants in various cell types. Functional investigation of DENND5B variants revealed defective intracellular vesicle trafficking, with significant impairment of lipid uptake and distribution. Although none of the variants affected the DENND5B-RAB39A interface, all were predicted to disrupt protein folding. Overall, our findings indicate that DENND5B variants perturb intracellular membrane trafficking pathways and cause a complex neurodevelopmental syndrome with variable epilepsy and white matter involvement.

The different clinical facets of SYN1-related neurodevelopmental disorders.

Synapsin-I (SYN1) is a presynaptic phosphoprotein crucial for synaptogenesis and synaptic plasticity. Pathogenic SYN1 variants are associated with variable X-linked neurodevelopmental disorders mainly affecting males. In this study, we expand on the clinical and molecular spectrum of the SYN1-related neurodevelopmental disorders by describing 31 novel individuals harboring 22 different SYN1 variants. We analyzed newly identified as well as previously reported individuals in order to define the frequency of key features associated with these disorders. Specifically, behavioral disturbances such as autism spectrum disorder or attention deficit hyperactivity disorder are observed in 91% of the individuals, epilepsy in 82%, intellectual disability in 77%, and developmental delay in 70%. Seizure types mainly include tonic-clonic or focal seizures with impaired awareness. The presence of reflex seizures is one of the most representative clinical manifestations related to SYN1. In more than half of the cases, seizures are triggered by contact with water, but other triggers are also frequently reported, including rubbing with a towel, fever, toothbrushing, fingernail clipping, falling asleep, and watching others showering or bathing. We additionally describe hyperpnea, emotion, lighting, using a stroboscope, digestive troubles, and defecation as possible triggers in individuals with SYN1 variants. The molecular spectrum of SYN1 variants is broad and encompasses truncating variants (frameshift, nonsense, splicing and start-loss variants) as well as non-truncating variants (missense substitutions and in-frame duplications). Genotype-phenotype correlation revealed that epileptic phenotypes are enriched in individuals with truncating variants. Furthermore, we could show for the first time that individuals with early seizures onset tend to present with severe-to-profound intellectual disability, hence highlighting the existence of an association between early seizure onset and more severe impairment of cognitive functions. Altogether, we present a detailed clinical description of the largest series of individuals with SYN1 variants reported so far and provide the first genotype-phenotype correlations for this gene. A timely molecular diagnosis and genetic counseling are cardinal for appropriate patient management and treatment.

Characterization of PARP6 Function in Knockout Mice and Patients with Developmental Delay.

PARP6, a member of a family of enzymes (17 in humans) known as poly-ADP-ribose polymerases (PARPs), is a neuronally enriched PARP. While previous studies from our group show that Parp6 is a regulator of dendrite morphogenesis in rat hippocampal neurons, its function in the nervous system in vivo is poorly understood. Here, we describe the generation of a Parp6 loss-of-function mouse model for examining the function of Parp6 during neurodevelopment in vivo. Using CRISPR-Cas9 mutagenesis, we generated a mouse line that expressed a Parp6 truncated variant (Parp6TR) in place of Parp6WT. Unlike Parp6WT, Parp6TR is devoid of catalytic activity. Homozygous Parp6TR do not exhibit obvious neuromorphological defects during development, but nevertheless die perinatally. This suggests that Parp6 catalytic activity is important for postnatal survival. We also report PARP6 mutations in six patients with several neurodevelopmental disorders, including microencephaly, intellectual disabilities, and epilepsy. The most severe mutation in PARP6 (C563R) results in the loss of catalytic activity. Expression of Parp6C563R in hippocampal neurons decreases dendrite morphogenesis. To gain further insight into PARP6 function in neurons we also performed a BioID proximity labeling experiment in hippocampal neurons and identified several microtubule-binding proteins (e.g., MAP-2) using proteomics. Taken together, our results suggest that PARP6 is an essential microtubule-regulatory gene in mice, and that the loss of PARP6 catalytic activity has detrimental effects on neuronal function in humans.

Neurodevelopmental phenotypes in individuals with pathogenic variants in CHAMP1.

De novo pathogenic variants in CHAMP1 (chromosome alignment maintaining phosphoprotein 1), which encodes kinetochore-microtubule associated protein on 13q34, cause a rare neurodevelopmental disorder. We enrolled 14 individuals with pathogenic variants in CHAMP1 that were documented by exome sequencing or gene panel sequencing. Medical history interviews, seizure surveys, Vineland Adapted Behavior Scales Second Edition, and other behavioral surveys were completed by primary caregivers of available participants in Simons Searchlight. Clinicians extracted clinical data from the medical record for two participants. We report on clinical features of 14 individuals (ages 2-26) with de novo predicted loss-of-function variants in CHAMP1 and compare them with previously reported cases (total n = 32). At least two individuals have the same de novo variant: p.(Ser181Cysfs*5), p.(Trp348*), p.(Arg398*), p.(Arg497*), or p.(Tyr709*). Common phenotypes include intellectual disability/developmental delay, language impairment, congenital and acquired microcephaly, behavioral problems including autism spectrum disorder, seizures, hypotonia, gastrointestinal issues of reflux and constipation, and ophthalmologic issues. Other rarely observed phenotypes include leukemia, failure to thrive, and high pain tolerance. Pathogenic variants in CHAMP1 are associated with a variable clinical phenotype of developmental delay/intellectual disability and seizures.

A Retrospective Chart Review of Children in Neurocutaneous Clinic Who May Benefit from Further Evaluation Beyond Neurofibromatosis Type I.

While most individuals with a clinical diagnosis of Neurofibromatosis type 1 (NF1) have a detectable pathogenic variant in the NF1 gene, other conditions have phenotypic features overlapping with NF1. Without molecular confirmation, individuals may be misdiagnosed and have a different underlying condition. Namely, if a child has constitutional mismatch repair deficiency (CMMRD), early detection and prevention strategies for cancer risk would include surveillance recommendations not typically recommended for children with NF1. This study aimed to explore phenotypes of individuals with a clinical diagnosis of NF1 to identify subpopulations who may benefit from further genetic counseling or testing for an alternate diagnosis. Retrospective review of 240 medical records of children who attended a neurocutaneous clinic identified 135 children with a molecularly confirmed pathogenic variant in NF1 or autosomal dominant pattern of clinical NF1 ("controls") and 102 children deemed "at-risk" for another condition like CMMRD. Clinical presentation, family history of NF1, personal history of cancer, and family history of cancer were compared. When comparing clinical presentation, family history, and cancer history, minimal statistical differences were found, indicating that the at-risk population appears clinically indistinguishable from those with a clear diagnosis of NF1. Given the lack of distinguishable features between the at-risk and control population, this study suggests that tiered genetic testing for all individuals being evaluated for NF1 may be beneficial for identifying patients who may be misdiagnosed with NF1 and subsequently mismanaged. This study suggests that at-risk population with a suspected NF1 diagnosis may benefit from further evaluation. Correct diagnosis of constitutional mismatch repair deficiency is crucial to diagnose cancer at an early stage or prevent cancer from occurring. PREVENTION RELEVANCE: This study suggests that at-risk population with a suspected NF1 diagnosis may benefit from further evaluation. Correct diagnosis of constitutional mismatch repair deficiency is crucial to diagnose cancer at an early stage or prevent cancer from occurring.

The novel duplication HRAS c.186_206dup p.(Glu62_Arg68dup): clinical and functional aspects.

Specific activating missense HRAS variants cause Costello syndrome (CS), a RASopathy with recognizable facial features. The majority of these dominant disease causing variants affect the glycine residues in position 12 or 13. A clinically suspected CS diagnosis can be confirmed through identification of a dominant pathogenic HRAS variant. A novel HRAS variant predicting p.(Glu62_Arg68dup) was identified in an individual with hypertrophic cardiomyopathy, Chiari 1 malformation and ectodermal findings consistent with a RASopathy. Functional studies showed that the p.Glu62_Arg68dup alteration affects HRAS interaction with effector protein PIK3CA (catalytic subunit of phosphoinositide 3-kinase) and the regulator neurofibromin 1 (NF1) GTPase-activating protein (GAP). HRASGlu62_Arg68dup binding with effectors rapidly accelerated fibrosarcoma (RAF1), RAL guanine nucleotide dissociation stimulator (RALGDS) and phospholipase C1 (PLCE1) was enhanced. Accordingly, p.Glu62_Arg68dup increased steady-state phosphorylation of MEK1/2 and ERK1/2 downstream of RAF1, whereas AKT phosphorylation downstream of PI3K was not significantly affected. Growth factor stimulation revealed that expression of HRASGlu62_Arg68dup abolished the HRAS' capacity to modulate downstream signaling. Our data underscore that different qualities of dysregulated HRAS-dependent signaling dynamics determine the clinical severity in CS.

Automated syndrome diagnosis by three-dimensional facial imaging.

PURPOSE: Deep phenotyping is an emerging trend in precision medicine for genetic disease. The shape of the face is affected in 30-40% of known genetic syndromes. Here, we determine whether syndromes can be diagnosed from 3D images of human faces. METHODS: We analyzed variation in three-dimensional (3D) facial images of 7057 subjects: 3327 with 396 different syndromes, 727 of their relatives, and 3003 unrelated, unaffected subjects. We developed and tested machine learning and parametric approaches to automated syndrome diagnosis using 3D facial images. RESULTS: Unrelated, unaffected subjects were correctly classified with 96% accuracy. Considering both syndromic and unrelated, unaffected subjects together, balanced accuracy was 73% and mean sensitivity 49%. Excluding unrelated, unaffected subjects substantially improved both balanced accuracy (78.1%) and sensitivity (56.9%) of syndrome diagnosis. The best predictors of classification accuracy were phenotypic severity and facial distinctiveness of syndromes. Surprisingly, unaffected relatives of syndromic subjects were frequently classified as syndromic, often to the syndrome of their affected relative. CONCLUSION: Deep phenotyping by quantitative 3D facial imaging has considerable potential to facilitate syndrome diagnosis. Furthermore, 3D facial imaging of "unaffected" relatives may identify unrecognized cases or may reveal novel examples of semidominant inheritance.

Diagnosis of pili trianguli et canaliculi by frozen section: A rapid and inexpensive method of diagnosis.

We present frozen section as a novel method in the diagnosis of pili trianguli et canaliculi that may serve as a more time- and resource- efficient alternative to current gold- standard electron microscopy. In this case series, three children between ages one and four presented with blonde hair unable to be combed into place. Frozen section was performed and evaluated under light microscopy with easy visualization of the hair shaft abnormality, consistent with the diagnosis of pili trianguli et canaliculi.

Deficient histone H3 propionylation by BRPF1-KAT6 complexes in neurodevelopmental disorders and cancer.

Lysine acetyltransferase 6A (KAT6A) and its paralog KAT6B form stoichiometric complexes with bromodomain- and PHD finger-containing protein 1 (BRPF1) for acetylation of histone H3 at lysine 23 (H3K23). We report that these complexes also catalyze H3K23 propionylation in vitro and in vivo. Immunofluorescence microscopy and ATAC-See revealed the association of this modification with active chromatin. Brpf1 deletion obliterates the acylation in mouse embryos and fibroblasts. Moreover, we identify BRPF1 variants in 12 previously unidentified cases of syndromic intellectual disability and demonstrate that these cases and known BRPF1 variants impair H3K23 propionylation. Cardiac anomalies are present in a subset of the cases. H3K23 acylation is also impaired by cancer-derived somatic BRPF1 mutations. Valproate, vorinostat, propionate and butyrate promote H3K23 acylation. These results reveal the dual functionality of BRPF1-KAT6 complexes, shed light on mechanisms underlying related developmental disorders and various cancers, and suggest mutation-based therapy for medical conditions with deficient histone acylation.

Correction: Expanding the clinical phenotype of individuals with a 3-bp in-frame deletion of the NF1 gene (c.2970_2972del): an update of genotype-phenotype correlation.

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Expanding the clinical phenotype of individuals with a 3-bp in-frame deletion of the NF1 gene (c.2970_2972del): an update of genotype-phenotype correlation.

PURPOSE: Neurofibromatosis type 1 (NF1) is characterized by a highly variable clinical presentation, but almost all NF1-affected adults present with cutaneous and/or subcutaneous neurofibromas. Exceptions are individuals heterozygous for the NF1 in-frame deletion, c.2970_2972del (p.Met992del), associated with a mild phenotype without any externally visible tumors. METHODS: A total of 135 individuals from 103 unrelated families, all carrying the constitutional NF1 p.Met992del pathogenic variant and clinically assessed using the same standardized phenotypic checklist form, were included in this study. RESULTS: None of the individuals had externally visible plexiform or histopathologically confirmed cutaneous or subcutaneous neurofibromas. We did not identify any complications, such as symptomatic optic pathway gliomas (OPGs) or symptomatic spinal neurofibromas; however, 4.8% of individuals had nonoptic brain tumors, mostly low-grade and asymptomatic, and 38.8% had cognitive impairment/learning disabilities. In an individual with the NF1 constitutional c.2970_2972del and three astrocytomas, we provided proof that all were NF1-associated tumors given loss of heterozygosity at three intragenic NF1 microsatellite markers and c.2970_2972del. CONCLUSION: We demonstrate that individuals with the NF1 p.Met992del pathogenic variant have a mild NF1 phenotype lacking clinically suspected plexiform, cutaneous, or subcutaneous neurofibromas. However, learning difficulties are clearly part of the phenotypic presentation in these individuals and will require specialized care.

Identification of novel candidate disease genes from de novo exonic copy number variants.

BACKGROUND: Exon-targeted microarrays can detect small (<1000 bp) intragenic copy number variants (CNVs), including those that affect only a single exon. This genome-wide high-sensitivity approach increases the molecular diagnosis for conditions with known disease-associated genes, enables better genotype-phenotype correlations, and facilitates variant allele detection allowing novel disease gene discovery. METHODS: We retrospectively analyzed data from 63,127 patients referred for clinical chromosomal microarray analysis (CMA) at Baylor Genetics laboratories, including 46,755 individuals tested using exon-targeted arrays, from 2007 to 2017. Small CNVs harboring a single gene or two to five non-disease-associated genes were identified; the genes involved were evaluated for a potential disease association. RESULTS: In this clinical population, among rare CNVs involving any single gene reported in 7200 patients (11%), we identified 145 de novo autosomal CNVs (117 losses and 28 intragenic gains), 257 X-linked deletion CNVs in males, and 1049 inherited autosomal CNVs (878 losses and 171 intragenic gains); 111 known disease genes were potentially disrupted by de novo autosomal or X-linked (in males) single-gene CNVs. Ninety-one genes, either recently proposed as candidate disease genes or not yet associated with diseases, were disrupted by 147 single-gene CNVs, including 37 de novo deletions and ten de novo intragenic duplications on autosomes and 100 X-linked CNVs in males. Clinical features in individuals with de novo or X-linked CNVs encompassing at most five genes (224 bp to 1.6 Mb in size) were compared to those in individuals with larger-sized deletions (up to 5 Mb in size) in the internal CMA database or loss-of-function single nucleotide variants (SNVs) detected by clinical or research whole-exome sequencing (WES). This enabled the identification of recently published genes (BPTF, NONO, PSMD12, TANGO2, and TRIP12), novel candidate disease genes (ARGLU1 and STK3), and further confirmation of disease association for two recently proposed disease genes (MEIS2 and PTCHD1). Notably, exon-targeted CMA detected several pathogenic single-exon CNVs missed by clinical WES analyses. CONCLUSIONS: Together, these data document the efficacy of exon-targeted CMA for detection of genic and exonic CNVs, complementing and extending WES in clinical diagnostics, and the potential for discovery of novel disease genes by genome-wide assay.

High Incidence of Noonan Syndrome Features Including Short Stature and Pulmonic Stenosis in Patients carrying NF1 Missense Mutations Affecting p.Arg1809: Genotype-Phenotype Correlation.

Neurofibromatosis type 1 (NF1) is one of the most frequent genetic disorders, affecting 1:3,000 worldwide. Identification of genotype-phenotype correlations is challenging because of the wide range clinical variability, the progressive nature of the disorder, and extreme diversity of the mutational spectrum. We report 136 individuals with a distinct phenotype carrying one of five different NF1 missense mutations affecting p.Arg1809. Patients presented with multiple café-au-lait macules (CALM) with or without freckling and Lisch nodules, but no externally visible plexiform neurofibromas or clear cutaneous neurofibromas were found. About 25% of the individuals had Noonan-like features. Pulmonic stenosis and short stature were significantly more prevalent compared with classic cohorts (P < 0.0001). Developmental delays and/or learning disabilities were reported in over 50% of patients. Melanocytes cultured from a CALM in a segmental NF1-patient showed two different somatic NF1 mutations, p.Arg1809Cys and a multi-exon deletion, providing genetic evidence that p.Arg1809Cys is a loss-of-function mutation in the melanocytes and causes a pigmentary phenotype. Constitutional missense mutations at p.Arg1809 affect 1.23% of unrelated NF1 probands in the UAB cohort, therefore this specific NF1 genotype-phenotype correlation will affect counseling and management of a significant number of patients.

Compound heterozygosity for a frame shift mutation and a likely pathogenic sequence variant in the planar cell polarity­ciliogenesis gene WDPCP in a girl with polysyndactyly, coarctation of the aorta, and tongue hamartomas.

We report on a young girl with polysyndactyly, coarctation of the aorta, and tongue hamartomas. These features are similar to those reported in individuals with variant forms of orofaciodigital syndrome known as congenital heart defects, hamartomas of the tongue and polysyndactly (CHDHTP: OMIM 217085) [Örstavik et al., 1992] and orocardiodigital syndrome [Digilio et al., 1996]. Whole exome sequencing revealed that she is a compound heterozygote for a frame shift mutation and a likely pathogenic sequence variant in WDPCP, a gene that regulates planar cell polarity and ciliogenesis. Results of genotyping in her parents and unaffected siblings were consistent with autosomal recessive inheritance of the mutation and the WDPCP variant. These results suggest that disruption of planar cell polarity and ciliogenesis may result in this unusual form of orofaciodigital syndrome.

Recurrent deletions and reciprocal duplications of 10q11.21q11.23 including CHAT and SLC18A3 are likely mediated by complex low-copy repeats.

We report 24 unrelated individuals with deletions and 17 additional cases with duplications at 10q11.21q21.1 identified by chromosomal microarray analysis. The rearrangements range in size from 0.3 to 12 Mb. Nineteen of the deletions and eight duplications are flanked by large, directly oriented segmental duplications of >98% sequence identity, suggesting that nonallelic homologous recombination (NAHR) caused these genomic rearrangements. Nine individuals with deletions and five with duplications have additional copy number changes. Detailed clinical evaluation of 20 patients with deletions revealed variable clinical features, with developmental delay (DD) and/or intellectual disability (ID) as the only features common to a majority of individuals. We suggest that some of the other features present in more than one patient with deletion, including hypotonia, sleep apnea, chronic constipation, gastroesophageal and vesicoureteral refluxes, epilepsy, ataxia, dysphagia, nystagmus, and ptosis may result from deletion of the CHAT gene, encoding choline acetyltransferase, and the SLC18A3 gene, mapping in the first intron of CHAT and encoding vesicular acetylcholine transporter. The phenotypic diversity and presence of the deletion in apparently normal carrier parents suggest that subjects carrying 10q11.21q11.23 deletions may exhibit variable phenotypic expressivity and incomplete penetrance influenced by additional genetic and nongenetic modifiers.

Identical twin sisters with Rubinstein-Taybi syndrome associated with Chiari malformations and syrinx.

Chiari malformations are multifactorial and heterogeneous entities, characterized by abnormalities in the posterior fossa. They have been identified in association with various genetic syndromes in recent years. Two previous studies have noted an association of Chiari malformations with Rubinstein-Taybi syndrome (RTS). In this clinical report, we highlight identical twins with RTS caused by a mutation in CREBBP that presented with slightly different Chiari malformations in association with an extensive multiloculated syrinx and scoliosis. RTS has been found to be associated with craniocervical abnormalities in literature review, and this clinical report demonstrates the prudent consideration of the physician who cares for patients impacted by RTS to effectively screen via symptomatology and physical examination for Chiari pathology or other craniocervical abnormalities.

Identification of SPRED1 deletions using RT-PCR, multiplex ligation-dependent probe amplification and quantitative PCR.

Legius syndrome, is a recently identified autosomal dominant disorder caused by loss of function mutations in the SPRED1 gene, with individuals mainly presenting with multiple café-au-lait macules (CALM), freckling and macrocephaly. So far, only SPRED1 point mutations have been identified as the cause of this syndrome. To determine if copy number changes (CNCs) are a cause of Legius syndrome, we have used a Multiplex Ligation-dependent Probe Amplification (MLPA) assay covering all SPRED1 exons in a cohort of 510 NF1-negative patients presenting with multiple CALMs with or without freckling, but no other NF1 diagnostic signs. Four different deletions were identified by MLPA and confirmed by quantitative PCR, reverse transcriptase PCR and/or array CGH: a deletion of exon 1 and the SPRED1 promoter region in a proband and two first-degree relatives; a deletion of the entire SPRED1 gene in a sporadic patient; a deletion of exon 2-6 in a proband and her father; and an ∼6.6 Mb deletion on chromosome 15 that spans SPRED1 in a sporadic patient. Deletions account for ∼10% of the 40 detected SPRED1 mutations in this cohort of 510 individuals. These results indicate the need for dosage analysis to complement sequencing-based SPRED1 mutation analyses.

Immunosuppression and sebaceous tumors: a confirmed diagnosis of Muir-Torre syndrome unmasked by immunosuppressive therapy.

Muir-Torre syndrome (MTS) is an autosomal dominant genodermatosis caused by mutations in the DNA mismatch repair genes MLH1 and MSH2. This case describes a patient with an extensive family history of colon cancer who experienced the onset of multiple sebaceous adenomas and carcinomas after undergoing kidney transplantation and receiving immunosuppressive therapy. The finding of deficient MSH2 expression in the immunohistochemical analysis of a sebaceous carcinoma prompted genetic testing for a systemic mutation in the mismatch repair gene. A systemic mutation of the MSH2 gene was detected and, despite the absence of a visceral malignancy, the diagnosis of MTS was made. Immunosuppression has previously been thought to play a possible role in unmasking a latent MTS phenotype in transplant recipients, but systemic mutations have not previously been analyzed. The relationship between immunosuppression and sebaceous tumors with the possibility of unmasking a MTS phenotype in transplant recipients is discussed.

Early-onset seizures due to mosaic exonic deletions of CDKL5 in a male and two females.

PURPOSE: Mutations in the CDKL5 gene have been associated with an X-linked dominant early infantile epileptic encephalopathy-2. The clinical presentation is usually of severe encephalopathy with refractory seizures and Rett syndrome (RTT)-like phenotype. We attempted to assess the role of mosaic intragenic copy number variation in CDKL5. METHODS: We have used comparative genomic hybridization with a custom-designed clinical oligonucleotide array targeting exons of selected disease and candidate genes, including CDKL5. RESULTS: We have identified mosaic exonic deletions of CDKL5 in one male and two females with developmental delay and medically intractable seizures. These three mosaic changes represent 60% of all deletions detected in 12,000 patients analyzed by array comparative genomic hybridization and involving the exonic portion of CDKL5. CONCLUSION: We report the first case of an exonic deletion of CDKL5 in a male and emphasize the importance of underappreciated mosaic exonic copy number variation in patients with early-onset seizures and RTT-like features of both genders.

Male with mosaicism for supernumerary ring X chromosome: analysis of phenotype and characterization of genotype using array comparative genome hybridization.

Supernumerary, derivative, and ring X chromosomes are relatively common in Turner syndrome females but have been reported rarely in males. To date, less than 10 cases have been published, of which only 2 have been partially characterized in defining the breakpoints and genetic content of the derivative X chromosome. We describe a male with mosaicism for a supernumerary X chromosome (46,XY/47,XY, r(X)) who has multiple congenital anomalies, including features of craniofrontonasal dysplasia (Mendelian Inheritance in Man 304110) and the presence of ectopic female reproductive organs. Using comparative genomic hybridization array mapping, we determined that the derivative X is composed of a 24-Mb fragment that contains the regions Xp11.3 through Xq13.1 and lacks the XIST gene. This is the first report to describe a detailed molecular characterization of a ring X chromosome in a male by comparative genomic hybridization array analysis. We compare the clinical and molecular findings in this patient to other 46,XY, r(X) patients reported in the literature and discuss the potential role of disomy for known genes contained on the ring X chromosome.