Cynthia Fernández-Lainez

Clinical and biochemical characteristics of patients with urea cycle disorders in a developing country

OBJECTIVES To report the clinical and laboratory characteristics of urea cycle disorder (UCD) patients at a tertiary care center in a developing country. DESIGN AND METHODS Retrospective study of clinical and laboratory data of UCD patients. RESULTS Thirty-seven UCD patients were studied, 31 symptomatic (high risk) patients (15 neonatal onset, 16 late onset) and 6 with positive neonatal screening. Argininosuccinate synthetase deficiency was the most frequent disease (17/37, 46%), followed by ornithine transcarbamylase (10/37, 27%), arginase (7/37, 19%), and argininosuccinate lyase (3/37, 8%) deficiencies. Mortality of symptomatic patients was 38% (10/26), neonatal onset had the worst outcome, with 50% of survival. CONCLUSIONS In Mexico, the mortality of the UCD patients is higher than those reported in other countries, and neurological sequels are frequent and severe. It is essential to implement practice guidelines for the professional management of these patients.

Phenylalanine hydroxylase deficiency in Mexico: genotype–phenotype correlations, BH4 responsiveness and evidence of a founder effect

The mutational spectrum of the phenylalanine hydroxylase gene (PAH) in Mexico is unknown, although it has been suggested that PKU variants could have a differential geographical distribution. Genotype–phenotype correlations and genotype‐based predictions of responsiveness to tetrahydrobiopterin (BH4) have never been performed. We sequenced the PAH gene and determined the geographic origin of each allele, mini‐haplotype associated, genotype–phenotype correlations and genotype‐based prediction of BH4 responsiveness in 48 Mexican patients. The mutational spectrum included 34 variants with c.60+5G>T being the most frequent (20.8%) and linked to haplotype 4.3 possibly because of a founder effect and/or genetic drift. Two new variants were found c.1A>T and c.969+6T>C. The genotype–phenotype correlation was concordant in 70.8%. The genotype‐based prediction to BH4‐responsiveness was 41.7%, this information could be useful for the rational selection of candidates for BH4 testing and therapy.

Higher incidence of thyroid agenesis in Mexican newborns with congenital hypothyroidism associated with birth defects

BACKGROUND Congenital hypothyroidism (CH) is the most common endocrine system disorder in newborns. Ectopic thyroid and agenesis are the most frequent thyroid structural malformations. Several reports have shown that CH is associated with birth defects (BD) ranging from congenital heart disease to ocular and gastrointestinal anomalies. AIMS We investigated how many and what types of BD were associated with CH in Mexican children. STUDY DESIGN Cross-sectional study conducted in patients with confirmed CH. SETTING Highly specialized government pediatric center in Mexico City. SUBJECTS We included 212 patients with permanent CH identified by newborn screening. RESULTS We found that 24% of patients with CH also had BD, and that there was a higher prevalence of thyroid agenesis in the group of patients with CH associated with BD (CH+BD) versus the isolated CH group (p=0.007). There were more females than males in both groups. The most common BD were congenital heart diseases, especially those of the atrial septum, followed by patent ductus arteriosus, found as a single malformation or as part of a complex congenital heart disease. In this study, we found Hirschsprung disease, Beckwith-Wiedemann syndrome, Pierre Robin sequence, Albrights osteodystrophy, VATER association, and frontonasal dysplasia associated with CH. CONCLUSIONS In this study population, there was a high prevalence of BD in patients with permanent CH. Thyroid agenesis was the main etiological cause of CH in patients with associated congenital malformations. The high prevalence of CH+BD underlines the need for a comprehensive clinical diagnostic approach of the patients with CH.

Kernicterus in a boy with ornithine transcarbamylase deficiency: A case report

Ornithine transcarbamylase deficiency (OTCD) is an X‐linked urea cycle defect associated with severe and usually fatal hyperammonemia. This study describes a patient with early onset lethal OTCD due to a known pathogenic variant (c.298+1G>A), as well as the novel autopsy finding of kernicterus with relatively low blood concentration of unconjugated bilirubin (UCB) (11.55 mg/dL). The patient was a full‐term male with a family history of two previous male siblings who died as newborns after acute neurologic deterioration. The patients symptoms began at 24 h of life with lethargy that rapidly progressed to coma upon admission to the neonatal intensive care unit. Although hyperammonemia and hyperbilirubinemia were documented, hemofiltration could not be performed. OTCD diagnosis was biochemically established. Despite nutritional intervention and treatment for hyperammonemia, the patient died on the sixth day of life. At autopsy, external brain examination revealed a marked yellow pigmentation typical of kernicterus that included gray matter, particularly the thalamus and basal ganglia; dentate nuclei of the cerebellum and brain stem gray matter were also affected. Microscopic findings were consistent with the classical description of tissue damage in OTCD, including the presence of Alzheimer type II astrocytes in basal ganglia, necrosis, neuronal loss with spongiform degeneration and macrophage infiltration surrounded by astroglia. This condition may be an important comorbidity in newborns with hyperammonemia.

In silico prediction of the pathogenic effect of a novel variant of BCKDHA leading to classical maple syrup urine disease identified using clinical exome sequencing

Maple syrup urine disease (MSUD) is a metabolic disorder caused by mutations in three of the branched-chain α-keto acid dehydrogenase complex (BCKDC) genes. Classical MSUD symptom can be observed immediately after birth and include ketoacidosis, irritability, lethargy, and coma, which can lead to death or irreversible neurodevelopmental delay in survivors. The molecular diagnosis of MSUD can be time-consuming and difficult to establish using conventional Sanger sequencing because it could be due to pathogenic variants of any of the BCKDC genes. Next-generation sequencing-based methodologies have revolutionized the molecular diagnosis of inborn errors in metabolism and offer a superior approach for genotyping these patients. Here, we report an MSUD case whose molecular diagnosis was performed by clinical exome sequencing (CES), and the possible structural pathogenic effect of a novel E1α subunit pathogenic variant was analyzed using in silico analysis of α and β subunit crystallographic structure. Molecular analysis revealed a new homozygous non-sense c.1267C>T or p.Gln423Ter variant of BCKDHA. The novel BCKDHA variant is considered pathogenic because it caused a premature stop codon that probably led to the loss of the last 22 amino acid residues of the E1α subunit C-terminal end. In silico analysis of this region showed that it is in contact with several residues of the E1β subunit mainly through polar contacts, hydrogen bonds, and hydrophobic interactions. CES strategy could benefit the patients and families by offering precise and prompt diagnosis and better genetic counseling.

Mutational spectrum of PTS gene and in silico pathological assessment of a novel variant in Mexico

BACKGROUND Tetrahydrobiopterin (BH4) is the cofactor for 6-pyruvoyl-tetrahydropterin synthase (PTPS); it is involved in BH4 biosynthesis and is encoded by PTS gene. Its deficiency (PTPSD) is characterized by hyperphenylalaninemia (HPA) and deficit in central monoamine neurotransmitters. We describe the clinical and mutational spectrum of five patients with PTPSD, from four unrelated Mexican families. All patients had symptomatic diagnosis and presented severe early neurological manifestations and HPA. METHODS Clinical and biochemical data from studied patients were recorded. Responsible PTPSD genotypes was determined by direct and bidirectional Sanger DNA sequencing of the six PTS coding exons and their exon-intron borders, and these were directly searched in the available relatives. The novel PTS missense variant [NM_3000317.2:331G > T, p.(Ala111Ser)] was subjected to in silico, to predict a possible deleterious effect. RESULTS Diminished fetal movements were perceived as a uniform characteristic in the studied group. DNA sequencing showed two known p.(Arg25∗) and p.(Val132TyrFs∗19) and the novel missense p.(Ala111Ser) PTS variants, the latter representing potentially a frequent PTPSD-responsible allele (50%, 4/8) in Mexican patients. In silico protein modeling analysis of the p.(Ala111Ser) variant revealed loss of hydrophobic interactions between the alanine and neighboring valines, suggesting that these changes in polarity may be detrimental for enzyme function, structure and/or stability. CONCLUSIONS This work contributes to the knowledge of PTPS molecular spectrum. The delayed diagnosis of these patients emphasizes the importance of considering BH4 metabolism defects in the differential diagnosis of HPA, especially for countries that are beginning their HPA newborn screening programs.

Hepatorenal Tyrosinemia in Mexico: A Call to Action

Hepatorenal tyrosinemia is a treatable metabolic disease characterized by progressive liver failure, renal damage and pronounced coagulopathy. Its clinical diagnosis is difficult because of its low prevalence and heterogeneous symptoms. In developed countries, expanded newborn screening, based on succinylacetone quantification by tandem mass spectrometry, has been very valuable in the early detection of hepatorenal tyrosinemia, providing the opportunity for rapid treatment of affected patients. In developing countries without systematic expanded newborn screening, however, diagnosis and treatment of this disease remain major challenges, as genetic diseases in these countries are not a health priority and there are few referral centers for infants with inherited errors of metabolism. This chapter describes the diagnosis, follow-up and outcome of 20 Mexican patients with hepatorenal tyrosinemia. This chapter also constitutes a call to action to pediatricians, gastroenterologists, geneticists and other health professionals, and to academic organizations, health authorities and patient advocacy groups, to promote early patient detection and treatment, reducing the unacceptably high mortality rate (75%) in Mexican infants with this potentially deadly but eminently treatable condition.

Crisis neuropática por suspensión de nitisinona en una paciente con tirosinemia: informe de un caso

Se presenta el caso de una paciente con tirosinemia hepatorrenal (TYR- 1) que, debido a la interrupcion por cuatro semanas de tratamiento con nitisinona, tuvo una grave crisis neurologica de pseudoporfiria caracterizada por vomito, dolor abdominal, irritabilidad e hipertension arterial, con gran elevacion de la succinilacetona y alfafetoproteina. La crisis requirio tratamiento intrahospitalario. Una semana despues de reiniciar la administracion del farmaco revirtio totalmente. Este caso enfatiza la importancia de mantener el tratamiento ininterrumpido con nitisinona en pacientes con tirosinemia hepatorrenal. Tambien es util para reconocer el cuadro clinico y la fisiopatologia de las crisis neurologicas caracteristicas de esta enfermedad.

CHAPTER 7:The Chemistry and Biochemistry of Niacin (B3)

Niacin, also known as vitamin B3, nicotinic acid or vitamin PP, is a water-soluble B-complex vitamin. This vitamin is the generic descriptor for two vitamers, niacin and niacinamide, which are based on a pyridine ring bound to a carboxylic group or to a carboxamide group, respectively. The vitamin is obtained from the diet in the form of nicotinic acid, nicotinamide and tryptophan, the latter being transformed in nicotinamide adenine dinucleotides, NAD and NADP. These compounds play a central role in energy metabolism, both being involved in many cellular oxidation–reduction reactions of the metabolic processes of all life forms in which they act as a hydride ion acceptor. Besides its classical role as redox coenzyme, nicotinic acid participates in a wide variety of ADP-ribosylation reactions such as DNA repair, calcium mobilization and deacetylation. In this chapter we revise chemical and biochemical aspects of the vitamin and summarize recent advances in the understanding of the biosynthesis and signalling functions of NAD and NADP.

Experiencia con sapropterina en pacientes mexicanos con hiperfenilalaninemia

Hyperphenylalaninemia is caused by deficient enzyme activity of phenylalanine hydroxylase. It was one of the first genetic disorders susceptible to treatment with a natural protein restricted diet for life. While this treatment has proven effective in preventing mental retardation, eliminating certain foods from the diet entails the risk of nutritional deficiencies. For these reasons, new non-nutritional therapeutic strategies have been developed. One is the administration of sapropterin dihydrochloride, the synthetic form of tetrahydrobiopterin (BH4), which is the natural cofactor of phenylalanine hydroxylase, whose purpose is to reduce blood phenylalanine levels. We studied 6 patients with confirmed diagnosis of hyperphenylalaninemia or phenylketonuria. Sapropterin dihydrochloride was administered for 28 days and the intake of phenylalanine was calculated in each patient. To evaluate the response to sapropterin phenylalanine blood levels were measured at zero, eight and 24 hours and on days seven, 14, 21 and 28. The 24-hours recall was used to establish the intake of phenylalanine before and during the study. A positive response was determined as a reduction of phenylalanine blood levels ≥30% Four of the six patients responded positively to sapropterin dihydrochloride. The aim of this paper is to present the experience with sapropterin dihydrochloride in a group of Mexican patients with hyperphenylalaninemia.