Mutations in the Translated Region of the Lactase Gene (LCT) Underlie Congenital Lactase Deficiency

Department of Molecular Medicine, National Public Health Institute, Helsinki, Finland.
The American Journal of Human Genetics (Impact Factor: 10.93). 02/2006; 78(2):339-44. DOI: 10.1086/500053
Source: PubMed


Congenital lactase deficiency (CLD) is a severe gastrointestinal disorder characterized by watery diarrhea in infants fed with breast milk or other lactose-containing formulas. We initially assigned the CLD locus by linkage and linkage disequilibrium on 2q21 in 19 Finnish families. Here we report the molecular background of CLD via characterization of five distinct mutations in the coding region of the lactase (LCT) gene. Twenty-seven patients out of 32 (84%) were homozygous for a nonsense mutation, c.4170T-->A (Y1390X), designated "Fin(major)." Four rare mutations--two that result in a predicted frameshift and early truncation at S1666fsX1722 and S218fsX224 and two point mutations that result in substitutions Q268H and G1363S of the 1,927-aa polypeptide--confirmed the lactase mutations as causative for CLD. These findings facilitate genetic testing in clinical practice and enable genetic counseling for this severe disease. Further, our data demonstrate that, in contrast to common adult-type hypolactasia (lactose intolerance) caused by a variant of the regulatory element, the severe infancy form represents the outcome of mutations affecting the structure of the protein inactivating the enzyme.

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Available from: Erkki Savilahti, Feb 03, 2014
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    • "Lactose malabsorption (hypolactasia) exists in three different forms: congenital, primary, and secondary [3, 7]. The congenital lactase deficiency is an extremely rare autosomal recessive lifelong gastrointestinal disorder, leading to watery diarrhea from the first exposure to breast milk in infants [2, 3, 8]. The primary lactose malabsorption, also known as adult-type hypolactasia or lactase nonpersistence, is the most common phenotype found in humans. "
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    ABSTRACT: The aim of this study was to establish a retrospective evaluation and comparison of the hydrogen/methane (H2/CH4) breath test and genetic test (C/T-13910 polymorphism) results in lactose malabsorption testing. In total 263 consecutive patients with suspected lactose malabsorption were included in this study. They underwent the H2/CH4 breath test following the ingestion of 50 g lactose and were tested for the C/T-13910 polymorphism. In total 51 patients (19.4%) had a C/C-13910 genotype, indicating primary lactose malabsorption. Only 19 patients (7.2%) also had a positive H2/CH4 breath test. All in all 136 patients (51.69%) had a C/T-13910 and 76 patients (28.91%) a T/T-13910 genotype, indicating lactase persistence. Four patients (1.5%) with the C/T-13910 genotype and one patient (0.4%) with the T/T-13910 genotype had a positive H2/CH4 breath test result, indicating secondary lactose malabsorption. Cohen's Kappa measuring agreement between the two methods was 0.44. Twenty patients (7.6%) with a positive H2/CH4 peak within 60 minutes after lactose ingestion were classified as patients with lactose-dependent small intestinal bacterial overgrowth (SIBO). In conclusion, only moderate agreement between the breath test and the genetic test was shown. Secondary lactose malabsorption as well as preanalytical limitations of the combined H2/CH4 breath test procedure can cause discrepant results. This trial is registered with K-42-13.
    Gastroenterology Research and Practice 04/2014; 2014(3):464382. DOI:10.1155/2014/464382 · 1.75 Impact Factor
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    • "All patients were diagnosed at the first weeks of age based on severe watery diarrhoea and loss of weight. Nine of them were homozygous for the major mutation Y1390X further confirming the original results that only one major mutation is enriched in the Finnish population [10]. Two patients were heterozygous for the founder mutation. "
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    ABSTRACT: Congenital lactase deficiency (CLD) is a severe gastrointestinal disorder of newborns. The diagnosis is challenging and based on clinical symptoms and low lactase activity in intestinal biopsy specimens. The disease is enriched in Finland but is also present in other parts of the world. Mutations encoding the lactase (LCT) gene have recently been shown to underlie CLD. The purpose of this study was to identify new mutations underlying CLD in patients with different ethnic origins, and to increase awareness of this disease so that the patients could be sought out and treated correctly. Disaccharidase activities in intestinal biopsy specimens were assayed and the coding region of LCT was sequenced from five patients from Europe with clinical features compatible with CLD. In the analysis and prediction of mutations the following programs: ClustalW, Blosum62, PolyPhen, SIFT and Panther PSEC were used. Four novel mutations in the LCT gene were identified. A single nucleotide substitution leading to an amino acid change S688P in exon 7 and E1612X in exon 12 were present in a patient of Italian origin. Five base deletion V565fsX567 leading to a stop codon in exon 6 was found in one and a substitution R1587H in exon 12 from another Finnish patient. Both Finnish patients were heterozygous for the Finnish founder mutation Y1390X. The previously reported mutation G1363S was found in a homozygous state in two siblings of Turkish origin. This is the first report of CLD mutations in patients living outside Finland. It seems that disease is more common than previously thought. All mutations in the LCT gene lead to a similar phenotype despite the location and/or type of mutation.
    BMC Gastroenterology 02/2009; 9(1):8. DOI:10.1186/1471-230X-9-8 · 2.37 Impact Factor
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    ABSTRACT: Adult-type hypolactasia (primary lactose malabsorption, lactase non-persistence) is the most common enzyme deficiency worldwide, and manifests with symptoms of lactose intolerance such as abdominal pain, gas formation and diarrhea. In humans with adult-type hypolactasia, lactase activity is high at birth, but declines during childhood to about one-tenth of the activity at birth. In 2002, a one base polymorphism C/T-13910, located 14 kilobases from the starting codon of the lactase-phlorizin hydrolase (LPH) gene was observed to be associated with the persistence of lactase activity. The T-13910 allele (C/T-13910 and T/T-13910 genotypes) associates with persistence of lactase activity throughout life, whereas the C/C-13910 genotype associates with adult-type hypolactasia. In this thesis work, the timing and mechanism of decline of lactase enzyme activity during development was studied using the C/T-13910 polymorphism as a molecular marker. We observed an excellent correlation between low lactase activity and the C/C-13910 genotype in all subjects > 12 years of age, irrespective their ethnicity. In children of African origin, the lactase activity declined somewhat earlier than among Finnish children. Furthermore, we observed an increasing imbalance in the relative lactase mRNA expression from the C-13910 and T-13910 alleles in Finnish children beginning from five years of age. The genetic test for adult-type hypolactasia showed a sensitivity of 93% and a specificity of 100% in the Finnish children and adolescents > 12 years of age. The relation of milk consumption and the milk-related abdominal complaints to the C/T-13910 genotypes associated with lactase persistence/non-persistence was studied by a questionnaire-based approach in > 2100 Finns. Both Finnish children and adults with the C/C-13910 genotype consumed significantly less dairy products compared to those with the C/T-13910 and T/T-13910 genotypes. Flatulence was the only of the abdominal symptoms of lactose intolerance that subjects with the C/C-13910 genotype reported significantly more often than those with the C/T-13910 and T/T-13910 genotypes. A minor proportion (<10%) of subjects with the C/C-13910 genotype, nevertheless, reported drinking milk without any symptoms afterwards. There was no association between cow's milk allergy starting as a newborn and adult-type hypolactasia. In an association study an increased risk of colorectal cancer was observed among those with molecular diagnosis of adult-type hypolactasia. It warrants further studies to clarify whether the increased risk observed in the Finnish population is associated with lactose or decreased intake of dairy products in these subjects. Laktoosin imeytymishäiriö: perimästä ilmiasuun Laktoosin eli maitosokerin imeytymishäiriö on kaikille nisäkkäille tyypillinen ilmiö, joka johtuu laktoosia imeytyvään muotoon hajottavan laktaasi-entsyymin aktiivisuuden alenemisesta imeväisen suolen limakalvolla emon maidon tullessa tarpeettomaksi ravinnonlähteenä. Ihmiselle on vuosituhansia sitten tapahtunut mutaatio, jonka seurauksena osalla maapallon väestöstä laktaasin aktiivisuus säilyy suolessa läpi elämän. Tutkimusryhmämme tunnisti laktoosin imeytymishäiriöön liittyvän geenimuutoksen, yhden emäksen polymorfian C>T-13910 vuonna 2002. C/C-13910 perintötekijätyyppi (genotyyppi) liittyy laktoosin imeytymishäiriöön, kun taas C/T-13910 tai T/T-13910 -genotyyppisillä laktaasi-aktiivisuus säilyy korkeana läpi elämän. Suomalaisista 18%:lla on laktoosin imeytymishäiriö. Väitöskirjatyössäni tutkin normaaliin kehitykseen kuuluvan laktaasi-entsyymin aktiivisuuden laskun yhteyttä äskettäin tunnistettuun C/T-13910 emäsmuutokseen sekä muutoksen mekanismia. Töissämme totesimme C/C-13910 -genotyypin assosioituvan suolen matalaan laktaasi-aktiivisuuteen kaikilla yli 12-vuotiailla lapsilla etnisyydestä riippumatta. Suomalaislapsilla laktaasin aktiivisuus aleni 5-12 vuoden iässä ja afrikkalaista syntyperää olevilla ennen 8 vuoden ikää. Laktoosin imeytymishäiriön geenitestin sensitiivisyys yli 12-vuotiailla oli 93% ja spesifisyys 100%. Totesimme myös laktaasi-geenin lähetti-RNA:n tuoton C-13910 -alleelista vähenevän viidesosaan 4-6 vuoden iässä T-13910 alleeliin verrattuna, osoittaen näin geenimuutoksen osallistuvan laktaasi-aktiivisuuden alenemiseen transkription tasolla. Tutkimuksessa selvitimme myös maitotuotteiden käytön ja niiden aiheuttamien oireiden yhteyttä laktoosin imeytymishäiriön perintötekijätyyppeihin yli 2100 suomalaislapsen ja aikuisen aineistossa. Lapset ja aikuiset, joilla on C/C-13910 -genotyyppi, käyttivät merkitsevästi vähemmän maitotuotteita C/T-13910 ja T/T-13910 genotyyppisiin verrattuna. Klassisista laktoosi-intoleranssin oireista vain ilmavaivat olivat merkitsevästi yleisempiä C/C-13910 genotyyppisillä. Varhaislapsuudessa ilmenevän maitoallergian ja laktoosin imeytymishäiriön genotyypin välillä emme todenneet yhteyttä. Lisäksi tutkimuksessa selvitimme laktaasi-aktiivisuuden yhteyttä pakusuolensyövän syntyyn. Totesimme matalan laktaasi-aktiivisuuden määrittävän C/C-13910 genotyypin liittyvän suomalaisilla merkitsevästi kohonneeseen paksusuolensyövän riskiin, joskaan emme pystyneet erottelemaan, johtuiko havaintomme itse laktoosin imeytymishäiriöstä vai maitotuotteiden käytöstä. Laktosmalabsorption: från genotyp till fenotyp Malabsorption av mjölksocker, dvs. laktos, (vuxen-typs hypolaktasi) är karakteristiskt för alla däggdjur, och beror på att endast ungar som ammas uttrycker hög mängd av laktasenzym i tarmen för att kunna bryta ner laktos så att den kan absorberas. Enzymaktiviteten vid vuxen-typs hypolaktasi avtar successivt under uppväxten till ungefär 10-15% av aktiviteten vid födseln. Hos människan har det för årtusenden sedan skett en mutation som medförde att vissa individer uppvisar höga nivåer av laktas i tarmen även som vuxna. Vår forskningsgrupp upptäckte år 2002 denna mutation som är ett enbasparsutbyte C>T-13910 och är belägen 14 kb uppströms från genen som kodar för själva laktas-enzymet. Mutationen nedärvs recessivt, dvs individer med genotypen C/C-13910 har låg laktasaktivitet i tarmen medan individer med genotyperna C/T-13910 och T/T-13910 uttrycker hög mängd laktas även som vuxna. Av finländare har 18% laktosmalabsorption. I min doktorsavhandling studerade jag minskningen av laktasaktiviteten i tarmen m.h.a. den nyligen identifierade polymorfismen C>T-13910, och mekanismen hos denna nedgång. I delarbeten upptäckte vi att genotypen C/C-13910 är associerad med låg aktivitet av laktasenzymet i tarmen hos alla barn över 12 år, oberoende av deras etniska bakgrund. Hos finska barn skedde sänkningen vid 5-12 års ålder, och hos barn med afrikansk bakgrund före 8 års ålder. Sensitiviteten av gentestet för laktosmalabsorption var 93% och specificiteten 100% hos barn över 12 år. Vi konstaterade även att laktas budbärar-RNA:t som producerats av allelen C-13910 minskade till en femtedel vid 4-6 års ålder jämfört med det som producerats av T-13910 allelen, och bevisade med det här experimentet att polymorfismen associerar sig med regleringen av laktasaktiviteten på transkriptionsnivån. I den här studien undersökte vi även konsumtionen av mjölkprodukter och symptomen de orsakar i ett underlag på > 2100 finska barn och vuxna med hänsyn till deras C/T-13910 genotyper. Både barn och vuxna med genotypen C/C-13910 drack signifikant mindre mjölk jämfört med de med genotyperna C/T-13910 och T/T-13910. Av de klassiska symptomen förknippade med laktosintolerans rapporterades endast luftbesvären signifikant oftare av de med laktosmalabsorption. Någon association mellan mjölkallergi i barnåldern och laktosmalabsorption upptäckte vi inte. Våra forskningsresultat tyder även på en association mellan låg laktasaktivitet och tjocktarmscancer i den finska populationen. Eftersom vi inte hade möjlighet att studera mjölkkonsumtionen av deltagarna, har vi pågående studier som syftar till att reda ut den intagna laktosmängdens betydelse för uppkomsten av tjocktarmscancer.
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