Novel <i>DNM1L</i> variants impair mitochondrial dynamics through divergent mechanisms.

Imbalances in mitochondrial and peroxisomal dynamics are associated with a spectrum of human neurological disorders. Mitochondrial and peroxisomal fission both involve dynamin-related protein 1 (DRP1) oligomerisation and membrane constriction, although the precise biophysical mechanisms by which distinct DRP1 variants affect the assembly and activity of different DRP1 domains remains largely unexplored. We analysed four unreported de novo heterozygous variants in the dynamin-1-like gene <i>DNM1L</i>, affecting different highly conserved DRP1 domains, leading to developmental delay, seizures, hypotonia, and/or rare cardiac complications in infancy. Single-nucleotide DRP1 stalk domain variants were found to correlate with more severe clinical phenotypes, with in vitro recombinant human DRP1 mutants demonstrating greater impairments in protein oligomerisation, DRP1-peroxisomal recruitment, and both mitochondrial and peroxisomal hyperfusion compared to GTPase or GTPase-effector domain variants. Importantly, we identified a novel mechanism of pathogenesis, where a p.Arg710Gly variant uncouples DRP1 assembly from assembly-stimulated GTP hydrolysis, providing mechanistic insight into how assembly-state information is transmitted to the GTPase domain. Together, these data reveal that discrete, pathological <i>DNM1L</i> variants impair mitochondrial network maintenance by divergent mechanisms.

Natural history of a fibrous cephalic plaque and sustained eight decade follow-up in an 80 year old with tuberous sclerosis complex type 2.

INTRODUCTION: Fibrous cephalic plaques (FCP) are a characteristic manifestation of tuberous sclerosis complex (TSC) and occur in one third of cases. Their natural history and long term course is unknown, as is the outcome of long term follow-up of TSC cases in old age. PHENOTYPE AND METHODS: We describe an 80 year old with TSC due to a c.2784dupC TSC2 mutation, who was diagnosed in infancy with an FCP and was regularly followed up at the TSC clinic over 8 decades with regular epilepsy treatment and renal monitoring. RESULTS: Regular clinical photography and clinical records document the plaque at different ages. The FCP naturally resolved at 74 years. Facial angiofibromas also faded with time in the last decade. His epilepsy and renal abnormalities remained under control with careful surveillance and monitoring. DISCUSSION: Natural aging in the eighth decade causes progressive laxity of collagen and leads to natural resolution of FCPs. This novel finding with a unique 80 year follow up yields valuable insights into the aging changes within FCPs and facial angiofibromas as the pathways linking facial angiofibromas and FCP's through the TGF-ß1 pathway are now being elucidated. CONCLUSION: We present a clinical odyssey showing the natural progression and history of FCPs in TSC and comment on the mechanistic pathways allowing potential interventions in this disfiguring condition. TSC cases can be successfully managed and complications - particularly in the brain and kidney, can be avoided over an entire lifetime. This is encouraging for long term prospects for patients with TSC.

QRICH1 mutations cause a chondrodysplasia with developmental delay.

In many children with short stature, the etiology of the decreased linear growth remains unknown. We sought to identify the underlying genetic etiology in a patient with short stature, irregular growth plates of the proximal phalanges, developmental delay, and mildly dysmorphic facial features. Exome sequencing identified a de novo, heterozygous, nonsense mutation (c.1606C>T:p.R536X) in QRICH1. In vitro studies confirmed that the mutation impaired expression of the QRICH1 protein. SiRNA-mediated knockdown of Qrich1 in primary mouse epiphyseal chondrocytes caused downregulation of gene expression associated with hypertrophic differentiation. We then identified an unrelated individual with another heterozygous de novo nonsense mutation in QRICH1 who had a similar phenotype. A recently published study identified QRICH1 mutations in three patients with developmental delay, one of whom had short stature. Our findings indicate that QRICH1 mutations cause not only developmental delay but also a chondrodysplasia characterized by diminished linear growth and abnormal growth plate morphology due to impaired growth plate chondrocyte hypertrophic differentiation.

De novo mutations in HNRNPU result in a neurodevelopmental syndrome.

Exome sequencing in the context of developmental disorders is a useful technique, but variants found need to be interpreted in the context of detailed phenotypic information. Whole gene deletions and loss-of-function-mutations in the HNRNPU gene have been associated with intellectual disability and seizures in some patients. However, a unifying syndromic phenotype has not been previously elucidated. Here, we report a total of seven patients (six patients identified through the Wellcome Trust Deciphering Developmental Disorders study, with one additional patient), who have heterozygous de novo mutations in HNRNPU. These were found via trio-based exome sequencing. All but one of the mutations is predicted to cause loss-of-function. These patients have dysmorphic features in common, including prominent eyebrows, long palpebral fissures, overhanging columella, and thin upper lip. All patients have developmental delay and intellectual disability (ID), ranging from moderate to severe. Seizures are common from early childhood. These initially occur in the context of febrile episodes. This series demonstrates common phenotypic features, including emerging dysmorphism, associated with heterozygous HNRNPU mutations. This allows us to define a novel neurodevelopmental syndrome, with a likely mechanism of haploinsufficiency.

Incidence of Fragile X syndrome in Ireland.

Described as the commonest single gene cause of learning disability internationally, the incidence of Fragile X syndrome (FXS) has never previously been determined in Ireland. The aim of this work was to determine the observed incidence of FXS in the island of Ireland; the Republic of Ireland (ROI) and Northern Ireland (NI) separately and combined. Ascertainment was achieved for a cross-sectional study by a retrospective, clinical and laboratory database review of positive FXS cases, born in either ROI or NI, between years 2000-2009 inclusive. The observed incidence of FXS per 10,000 live births in the island of Ireland in males was 0.94 (95%CI: 0.75-1.13) or ∼1:10,600 and in females was 0.23 (95%CI: 0.14-0.32) or ∼1:43,000. Comparable testing rates for FXS are present in ROI and NI, with on average 1.48% (1.30% in ROI, 1.96% in NI) of live male births and 0.4% (0.35% in ROI, 0.55% in NI) of live female births undergoing analysis which is comparable to other centres internationally. This study demonstrates the observed incidence of FXS in the island of Ireland is (i) approximately half the estimated worldwide incidence in males and is not explained by low levels of testing, and (ii) approximately one quarter the estimated worldwide incidence in females which may be explained by low levels of testing. © 2017 Wiley Periodicals, Inc.

The prevalence of pica in tuberous sclerosis complex.

BACKGROUND: Pica and Tuberous sclerosis complex (TSC) are rare disorders. We carried out a population survey of pica in our TSC patient population. FINDINGS: Pica was identified in four percent of cases of TSC. It was associated with adult onset or persistence into adulthood, epilepsy, severe learning difficulties and anaemia. CONCLUSIONS: Pica in TSC is a rare disorder and a coherent history may be difficult to obtain from patients. The prevalence of pica is likely to be underdiagnosed. Pica is a recognised feature in adults with TSC and prompt recognition of this disorder should allow better management of patients with TSC.

Hereditary Gigantism-the biblical giant Goliath and his brothers.

The biblical giant Goliath has an identifiable family tree suggestive of autosomal dominant inheritance. We suggest that he had a hereditary pituitary disorder possibly due to the AIP gene, causing early onset and familial acromegaly or gigantism. We comment on the evidence within the scriptures for his other relatives including a relative with six digits and speculate on possible causes of the six digits. Recognition of a hereditary pituitary disorder in the biblical Goliath and his family sheds additional information on his and other family members' battles with David and his relatives.

Familial urothelial cell carcinoma of the bladder with autosomal dominant inheritance and late onset phenotype.

OBJECTIVE: Familial Urothelial cell bladder cancer is rare. We report two families with urothelial cell carcinoma (UCC) of bladder with family history in other relatives, displaying probable autosomal dominant inheritance and a late onset pure UCC phenotype, and document the phenotype in each family. METHODS: Descriptive familial study on two pedigrees over three generations. RESULTS: Two families with UCC bladder were identified, and the phenotype documented, each family having three cases of late onset UCC. CONCLUSION: Some cases of UCC are hereditary and may display autosomal dominant inheritance with late onset of the cancer. Clinicians should be aware of the existence of a familial late onset UCC phenotype when managing cases of UCC.

A silent nucleotide substitution in the ATP7A gene in a child with Menkes disease.

We present a case of classical Menkes disease (MD) due to a novel "silent" substitution in the ATP7A gene; c.2781G>A (p.K927K). The affected nucleotide is the last nucleotide in exon 13, and affects mRNA splicing. Transcripts missing exon 13; and transcripts missing exons 11, 12 and 13 in addition to a very small amount of normal spliced ATP7A transcripts were expressed. This is the first report of a synonymous ATP7A substitution being responsible for MD.

The clinical spectrum of the m.10191T>C mutation in complex I-deficient Leigh syndrome.

Mitochondrial respiratory chain diseases represent one of the most common inherited neurometabolic disorders of childhood, affecting a minimum of 1 in 7500 live births. The marked clinical, biochemical, and genetic heterogeneity means that accurate genetic counselling relies heavily upon the identification of the underlying causative mutation in the individual and determination of carrier status in the parents. Isolated complex I deficiency is the most common respiratory chain defect observed in children, resulting in organ-specific or multisystem disease, but most often presenting as Leigh syndrome, for which mitochondrial DNA mutations are important causes. Several recurrent, pathogenic point mutations in the MTND3 gene - including m.10191T>C (p.Ser45Pro) - have been previously identified. In this short clinical review we evaluate the case reports of the m.10191T>C mutation causing complex I-deficient Leigh syndrome described in the literature, in addition to two new ones diagnosed in our laboratory. Both of these appear to have arisen de novo without transmission of the mutation from mother to offspring, illustrating the importance not only of fully characterizing the mitochondrial genome as part of the investigation of children with complex I-deficient Leigh syndrome but also of assessing maternal samples to provide crucial genetic advice for families.

How genetically heterogeneous is Kabuki syndrome?: MLL2 testing in 116 patients, review and analyses of mutation and phenotypic spectrum.

MLL2 mutations are detected in 55 to 80% of patients with Kabuki syndrome (KS). In 20 to 45% patients with KS, the genetic basis remains unknown, suggesting possible genetic heterogeneity. Here, we present the largest yet reported cohort of 116 patients with KS. We identified MLL2 variants in 74 patients, of which 47 are novel and a majority are truncating. We show that pathogenic missense mutations were commonly located in exon 48. We undertook a systematic facial KS morphology study of patients with KS at our regional dysmorphology meeting. Our data suggest that nearly all patients with typical KS facial features have pathogenic MLL2 mutations, although KS can be phenotypically variable. Furthermore, we show that MLL2 mutation-positive KS patients are more likely to have feeding problems, kidney anomalies, early breast bud development, joint dislocations and palatal malformations in comparison with MLL2 mutation-negative patients. Our work expands the mutation spectrum of MLL2 that may help in better understanding of this molecule, which is important in gene expression, epigenetic control of active chromatin states, embryonic development and cancer. Our analyses of the phenotype indicates that MLL2 mutation-positive and -negative patients differ systematically, and genetic heterogeneity of KS is not as extensive as previously suggested. Moreover, phenotypic variability of KS suggests that MLL2 testing should be considered even in atypical patients.

Familial pediatric endocrine tumors.

Pediatric endocrine tumors are rare but have fairly characteristic presentations. We describe an approach to diagnosis and management of five of the most common presentations including gonadoblastoma, paraganglioma, medullary thyroid cancer, adrenal cancer, and pituitary adenoma. Genetic testing can aid in the early detection and prevention and management of tumors in patients and in other family members.

Phenotypic variability in a three-generation Northern Irish family with Sotos syndrome.

Sotos syndrome is an overgrowth disorder with autosomal dominant inheritance caused by mutations and deletions in the nuclear receptor Set domain-containing protein 1 gene. In general, affected individuals have an advanced bone age, macrocephaly, characteristic facial gestalt and learning difficulties. Genotype-phenotype correlations are unclear. Full penetrance is seen and 95% of cases are de novo. Here, we report a three-generation pedigree, with at least eight affected individuals, shown to harbour the nuclear receptor Set domain-containing protein 1 missense mutation c. 6115C>T. To our knowledge, this is the largest Sotos family reported. The observed phenotype is extremely variable, thus highlighting the clinical heterogeneity that may occur.

Advances in the genetics of familial renal cancer.

We discuss recent advances in the diagnosis and management of renal cell cancer (RCC) given the enhanced molecular genetics knowledge in this area. A number of hereditary renal cancer syndromes have been described, including von Hippel-Lindau disease, Birt-Hogg-Dubé syndrome, hereditary leiomyomatosis/RCC syndrome, and hereditary papillary renal cancer. Early molecular diagnosis now facilitates the management and prevention of RCC in families. Recommendations for screening in families are discussed.