J. Lawrence Merritt

AMMONIA CONTROL AND NEUROCOGNITIVE OUTCOME AMONG UREA CYCLE DISORDER PATIENTS TREATED WITH GLYCEROL PHENYLBUTYRATE

Glycerol phenylbutyrate is under development for treatment of urea cycle disorders (UCDs), rare inherited metabolic disorders manifested by hyperammonemia and neurological impairment. We report the results of a pivotal Phase 3, randomized, double‐blind, crossover trial comparing ammonia control, assessed as 24‐hour area under the curve (NH3‐AUC0‐24hr), and pharmacokinetics during treatment with glycerol phenylbutyrate versus sodium phenylbutyrate (NaPBA) in adult UCD patients and the combined results of four studies involving short‐ and long‐term glycerol phenylbutyrate treatment of UCD patients ages 6 and above. Glycerol phenylbutyrate was noninferior to NaPBA with respect to ammonia control in the pivotal study, with mean (standard deviation, SD) NH3‐AUC0‐24hr of 866 (661) versus 977 (865) μmol·h/L for glycerol phenylbutyrate and NaPBA, respectively. Among 65 adult and pediatric patients completing three similarly designed short‐term comparisons of glycerol phenylbutyrate versus NaPBA, NH3‐AUC0‐24hr was directionally lower on glycerol phenylbutyrate in each study, similar among all subgroups, and significantly lower (P < 0.05) in the pooled analysis, as was plasma glutamine. The 24‐hour ammonia profiles were consistent with the slow‐release behavior of glycerol phenylbutyrate and better overnight ammonia control. During 12 months of open‐label glycerol phenylbutyrate treatment, average ammonia was normal in adult and pediatric patients and executive function among pediatric patients, including behavioral regulation, goal setting, planning, and self‐monitoring, was significantly improved. Conclusion: Glycerol phenylbutyrate exhibits favorable pharmacokinetics and ammonia control relative to NaPBA in UCD patients, and long‐term glycerol phenylbutyrate treatment in pediatric UCD patients was associated with improved executive function (ClinicalTrials.gov NCT00551200, NCT00947544, NCT00992459, NCT00947297). (HEPATOLOGY 2012)

Establishing a consortium for the study of rare diseases: The Urea Cycle Disorders Consortium

The Urea Cycle Disorders Consortium (UCDC) was created as part of a larger network established by the National Institutes of Health to study rare diseases. This paper reviews the UCDCs accomplishments over the first 6years, including how the Consortium was developed and organized, clinical research studies initiated, and the importance of creating partnerships with patient advocacy groups, philanthropic foundations and biotech and pharmaceutical companies.

Next-generation sequencing for mitochondrial diseases: a wide diagnostic spectrum.

Background:  The current diagnostic approach for mitochondrial disorders requires invasive procedures such as muscle biopsy and multiple biochemical testing but the results are often inconclusive. Clinical sequencing tests are available only for a limited number of genes. Recently, massively parallel sequencing has become a powerful tool for testing genetically heterogeneous conditions such as mitochondrial disorders.

Extensive acrochordons and pancreatic islet-cell tumors in tuberous sclerosis associated with TSC2 mutations.

Acrochordons are frequently encountered benign skin lesions that may occasionally represent underlying pathology. Pancreatic islet‐cell tumors are rare neoplasms and few cases have been described in patients with tuberous sclerosis complex (TSC). A 39‐year‐old man presenting in acute renal failure was referred to us for further diagnostic evaluation of coincidentally noted dysmorphic features. Physical examination revealed over 1,000 acrochordons in addition to findings meeting criteria for TSC. The diagnosis was confirmed by disclosure of mutation in the TSC2 gene. Further evaluation revealed pancreatic islet cell tumors. Acrochordons are a common skin lesion, but when presenting in an atypical manner or unusual number may be a sign of TSC and underlying occult pathology thereby warranting evaluation of TSC2. Additionally, mutations in TSC2 gene may be a risk factor for developing pancreatic islet‐cell tumors.

Delineation of the cryptic 1qter deletion phenotype

The 1qter microdeletion is often reported in the literature as a part of a complex chromosome rearrangement. We describe a patient with a normal initial cytogenetic analysis later found by subtelomeric FISH to have a de novo isolated 1qter microdeletion. Further characterization was completed through microarray comparative genomic hybridization (CGH) and specific bacterial artificial chromosomes (BACs) to a region of 5.2–5.3 Mbp. Six additional cases were reviewed from a literature search. While no particular feature is specifically unique, the most frequently associated features include short stature, developmental delay and mental retardation, microcephaly, seizures, abnormal corpus callosum, and abnormal ear shape. This further delineates the phenotype and further narrows the chromosomal region responsible for a 1qter microdeletion phenotype.

Sodium phenylbutyrate decreases plasma branched-chain amino acids in patients with urea cycle disorders

Sodium phenylbutyrate (NaPBA) is a commonly used medication for the treatment of patients with urea cycle disorders (UCDs). Previous reports involving small numbers of patients with UCDs have shown that NaPBA treatment can result in lower plasma levels of the branched-chain amino acids (BCAA) but this has not been studied systematically. From a large cohort of patients (n=553) with UCDs enrolled in the Longitudinal Study of Urea Cycle Disorders, a collaborative multicenter study of the Urea Cycle Disorders Consortium, we evaluated whether treatment with NaPBA leads to a decrease in plasma BCAA levels. Our analysis shows that NaPBA use independently affects the plasma BCAA levels even after accounting for multiple confounding covariates. Moreover, NaPBA use increases the risk for BCAA deficiency. This effect of NaPBA seems specific to plasma BCAA levels, as levels of other essential amino acids are not altered by its use. Our study, in an unselected population of UCD subjects, is the largest to analyze the effects of NaPBA on BCAA metabolism and potentially has significant clinical implications. Our results indicate that plasma BCAA levels should to be monitored in patients treated with NaPBA since patients taking the medication are at increased risk for BCAA deficiency. On a broader scale, these findings could open avenues to explore NaPBA as a therapy in maple syrup urine disease and other common complex disorders with dysregulation of BCAA metabolism.

Biochemical Correction of Very Long–chain Acyl-CoA Dehydrogenase Deficiency Following Adeno-associated Virus Gene Therapy

We report the development of a gene replacement strategy for very long-chain acyl-CoA dehydrogenase (VLCAD) deficiency. VLCAD is a mitochondrial enzyme involved in fatty acid beta-oxidation, a key step in energy production during times of fasting or stress. Deficiency of VLCAD classically presents as hepatic dysfunction, hypoglycemia, cardiomyopathy, rhabdomyolysis, and/or sudden death. While dietary therapy for VLCAD deficiency has proven beneficial in preventing some symptoms, a risk of metabolic catastrophic decompensation remains throughout life during times of increased energy demand. We designed a recombinant adeno-associated virus (AAV) expressing the human VLCAD gene (AAV8-hVLCAD). To demonstrate its in vivo activity, AAV8-hVLCAD was administered via the tail vein to VLCAD-knockout mice. A reduction in accumulated serum long-chain acylcarnitines and increased fasting tolerance judged on blood glucose concentrations were observed as of 11 days postinjections through >100 days. Western analysis of liver, skeletal muscle, and heart extracts using PEP1 anti-hVLCAD antibody revealed short-term hVLCAD expression in the liver and muscle and longer-term expression in heart. This demonstrates the ability of human VLCAD to correct the biochemical phenotype of VLCAD-deficient mice.

Blood ammonia and glutamine as predictors of hyperammonemic crises in patients with urea cycle disorder

Purpose:The aim of this study was to examine predictors of ammonia exposure and hyperammonemic crises in patients with urea cycle disorders.Methods:The relationships between fasting ammonia, daily ammonia exposure, and hyperammonemic crises were analyzed in >100 patients with urea cycle disorders.Results:Fasting ammonia correlated strongly with daily ammonia exposure (r = 0.764; P < 0.001). For patients with fasting ammonia concentrations <0.5 upper limit of normal (ULN), 0.5 to <1.0 ULN, and ≥1.0 ULN, the probability of a normal average daily ammonia value was 87, 60, and 39%, respectively, and 10.3, 14.1, and 37.0% of these patients, respectively, experienced ≥1 hyperammonemic crisis over 12 months. Time to first hyperammonemic crisis was shorter (P = 0.008) and relative risk (4.5×; P = 0.011) and rate (~5×, P = 0.006) of hyperammonemic crises were higher in patients with fasting ammonia ≥1.0 ULN vs. <0.5ULN; relative risk was even greater (20×; P = 0.009) in patients ≥6 years old. A 10- or 25-µmol/l increase in ammonia exposure increased the relative risk of a hyperammonemic crisis by 50 and >200% (P < 0.0001), respectively. The relationship between ammonia and hyperammonemic crisis risk seemed to be independent of treatment, age, urea cycle disorder subtype, dietary protein intake, or blood urea nitrogen. Fasting glutamine correlated weakly with daily ammonia exposure assessed as 24-hour area under the curve and was not a significant predictor of hyperammonemic crisis.Conclusion:Fasting ammonia correlates strongly and positively with daily ammonia exposure and with the risk and rate of hyperammonemic crises, suggesting that patients with urea cycle disorder may benefit from tight ammonia control.Genet Med 17 7, 561–568.

Erratum: Blood ammonia and glutamine as predictors of hyperammonemic crises in patients with urea cycle disorder (Genetics in Medicine (2014))

Purpose:The aim of this study was to examine predictors of ammonia exposure and hyperammonemic crises in patients with urea cycle disorders.Methods:The relationships between fasting ammonia, daily ammonia exposure, and hyperammonemic crises were analyzed in >100 patients with urea cycle disorders.Results:Fasting ammonia correlated strongly with daily ammonia exposure (r = 0.764; P < 0.001). For patients with fasting ammonia concentrations <0.5 upper limit of normal (ULN), 0.5 to <1.0 ULN, and ≥1.0 ULN, the probability of a normal average daily ammonia value was 87, 60, and 39%, respectively, and 10.3, 14.1, and 37.0% of these patients, respectively, experienced ≥1 hyperammonemic crisis over 12 months. Time to first hyperammonemic crisis was shorter (P = 0.008) and relative risk (4.5×; P = 0.011) and rate (~5×, P = 0.006) of hyperammonemic crises were higher in patients with fasting ammonia ≥1.0 ULN vs. <0.5ULN; relative risk was even greater (20×; P = 0.009) in patients ≥6 years old. A 10- or 25-µmol/l increase in ammonia exposure increased the relative risk of a hyperammonemic crisis by 50 and >200% (P < 0.0001), respectively. The relationship between ammonia and hyperammonemic crisis risk seemed to be independent of treatment, age, urea cycle disorder subtype, dietary protein intake, or blood urea nitrogen. Fasting glutamine correlated weakly with daily ammonia exposure assessed as 24-hour area under the curve and was not a significant predictor of hyperammonemic crisis.Conclusion:Fasting ammonia correlates strongly and positively with daily ammonia exposure and with the risk and rate of hyperammonemic crises, suggesting that patients with urea cycle disorder may benefit from tight ammonia control.Genet Med 17 7, 561–568.

14q32.3 deletion syndrome with autism.

Terminal deletions of 14q32.3 are a rare entity with few published cases that have been defined as a specific phenotype [Ortigas et al., 1997]. We describe a patient with the smallest known terminal 14q deletion, presenting with autism. This clinical presentation has not previously been reported as a part of this chromosomal disorder. A 6-year-old female with 14q32.33 terminal deletion presented with developmental delay and autistic phenotype. She was the first child of a 28-year-old, healthy female, born after an uncomplicated pregnancy. Her birth weight was 2.59 kg with exam noting microcephaly, hypotonia, and a short tongue frenulum requiring frenotomy. During the first year of life, she had feeding difficulties, chronic constipation, failure to thrive, and petite mal seizures. Diagnostic evaluation for global developmental delay at 1 year of age included chromosome analysis revealing an unbalanced 14;21 translocation. Magnetic resonance imaging of the head did not disclose any structural abnormalities. Her electroencephalogram done at 4 years of age reported bilateral centrotemporal spike waves consistent with benign focal epilepsx of childhood. Early intervention services were provided, including physical, occupational, and speech therapy. She beganwalking unsupported at 23 months of age, but communication skills at that time were restricted to pointing and leading her parents to objects. At 65 months of age, her age equivalent score was 20 months on the Bayley Scales of Infant Development, Mental Developmental Index (BSID, MDI). She spoke 20 single words but did not consistently use thesewords in a functionalmanner. Toilet training had progressed to where she would wear ‘‘pull-ups’’ but didnot express interest inusing the toilet unless brought to the bathroom by her parents. Except for recurrent otitis media and accommodative esotropia, she did not have significant medical problems. She was 66-month-old at our first examination. She had a tilted head, increased mandibular length, bifrontal narrowing and microcephaly (<3rd centile) with normal height and weight (25th–50th centile). Facial features included telecanthus/hypertelorism,mild ptosis, blepharophimosis, epicanthal folds, sparse medial eyebrows, up-slanted palpebral fissures, long eyelashes, and right esotropia. Her ear lobes were overfolded and low set. Her nosewas short with awide nasal bridge and under-developed alae (Fig. 1). Her torso was long and narrow and she had small bilateral inguinal hernias. The nailswere short, palmswere soft andfleshy, and therewas mild fifth digit clinodactyly. She had thick skin on her soles with wide I–II toe interspaces. Comprehensive developmental assessment by a Developmental and Behavioral Pediatrician and psychologist at 73 months revealed significant global developmental delay, with an age equivalent score estimated at 18–25 months on the BSID-MDI. She manifested problems with pragmatic language, limited reciprocal social interaction, absence of pretend play, and repetitive, self-stimulatory behaviors consistent with a diagnosis of autistic disorder [DSM-TR, 2000]. Her score on the Childhood Autism Rating Rcale placed her in the severely autistic category. Cytogenetic studies at the Cytogenetics Laboratory at Mayo Clinic using high-resolution karyotype, whole chromosome 14 and chromosome 21 painting probes, and subtelomeric FISH reported the karyotype as: 45,XX,der(14)t(14;21) (q32.3;q11.2),-21.ish del(14)(qter-). This demonstrates the subtelomere loss from the long arm of chromosome 14 and the presence of the long arm of chromosome 21, although some loss of chromatin from very near the centromere cannot be ruled out (Fig. 2). Parental karyotypes were normal except the presence of the normal polymorphic variant inv(9) in the mother, thereby indicating that the der(14) abnormality in our patient was de novo. Autistic features have not previously been described in conjunction with terminal deletions of 14q32.33, and they widen the spectrum of known 14q32.3 deletion phenotype and have importance for designing an optimal patient care plan. Our patient also emphasizes the importance of searching