Constance Stumpel

Mutations in PIEZO2 Cause Gordon Syndrome, Marden-Walker Syndrome, and Distal Arthrogryposis Type 5

Gordon syndrome (GS), or distal arthrogryposis type 3, is a rare, autosomal-dominant disorder characterized by cleft palate and congenital contractures of the hands and feet. Exome sequencing of five GS-affected families identified mutations in piezo-type mechanosensitive ion channel component 2 (PIEZO2) in each family. Sanger sequencing revealed PIEZO2 mutations in five of seven additional families studied (for a total of 10/12 [83%] individuals), and nine families had an identical c.8057G>A (p.Arg2686His) mutation. The phenotype of GS overlaps with distal arthrogryposis type 5 (DA5) and Marden-Walker syndrome (MWS). Using molecular inversion probes for targeted sequencing to screen PIEZO2, we found mutations in 24/29 (82%) DA5-affected families and one of two MWS-affected families. The presence of cleft palate was significantly associated with c.8057G>A (Fishers exact test, adjusted p value < 0.0001). Collectively, although GS, DA5, and MWS have traditionally been considered separate disorders, our findings indicate that they are etiologically related and perhaps represent variable expressivity of the same condition.

Phenotype and genotype in 52 patients with Rubinstein–Taybi syndrome caused by EP300 mutations

Rubinstein–Taybi syndrome (RSTS) is a developmental disorder characterized by a typical face and distal limbs abnormalities, intellectual disability, and a vast number of other features. Two genes are known to cause RSTS, CREBBP in 60% and EP300 in 8–10% of clinically diagnosed cases. Both paralogs act in chromatin remodeling and encode for transcriptional co‐activators interacting with >400 proteins. Up to now 26 individuals with an EP300 mutation have been published. Here, we describe the phenotype and genotype of 42 unpublished RSTS patients carrying EP300 mutations and intragenic deletions and offer an update on another 10 patients. We compare the data to 308 individuals with CREBBP mutations. We demonstrate that EP300 mutations cause a phenotype that typically resembles the classical RSTS phenotype due to CREBBP mutations to a great extent, although most facial signs are less marked with the exception of a low‐hanging columella. The limb anomalies are more similar to those in CREBBP mutated individuals except for angulation of thumbs and halluces which is very uncommon in EP300 mutated individuals. The intellectual disability is variable but typically less marked whereas the microcephaly is more common. All types of mutations occur but truncating mutations and small rearrangements are most common (86%). Missense mutations in the HAT domain are associated with a classical RSTS phenotype but otherwise no genotype–phenotype correlation is detected. Pre‐eclampsia occurs in 12/52 mothers of EP300 mutated individuals versus in 2/59 mothers of CREBBP mutated individuals, making pregnancy with an EP300 mutated fetus the strongest known predictor for pre‐eclampsia.

Phenotypic and molecular insights into CASK-related disorders in males

BackgroundHeterozygous loss-of-function mutations in the X-linked CASK gene cause progressive microcephaly with pontine and cerebellar hypoplasia (MICPCH) and severe intellectual disability (ID) in females. Different CASK mutations have also been reported in males. The associated phenotypes range from nonsyndromic ID to Ohtahara syndrome with cerebellar hypoplasia. However, the phenotypic spectrum in males has not been systematically evaluated to date.MethodsWe identified a CASK alteration in 8 novel unrelated male patients by targeted Sanger sequencing, copy number analysis (MLPA and/or FISH) and array CGH. CASK transcripts were investigated by RT-PCR followed by sequencing. Immunoblotting was used to detect CASK protein in patient-derived cells. The clinical phenotype and natural history of the 8 patients and 28 CASK-mutation positive males reported previously were reviewed and correlated with available molecular data.ResultsCASK alterations include one nonsense mutation, one 5-bp deletion, one mutation of the start codon, and five partial gene deletions and duplications; seven were de novo, including three somatic mosaicisms, and one was familial. In three subjects, specific mRNA junction fragments indicated in tandem duplication of CASK exons disrupting the integrity of the gene. The 5-bp deletion resulted in multiple aberrant CASK mRNAs. In fibroblasts from patients with a CASK loss-of-function mutation, no CASK protein could be detected. Individuals who are mosaic for a severe CASK mutation or carry a hypomorphic mutation still showed detectable amount of protein.ConclusionsBased on eight novel patients and all CASK-mutation positive males reported previously three phenotypic groups can be distinguished that represent a clinical continuum: (i) MICPCH with severe epileptic encephalopathy caused by hemizygous loss-of-function mutations, (ii) MICPCH associated with inactivating alterations in the mosaic state or a partly penetrant mutation, and (iii) syndromic/nonsyndromic mild to severe ID with or without nystagmus caused by CASK missense and splice mutations that leave the CASK protein intact but likely alter its function or reduce the amount of normal protein. Our findings facilitate focused testing of the CASK gene and interpreting sequence variants identified by next-generation sequencing in cases with a phenotype resembling either of the three groups.

SAMS, a Syndrome of Short Stature, Auditory-Canal Atresia, Mandibular Hypoplasia, and Skeletal Abnormalities Is a Unique Neurocristopathy Caused by Mutations in Goosecoid

Short stature, auditory canal atresia, mandibular hypoplasia, and skeletal abnormalities (SAMS) has been reported previously to be a rare, autosomal-recessive developmental disorder with other, unique rhizomelic skeletal anomalies. These include bilateral humeral hypoplasia, humeroscapular synostosis, pelvic abnormalities, and proximal defects of the femora. To identify the genetic basis of SAMS, we used molecular karyotyping and whole-exome sequencing (WES) to study small, unrelated families. Filtering of variants from the WES data included segregation analysis followed by comparison of in-house exomes. We identified a homozygous 306 kb microdeletion and homozygous predicted null mutations of GSC, encoding Goosecoid homeobox protein, a paired-like homeodomain transcription factor. This confirms that SAMS is a human malformation syndrome resulting from GSC mutations. Previously, Goosecoid has been shown to be a determinant at the Xenopus gastrula organizer region and a segment-polarity determinant in Drosophila. In the present report, we present data on Goosecoid protein localization in staged mouse embryos. These data and the SAMS clinical phenotype both suggest that Goosecoid is a downstream effector of the regulatory networks that define neural-crest cell-fate specification and subsequent mesoderm cell lineages in mammals, particularly during shoulder and hip formation. Our findings confirm that Goosecoid has an essential role in human craniofacial and joint development and suggest that Goosecoid is an essential regulator of mesodermal patterning in mammals and that it has specific functions in neural crest cell derivatives.

Mutations in the Chromatin Regulator Gene BRPF1 Cause Syndromic Intellectual Disability and Deficient Histone Acetylation.

Identification of over 500 epigenetic regulators in humans raises an interesting question regarding how chromatin dysregulation contributes to different diseases. Bromodomain and PHD finger-containing protein 1 (BRPF1) is a multivalent chromatin regulator possessing three histone-binding domains, one non-specific DNA-binding module, and several motifs for interacting with and activating three lysine acetyltransferases. Genetic analyses of fish brpf1 and mouse Brpf1 have uncovered an important role in skeletal, hematopoietic, and brain development, but it remains unclear how BRPF1 is linked to human development and disease. Here, we describe an intellectual disability disorder in ten individuals with inherited or de novo monoallelic BRPF1 mutations. Symptoms include infantile hypotonia, global developmental delay, intellectual disability, expressive language impairment, and facial dysmorphisms. Central nervous system and spinal abnormalities are also seen in some individuals. These clinical features overlap with but are not identical to those reported for persons with KAT6A or KAT6B mutations, suggesting that BRPF1 targets these two acetyltransferases and additional partners in humans. Functional assays showed that the resulting BRPF1 variants are pathogenic and impair acetylation of histone H3 at lysine 23, an abundant but poorly characterized epigenetic mark. We also found a similar deficiency in different lines of Brpf1-knockout mice. These data indicate that aberrations in the chromatin regulator gene BRPF1 cause histone H3 acetylation deficiency and a previously unrecognized intellectual disability syndrome.

Growth Hormone Therapy in Children with Kabuki Syndrome : 1-year Treatment Results

Background/Aims: Kabuki syndrome (KS) is a rare genetic malformation syndrome, resulting in characteristic features such as short stature. We investigate whether growth hormone (GH) treatment increases linear height and influences body proportions in KS children. Methods: In this prospective study, 18 genetically confirmed prepubertal KS children (9 females and 9 males) aged from 3.8 to 10.1 years (mean 6.8 ± 2.1 years) were treated with recombinant human GH (rhGH) for 1 year. Calculations for height, height velocity, BMI, sitting height, and subischial leg length were made. Bone age, insulin-like growth factor (IGF-I), and IGF binding protein 3 (IGFBP-3) were also measured. Results: This study showed an increase in height standard deviation score (SDS) for the whole group from –2.40 to –1.69 (p < 0.05) after 1 year of rhGH treatment. The change in height SDS within 1 year was >0.7 SDS for 10 subjects and >0.5 SDS for 3 subjects. The mean IGF-I SDS at the start of the study was –0.70 (±1.07), which increased after 12 months to 1.41 (±0.91) (p < 0.05). KS children who received rhGH at a younger age displayed significantly greater increases in height than those who started when they were older. The same was true for both gene mutation KMT2D versus KDM6A and for GH deficiency versus non-GH deficiency KS children (p < 0.05). Throughout the course of rhGH treatment, the subjects’ body proportions remained normal. Conclusions: All participants experienced catch-up growth during the year of rhGH treatment, but without an influence on body proportions.

Growth Hormone Stimulation Tests in Children with Kabuki Syndrome.

Background/Aims: Kabuki syndrome is a multiple congenital malformation syndrome with a variety of clinical features including short stature. The cause of this postnatal short stature remains unknown. Methods: Eighteen children with genetically proven Kabuki syndrome (8 boys and 10 girls; ages 3.3-9.9 years, with a mean of 6.7 years) who underwent growth hormone (GH) stimulation tests were evaluated in a prospective study. Two GH stimulation tests were conducted, including insulin-like growth factor I (IGF-I) and IGF-binding protein 3 (IGFBP-3) serum levels. GH stimulation peaks in relation to age, sex, height, body mass index (BMI), IGF-I, and IGFBP-3 SD scores (SDS) were analyzed. Results: Five of the 18 children (27.8%) were biochemically GH deficient. This was not correlated with BMI SDS. Of all patients, only 1 had an IGF-I below -2 SD and did not fulfill the GH deficiency criteria. The mean IGF-I level was below normal (-0.8 SD). All subjects had normal IGFBP-3 levels. Conclusions: The utility of performing GH stimulation tests on Kabuki syndrome children as an indication of GH status in short stature is questionable. IGF-I levels did correlate neither with the GH stimulation peak nor consequently with the diagnosis of GH deficiency.

Growth pattern in Kabuki syndrome with a KMT2D mutation

Kabuki syndrome is a multiple congenital malformation syndrome with a spectrum of clinical features including short stature. Since there is no growth data on Kabuki syndrome patients with a proven KMT2D gene mutation, further research on growth and growth patterns is indicated. Data for this growth study on subjects with Kabuki syndrome were collected from referring clinicians. Subjects were eligible for inclusion in the study if the following criteria were met: a genetically confirmed diagnosis of Kabuki syndrome and no current treatment with growth hormones or other drugs that could influence growth. We present a report on growth data (n = 39) in Kabuki syndrome patients. The data showed that postnatal growth retardation is a clinical feature in all cases. All Kabuki syndrome subjects showed a growth deflection during childhood and a diminution of the pubertal growth spurt. A genotype–phenotype correlation was not observed. Further research is required in order to determine whether a defect in the growth hormone/IGF‐I axis and estrogen receptor plays a role in the growth retardation.

The 6p25 deletion syndrome: An update on a rare neurocristopathy.

ABSTRACT Anterior segment dysgeneses are developmental anomalies of the anterior eye segment that can occur as isolated defects or as part of various syndromes. A subgroup is caused by abnormal embryonic neural crest development. The Axenfeld-Rieger syndrome is an umbrella term for a continuum of anterior segment dysgeneses of neural crest origin, characterized by the presence of the Axenfeld or Rieger eye malformation predisposing for glaucoma. Additionally, other structures of neural crest origin can be variably affected giving rise to a wide spectrum of associated extra-ocular malformations. Key clinical features comprise facial dysmorphism including mid-face and dental hypoplasia, hearing loss, cardiac anomalies, and involuted periumbilical skin. The Axenfeld-Rieger syndrome is genetically heterogeneous and about 16% of cases are caused by heterozygous mutations in FOXC1 at 6p25.3, a transcription factor gene regulating neural crest cell development. There is considerable clinical overlap between the Axenfeld-Rieger syndrome and the 6p25 deletion syndrome, a microdeletion syndrome characterized by heterozygous loss of FOXC1. In both syndromes, FOXC1 haploinsufficiency seems to be pathogenic. Here, we review the clinical features and pathogenesis of the 6p25 deletion syndrome.

A novel mutation in L1CAM causes a mild form of L1 syndrome: a case report

Clinical geneticists, neurologists, psychiatrists, and other healthcare providers can learn from this case report that patients with a behavioral phenotype that includes a mild learning disability may also require a thorough examination, including brain MRI and whole‐exome sequencing.