Inherited metabolic diseases: aminoacidopathies, organic acidemia, defects of mitochondrial β-oxidation. A brief overview

Inherited metabolic diseases are a large group of inherited monogenic diseases. Metabolic disorders can cause child disability and mortality. Tandem mass spectrometry is a powerful technology that allows to diagnosis a large number of hereditary metabolic diseases. Clinical manifestations are variable, but more often the damages of nervous system, heart, liver, kidneys, hyperammonemia, hypo/hyperglycemia take place. The disease can make its debut at any age, but the severe forms of the disease manifest at infancy. Early diagnosis and treatment can significantly improve the prognosis; many countries expand the list of diseases included in screening programs. At the beginning of 2021 in most regions of the Russian Federation mass newborn screening is carried out for five hereditary metabolic diseases. The age and the range of clinical manifestation are variable; therefore, knowledge of this pathology is very important both for pediatricians and therapists, and for specialized doctors. The article presents a brief description of next groups of metabolic diseases: aminoacidopathies, organic acidurias and fatty acid oxidation defects.

Biochemical and genetic characterization of 16 patients with propionic acidemia

Пропионовая ацидемия (ПА) - редкое наследственное заболевание с аутосомно-рецессивным типом наследования, относится к «классическим», т.е. наиболее часто диагностируемым органическим ацидемиям. В данной работе представлена биохимическая и молекулярно-генетическая характеристика 16 пациентов с ПА, выявленных в Российской Федерации. У большинства обследованных пациентов первые симптомы проявились в первые месяцы жизни, наиболее частые из них: нарушения вскармливания, судороги, мышечная гипотония, угнетение сознания. При биохимическом исследовании (ГХ-МС и МС/МС) у пациентов было выявлено повышение концентрации 3-гидроксипропионой кислоты, метилцитрата, пропионилглицина, C3, глицина, которые являются патогномоничными маркерами этой патологии. В результате молекулярно-генетического анализа в генах PCCA и PCCB было выявлено 6 неописанных ранее вариантов нуклеотидной последовательности (4 варианта в гене PCCA, 2 - в гене PCCB), один из которых (PCCB: c.655-2A>G) имеет высокую частоту (17,2%, 5/29 мутантных аллелей генов PCCA и PCCB) в исследуемой выборке. Локализация миссенс-вариантов и их влияние на структуру белка были продемонстрированы на 3D-модели фермента пропионил-КоА-карбоксилазы. Выявленным вариантам были присвоены критерии патогенности в соответствии с рекомендациями American College of Medical Genetics and Genomics (ACMG). Propionic acidemia is a rare autosomal recessive metabolic disorder, characterized as classic organic acidemia. The article represents biochemical and molecular characterization of 16 patients diagnosed with propionic acidemia in Russia. Symptoms appeared during the first months after birth in most cases. Poor feeding, seizures, hypotonia, lethargy were the most frequent symptoms. Biochemical tests (GC-MS and MS/MS) showed elevated 3-hydroxypropionic acid, methylcitrate, propionylglycine, C3 in patients blood. Six undescribed earlier variants were found as a result of PCCA & PCCB (4 variants - PCCA, 2 - PCCB) genes DNA-tests. Variant c.655-2A>G in PCCB is the most frequent in this group (17.2%). Localization of missense variants and their effect on protein was demonstrated using propionyl-CoA carboxylase 3D model. New variants were classified according to the American College of Medical Genetics and Genomics (ACMG) guidelines.

Pancytopenia –An Uncommon Presentation of an Inborn Error of Metabolism

Pancytopenia as a presenting feature of an Inborn Error of Metabolism (IEM) is rare. Two children with pancytopenia mimicking sepsis are presented here. Investigations revealed pancytopenia and metabolic acidosis. Both had previous episodes of encephalopathy. In view of the persisting pancytopenia, episodic encephalopathy and metabolic acidosis, despite therapy for sepsis, an underlying IEM was considered and further workup revealed organic acidemia. Both children were started on dietary modifications and supplements, to which they responded, however one of them succumbed to an intercurrent infection. IEM should be considered in children with episodic encephalopathy, metabolic acidosis and pancytopenia after ruling out sepsis. Timely intervention can reduce morbidity and mortality.