Galactokinase deficiency as a cause of cataracts

Galactokinase deficiency: a treatable cause of bilateral cataracts

Congenital cataract can be caused by several systemic diseases and differential diagnosis should be done between infections, genetic or metabolic diseases. We present a case of a 12-month-old girl with bilateral nuclear cataracts that was referred for investigation. Since she did not present a family history of congenital cataracts or metabolic diseases, and her physical examination was normal, a systemic evaluation was performed. Biochemical studies disclosed abnormal galactose metabolism signs. The diagnosis of galactokinase (GALK1) deficiency was considered and the study of the GALK1 gene allowed identifying a pathogenic genetic variant and a predictably pathogenic missense mutation, previously not described. Dietary measures were imposed with a good evolution.

Is Dietary Milk Intake Associated with Cataract Extraction History in Older Adults? An Analysis from the US Population

BACKGROUND

Galactose accumulation in the lens tissue is known to be cataractogenic. Whether consistent dietary intake of lactose-which consists of glucose and galactose-predisposes to senile cataract remains unclear. This study was conducted to investigate the association between a number of dietary milk intake indicators and cataract extraction history in a representative sample of older adults from the US population. Methods and Materials. This is a cross-sectional, population-based study. Participants of the United States National Health and Nutrition Examination Survey 2001-2008 who were ≥50 years old and provided a complete history of their usual daily dietary intake were included. Exclusion criteria were special diets, extreme daily energy intake, and missing outcome (i.e., cataract extraction history). Indicators of milk intake used were early-life intake regularity, current daily milk/total dairy intake amounts, and estimated lifelong milk exposure. Odds ratios (OR) and 99% confidence intervals (99% CI) were calculated with fitting weights to better represent the population-based estimates.

RESULTS

Among the 5930 studied participants, early-life milk intake regularity was not associated with cataract extraction history in age/sex/ethnicity-adjusted and multivariable-adjusted models (p trend = 0.064 and 0.094, respectively). Current daily milk intake was associated with a slight reduction in the likelihood of cataract extraction in the age/sex/ethnicity-adjusted model (OR = 0.885 per cup equivalents, 99% CI = 0.795-0.986) and in the multivariable model (OR = 0.871 per cup equivalents, 99% CI = 0.746-0.993). However, no such association was observed between quartiles of current dietary milk intake and cataract extraction history (p trend = 0.064 and 0.094, respectively). Current daily milk intake was associated with a slight reduction in the likelihood of cataract extraction in the age/sex/ethnicity-adjusted model (OR = 0.885 per cup equivalents, 99% CI = 0.795-0.986) and in the multivariable model (OR = 0.871 per cup equivalents, 99% CI = 0.746-0.993). However, no such association was observed between quartiles of current dietary milk intake and cataract extraction history (p trend = 0.064 and 0.094, respectively). Current daily milk intake was associated with a slight reduction in the likelihood of cataract extraction in the age/sex/ethnicity-adjusted model (OR = 0.885 per cup equivalents, 99% CI = 0.795-0.986) and in the multivariable model (OR = 0.871 per cup equivalents, 99% CI = 0.746-0.993). However, no such association was observed between quartiles of current dietary milk intake and cataract extraction history (.

CONCLUSION

There appears to be no direct relationship between several indicators of dietary milk consumption and cataract extraction history in the general American population.

Ketotifen suppression of NF1 neurofibroma growth over 30 years

A patient with NF1 was treated with oral ketotifen for 30 years since infancy. Review of the patient's course and treatment details establishes a basis for reconsideration of several fundamental precepts about NF1 pathogenesis. The data suggest a distinctive benefit to treating an NF1 patient with an inhibitor of mast cell degranulation before cutaneous neurofibromas are clinically apparent: the neurofibromas appear to be arrested at a very early stage of development. The patient's skin was especially remarkable for both the paucity of cutaneous neurofibromas and the distinctive monotonous uniformity of those present, which were small and flat or barely sessile. While the data do not, of themselves, prove that ketotifen treatment commencing in childhood preempts neurofibroma maturation, in the context of earlier publications, they certainly warrant further investigation.

Pediatric cataract: challenges and future directions

Cataract is a significant cause of visual disability in the pediatric population worldwide and can significantly impact the neurobiological development of a child. Early diagnosis and prompt surgical intervention is critical to prevent irreversible amblyopia. Thorough ocular evaluation, including the onset, duration, and morphology of a cataract, is essential to determine the timing for surgical intervention. Detailed assessment of the general health of the child, preferably in conjunction with a pediatrician, is helpful to rule out any associated systemic condition. Although pediatric cataracts have a diverse etiology, with the majority being idiopathic, genetic counseling and molecular testing should be undertaken with the help of a genetic counselor and/or geneticist in cases of hereditary cataracts. Advancement in surgical techniques and methods of optical rehabilitation has substantially improved the functional and anatomic outcomes of pediatric cataract surgeries in recent years. However, the phenomenon of refractive growth and the process of emmetropization have continued to puzzle pediatric ophthalmologists and highlight the need for future prospective studies. Posterior capsule opacification and secondary glaucoma are still the major postoperative complications necessitating long-term surveillance in children undergoing cataract surgery early in life. Successful management of pediatric cataracts depends on individualized care and experienced teamwork. We reviewed the etiology, preoperative evaluation including biometry, choice of intraocular lens, surgical techniques, and recent developments in the field of childhood cataract.

GALK inhibitors for classic galactosemia

Classic galactosemia is an inherited metabolic disease for which, at present, no therapy is available apart from galactose-restricted diet. However, the efficacy of the diet is questionable, since it is not able to prevent the insurgence of chronic complications later in life. In addition, it is possible that dietary restriction itself could induce negative side effects. Therefore, there is a need for an alternative therapeutic approach that can avert the manifestation of chronic complications in the patients. In this review, the authors describe the development of a novel class of pharmaceutical agents that target the production of a toxic metabolite, galactose-1-phosphate, considered as the main culprit for the cause of the complications, in the patients.

Early cataract formation due to galactokinase deficiency: impact of newborn screening

BACKGROUND AND AIMS

Galactokinase (GALK) deficiency is an autosomal recessive disorder causing cataract formation that can be prevented or mitigated by early diagnosis and galactose-restricted diet. The aim of this retrospective study was to explore whether GALK-deficiency meets the criteria for neonatal mass screening programs.

METHODS

From 2000 until 2010, the Screening Laboratory Hannover performed newborn screening in 1,950,927 infants from Germany for galactosemia by measuring galactose-1-phosphate-uridyl-transferase and total galactose concentration (free galactose plus galactose-1-phosphate), including automatic screening for GALK deficiency.

RESULTS

Eleven cases were found with elevated galactose levels accompanied by normal transferase activity. Nine of 11 cases were informative; the diagnosis was established by demonstrating deficient activity of the GALK enzyme in erythrocytes. To our knowledge, screening did not produce any false negative results. All patients were treated with a galactose-restricted diet from the neonatal period or infancy. Three of nine patients suffered from congenital cataracts or eventual development of cataracts, despite normal galactose concentrations in blood.

CONCLUSIONS

Newborn screening for GALK deficiency prevents or at least mitigates cataract formation. As screening for GALK deficiency is technically simple, it seems to be reasonable to include this disorder in routine screening programs by simultaneous determination of transferase activity and quantification of galactose plus galactose-1-phosphate in dried blood spots.

Galactose toxicity in animals

In most organisms, productive utilization of galactose requires the highly conserved Leloir pathway of galactose metabolism. Yet, if this metabolic pathway is perturbed due to congenital deficiencies of the three associated enzymes, or an overwhelming presence of galactose, this monosaccharide which is abundantly present in milk and many non-dairy foodstuffs, will become highly toxic to humans and animals. Despite more than four decades of intense research, little is known about the molecular mechanisms of galactose toxicity in human patients and animal models. In this contemporary review, we take a unique approach to present an overview of galactose toxicity resulting from the three known congenital disorders of galactose metabolism and from experimental hypergalactosemia. Additionally, we update the reader about research progress on animal models, as well as advances in clinical management and therapies of these disorders.

Diabetic and galactosaemic cataracts

An increased prevalence of cataract is associated with diabetes. Biochemical studies of diabetic lenses have revealed a variety of metabolic abnormalities including changes in the levels of electrolytes, glutathione, nucleotides and sugars. Similar biochemical changes have also been observed in cataracts associated with galactosaemia, suggesting that these sugar cataracts have a common biochemical aetiology. The common biochemical factor found to initiate both types of sugar cataract is the formation of sugar alcohols (polyols) from either glucose or galactose by the enzyme aldose reductase (alditol: NADP+ 1-oxidoreductase, EC 1.1.1.21). Increased intracellular levels of these polar alcohols have a hyperosmotic effect which leads to lens fibre swelling, vacuole formation and subsequent opacification. The process of sugar cataract formation in animals can be prevented by inhibiting aldose reductase.

Clinical features of galactokinase deficiency: a review of the literature

Galactokinase deficiency (McKusick 230200) is a rare autosomal recessive inborn error of galactose metabolism. Cataract and, rarely, pseudotumor cerebri caused by galactitol accumulation seem to be the only consistently reported abnormalities in this disorder. We performed a literature search to obtain information on the clinical spectrum of galactokinase deficiency. A total of 25 publications were traced describing 55 galactokinase-deficient patients. Cataract was reported in most patients. Clinical abnormalities other than cataract were reported in 15 (35%) out of 43 cases on which information was available. However, all symptoms were reported infrequently and a causal relationship with the galactokinase deficiency is unlikely. As cataract and pseudotumor cerebri appear to be the sole complications of galactokinase deficiency, the outcome for patients with galactokinase deficiency is much better than for patients with classical galactosaemia (McKusick 230400), a more common autosomal recessive disorder of galactose metabolism caused by galactose-1-phosphate uridyltransferase (GALT; EC 2.7.7.12) deficiency. Long-term follow-up of patients with this disorder has shown that, in spite of a severely galactose-restricted diet, most patients develop abnormalities such as a disturbed mental and/or motor development, dyspraxia and hypergonadotropic hypogonadism. Endogenous production of galactose has been considered an important aetiological factor. Although damage may well occur in utero, available evidence suggests that damage will continue after birth. Inhibition of galactokinase may then be a promising approach for controlling damage in GALT-deficient patients.

Inherited metabolic diseases affecting the carrier

The objective of this review is to draw attention to those inherited metabolic traits which are potentially harmful also for the carrier, and to outline preventive measures, at least for obligate heterozygotes, i.e. parents of homozygous children. Concerning carriers of food-dependent abnormalities, early vascular disease in homocystinuria, hyperammonaemic episodes in ornithine transcarbamylase deficiency, presenile cataracts in galactosaemia as well as galactokinase deficiency, spastic paraparesis in X-linked adrenoleukodystrophy, and HELLP syndrome in mothers of babies with long-chain 3-hydroxyacyl-coenzyme A dehydrogenase deficiency have to be mentioned. In the group of food-independent disorders, clinical features in carriers may be paraesthesias and corneal dystrophy in Fabry disease, lens clouding in Lowe syndrome, lung and/or liver diseases in alpha 1-antitrypsin deficiency, and renal stones in cystinuria type II and III. Finally, two monogenic carrier states are known which in pregnant individuals could possibly afflict the developing fetus, i.e. heterozygosity for galactosaemia and for phenylketonuria. Elevated levels of galactose-1-phosphate have been found in red blood cells of infants heterozygous for galactosaemia born to heterozygous mothers. Aspartame in very high doses is reported to increase blood phenylalanine levels in heterozygotes for phenylketonuria, thus being a risk for the fetus of a heterozygous mother. For some of these carrier states preventive measures can be recommended, e.g. restriction of lactose in parents and heterozygous grandparents of children with galactosaemia and galactokinase deficiency as well as transiently in infants heterozygous for galactosaemia, dietary supplementation with monounsaturated fatty acids in symptomatic carriers for X-linked adrenoleukodystrophy, avoidance of smoking and alcohol in heterozygotes for alpha 1-antitrypsin deficiency, avoidance of episodes of dehydration in heterozygotes for cystinuria, and restriction of aspartame in pregnant women.

A progressive early onset cataract gene maps to human chromosome 17q24

Cerulean cataract is an autosomal dominant, early onset, progressive cataract characterized by blue or white opacifications in the nucleus and cortex of the lens. A large four-generation pedigree in which cerulean cataract segregates was studied for linkage analysis. A genome wide search was undertaken after the plausible candidate genes were excluded and the cerulean cataract phenotype was mapped to chromosome 17q24. The three markers closest to the disease gene are D17S802 (Z)(theta) = 9.46 at (theta) = 0.085), D17S836 (Z(theta) = 5.26 at (theta) = 0.031) and AFMa238yb5 (Z(theta) = 7.11 at (theta) = 0.032). Multipoint linkage analyses yielded a maximum lod score of Z(theta) = 13.71, placing the cerulean cataract gene between D17S802 and D17S836 at (theta) = 0.048 and (theta) = 0.013, respectively.

Galactosemia: screening and diagnosis

Galactose is normally metabolized to glucose through the coordinated activities of three enzymes: galactokinase, galactose-1-phosphate uridyl transferase (GALT), and uridine diphospho-glucose 4-epimerase (epimerase). High concentrations of galactose and their metabolites are toxic to mammals. Hereditary deficiencies of galactokinase and of GALT and perhaps rarely of epimerase cause clinical disorders that can be prevented by early recognition and institution of a galactose-free diet. The genetics of disorders of galactose metabolisms and the methods used currently for their detection are reviewed. Future prospects in the diagnosis of these disorders are discussed.

Galactose metabolism and reproductive history in women with type 1 neurofibromatosis

To explore a possible relationship between neurofibromatosis and abnormalities of galactose metabolism, we examined the activity and characteristics of red cell galactokinase and galactose-1-phosphate uridyl transferase in 14 white women with type 1 neurofibromatosis and in 28 control women. Women with NF1 had a significantly lower activity of galactokinase and were more likely to have the 3-band pattern on electrophoresis of their transferase enzyme known as the Duarte variant. In addition, we found that women with NF1 were more likely to have reproductive histories suggestive of hypogonadism, including irregular menses, infertility, ovarian cysts, and early menopause. We conclude that abnormalities of galactose metabolism may be linked to abnormalities of both germ cell and neural crest development.

Lactose and cataract in humans: a review

In this review, the relationship between lactose and human cataract is examined from the presently available biochemical, metabolic, and epidemiological data. The exceptional cases of homozygous enzyme deficiency being excluded, fragmentary data give reason to believe that a risk of cataract secondary to lactose and galactose ingestion is present in certain subpopulations. In these population groups, the size of which is unknown, the lens could be exposed to intermittent episodes of hypergalactosemia due to the presence of a partial enzyme deficiency in the galactose metabolic pathway, and/or the persistence of a high adult jejunal lactase activity, and/or to a large and repeated consumption of either whole lactose or easily absorbed lactose (hydrolyzed forms and nonpasteurized yogurt).

Cataract and metabolic disease

In addition to the already recognized metabolic diseases which have been associated with cataract formation, e.g. galactosaemia, galactokinase deficiency, Lowe's syndrome and diabetes, several other disorders can also lead to the development of cataracts. They are sorbitol dehydrogenase deficiency, uridine diphosphate galactose-4-epimerase deficiency, marginal maternal transferase and galactokinase deficiency, galactitol and sorbitol accumulation of unknown origin, heterozygosity for galactosaemia and galactokinase deficiency as well as the carrier state for Lowe's syndrome. In this review these metabolic disorders have been divided into five groups according to the age at the first appearance of lens clouding and the possible means of treatment have been discussed.

Galactose and cataract

Galactosemia is a disorder caused by a deficiency of any one of three possible enzymes involved in the metabolism of galactose: galactokinase, transferase or epimerase. Any single deficient enzyme can result in cataract through the accumulation of galactitol in the lens. The ophthalmologist may play an important role in this disease, since early recognition of cataract development followed by the initiation of a galactose-free diet may lead to clearing of lenticular opacities. The clinical and laboratory findings that distinguish the three enzyme deficiency disorders of galactosemia are discussed. The biochemical genetics of each enzyme also are reviewed, along with the recent evidence linking heterozygous galactokinase deficiency and presenile cataract.

Selected eye defects of special importance in pediatrics

This article reviews six defects of special importance in the care of children: aniridia, ectopia lentis, cataracts, glaucoma, colobomata, and optic nerve hypoplasia. In addition to causing potentially serious impairment of vision, these ocular disorders may be associated with significant systemic disease and genetic abnormalities.

Galactokinase activity in patients with idiopathic cataracts

Ninety-four consecutive patients admitted for elective cataract surgery were prospectively examined for erythrocyte galactokinase activity. The presumed etiology for the cataract was established by history and physical examination in 51 patients (21 were diabetic). The cataract was classified as idiopathic in 43 patients. Galactokinase activity was significantly lower in idiopathic vs. presumed (nondiabetic) etiology patients 50 years of age or younger (P less than 0.05) and in idiopathic cataract patients 50 years of age or younger vs. those older than 51 years of age (P = 0.0033). Three of the idiopathic cataract patients (6.9%) had galactokinase levels less than two standard deviations below the mean galactokinase level for age-matched patients with suspected (nondiabetic) etiology. Compared with the expected distribution for the heterozygote in the general population (0.2%), this was highly significant (P = 0.0001). Diminished galactokinase activity may increase the risk of developing presenile cataracts requiring surgery by the fourth decade.

Perinatal galactose metabolism

Galactose is a major nutrient in normal newborn infants and serves as a substrate for energy production and fuel storage and a regulator of carbohydrate assimilation. Inborn errors of galactose metabolism have contributed to our understanding of the potential toxicity of this carbohydrate. In addition to the classic acute manifestations of neonatal galactosemia, long-term follow-up of surviving patients have revealed unusual neurodevelopmental and reproductive problems. Many investigators have suggested that the newborn infant can utilize galactose better than adults and that neonatal galactose assimilation exceeds that of glucose. Galactose may be an excellent substitute for glucose among hyperinsulinemic infants of diabetic mothers or premature infants with glucose intolerance. However, until further investigations are performed to define the role of galactose in newborn nutrition and to determine its potential toxicity, galactose should not be used as the primary carbohydrate in sick newborn infants.

Juvenile cataract in Hutterites

Isolated juvenile or congenital cataract is a rare disorder. It occurs commonly as part of a more generalized or systemic condition or as a component of a syndrome. When encountered per se it may be genetically determined. The inheritance then often is autosomal dominant; autosomal recessive transmission of isolated juvenile cataract is rare. Here we present, four sibships from an extensive kindred including nine individuals affected with juvenile (or congenital) cataracts. The kindred belongs to the Lehrerleut Hutterite group from the provinces of Saskatchewan and Alberta in Canada and the state of Montana in the United States. Apart from the cataracts, all the patients were healthy and of normal growth and development. Specifically, no metabolic disorder could be identified. Intellect, hearing and behavior were all normal and the patients were neurologically intact. Furthermore, there were no other ocular lesions aside from the cataracts. In this kindred cataracts appear to be a recessive trait.

Galactosemic enzyme levels in presenile cataracts

Galactose-1-phosphate uridyl transferase and galactokinase activities have been measured in the red blood cells of a group of patients with "idiopathic" presenile cataract and of a group of nondiabetic patients with senile cataract. The activity of both galactosemic enzymes was found to be within the normal range in all the patients with presenile cataract. In the group of patients with senile cataract, galactokinase activity was normal in all 24 subjects examined, and galactose-1-phosphate uridyl transferase activity was moderately reduced in 3 of 14.

A geographic approach to senile cataracts: possible links with milk consumption, lactase activity, and galactose metabolism

Examined in this article is presently available evidence for the hypothesis that some types of senile cataracts may be brought on by decades-long consumption of milk and milk products. The author approaches the question from a background of research in the geography and history of dairying as these relate to present-day differences among the world's peoples in prevalence of primary adult lactose malabsorption, which is based on a deficiency of the enzyme lactase in adulthood. Among peoples who have consumed milk in lactose-rich forms over a long historical period, there seems to have been a mutation for persistence of high lactase activity throughout life (PHLA), which distinguishes them from human populations of nonmilking tradition and from most land mammals. PHLA permits greater intestinal hydrolysis of lactose and absorption of galactose by adults. The mutation for PHLA, however, was not accompanied by a second one raising galactokinase activity to high levels through life. The result may be that adults who consume large quantities of milk, who have high lactase activity, lactose hydrolysis, and galactose absorption, suffer repeated small galactose challenges, accumulation of galactitol in the lens, and a greater likelihood of developing senile cataracts.

The syndrome of functional dysautonomia

A perspective on disease is proposed which treats the brain and psyche as part of the soma. The brain, operating as a computer, coordinates energy metabolism in all organs, modulating the organisms's response to stress which results in a complex mixture of sympathetic, parasympathetic and endocrine drive governing behavior and host resistance. It is postulated that automatic activity in health maintains a balanced state of autonomic neurotransmission with behavioral responses varying according to the physiologic state of either sympathetic or parasympathetic dominance. The sympathetic system, irrespective of neurotransmitters involved, is defined as an action system which uses energy and the parasympathetic system is the opposing or balancing force. Genetic influences may create a greater state of sensitivity with one or other of these systems, thus governing behavior characteristics. The degree of dominance may be responsible for the unbalanced response to stress which will in turn have a major influence on the causation of organic disease. The state of reactivity within this system is influenced by the efficiency of the oxidative process which is in turn closely related to the quantity and quality of nutrition.

Association of presenile cataracts with heterozygosity for galactosaemic states and with riboflavin deficiency

Red cells and the lens of the eye are non-nucleated cells; moreover, they have metabolic similarities. Cataracts develop in childhood in homozygotes for galactosaemic abnormalities, which can be detected by biochemical measurements in red blood-cells. It has not been determined whether heterozygotes for these defects are at greater risk for cataract development later in life. Similarly, riboflavin deficiecy for which the erythrocyte is a sensitive indicator, has been associated with cataracts in animals. Red-cell studies were carried out in 22 patients, aged under 50, with cataracts. Heterozygosity for galactokinase deficiency was detected in 5 patients, for galactose-uridyl transferase in 2, and evidence of an erythrocytic deficiency of riboflavin in 8. Even when Black subjects were excluded from analysis because of their high incidence of polymorphism for galactokinase, these findings are significantly different from those expected from population surveys and suggest that many patients with presenile cataracts have a biochemical abnormality which can be detected by examination of red blood-cells and which may be corrected by dietary restrictions or supplements.

Cataracts as an epidemiologic problem

Cataracts are an enormous medical, financial, and social burden. At least 300,000 to 400,000 new, visually disabling cataracts occur yearly in the United States, and 5 to 10 million worldwide. Complications of modern surgical techniques alone probably result in at least 7,000 irreversibly blind eyes annulally in the United States, and a potential 100,000 to 200,000 worldwide. These figures must be refined through well-standardized prevalence surveys and careful monitoring of indications and results of surgery. Senile cataracts probably result from many, possibly compound, obscure causes. Race, altitude, dietary habits, and deranged carbohydrate metabolism are some that have been suggested. There is little basis for the common belief that senile cataracts are more prevalent, or mature more rapidly, in diabetics. Carefully conducted case control and long-term studies are needed to assess the importance of each of these factors and to identify additional ones. The rapid increase of intraocular lens implantation raises serious questions of safety and efficacy. Implantation increases the risk of corneal and macular edema, iritis, and reoperation for lens dislocation and membrane formation, while complicating the treatment of retinal detachments and retinovascular disease. They require controlled clinical evaluation.