Un caso de hipofosfatasia perinatal grave con una mutación novedosa / Severe perinatal hypophosphatasia case with a novel mutation

La hipofosfatasia es un trastorno hereditario raro causado por mutaciones en el gen ALPL. Causa defectos en la mineralización ósea y dental, función respiratoria anormal, convulsiones, hipotonía, dolor óseo y nefrocalcinosis. Las formas clínicas se reconocen según la edad al diagnóstico y la gravedad. Presentamos el caso de una lactante con fontanela anterior agrandada, bóveda craneal blanda, fracturas, dificultad respiratoria y convulsiones. El análisis bioquímico mostró hipercalcemia, fosfato sérico normal y fosfatasa alcalina sérica baja. La radiografía mostró hipomineralización, fracturas y callos. La concentración plasmática de piridoxal-5'-fosfato era de 762 mg/l (intervalo normal: 5-50) y la concentración de fosfoetanolamina en orina era de 1015 mmol/l (intervalo normal: 15-341). El análisis del gen ALPL mostró dos mutaciones heterocigotas compuestas, una de las cuales es novedosa. El diagnóstico y tratamiento tempranos de la hipofosfatasia perinatal podría mejorar los resultados y tener un impacto positivo en la sobrevida.

Hypophosphatasia (HPP) is a rare inherited disorder caused by mutations in the ALPL gene. Mineralization defect in bones and teeth, abnormal respiratory function, seizures, hypotonia, bone pain, and nephrocalcinosis can be observed. Clinical forms are usually recognized based on age at diagnosis and severity of features. We present an infant with an enlarged anterior fontanelle, soft calvarium, fractures, respiratory distress, and seizures. Biochemical analysis showed hypercalcemia, normal serum phosphate, and low serum alkaline phosphatase (ALP) levels. X-ray showed hypomineralization, fractures, and callus formations. Plasma pyridoxal 5'-phosphate (PLP) was 762 mg/L (NV : 5-50) and urine phosphoethanolamine (PEA) was 1015 mmol/L (NV : 15-341) and ALPL gene analysis showed two compound heterozygous mutations, one of which is a novel one. Early diagnosis and treatment of perinatal HPP may improve outcomes and might have a positive impact on survival.

Study on genetic etiology of two cases with hypophosphatasia(HPP) using whole-exome sequencing / 中华内分泌代谢杂志

Objective:Clinical and genetic analysis were conducted in 2 patients with hypophosphatasia(HPP) and their families to explore the pathogenic mechanism of HPP.Methods:The genomic DNA was extracted from peripheral blood of two patients with HPP and their family members. Sanger sequencing and pedigree verification were performed on the pathogenic variants identified using whole-exome sequencing. Then the function of the mutation sites was analyzed with bioinformatics software.Results:Proband 1 presented with developmental retardation, pectus funnel and premature loss of deciduous tooth, of which the serum alkaline phosphatase level was slightly lower than the bound of the normal range. Two complex heterozygous missense variants c. 1120G>A and c. 1334C>G of ALPL gene were detected in the proband 1 which were inherited from his parents respectively, showing an autosomal recessive inheritance. Both the variants were predicted to inflict deleterious effects on ALPL gene function by multiple bioinformatics program, and were classified as likely pathogenetic variants according to American College of Medical Genetics and Genomics(ACMG) guidelines. Proband 2 showed three missing permanent teeth and the significantly lower level of serum alkaline phosphatase than normal range. A heterozygous variant c. 1190-3C>G of ALPL gene was detected in proband 2 whose pattern of inheritance was unknown. The clinical significance of this variant was unknown according to ACMG standards and guidelines. All of these variants were considered as novel since none of them has been reported. Along with the above combined results, proband 1 and 2 were diagnosed as childhood HPP and Odontohypophosphatasia, respectively.Conclusion:This study reinforced the relationship between HPP and variants in ALPL gene. Two variants, c. 1120G>A and c. 1334C>G, were located in the homodimer interface and crown domain of tissue-nonspecific alkaline phosphatase(TNSALP), respectively, while c. 1190-3C>G were located in the splice sites, which might result in low TNSALP activity.

Adult hypophosphatasia caused by ALPL mutation: one pedigree study / 中华内分泌代谢杂志

An adult patient with hypophosphatasia caused by compound heterozygous mutations in alkaline phosphatase,liver /bone /kidney(ALPL)gene was investigated through comprehensively reviewing the medical history and clinical records of the proband and her family members in order to better understand the disease.The proband and her older sister had mild decreased serum alkaline phosphatase level accompanied with frequently nontraumatic fractures at limbs and all the teeth fell off at the age of 20 and 7, respectively.Both of them carried a missense mutation c.407G>A(p.Arg136His)in exon 5 and a deletion mutation c.1318_1320delAAC(p.Asn440del)in exon 12 simultaneously.Other four family members were p.Arg136His mutation carriers and two members were p.Asn440del mutation carriers.We found that p.Asn440del mutation was associated with the oral disorders.In this family, compound heterozygous manifested more serious symptoms, while heterozygous showed relatively mild symptoms.In addition, it is necessary to differentiate it from primary osteoporosis and other diseases of disturbed bone mineralization.