We correlate chromosome 5 haplotypes and SMN2 copy number with disease expression in 42 Mennonite and 14 Amish patients with spinal muscular atrophy (SMA). A single haplotype (A1) with 1 copy of SMN2 ...segregated among all Amish patients. SMN1 deletions segregated on four different Mennonite haplotypes that carried 1 (M1a, M1b, M1c) or 2 (M2) copies of SMN2. DNA microsatellite and microarray data revealed structural similarities among A1, M1a, M1b, and M2. Clinical data were parsed according to both SMN1 genotype and SMN2 copy number (2 copies, n = 44; 3 copies, n = 9; or 4 copies, n = 3). No infant with 2 copies of SMN2 sat unassisted. In contrast, all 9 Mennonites with the M1a/M2 genotype (3 copies of SMN2) sat during infancy at a median age of 7 months, and 5 (56%) walked and dressed independently at median ages of 18 and 36 months, respectively. All are alive at a median age of 11 (range 2-31) years without ventilatory support. Among 13 Amish and 26 Mennonite patients with 2 copies of SMN2 who did not receive feeding or ventilatory support, A1/A1 as compared to M1a/M1a genotype was associated with earlier clinical onset (p = 0.0040) and shorter lifespan (median survival 3.9 versus 5.7 months, p = 0.0314). These phenotypic differences were not explained by variation in SMN1 deletion size or SMN2 coding sequence, which were conserved across haplotypes. Distinctive features of SMA within Plain communities provide a population-specific framework to study variations of disease expression and the impact of disease-modifying therapies administered early in life.
Founder populations have long contributed to our knowledge of rare disease genes and phenotypes. From the pioneering work of Dr. Victor McKusick to today, research in these groups has shed light on ...rare recessive phenotypes, expanded the clinical spectrum of disease, and facilitated disease gene identification. Current clinical and research studies in these special groups augment the wealth of knowledge already gained, provide new insights into emerging problems such as variant interpretation and reduced penetrance, and contribute to the development of novel therapies for rare genetic diseases. Clinical developments over the past 30 years have altered the fundamental relationship with the Lancaster Plain communities: research has become more collaborative, and the knowledge imparted by these studies is now being harnessed to provide cutting‐edge translational medicine to the very community of vulnerable individuals who need it most.
We conducted blinded psychiatric assessments of 26 Amish subjects (52 ± 11 years) from four families with prevalent bipolar spectrum disorder, identified 10 potentially pathogenic alleles by exome ...sequencing, tested association of these alleles with clinical diagnoses in the larger Amish Study of Major Affective Disorder (ASMAD) cohort, and studied mutant potassium channels in neurons. Fourteen of 26 Amish had bipolar spectrum disorder. The only candidate allele shared among them was rs78247304, a non-synonymous variant of KCNH7 (c.1181G>A, p.Arg394His). KCNH7 c.1181G>A and nine other potentially pathogenic variants were subsequently tested within the ASMAD cohort, which consisted of 340 subjects grouped into controls subjects and affected subjects from overlapping clinical categories (bipolar 1 disorder, bipolar spectrum disorder and any major affective disorder). KCNH7 c.1181G>A had the highest enrichment among individuals with bipolar spectrum disorder (χ(2) = 7.3) and the strongest family-based association with bipolar 1 (P = 0.021), bipolar spectrum (P = 0.031) and any major affective disorder (P = 0.016). In vitro, the p.Arg394His substitution allowed normal expression, trafficking, assembly and localization of HERG3/Kv11.3 channels, but altered the steady-state voltage dependence and kinetics of activation in neuronal cells. Although our genome-wide statistical results do not alone prove association, cumulative evidence from multiple independent sources (parallel genome-wide study cohorts, pharmacological studies of HERG-type potassium channels, electrophysiological data) implicates neuronal HERG3/Kv11.3 potassium channels in the pathophysiology of bipolar spectrum disorder. Such a finding, if corroborated by future studies, has implications for mental health services among the Amish, as well as development of drugs that specifically target HERG3/Kv11.3.
The study of inherited retinal diseases has advanced our knowledge of the cellular and molecular mechanisms involved in sensory neural signaling. Dysfunction of two specific sensory modalities, ...vision and proprioception, characterizes the phenotype of the rare, autosomal-recessive disorder posterior column ataxia and retinitis pigmentosa (PCARP). Using targeted DNA capture and high-throughput sequencing, we analyzed the entire 4.2 Mb candidate sequence on chromosome 1q32 to find the gene mutated in PCARP in a single family. Employing comprehensive bioinformatic analysis and filtering, we identified a single-nucleotide coding variant in the feline leukemia virus subgroup C cellular receptor 1 (
FLVCR1), a gene encoding a heme-transporter protein. Sanger sequencing confirmed the
FLVCR1 mutation in this family and identified different homozygous missense mutations located within the protein's transmembrane channel segment in two other unrelated families with PCARP. To determine whether the selective pathologic features of PCARP correlated with
FLVCR1 expression, we examined wild-type mouse
Flvcr1 mRNA levels in the posterior column of the spinal cord and the retina via quantitative real-time reverse-transcriptase PCR. The
Flvcr1 mRNA levels were most abundant in the retina, followed by the posterior column of the spinal cord and other brain regions. These results suggest that aberrant FLVCR1 causes a selective degeneration of a subpopulation of neurons in the retina and the posterior columns of the spinal cord via dysregulation of heme or iron homeostasis. This finding broadens the molecular basis of sensory neural signaling to include common mechanisms that involve proprioception and vision.
Familial hypercholesterolemia (FH) due to a founder variant in Apolipoprotein B (ApoB
) is reported in 12% of the Pennsylvania Amish community. By studying a cohort of ApoB
heterozygotes and ...homozygotes, we aimed to characterize the biochemical and cardiac imaging features in children and young adults with a common genetic background and similar lifestyle.
We employed advanced lipid profile testing, carotid intima media thickness (CIMT), pulse wave velocity (PWV), and peripheral artery tonometry (PAT) to assess atherosclerosis in a cohort of Amish ApoB
heterozygotes (n = 13), homozygotes (n = 3), and their unaffected, age-matched siblings (n = 9). ApoB
homozygotes were not included in statistical comparisons.
LDL cholesterol (LDL-C) was significantly elevated among ApoB
heterozygotes compared to sibling controls, though several ApoB
heterozygotes had LDL-C levels in the normal range. LDL particles (LDL-P), small, dense LDL particles, and ApoB were also significantly elevated among subjects with ApoB
. Despite these differences in serum lipids and particles, CIMT and PWV were not significantly different between ApoB
heterozygotes and controls in age-adjusted analysis.
We provide a detailed description of the serum lipids, atherosclerotic plaque burden, vascular stiffness, and endothelial function among children and young adults with FH due to heterozygous ApoB
. Fasting LDL-C was lower than what is seen with other forms of FH, and even normal in several ApoB
heterozygotes, emphasizing the importance of cascade genetic testing among related individuals for diagnosis. We found increased number of LDL particles among ApoB
heterozygotes but an absence of detectable atherosclerosis.
We identified an autosomal recessive condition in 11 individuals in the Old Order Amish of northeastern Ohio. The syndrome was characterized by distinctive craniofacial dysmorphism, skeletal ...anomalies, and mental retardation. The typical craniofacial dysmorphism included brachycephaly, highly arched bushy eyebrows, synophrys, long eyelashes, low-set ears, microdontism of primary teeth, and generalized gingival hyperplasia, whereas Sprengel deformity of scapula, fusion of spine, rib abnormities, pectus excavatum, and pes planus represented skeletal anomalies. The genome-wide homozygosity mapping using six affected individuals localized the disease gene to a 3.3-Mb region on chromosome 1q23.3-q24.1. Candidate gene sequencing identified a homozygous frameshift mutation, c.139_140delAG, in the transmembrane and coiled-coil domains 1 (TMCO1) gene, as the pathogenic change in all affected members of the extended pedigree. This mutation is predicted to result in a severely truncated protein (p.Ser47Ter) of only one-fourth the original length. The TMCO1 gene product is a member of DUF841 superfamily of several eukaryotic proteins with unknown function. The gene has highly conserved amino acid sequence and is universally expressed in all human tissues examined. The high degree of conservation and the ubiquitous expression pattern in human adult and fetal tissues suggest a critical role for TMCO1. This report shows a TMCO1 sequence variant being associated with a genetic disorder in human. We propose "TMCO1 defect syndrome" as the name of this condition.
Striatal degeneration from glutaryl-CoA dehydrogenase deficiency (glutaric aciduria type 1, GA1) is associated with cerebral formation and entrapment of glutaryl-CoA and its derivatives that depend ...on cerebral lysine influx. In 2006 we designed a lysine-free study formula enriched with arginine to selectively block lysine transport across cerebral endothelia and thereby limit glutaryl-CoA production by brain. Between 2006 and present, we treated twelve consecutive children with study formula (LYSx group) while holding all other treatment practices constant. Clinical and biochemical outcomes were compared to 25 GA1 patients (PROx group) treated between 1995 and 2005 with natural protein restriction (dietary lysine/arginine ratio of 1.7±0.3mg:mg). We used published kinetic parameters of the y+and LAT1 blood–brain barrier transporters to model the influx of amino acids into the brain. Arginine fortification to achieve a mean dietary lysine/arginine ratio of 0.7±0.2mg:mg was neuroprotective. All 12 LYSx patients are physically and neurologically healthy after 28 aggregate patient-years of follow up (current ages 28±21months) and there were no adverse events related to formula use. This represents a 36% reduction of neurological risk (95% confidence interval 14–52%, p=0.018) that we can directly attribute to altered amino acid intake. During the first year of life, 20% lower lysine intake and two-fold higher arginine intake by LYSx patients were associated with 50% lower plasma lysine, 3-fold lower plasma lysine/arginine concentration ratio, 42% lower mean calculated cerebral lysine influx, 54% higher calculated cerebral arginine influx, 15–26% higher calculated cerebral influx of several anaplerotic precursors (isoleucine, threonine, methionine, and leucine), 50% less 3-hydroxyglutarate excretion, and a 3-fold lower hospitalization rate (0.8 versus 2.3 hospitalizations per patient per year). The relationship between arginine fortification and plasma lysine indicates that transport competition exists at both cerebrovascular and gastrointestinal barriers, suggesting their co-administration is key to efficacy. Monitoring the ratio between lysine and arginine in diet and plasma may prove a useful strategy for treating children with GA1.
Type I glutaric aciduria, part 1: Natural history of 77 patients Strauss, Kevin A.; Puffenberger, Erik G.; Robinson, Donna L. ...
American journal of medical genetics. Part C, Seminars in medical genetics,
15 August 2003, Volume:
121C, Issue:
1
Journal Article
S-adenosylhomocysteine hydrolase (AHCY) deficiency is a rare autosomal recessive disorder in methionine metabolism caused by mutations in the AHCY gene. Main characteristics are psychomotor delay ...including delayed myelination and myopathy (hypotonia, absent tendon reflexes etc.) from birth, mostly associated with hypermethioninaemia, elevated serum creatine kinase levels and increased genome wide DNA methylation. The prime function of AHCY is to hydrolyse and efficiently remove S-adenosylhomocysteine, the by-product of transmethylation reactions and one of the most potent methyltransferase inhibitors. In this study, we set out to more specifically characterize DNA methylation changes in blood samples from patients with AHCY deficiency. Global DNA methylation was increased in two of three analysed patients. In addition, we analysed the DNA methylation levels at differentially methylated regions (DMRs) of six imprinted genes (MEST, SNRPN, LIT1, H19, GTL2 and PEG3) as well as Alu and LINE1 repetitive elements in seven patients. Three patients showed a hypermethylation in up to five imprinted gene DMRs. Abnormal methylation in Alu and LINE1 repetitive elements was not observed. We conclude that DNA hypermethylation seems to be a frequent but not a constant feature associated with AHCY deficiency that affects different genomic regions to different degrees. Thus AHCY deficiency may represent an ideal model disease for studying the molecular origins and biological consequences of DNA hypermethylation due to impaired cellular methylation status.
To evaluate an approach to the diagnosis and treatment of maple syrup disease (MSD).
Family histories and molecular testing for the Y393N mutation of the E1alpha subunit of the branched-chain ...alpha-ketoacid dehydrogenase allow us to identify infants who were at high risk for MSD. Amino acid concentrations were measured in blood specimens from these at-risk infants between 12 and 24 hours of age. An additional 18 infants with MSD were diagnosed between 4 and 16 days of age because of metabolic illness. A treatment protocol for MSD was designed to 1) inhibit endogenous protein catabolism, 2) sustain protein synthesis, 3) prevent deficiencies of essential amino acids, and 4) maintain normal serum osmolarity. Our protocol emphasizes the enhancement of protein anabolism and dietary correction of imbalances in plasma amino acids rather than removal of leucine by dialysis or hemofiltration. During acute illnesses, the rate of decrease of the plasma leucine level was monitored as an index of net protein synthesis. The treatment protocol for acute illnesses included the use of mannitol, furosemide, and hypertonic saline to maintain or reestablish normal serum sodium and extracellular osmolarity and thereby prevent or reverse life-threatening cerebral edema. Similar principles were followed for both sick and well outpatient management, especially during the first year, when careful matching of branched-chain amino acid intake with rapidly changing growth rates was necessary. Branched-chain ketoacid excretion was monitored frequently at home and branched-chain amino acid levels were measured within the time of a routine clinic visit, allowing immediate diagnosis and treatment of metabolic derangements.
1) Eighteen neonates with MSD were identified in the high-risk group (n = 39) between 12 and 24 hours of age using amino acid analysis of plasma or whole blood collected on filter paper. The molar ratio of leucine to alanine in plasma ranged from 1.3 to 12.4, compared with a control range of 0.12 to 0.53. None of the infants identified before 3 days of age and managed by our treatment protocol became ill during the neonatal period, and 16 of the 18 were managed without hospitalization. 2) Using our treatment protocol, 18 additional infants who were biochemically intoxicated at the time of diagnosis recovered rapidly. In all infants, plasma leucine levels decreased to <400 micromol/L between 2 to 4 days after diagnosis. Rates of decrease of the plasma leucine level using a combination of enteral and parenteral nutrition were consistently higher than those reported for dialysis or hemoperfusion. Prevention of acute isoleucine, valine, and other plasma amino acid deficiencies by appropriate supplements allowed a sustained decrease of plasma leucine levels to the therapeutic range of 100 to 300 micromol/L, at which point dietary leucine was introduced. 3) Follow-up of the 36 infants over >219 patient years showed that, although common infections frequently cause loss of metabolic control, the overall rate of hospitalization after the neonatal period was only 0.56 days per patient per year of follow-up, and developmental outcomes were uniformly good. Four patients developed life-threatening cerebral edema as a consequence of metabolic intoxication induced by infection, but all recovered. These 4 patients each showed evidence that acutely decreased serum sodium concentration and decreased serum osmolarity were associated with rapid progression of cerebral edema during their acute illnesses.
Classical MSD can be managed to allow a benign neonatal course, normal growth and development, and low hospitalization rates. However, neurologic function may deteriorate rapidly at any age because of metabolic intoxication provoked by common infections and injuries. Effective management of the complex pathophysiology of this biochemical disorder requires integrated management of general medical care and nutrition, as well as control of several variables that influence endogenous protein anabolism and catabolism, plasma amino acid concentrations, and serum osmolarity.
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