Galactose-1-phosphate inhibits cytochrome c oxidase and causes mitochondrial dysfunction in classic galactosemia.

Classic galactosemia is an inborn error of metabolism caused by mutations in the GALT gene resulting in the diminished activity of the galactose-1-phosphate uridyltransferase enzyme. This reduced GALT activity leads to the buildup of the toxic intermediate galactose-1-phosphate and a decrease in ATP levels upon exposure to galactose. In this work, we focused our attention on mitochondrial oxidative phosphorylation in the context of this metabolic disorder. We observed that galactose-1-phosphate accumulation reduced respiratory rates in vivo and changed mitochondrial function and morphology in yeast models of galactosemia. These alterations are harmful to yeast cells since the mitochondrial retrograde response is activated as part of the cellular adaptation to galactose toxicity. In addition, we found that galactose-1-phosphate directly impairs cytochrome c oxidase activity of mitochondrial preparations derived from yeast, rat liver, and human cell lines. These results highlight the evolutionary conservation of this biochemical effect. Finally, we discovered that two compounds - oleic acid and dihydrolipoic acid - that can improve the growth of cell models of mitochondrial diseases, were also able to improve galactose tolerance in this model of galactosemia. These results reveal a new molecular mechanism relevant to the pathophysiology of classic galactosemia - galactose-1-phosphate-dependent mitochondrial dysfunction - and suggest that therapies designed to treat mitochondrial diseases may be repurposed to treat galactosemia.

Heterologous expression of a novel galactose-1-phosphate uridylyltransferase from Thermodesulfatator indicus and its application for bioproduction of Gal-ß-1,4-GlcNAc-X.

Nucleotide sugars (UDP-Sugars) are essential for the production of polysaccharides and glycoconjugates utilized in medicines, cosmetics, and food industries. The enzyme Galactose-1-phosphate uridylyltransferase (GalU; EC 2.7.7.12) is responsible for the synthesis of UDP-galactose from α-d-galactose-1-phosphate (Gal-1P) and UTP. A novel bacterial GalU (TiGalU) encoded from a thermophilic bacterium, Thermodesulfatator indicus, was successfully purified using the Ni-NTA column after being expressed in Escherichia coli. The optimal pH for recombinant TiGalU was determined to be 5.5. The optimum temperature of the enzyme was 45 °C. The activity of TiGalU was not dependent on Mg2+ and was strongly inhibited by SDS. When coupled with galactose kinase (GALK1) and ß-1,4-galactosyltransferase 1 (B4GALT1), the enzyme enabled the one-pot synthesis of Gal-ß-1,4-GlcNAc-X by utilizing galactose and UTP as substrates. This study reported the in vitro biosynthesis of Gal-ß-1,4-GlcNAc-X for the first time, providing an environmentally friendly way to biosynthesis glycosides and other polysaccharides.

A case report of classic galactosemia with a GALT gene variant and a literature review.

BACKGROUND: Galactosemia is an autosomal recessive disorder resulting from an enzyme defect in the galactose metabolic pathway. The most severe manifestation of classic galactosemia is caused by galactose-1-phosphate uridylyltransferase (GALT) deficiency, and this condition can be fatal during infancy if left untreated. It also may result in long-term complications in affected individuals. CASE PRESENTATION: This report describes a patient whose initial clinical symptoms were jaundice and liver dysfunction. The patient's liver and coagulation functions did not improve after multiple admissions and treatment with antibiotics, hepatoprotective and choleretic agents and blood transfusion. Genetic analysis revealed the presence of two variants in the GALT gene in the compound heterozygous state: c.377 + 2dup and c.368G > C (p.Arg123Pro). Currently, the variant locus (c.377 + 2dup) in the GALT gene has not been reported in the Human Gene Mutation Database (HGMD), while c.368G > C (p.Arg123Pro) has not been reported in the Genome Aggregation Database (GnomAD) nor the HGMD in East Asian population. We postulated that the two variants may contribute to the development of classical galactosemia. CONCLUSIONS: Applications of whole-exome sequencing to detect the two variants can improve the detection and early diagnosis of classical galactosemia and, more specifically, may identify individuals who are compound heterozygous with variants in the GALT gene. Variants in the GALT gene have a potential therapeutic significance for classical galactosemia.

Classical Hereditary galactosemia: findings in patients and animal models.

Classic galactosemia is a rare inborn error of metabolism that affects the metabolism of galactose, a sugar derived from milk and derivates. Classic galactosemia is caused by variants of the GALT gene, which lead to absent or misfolded forms of the ubiquitously present galactose-1-phosphate uridylyltransferase enzyme (GALT) driving galactose metabolites to accumulate, damaging cells from neurons to hepatocytes. The disease has different prevalence around the world due to different allele frequencies among populations and its symptoms range from cognitive and psychomotor impairment to hepatic, ophthalmological, and bone structural damage. The practice of newborn screening still varies among countries, dairy restriction treatment is a consensus despite advances in preclinical treatment strategies. Recent clinical studies in Duarte variant suggest dairy restriction could be reconsidered in these cases. Despite noteworthy advances in the classic galactosemia understanding, preclinical trials are still crucial to fully understand the pathophysiology of the disease and help propose new treatments. This review aims to report a comprehensive analysis of past studies and state of art research on galactosemia screening, its clinical and preclinical trials, and treatments with the goal of shedding light on this complex and multisystemic innate error of the metabolism.

Classic Galactosemia: Clinical and Computational Characterization of a Novel GALT Missense Variant (p.A303D) and a Literature Review.

Classic galactosemia is an autosomal recessive inherited liver disorder of carbohydrate metabolism caused by deficient activity of galactose-1-phosphate uridylyltransferase (GALT). While a galactose-restricted diet is lifesaving, most patients still develop long-term complications. In this study, we report on a two-week-old female patient who is a compound heterozygote for a known pathogenic variant (p.K285N) and a novel missense variant (p.A303D) in the GALT gene. Segregation analysis showed that the patient inherited the p.K285N pathogenic variant from her father and the p.A303D variant from her mother. A bioinformatics analysis to predict the impact of the p.A303D missense variant on the structure and stability of the GALT protein revealed that it may be pathogenic. Based on this finding, we performed a literature review of all GALT missense variants identified in homozygous and compound heterozygous galactosemia patients carrying the p.K285N pathogenic variant to explore their molecular effects on the clinical phenotype of the disease. Our analysis revealed that these missense variants are responsible for a wide range of molecular defects. This study expands the clinical and mutational spectrum in classic galactosemia and reinforces the importance of understanding the molecular consequences of genetic variants to incorporate genetic analysis into clinical care.

Grip strength in patients with galactosemia and in a galactose-1-phosphate uridylyltransferase (GALT)-null rat model.

Classic galactosemia (CG) and clinical variant galactosemia (CVG) are allelic inborn errors of metabolism that result from profound deficiency, and near-profound deficiency, respectively, of galactose-1-P uridylyltransferase (GALT). Despite early detection and lifelong dietary restriction of galactose, which is the current standard of care, most patients with CG/CVG grow to experience a range of long-term developmental and other complications. One of the less well-understood complications of CG/CVG is decreased hand grip strength, as reported by Potter et al. (2013). Here, we confirm this phenotype in an independent cohort of 36 cases (4-18 years) and 19 controls (4-17 years), and further demonstrate that the grip strength deficit observed in cases may be secondary to growth delay. Specifically, we found that when grip strength of cases and controls in a new cohort recruited in 2022 was plotted by weight, rather than age, the difference between cases and controls for both sexes disappeared. Reanalyzing data from the original 2013 cohort, we found that differences in weight accounted for grip strength differences between cases and controls in girls and young women, but not in boys and young men. Finally, we tested whether a GALT-null rat model of CG also showed a grip strength deficit-it did-and again the difference between GALT-null and wild-type rats associated with differences in body mass. Combined, these results confirm that GALT deficiency is associated with a grip strength deficit in both young patients with CG/CVG and GALT-null rats, and further demonstrate that this phenotype may be secondary to growth delay, and therefore not evidence of a muscle abnormality.

Racial and ethnic diversity of classic and clinical variant galactosemia in the United States.

Classic and clinical variant galactosemia (CG/CVG) are allelic, autosomal recessive disorders that result from deficiency of galactose-1-P uridylyltransferase (GALT). CG/CVG has been reported globally among patients of diverse ancestries, but most large studies of outcomes have included, almost exclusively, patients categorized as White or Caucasian. As a first step to explore whether the cohorts studied are representative of the CG/CVG population at large, we sought to define the racial and ethnic makeup of CG/CVG newborns in a diverse population with essentially universal newborn screening (NBS) for galactosemia: the United States (US). First, we estimated the predicted racial and ethnic distribution of CG/CVG by combining the reported demographics of US newborns from 2016 to 2018 with predicted homozygosity or compound heterozygosity of pathogenic, or likely pathogenic, GALT alleles from the relevant ancestral groups. Incorporating some simplifying assumptions, we predicted that of US newborns diagnosed with CG/CVG, 65% should be White (non-Hispanic), 23% should be Black (non-Hispanic), 10% should be Hispanic, and 2% should be Asian (non-Hispanic). Next, we calculated the observed racial and ethnic distribution of US newborns diagnosed with CG/CVG using available de-identified data from state NBS programs from 2016 to 2018. Of the 235 newborns in this cohort, 41 were categorized as other or unknown. Of the remaining 194, 66% were White (non-Hispanic or ethnicity unknown), 16% were Black (non-Hispanic or ethnicity unknown),15% were Hispanic, and 2% were Asian (non-Hispanic or ethnicity unknown). This observed distribution was statistically indistinguishable from the predicted distribution. To the limits of our study, these data confirm the racial and ethnic diversity of newborns with CG/CVG in the US, demonstrate an approach for estimating CG/CVG racial and ethnic diversity in other populations, and raise the troubling possibility that current understanding of long-term outcomes in CG/CVG may be skewed by ascertainment bias of the cohorts studied.

Demonstrating the utility of sugar-phosphate phosphatases in coupled enzyme assays: galactose-1-phosphate uridylyltransferase as proof-of-concept.

During our biochemical characterization of select bacterial phosphatases belonging to the haloacid dehalogenase superfamily of hydrolases, we discovered a strong bias of Salmonella YidA for glucose-1-phosphate (Glc-1-P) over galactose-1-phosphate (Gal-1-P). We sought to exploit this ability of YidA to discriminate these two sugar-phosphate epimers in a simple coupled assay that could be a substitute for current cumbersome alternatives. To this end, we focused on Gal-1-P uridylyltransferase (GalT) that is defective in individuals with classical galactosemia, an inborn disorder. GalT catalyzes the conversion of Gal-1-P and UDP-glucose to Glc-1-P and UDP-galactose. When recombinant YidA was coupled to GalT, the final orthophosphate product (generated from selective hydrolysis of Glc-1-P by YidA) could be easily measured using the inexpensive malachite green reagent. When this new YidA-based colorimetric assay was benchmarked using a recombinant Duarte GalT variant, it yielded kcat/Km values that are ~2.5-fold higher than the standard coupled assay that employs phosphoglucomutase and glucose-6-phosphate dehydrogenase. Although the simpler design of our new GalT coupled assay might find appeal in diagnostics, a testable expectation, we spotlight the GalT example to showcase the untapped potential of sugar-phosphate phosphatases with distinctive substrate-recognition properties for measuring the activity of various metabolic enzymes (e.g. trehalose-6-phosphate synthase, N-acetyl-glucosamine-6-phosphate deacetylase, phosphofructokinase).

Early postnatal alterations in follicular stress response and survival in a mouse model of Classic Galactosemia.

Primary ovarian insufficiency is characterized by accelerated loss of primordial follicles, which results in ovarian failure and concomitant menopause before age 40. About 1-3% of females in the general population are diagnosed with POI; however, greater than 80% of females with the inherited disease Classic Galactosemia will develop POI. Classic Galactosemia is caused by mutations in the GALT gene encoding the enzyme galactose-1 phosphate uridylyltransferase. While dietary restriction of galactose is lifesaving in the neonatal period, the development of complications including primary ovarian insufficiency is not mitigated. Additionally, the pattern(s) of follicle loss have not been completely characterized. The chronic accumulation of aberrant metabolites such as galactose-1-phosphate and galactitol are suspected culprits in the development of the sequelae, yet the mechanisms remain elusive.Our group uses a GalT gene-trapped mouse model to study the pathophysiology of primary ovarian insufficiency in Classic Galactosemia. We recently showed that differences in the Integrated Stress Response pathway occur in mutant ovaries that likely contribute to their primary ovarian insufficiency phenotype. Using immunofluorescent staining of histological sections of ovaries at progressive ages, we saw evidence of altered Integrated Stress Response activity in granulosa cells and primordial oocytes consistent with accelerated primordial follicle growth activation, aberrant DNA damage and/or repair, and increased cellular stress/death. Overall, our findings indicate that abnormal Integrated Stress Response in the Classic Galactosemia model ovary results in accelerated primordial follicle growth activation, sometimes referred to as "burnout." These aberrant early events help further clarify when/how the primary ovarian insufficiency phenotype arises under galactosemic conditions.

A multinational study of acute and long-term outcomes of Type 1 galactosemia patients who carry the S135L (c.404C > T) variant of GALT.

Patients with galactosemia who carry the S135L (c.404C > T) variant of galactose-1-P uridylyltransferase (GALT), documented to encode low-level residual GALT activity, have been under-represented in most prior studies of outcomes in Type 1 galactosemia. What is known about the acute and long-term outcomes of these patients, therefore, is based on very limited data. Here, we present a study comparing acute and long-term outcomes of 12 patients homozygous for S135L, 25 patients compound heterozygous for S135L, and 105 patients homozygous for two GALT-null (G) alleles. This is the largest cohort of S135L patients characterized to date. Acute disease following milk exposure in the newborn period was common among patients in all 3 comparison groups in our study, as were long-term complications in the domains of speech, cognition, and motor outcomes. In contrast, while at least 80% of both GALT-null and S135L compound heterozygous girls and women showed evidence of an adverse ovarian outcome, prevalence was only 25% among S135L homozygotes. Further, all young women in this study with even one copy of S135L achieved spontaneous menarche; this is true for only about 33% of women with classic galactosemia. Overall, we observed that while most long-term outcomes trended milder among groups of patients with even one copy of S135L, many individual patients, either homozygous or compound heterozygous for S135L, nonetheless experienced long-term outcomes that were not mild. This was true despite detection by newborn screening and both early and life-long dietary restriction of galactose. This information should empower more evidence-based counseling for galactosemia patients with S135L.

Multi-omics in classical galactosemia: Evidence for the involvement of multiple metabolic pathways.

Classical galactosemia (CG) is one of the more frequent inborn errors of metabolism affecting approximately 1:40.000 people. Despite a life-saving galactose-restricted diet, patients develop highly variable long-term complications including intellectual disability and movement disorders. The pathophysiology of these complications is still poorly understood and development of new therapies is hampered by a lack of valid prognostic biomarkers. Multi-omics approaches may discover new biomarkers and improve prediction of patient outcome. In the current study, (semi-)targeted mass-spectrometry based metabolomics and lipidomics were performed in erythrocytes of 40 patients with both classical and variant phenotypes and 39 controls. Lipidomics did not show any significant changes or deficiencies. The metabolomics analysis revealed that CG does not only compromise the Leloir pathway, but also involves other metabolic pathways including glycolysis, the pentose phosphate pathway, and nucleotide metabolism in the erythrocyte. Moreover, the energy status of the cell appears to be compromised, with significantly decreased levels of ATP and ADP. This possibly is the consequence of two different mechanisms: impaired formation of ATP from ADP possibly due to reduced flux though the glycolytic pathway and trapping of phosphate in galactose-1-phosphate (Gal-1P) which accumulates in CG. Our findings are in line with the current notion that the accumulation of Gal-1P plays a key role in the pathophysiology of CG not only by depletion of intracellular phosphate levels but also by decreasing metabolite abundance downstream in the glycolytic pathway and affecting other pathways. New therapeutic options for CG could be directed towards the restoration of intracellular phosphate homeostasis.

Galactosemia: Biochemistry, Molecular Genetics, Newborn Screening, and Treatment.

Galactosemia is an inborn disorder of carbohydrate metabolism characterized by the inability to metabolize galactose, a sugar contained in milk (the main source of nourishment for infants), and convert it into glucose, the sugar used by the body as the primary source of energy. Galactosemia is an autosomal recessive genetic disease that can be diagnosed at birth, even in the absence of symptoms, with newborn screening by assessing the level of galactose and the GALT enzyme activity, as GALT defect constitutes the most frequent cause of galactosemia. Currently, galactosemia cannot be cured, but only treated by means of a diet with a reduced content of galactose and lactose. Although the diet is able to reverse the neonatal clinical picture, it does not prevent the development of long-term complications. This review provides an overview of galactose metabolism, molecular genetics, newborn screening and therapy of galactosemia. Novel treatments for galactosemia currently being investigated in (pre)clinical studies and potentially able to prevent long-term complications are also presented.

Neonatal GALT gene replacement offers metabolic and phenotypic correction through early adulthood in a rat model of classic galactosemia.

Classic galactosemia (CG) results from profound deficiency of galactose-1-P uridylyltransferase (GALT). Despite early detection by newborn screening and lifelong dietary restriction of galactose, most patients grow to experience a range of long-term complications. Recently, we developed and characterized a GALT-null rat model of CG and demonstrated that AAV9-hGALT, administered by tail vein injection to neonatal pups, dramatically improved plasma, liver, and brain galactose metabolites at 2 weeks posttreatment. Here we report a time-course study of GALT restoration in rats treated as neonates with scAAV9-hGALT and harvested at 8, 14, 30, and 60 days. Cohorts of rats in the two older groups were weaned to diets containing either 1% or 3% of calories from galactose. As expected, GALT activity in all treated animals peaked early and then diminished over time, most notably in liver, ostensibly due to dilution of the nonreplicating episomal vector as transduced cells divided. All treated rats showed dramatic metabolic rescue through 1 month, and those weaned to the lower galactose diet showed continued strong metabolic rescue into adulthood (2 months). Prepubertal growth delay and cataracts were both partially rescued by treatment. Finally, we found that UDP glucose pyrophosphorylase (UGP), which offers a metabolic bypass around missing GALT, was 3-fold more active in brain samples from adult rats than from young pups, offering a possible explanation for the improved ability of older GALT-null rats to metabolize galactose. Combined, these results document promising metabolic and phenotypic efficacy of neonatal GALT gene replacement in a rat model of classic galactosemia.

AAV-mediated expression of galactose-1-phosphate uridyltransferase corrects defects of galactose metabolism in classic galactosemia patient fibroblasts.

Classic galactosemia (CG) is a rare disorder of autosomal recessive inheritance. It is caused predominantly by point mutations as well as deletions in the gene encoding the enzyme galactose-1-phosphate uridyltransferase (GALT). The majority of the more than 350 mutations identified in the GALT gene cause a significant reduction in GALT enzyme activity resulting in the toxic buildup of galactose metabolites that in turn is associated with cellular stress and injury. Consequently, developing a therapeutic strategy that reverses both the oxidative and ER stress in CG cells may be helpful in combating this disease. Recombinant adeno-associated virus (AAV)-mediated gene therapy to restore GALT activity offers the potential to address the unmet medical needs of galactosemia patients. Here, utilizing fibroblasts derived from CG patients we demonstrated that AAV-mediated augmentation of GALT protein and activity resulted in the prevention of ER and oxidative stress. We also demonstrate that these CG patient fibroblasts exhibit reduced CD109 and TGFßRII protein levels and that these effectors of cellular homeostasis could be restored following AAV-mediated expression of GALT. Finally, we show initial in vivo proof-of-concept restoration of galactose metabolism in a GALT knockout mouse model following treatment with AAV-GALT.

The Importance of Neonatal Screening for Galactosemia.

Galactosemia is an inborn metabolic disorder caused by a deficient activity in one of the enzymes involved in the metabolism of galactose. The first description of galactosemia in newborns dates from 1908, ever since complex research has been performed on cell and animal models to gain more insights into the molecular and clinical bases of this challenging disease. In galactosemia, the newborn appears to be born in proper health, having a window of opportunity before developing major morbidities that may even be fatal following ingestion of milk that contains galactose. Galactosemia cannot be cured, but its negative consequences on health can be avoided by establishing precocious diagnosis and treatment. All the foods that contain galactose should be eliminated from the diet when there is a suspicion of galactosemia. The neonatal screening for galactosemia can urge early diagnosis and intervention, preventing complications. All galactosemia types may be detected during the screening of newborns for this disorder. The major target is, however, galactose-1-phosphate uridyltransferase (GALT) deficiency galactosemia, which is diagnosed by applying a combination of total galactose and GALT enzyme analysis as well as, in certain programs, mutation screening. Most critically, infants who exhibit symptoms suggestive of galactosemia should undergo in-depth testing for this condition even when the newborn screening shows normal results. The decision to enroll global screening for galactosemia among the specific population still faces many challenges. In this context, the present narrative review provides an updated overview of the incidence, clinical manifestations, diagnosis, therapy, and prognosis of galactosemia, questioning under the dome of these aspects related to the disease the value of its neonatal monitoring.

Analysis of the Structure-Function-Dynamics Relationships of GALT Enzyme and of Its Pathogenic Mutant p.Q188R: A Molecular Dynamics Simulation Study in Different Experimental Conditions.

The third step of the catabolism of galactose in mammals is catalyzed by the enzyme galactose-1-phosphate uridylyltransferase (GALT), a homodimeric enzyme with two active sites located in the proximity of the intersubunit interface. Mutations of this enzyme are associated to the rare inborn error of metabolism known as classic galactosemia; in particular, the most common mutation, associated with the most severe phenotype, is the one that replaces Gln188 in the active site of the enzyme with Arg (p.Gln188Arg). In the past, and more recently, the structural effects of this mutation were deduced on the static structure of the wild-type human enzyme; however, we feel that a dynamic view of the proteins is necessary to deeply understand their behavior and obtain tips for possible therapeutic interventions. Thus, we performed molecular dynamics simulations of both wild-type and p.Gln188Arg GALT proteins in the absence or in the presence of the substrates in different conditions of temperature. Our results suggest the importance of the intersubunit interactions for a correct activity of this enzyme and can be used as a starting point for the search of drugs able to rescue the activity of this enzyme in galactosemic patients.

Simulation of the Interactions of Arginine with Wild-Type GALT Enzyme and the Classic Galactosemia-Related Mutant p.Q188R by a Computational Approach.

Classic galactosemia is an inborn error of metabolism associated with mutations that impair the activity and the stability of galactose-1-phosphate uridylyltransferase (GALT), catalyzing the third step in galactose metabolism. To date, no treatments (including dietary galactose deprivation) are able to prevent or alleviate the long-term complications affecting galactosemic patients. Evidence that arginine is able to improve the activity of the human enzyme expressed in a prokaryotic model of classic galactosemia has induced researchers to suppose that this amino acid could act as a pharmacochaperone, but no effects were detected in four galactosemic patients treated with this amino acid. Given that no molecular characterizations of the possible effects of arginine on GALT have been performed, and given that the samples of patients treated with arginine are extremely limited for drawing definitive conclusions at the clinical level, we performed computational simulations in order to predict the interactions (if any) between this amino acid and the enzyme. Our results do not support the possibility that arginine could function as a pharmacochaperone for GALT, but information obtained by this study could be useful for identifying, in the future, possible pharmacochaperones for this enzyme.

Transient developmental delays in infants with Duarte-2 variant galactosemia.

Duarte galactosemia is not classic galactosemia, but rather an example of biochemical variant galactosemia that results in approximately 25% residual activity of galactose-1-phosphate uridylyltransferase (GALT) enzyme. In contrast, classic galactosemia is associated with complete or near complete absence of GALT activity. While infants with classic galactosemia are placed on galactose-restricted diets to prevent the acute and long-term manifestations of their metabolic disorder, while individuals with Duarte variant galactosemia (Duarte-2 galactosemia) do not require diet therapy. The long-term complications that are seen in classic galactosemia such as cerebellar ataxia, and hypergonadotropic hypogonadism do not occur in Duarte-2 galactosemia. While Duarte galactosemia does not appear to be a metabolic disease, it may have an impact on early neurodevelopmental outcomes. This study examined developmental outcomes and the need for special services in individuals with Duarte-2 galactosemia in comparison to individuals with classic galactosemia. We performed a medical record review of individuals with GALT deficiency who were evaluated at Boston Children's Hospital and enrolled in our study of outcomes in galactosemia. This included 95 participants, 21 with Duarte-2 galactosemia and 73 with classic galactosemia. Duarte-2 participants had developmental test scores within the average range. However, 42% of subjects with Duarte-2 galactosemia had participated in early intervention and/or special education and 32% received speech therapy. Their pattern of strengths and weaknesses in cognitive/language/motor domains was similar to that noted in participants with classic galactosemia, albeit to a milder degree. The data indicate that in children with Duarte-2 variant galactosemia, the cognitive/language and motor skills were within normal limits with their cognitive/language skills developing earlier than their motor skills during their first year of life. A history of diet treatment was not related to the use of special services. These results suggest that Duarte-2 galactosemia increases the risk for early mild developmental delays irrespective of treatment history, which resolves over time, and highlights the need to further assess neurodevelopment in early infancy, in Duarte-2 galactosemia. As Duarte-2 galactosemia is not a bona fide biochemical genetic disease, we hypothesize that elements in the genomic space that include the GALT gene are responsible for a transient delay in language-related motor skills during early infancy.

Galactosaemia occurring in association with primary ovarian insufficiency, Addison's disease and chronic myeloid leukaemia.

Classic galactosaemia is the most severe type, inherited in an autosomal recessive fashion and normally detected on newborn screening. It is caused by an inability to digest galactose due to a deficiency of galactose-1-phosphate uridyltransferase (GALT), resulting in an intolerance of feeds in the neonatal period, failure to thrive, hypoglycaemia, jaundice, cataracts, hepatomegaly, vomiting, diarrhoea, developmental delay and an increased risk of Escherichia coli sepsis. The long-term sequelae of this disorder include cognitive impairment, neurological symptoms, such as ataxia, nutritional deficiencies, such as calcium and vitamin D, and gonadal dysfunction. We report here a case of a 34-year-old woman with classic galactosaemia diagnosed in adulthood, developing primary ovarian insufficiency and osteoporosis as well as primary adrenal insufficiency and chronic myeloid leukaemia, which are two associations not seen in current literature. Further studies are needed to determine if an association exists between these diseases.

The genetic basis of classical galactosaemia in Polish patients.

Classic galactosemia (OMIM #230400) is an autosomal recessive disorder caused by homozygous or compound heterozygous pathogenic variants in the galactose-1-phosphate uridylyltransferase gene (GALT; 606999) on chromosome 9p13. Its diagnosis is established by detecting elevated erythrocyte galactose-1-phosphate concentration, reduced erythrocyte galactose-1-phosphate uridylyltransferase (GALT) enzyme activity. Biallelic pathogenic variants in the GALT gene is confirmed by DNA analysis. Our paper presents molecular characteristics of 195 Polish patients diagnosed with galactosemia I, intending to expand the current knowledge of this rare disease's molecular etiology. To the best of our knowledge, the described cohort of galactosemia patients is the largest single-center cohort presented so far.