Expanding the KIF4A-associated phenotype.

Kinesin super family (KIF) genes encode motor kinesins, a family of evolutionary conserved proteins, involved in intracellular trafficking of various cargoes. These proteins are critical for various physiological processes including neuron function and survival, ciliary function and ciliogenesis, and cell-cycle progression. Recent evidence suggests that alterations in motor kinesin genes can lead to a variety of human diseases, including monogenic disorders. Neuropathies, impaired higher brain functions, structural brain abnormalities and multiple congenital anomalies (i.e., renal, urogenital, and limb anomalies) can result from pathogenic variants in many KIF genes. We expand the phenotype associated with KIF4A variants from developmental delay and intellectual disability with or without epilepsy to a congenital anomaly phenotype with hydrocephalus and various brain anomalies at the more severe end of phenotypic manifestations. Additional anomalies of the kidneys and urinary tract, congenital lymphedema, eye, and dental anomalies seem to be variably associated and overlap with clinical signs observed in other kinesinopathies. Caution still applies to missense variants, but hopefully, future work will further establish genotype-phenotype correlations in a larger number of patients and functional studies may give further insights into the complex function of KIF4A.

ANKRD11 variants cause variable clinical features associated with KBG syndrome and Coffin-Siris-like syndrome.

KBG syndrome (KBGS) is an autosomal dominant multiple congenital anomaly-intellectual disability syndrome, characterized by developmental delay with neurological involvements, macrodontia of the upper central incisors, characteristic facial dysmorphism and skeletal anomalies. Variants in ANKRD11 cause KBGS. We present five individuals from four families with ANKRD11 variants identified by whole-exome sequencing. Four of the five were clinically affected, and their diagnoses were varied. One was typical KBGS, two were Coffin-Siris syndrome-like (CSS), and one was intellectual disability with infantile spasms. One individual showed extremely mild phenotype. All individuals fulfilled the proposed diagnostic criteria for KBGS. Phenotypic features overlap between KBGS and CSS to some extent, and characteristic dental and fifth finger/toe findings can indicate differential diagnosis. These findings indicate that patients with ANKRD11 variants occupy a wide spectrum of intellectual disability, including clinically normal individuals. This is the first report highlighting the clinical overlap between KBGS and CSS and supporting the recently proposed clinical concept, in which transcriptional machineries are disrupted.

Homozygous p.V116* mutation in C12orf65 results in Leigh syndrome.

BACKGROUND: Leigh syndrome (LS) is an early-onset progressive neurodegenerative disorder associated with mitochondrial dysfunction. LS is characterised by elevated lactate and pyruvate and bilateral symmetric hyperintense lesions in the basal ganglia, thalamus, brainstem, cerebral white matter or spinal cord on T2-weighted MRI. LS is a genetically heterogeneous disease, and to date mutations in approximately 40 genes related to mitochondrial function have been linked to the disorder. METHODS: We investigated a pair of female monozygotic twins diagnosed with LS from consanguineous healthy parents of Indian origin. Their common clinical features included optic atrophy, ophthalmoplegia, spastic paraparesis and mild intellectual disability. High-blood lactate and high-intensity signal in the brainstem on T2-weighted MRI were consistent with a clinical diagnosis of LS. To identify the genetic cause of their condition, we performed whole exome sequencing. RESULTS: We identified a homozygous nonsense mutation in C12orf65 (NM_001143905; c.346delG, p.V116*) in the affected twins. Interestingly, the identical mutation was previously reported in an Indian family with Charcot-Marie Tooth disease type 6, which displayed some overlapping clinical features with the twins. CONCLUSIONS: We demonstrate that the identical nonsense mutation in C12orf65 can result in different clinical features, suggesting the involvement of unknown modifiers.

Intermediate phenotype between CMT2Z and DIGFAN associated with a novel MORC2 variant: a case report.

Charcot-Marie-Tooth disease type 2Z is caused by MORC2 mutations and presents with axonal neuropathy. MORC2 mutations can also manifest as developmental delay, impaired growth, dysmorphic facies, and axonal neuropathy (DIGFAN). We report a patient exhibiting an intermediate phenotype between these diseases associated with a novel MORC2 variant. A literature review revealed that the genotype‒phenotype correlation in MORC2-related disorders is complex and that the same mutation can cause a variety of phenotypes.

Reduced histone H3K4 trimethylation in oral mucosa of patients with DYT-KMT2B.

BACKGROUND: DYT-KMT2B, also known as DYT28, is a childhood-onset hereditary dystonia caused by KMT2B mutation. The pathogenesis of DYT-KMT2B involves haploinsufficiency of KMT2B, an enzyme that catalyzes specific histone methylation (H3K4me3). Dysmorphic features in patients with DYT-KMT2B suggest that KMT2B dysfunction may extend beyond the neuronal system. Therefore, valuable diagnostic insights may be obtained from readily available tissue samples. OBJECTIVES: To explore the altered H3K4me3 levels in non-neural tissue of DYT-KMT2B patients. METHODS: A database analysis was performed to determine in which parts of the body and in which cells KMT2B is highly expressed. Twelve clinically and genetically diagnosed patients with DYT-KMT2B and 12 control subjects participated in this study. Oral mucosa-derived purified histone proteins were analyzed using Western blotting with anti-H3K4me3 and anti-H4 antibodies. RESULTS: Higher expression of KMT2B was observed in oral keratinocytes and gingival fibroblasts, constituting the oral mucosa. In oral mucosa analyses, DYT-KMT2B cases exhibited markedly reduced H3K4me3 levels compared with the controls. Using a cutoff window of 0.90-0.98, the H3K4me3/H4 expression ratio was able to distinguish patient groups. CONCLUSIONS: Oral mucosa H3K4me3 analysis is currently not sufficient as a diagnostic tool for DYT-KMT2B, but has the advantage for screening test since it is a non-invasive means.

A de novo deletion at 16q24.3 involving ANKRD11 in a Japanese patient with KBG syndrome.

KBG syndrome is a rare autosomal dominant congenital syndrome comprising developmental delay with various neurological involvements, macrodontia of the upper central incisors, characteristic facial dysmorphism, and skeletal anomalies. ANKRD11 was recently identified as the gene responsible for this syndrome. To date, there have been only five KBG syndrome families described, each carrying a single base substitution or a 1- to 14-bp deletion of this gene. Here, we present a patient with clinically confirmed KBG syndrome carrying a de novo 690-kb deletion at 16q24.3 involving part of ANKRD11. He had characteristic facial appearance, macrodontia of the upper central incisors, hand anomalies, delayed bone age and intellectual impairment without autistic features. Interestingly, the deleted region overlaps with the critical region for 16q24.3 microdeletion syndrome. We discuss the clinical entities of KBG syndrome and 16q24.3 microdeletion syndrome from a clinical and genetic point of view.

Siblings with the adult-onset slowly progressive type of pantothenate kinase-associated neurodegeneration and a novel mutation, Ile346Ser, in PANK2: clinical features and (99m)Tc-ECD brain perfusion SPECT findings.

Pantothenate kinase-associated neurodegeneration (PKAN), formerly known as Hallervorden-Spatz syndrome (HSS), is an autosomal recessive neurodegenerative disorder characterized by iron accumulation in the brain. Mutations in the pantothenate kinase 2 (PANK2) gene are known to be responsible for PKAN. Several studies have revealed correlations between clinical phenotypes and particular PANK2 mutations. The adult-onset slowly progressive type of PKAN with PANK2 mutations is very rare. In this report, we describe siblings with the adult-onset slowly progressive type of PKAN with a novel mutation, Ile346Ser, in PANK2. The siblings had the same mutation in PANK2 and had common clinical signs such as misalignment of teeth, a high arched palate, hollow feet, a slight cognitive decline, and an apparent executive dysfunction, although they showed different patterns of movement disorders. Thus, even if PKAN patients have identical mutations, it is likely that they will present with different types of movement disorders. Brain perfusion single photon emission computed tomography in both patients showed decreased regional cerebral blood flow in the bilateral frontoparietal lobes, the globus pallidus, the striatum, and around the ventriculus quartus. Cardiac uptake of [(123)I] meta-iodobenzylguanidine was normal in both patients. Analysis of genotype-phenotype correlations and the elucidation of mutational effects on pantothenate kinase 2 function, expression, and structure are important for understanding the mechanisms of PKAN.