Intrauterine death in megacystis-microcolon-intestinal hypoperistalsis syndrome.

Megacystis-microcolon-intestinal hypoperistalsis syndrome is an uncommon condition, possibly inherited as an autosomal recessive trait. This report describes an affected sib pair with intrauterine death of one of the sibs.     

Cardiac rhabdomyomata and megacystis-microcolon-intestinal hypoperistalsis syndrome.

Multiple cardiac rhabdomyomata were discovered on necropsy tissue review of a previously well child with megacystis-microcolon-intestinal hypoperistalsis syndrome, who died unexpectedly at home at 40 months of age. Multiple cardiac rhabdomyomata occur rarely and have not previously been reported with this syndrome. They are most frequently associated with tuberous sclerosis. The finding of multiple cardiac rhabdomyomata in this patient suggests the possibility that these two rare conditions may be associated. Putative gene loci for tuberous sclerosis have been assigned to the long arms of chromosomes 9 and 11 and it is possible that the cardiac rhabdomyomata seen in this patient are a serendipitous indicator of the location of the megacystis-microcolon-intestinal hypoperistalsis gene.     

Complexity of pathological interpretation in megacystis-microcolon-intestinal hypoperistalsis syndrome

Megacystis-microcolon-intestinal hypoperistalsis syndrome is very rare, and is the most severe of the chronic intestinal pseudoobstructions. Diagnosis is usually made in the neonatal period, is clinical and radiological, and is confirmed by manometric studies. Microscopic abnormalities are variable, inconstant and nonspecific. They involve the smooth muscle more often than the intrinsic innervation of the gut and the bladder. A girl, currently seven years old, presented with megacystis observed on prenatal ultrasound at 21 weeks of gestation. At first, amniotic fluid volume was appropriate for gestational age, and then hydramnios appeared at 30 weeks of gestation. Microcolon was discovered at birth, with microileum, dilatation of the duodenum and proximal jejunum, intestinal malposition, and severe hypoperistalsis of the entire gastrointestinal tract, which indicated enterostomy and total parenteral nutrition from birth. At pathological examination, rectal biopsy and enteric nervous plexuses were normal. There was hypoplasia of the external longitudinal layer of the muscularis propria in the colon and ileum. Cajal cells could not be demonstrated immunohistochemically in the colon. This case highlights the complexity and difficulties of pathological interpretation in this syndrome, and the necessity of a large study of controls at different ages and different levels of the digestive tract and the bladder.     

Prenatal diagnosis of the megacystis-microcolon-intestinal hypoperistalsis syndrome.

The ultrasonographic and necropsy findings in a male fetus with the megacystis-microcolon-intestinal hypoperistalsis syndrome are reported. The presence of vacuolation and degeneration in smooth muscle of bowel and bladder wall supports a previous suggestion that the macroscopic findings in this syndrome are the consequence of an underlying visceral myopathy. The unusual degree of severity of the findings in this fetus may explain the marked skewing of the sex ratio observed in affected liveborn infants.     

The megacystis-microcolon-intestinal hypoperistalsis syndrome: a fatal autosomal recessive condition.

We report the cases of two sibs with the megacystis-microcolon-intestinal hypoperistalsis syndrome. The parents are first cousins. These cases further support the view that this syndrome is inherited in an autosomal recessive fashion.     

Fatal neonatal encephalopathy and lactic acidosis caused by a homozygous loss-of-function variant in COQ9

Coenzyme Q₁₀ (CoQ₁₀) has an important role in mitochondrial energy metabolism by way of its functioning as an electron carrier in the respiratory chain. Genetic defects disrupting the endogenous biosynthesis pathway of CoQ₁₀ may lead to severe metabolic disorders with onset in early childhood. Using exome sequencing in a child with fatal neonatal lactic acidosis and encephalopathy, we identified a homozygous loss-of-function variant in COQ9. Functional studies in patient fibroblasts showed that the absence of the COQ9 protein was concomitant with a strong reduction of COQ7, leading to a significant accumulation of the substrate of COQ7, 6-demethoxy ubiquinone₁₀. At the same time, the total amount of CoQ₁₀ was severely reduced, which was reflected in a significant decrease of mitochondrial respiratory chain succinate-cytochrome c oxidoreductase (complex II/III) activity. Lentiviral expression of COQ9 restored all these parameters, confirming the causal role of the variant. Our report on the second COQ9 patient expands the clinical spectrum associated with COQ9 variants, indicating the importance of COQ9 already during prenatal development. Moreover, the rescue of cellular CoQ₁₀ levels and respiratory chain complex activities by CoQ₁₀ supplementation points to the importance of an early diagnosis and immediate treatment.     

A novel homozygous nonsense NDNF variant in Kallmann syndrome

Kallmann syndrome (KS) is a rare genetic disease characterized by pubertal failure and olfactory defects. Although many genes associated with KS have been reported, most are rare. Recently, heterozygous inactivating mutations in the neuron-derived neurotrophic factor gene (NDNF) were reported to cause KS. Here, we present a 14-year-old Kurdish boy with KS who has a novel homozygous nonsense c.1251C>A (p.Tyr417Ter) variant in NDNF. The variant was not observed in reference population databases and was predicted to be deleterious. Segregation analysis performed with Sanger sequencing indicated the autosomal recessive inheritance of the clinical phenotype. His heterozygous parents have experienced timely pubertal development and normal reproductive features. This study reported the first homozygous truncating NDNF variant, enabling the direct observation of the clinical consequences of predictively absent NDNF function. These results support the contention that the inactivating mutations in NDNF cause KS, and provide additional evidence for the complex inheritance of KS.     

A homozygous TTN gene variant associated with lethal congenital contracture syndrome

Pathogenic variants in the TTN gene have been reported to cause various cardiomyopathies and a range of skeletal muscle diseases, collectively known as titinopathies. We evaluated a consanguineous family multiple members affected with a lethal congenital contracture syndrome. Using exome sequencing, we identified a homozygous c.36122delC (p. P12041Lfs*20) variant in exon 167 in the fetal IC isoform of TTN. The finding expands the phenotypes that can be caused by pathogenic variants TTN, which should be considered in lethal congenital contracture syndromes, arthrogryposis multiplex congenita, congenital myopathies, and hydrops fetalis.     

Newly described recessive MYH11 disorder with clinical overlap of Multisystemic smooth muscle dysfunction and Megacystis microcolon hypoperistalsis syndromes

We describe a neonatal patient with fixed dilated pupils and pulmonary, bladder, and bowel dysfunction suspicious for the presence of ACTA2 R179 mediated multisystemic smooth muscle dysfunction syndrome. Whole exome sequencing revealed compound heterozygous mutations in MYH11 after ACTA2 specific testing revealed no abnormalities. The child lived until 18 months of age and represents the only reported case of an MYH11 compound heterozygote with widespread smooth muscle dysfunction.     

A homozygous loss-of-function mutation in FBXO43 causes human non-obstructive azoospermia

Non-obstructive azoospermia (NOA) represents one of the most serious forms of male infertility caused by spermatogenic failure. Despite multiple genes found to be associated with human NOA, the genetic basis of this idiopathic disease remains largely unknown. FBXO43 is a direct inhibitor of the anaphase-promoting complex/cyclosome (APC/C) E3 ligase and crucially important in mouse spermatogenesis. In this study, for the first time, we identified a homozygous nonsense mutation in FBXO43 c.1747C > T:p.Gln583X in two NOA brothers from a Chinese consanguineous family via whole-exome sequencing. FBXO43 was absent from testicular tissue of the proband, and FBXO43-immunostaining signals were invisible in the affected seminiferous tubules. Furthermore, in humans, FBXO43 defects cause meiotic arrest within early diplotene of prophase I. The results here demonstrate the pathogenicity of this loss-of-function mutation and confirmed that spermatocytes were unable to complete meiotic divisions without FBXO43 in humans. In mouse testicular protein extracts, three subunits of the APC/C, including ANAPC2, ANAPC8 and ANAPC10, were validated to interact directly with FBXO43, whereas no interactions were detected for FBXO43 and SKP1. This study furthers our understanding of the genetic basis of human NOA and provides insights into FBXO43 and male infertility.     

A homozygous ROR2 variant in a family with atypical Robinow syndrome and tetramelic transverse deficiency of autopods

We present five members of a consanguineous Pakistani kinship with the most severe familial tetramelic transverse autopod deficiency reported to date and additionally having some of the common autosomal recessive Robinow syndrome-1 (RRS1) features including short stature, short neck, severe vertebral anomalies of kyphoscoliosis, hemivertebrae, fusion of thoracic vertebrae, broad forehead, and dental crowding. We mapped the locus of this atypical RRS and detected homozygous 8-nucleotide deletion c.1353_1360del (p.(Met452Alafs*4)) in ROR2, the gene responsible for RRS1. We did not find any other variant shared by all affected individuals that could possibly act as a modifier of limb defect. Autopods are affected in RRS1, but severe autopod deficiency is not a characteristic feature. Over 30 biallelic variants dispersed throughout the gene are known in ROR2-related RS, with no genotype–phenotype correlation for specific RRS1 features. Considering together with the sporadic case homozygous for variant p.(Arg442*) and the case homozygous for p.(Arg441Thrfs*16) in a family where heterozygous members have brachydactyly type B1, we propose that homozygous truncating variants that originate at residues 441–452 can cause severe autopod reduction anomalies, suggesting some genotype–phenotype correlation for this particular phenotype.     

A novel functionally deficient MYH variant in individuals with colorectal adenomatous polyposis

Inherited biallelic mutations in the base excision repair gene MYH confer susceptibility to colorectal adenomas and carcinoma. Approximately 85% of Caucasians with MYH mutations carry the (c.494A>G) p.Y165C and (c.1145G>A) p.G382D variants. Only a few other clearly pathogenic mutations have been identified, and mutation analyses tend to focus on the two founder mutations rather than the whole coding region of the gene. We sequenced the entire coding region of MYH in a population-based series of 24 Finnish APC-mutation negative polyposis patients in order to identify novel pathogenic MYH variants. A population-based series of 1,042 Finnish colorectal cancer patients and 85 cancer-free controls were available for further evaluation. A functional cleavage assay was designed to evaluate consequences of possible novel variants to protein function. Three novel MYH variants, (c.270C>T) p.Y90Y, (c.1376C>A) p.A459D, and (c.1389G>C) p.T469T, were observed. p.A459D variant in exon 14 was identified in two patients from the polyposis series, once in homozygosity and once in compound heterozygosity with p.Y165C. In the population-based series of 1,042 colorectal cancer patients, the p.A459D mutation was identified once, in homozygosity (allele frequency 0.1%). No p.A459D mutations were identified in the control individuals. In vitro cleavage assay showed significantly reduced repair activity in p.A459D cells. Interestingly, another variant in the same codon has previously been described in a British study, supporting a key role for the codon 459 in MYH function. We therefore suggest that screening of mutations in MYH exon 14 should be added to the molecular analysis at-risk individuals.     

Identification of a dominant MYH11 causal variant in chronic intestinal pseudo-obstruction: Results of whole-exome sequencing

Chronic Intestinal Pseudo-Obstruction (CIPO) is a rare gastrointestinal disorder, which affects the smooth muscle contractions of the gastrointestinal tract. Dominant mutations in the smooth muscle actin gene, ACTG2, accounts for 44%-50% of CIPO patients. Other recessive or X-linked genes, including MYLK, LMOD1, RAD21, MYH11, MYL9, and FLNA were reported in single cases. In this study, we used Whole-Exome Sequencing (WES) to study 23 independent CIPO families including one extended family with 13 affected members. A dominantly inherited rare mutation, c.5819delC (p.Pro1940HisfsTer91), in the smooth muscle myosin gene, MYH11, was found in the extended family, shared by 7 affected family members but not by 3 unaffected family members with available DNA, suggesting a high probability of genetic linkage. Gene burden analysis indicates that additional genes, COL4A1, FBLN1 and HK2, may be associated with the disease. This study expanded our understanding of CIPO etiology and provided additional genetic evidence to physicians and genetic counselors for CIPO diagnosis.     

Lack of STK11 gene expression in homozygous twins with Peutz-Jeghers syndrome

Clinical features of Peutz-Jeghers syndrome (PJS), an autosomal dominant disorder, include clusters of melanotic spots on the lips and limbs, polyposis of the gastrointestinal (GI) tract, and propensity to develop neoplasms of the GI tract, ovaries, testes, and other sites. We report twin sisters with PJS who were found to be homozygous, based on analyses of 9 DNA markers containing short tandem repeats (STR). Aberrant expression of a putative tumor suppressor gene, STK11, which encodes a serine threonine kinase, has been suggested as the etiologic factor in PJS. In both of the twin sisters with PJS, mRNA analyses by RT-PCR demonstrated a complete lack of STK11 gene expression. These results provide direct evidence that STK11 gene expression is abnormal in PJS. Detecting abnormal expression of the STK11 gene may serve as a molecular approach to the diagnosis of PJS and may facilitate genotype-phenotype correlations in PJS patients.     

Identification and characterization of a loss-of-function human MPYS variant

MPYS, also known as STING and MITA, is an interferon (IFN)β stimulator essential for host defense against RNA, DNA viruses and intracellular bacteria. MPYS also facilitates the adjuvant activity of DNA vaccines. Here, we report identification of a distinct human MPYS haplotype that contains three non-synonymous single nucleotide polymorphisms (SNPs), R71H-G230A-R293Q (thus, named the HAQ haplotype). We estimate, in two cohorts (1,074 individuals), that ～3% of Americans are homozygous for this HAQ haplotype. HAQ MPYS exhibits a > 90% loss in the ability to stimulate IFNβ production. Furthermore, fibroblasts and macrophage cells expressing HAQ are defective in Listeria monocytogenes infection-induced IFNβ production. Lastly, we find that the loss of IFNβ activity is due primarily to the R71H and R293Q SNPs in HAQ. We hypothesize that individuals carrying HAQ may exhibit heightened susceptibility to viral infection and respond poorly to DNA vaccines.     

A homozygous nonsense variant in IFT52 is associated with a human skeletal ciliopathy

Intraflagellar transport (IFT) is vital for the functioning of primary cilia. Defects in several components of IFT complexes cause a spectrum of ciliopathies with variable involvement of skeleton, brain, eyes, ectoderm and kidneys. We examined a child from a consanguineous family who had short stature, narrow thorax, short hands and feet, postaxial polydactyly of hands, pigmentary retinopathy, small teeth and skeletal dysplasia. The clinical phenotype of the child shows significant overlap with cranioectodermal dysplasia type I (Sensenbrenner syndrome). Whole‐exome sequencing revealed a homozygous nonsense variant p.R142* in IFT52 encoding an IFT‐B core complex protein as the probable cause of her condition. This is the first report of a human disease associated with IFT52.     

A novel homozygous KY variant causing a complex neurological disorder

Mutations in the gene kyphoscoliosis peptidase (KY) are known to cause myofibrillar myopathy-7 and hereditary spastic paraplegia. We investigated the genetic cause of a complex neurological phenotype in a consanguineous Pakistani family with four affected members, manifesting lower limb spasticity and weakness, toe walking, pes equinovarus, and a speech disorder. Genome-wide linkage analysis with microsatellite markers delineated chromosome 3q22.2-q24 harboring the disease gene. Whole exome sequencing was performed for two subjects, identifying a homozygous 14-bp frameshift deletion NM_178554.6:c.842_855del; p(Val281GlyfsTer18) in KY. The variant segregated with the phenotype and was absent from public databases and 100 ethnically matched controls. We confirm a novel homozygous KY variant causing a complex neurological phenotype in this family. A review of previously reported KY variants suggests that variants in this gene can cause a spectrum of neurological phenotypes.