Urinary Phosphoethanolamine Research Articles

A Diagnostic Algorithm for Children with Low Alkaline Phosphatase Activities: Lessons Learned from Laboratory Screening for Hypophosphatasia

To explore the role of laboratory screening for hypophosphatasia and propose a diagnostic pathway for children with low serum alkaline phosphatase (ALP) activities. A retrospective hospital-based study over an 8-year period was conducted to identify children younger than 16years of age with low ALP activity (<100 U/L). Study-positive patients were contacted for repeat sampling, and those with persistently low ALP had plasma pyridoxal-5'-phosphate and urinary phosphoethanolamine measured. Of 323 064 analyzed samples, 1526 had ALP activities <100 U/L. Most patients had transient hypophosphatasemia. Of 50 patients with last-recorded ALP <100 U/L, 32 were excluded given previous ALP >100 U/L. Eighteen were identified as study-positive. Of the 15 surviving children, 13 were traceable. Four had persistently low ALP activity on retesting, of whom 2 had raised pyridoxal-5'-phosphate and phosphoethanolamine concentrations and were subsequently tested for ALPL gene mutations; a 4-year-old asymptomatic girl with a novel homozygous ALPL missense mutation and a 23-year-old female with a heterozygous mutation. There was significant overlap in ALP activities between study-positive and 11 current patients with hypophosphatasia. We propose a diagnostic algorithm for children with low ALP activities based on clinical and biochemical variables. Patients with persistently low ALP activity require further clinical, biochemical, and radiological assessment for hypophosphatasia, even in the absence of clinical symptoms. The proposed diagnostic algorithm for children with low ALP will facilitate early detection of cases of hypophosphatasia, which, with the availability of enzyme replacement for hypophosphatasia, can be life-saving or avoid years of undiagnosed morbidity.

Clinical, biochemical and genetic spectrum of low alkaline phosphatase levels in adults

BackgroundLow serum levels of alkaline phosphatase (ALP) are a hallmark of hypophosphatasia. However, the clinical significance and the underlying genetics of low ALP in unselected populations are unclear. MethodsIn order to clarify this issue, we performed a clinical, biochemical and genetic study of 42 individuals (age range 20–77yr) with unexplained low ALP levels. ResultsNine had mild hyperphosphatemia and three had mild hypercalcemia. ALP levels were inversely correlated with serum calcium (r=−0.38, p=0.012), pyridoxal phosphate (PLP; r=−0.51, p=0.001) and urine phosphoethanolamine (PEA; r=−0.49, p=0.001). Although many subjects experienced minor complaints, such as mild musculoskeletal pain, none had major health problems. Mutations in ALPL were found in 21 subjects (50%), including six novel mutations. All but one, were heterozygous mutations. Missense mutations were the most common (present in 18 subjects; 86%) and the majority were predicted to have a damaging effect on protein activity. The presence of a mutated allele was associated with tooth loss (48% versus 12%; p=0.04), slightly lower levels of serum ALP (p=0.002), higher levels of PLP (p<0.0001) and PEA (p<0.0001), as well as mildly increased serum phosphate (p=0.03). Ten individuals (24%) had PLP levels above the reference range; all carried a mutated allele. ConclusionOne-half of adult individuals with unexplained low serum ALP carried an ALPL mutation. Although the associated clinical manifestations are usually mild, in approximately 50% of the cases, enzyme activity is low enough to cause substrate accumulation and may predispose to defects in calcified tissues.

Hypophosphatasia: the clinical description of 3 cases of the disease with the molecular-genetic verification of the diagnosis

Hypophosphatasia is a rare hereditary rickets-like disease resulting from the impaired activity of tissue-specific alkaline phosphatase encoded by the ALPL gene. A few forms of this pathology are distinguished depending on the severity of its clinical picture and the age at which its symptoms begin to manifest themselves. The main clinical signs of the disease are skeletal deformations, muscular hypotonia, and respiratory insufficiency in the early childhood as well as the retardation of the physical and motor development and early loss of the teeth In the mature age, such patients suffer from stress fractures, muscle pain, calcification of the ligaments and joints. The biochemical markers of hypophosphatasia are the low blood alkaline phosphatase level and the high urinary phosphoethanolamine level. Also, the severe forms of the disease are associated with hypercalcemia, hyperphosphatemia, and the low parathormone level. The authors describe the patients presenting with Hypophosphatasia of different severity in whom the molecular-genetic verification of the diagnosis was undertaken for the first time in this country.

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Introduction: ES is a 7 month old Amish male born full term with a history of failure to thrive,hypotonia and developmental delay. He was evaluated by the pediatrician one day prior to admission for increased hypotonia, decreased suck, and decreased cry along with constipation. He had labs drawn and was found to have elevated calcium to 19.4 mg/dL. Mom reported uncomplicated pregnancy; he had been exclusively breastfed but was started on formula to increase his weight gain in the week prior to admission. Mom reported she was taking no medications other than multivitamins daily, namely suppratherapeutic dosing for Vitamin E, C and B. At admission, his vital statistics were normal for age, he weighted 5.9 kg. He was awake and alert with generalized hypotonia, there was no clonus appreciated and the remainder of the physical exam as within normal limits. Repeat laboratory studies were done which showed normal complete blood count, elevated calcium of 16.3 mg/dL, ionized calcium of 3.4 mg/dL, phosphate of 3.4 mg/dL, low parathyroid hormone 9.8 pg/mL, low alkaline phosphatase 79 U/L, elevated 25-Hydroxy D total 60 ng/mL, 25-Hydroxy D2 <4.0 ng/mL, 25-Hydroxy D3 60 ng/mL, elevated uric acid 7.4 mg/dL, normal thyroid panel. Urine studies revealed elevated fractional excretion of calcium of 3 along with random calcium/creatinine ratio elevated to 1.6. An electrocardiogram revealed sinus rhythm with prolonged PR interval of 183 milliseconds along with notched T-waves. ES was placed on three times maintenance intravenous fluids of 5% dextrose normal saline with 20 mEq/L of potassium chloride along with furosemide 1 mg/kg/dose IV every six hours. His x-rays revealed mild generalized osteopenia and his renal ultrasound demonstrated bilateral medullary nephrocalcinosis. Aggressive intravenous hydration plus furosemide was continued for three days and his calcium normalized. His urine phosphoethanolamine and plasma B6 were normal, inconsistent with hypophosphatasia. His comparative genomic hybridization revealed a large area of homozygosity encompassing the CYP24A1 gene which encodes 24-hydroxylase. Further sequencing showed homozygosity for a 3 base pair deletion in exon 2 consisted with the diagnosis of idiopathic infantile hypercalcemia. He was discharged from the hospital after normalization of calcium and improvement in tone. Upon follow up, the mother admitted to giving ES 1250 IU/day of vitamin D for one week at 5 and 6 months of age, as well as cod liver oil gel caps, 135 IU/cap of vitamin D, daily for 5 days at 7 months of age Idiopathic Infantile Hypercalcemia is a rare diagnosis due to mutation in the CYP24A1 which encodes the enzyme responsible for the inactivation of 1,25-dihydroxyvitamin D3, leading to profound hypercalcemia, suppressed intact parathyroid hormone and hypercalciuria. The importance of vitamin D supplementation for the prevention of rickets in childhood is well known. The usual recommended daily index of vitamin D is 400 IU, however in the general population there is a wide margin of safety of toxic levels of vitamin D. There have been several studies evaluating similar cohorts of patients presenting with clinical symptoms of vitamin D intoxication several weeks after receiving intermittent high doses of vitamin D prophylaxis. Severe hypercalcemia can lead to extreme morbidity and mortality if not recognized and corrected expediently. The initial management for hypercalcemia is based on the severity of elevation and symptoms. Regimens usually employed include a combined approach with bisphosphonates, calcitonin, glucocorticoids, and calcimemetics along with hydration. In this case the most effective treatment for his underlying condition included the judicious use of aggressive hydration along with loop diuretics to promote calcium excretion which allowed for rapid normalization of calcium and improvement in neurologic and cardiac symptoms.

Benign prenatal hypophosphatasia: a treatable disease not to be missed

Prenatal bowing of the long bones is often associated with severe bone dysplasias. We report a child who presented marked bowing of the long bones at birth but showed a relatively benign postnatal course with spontaneous improvement of bowing. The fetal imaging showed normal skeletal mineralization and normal chest and abdominal circumferences despite the limb bowing and shortening. Decreased serum alkaline phosphatase activity and elevated urine phosphoethanolamine was biochemically evident, and compound heterozygous mutations in the tissue-nonspecific alkaline phosphatase (TNSALP) gene were identified, which confirmed the diagnosis of a benign form of prenatal hypophosphatasia. Benign prenatal hypophosphatasia should be considered in the differential diagnosis of congenital bowing of the long bones.

PF.60 Neonatal Hypophosphatasia: A Rare Disorder and New Treatment

Hypophosphatasia is a rare inborn error of metabolism resulting from mutations in the gene for the tissue-nonspecific isozyme of alkaline phosphatase (TNSALP). There is deficiency of alkaline phosphatase activity leading...

Clinical spectrum of hypophosphatasia diagnosed in adults

The presentation of hypophosphatasia (HPP) diagnosed in adults demonstrates a wide range of clinical manifestations, many of which are nonspecific. We sought to assess clinical characteristics of adult HPP by evaluation of Mayo Clinic Rochester adults diagnosed with HPP from 1976 through 2008. Subjects were identified by diagnostic code or medical records. Inclusion criteria were age ≥18years at diagnosis; low serum alkaline phosphatase (AP) without bisphosphonate therapy; and one additional element: elevated pyridoxal 5′-phosphate (PLP) or urine phosphoethanolamine (PEA), evidence of osteomalacia, or family history. We were unable to distinguish manifesting carriers from silent unaffected carriers due to lack of a prospective standardized clinical evaluation and the absence of genetic testing. HPP was diagnosed in 22 unrelated adults (median age 49years; 68% women). Most patients (68%) were symptomatic at presentation with features including musculoskeletal pain (41%) or incident fracture (18%). A history of fracture was present in 54%: hip/femoral neck (23%), feet (23%, all women), wrist (18%), and spine (9%, all men). Nine patients (36%) had multiple fractures while 4 (all women) had subtrochanteric femur fractures. Radiographic chondrocalcinosis (27%) and documented pyrophosphate arthropathy (14%) were only observed in women. Median minimum serum AP was 43% below the lower normal limit. Urine PEA was elevated in 15/16 patients (94%). PLP median was 68μg/L (normal, 5–50μg/L) and all (n=8) were above normal. Symptomatic subjects had more fractures and chondrocalcinosis, lower median minimum AP and PLP and higher median PEA levels. Clinical features more common in fracture patients included symptoms at presentation, history of childhood rickets, dental abnormalities, lower median minimum AP and PLP, and higher median urine PEA. Four subjects had iliac crest bone biopsies, with 2/4 specimens consistent with osteomalacia.These results suggest that adult HPP demonstrates a wide spectrum of clinical manifestations including musculoskeletal pain, fractures, chondrocalcinosis and dental anomalies with some overlap in laboratory characteristics in relationship to disease severity. In addition to genetic and environmental factors, gender may influence the clinical expression of HPP.

A Case of Vitamin D Deficiency without Elevation of Serum Alkaline Phosphatase in a Carrier of Hypophosphatasia

Elevated serum alkaline phosphatase (ALP) is a screening marker for the diagnosis of vitamin D deficiency, which may fail to be diagnosed if serum ALP is not elevated. Here, we describe a case of vitamin D deficiency without elevation of serum ALP. A 1-year-old Japanese girl was referred to our hospital for the evaluation of genu varum. Her serum intact PTH level was elevated, while her serum ALP level was normal. Furthermore, her serum 25-hydroxyvitamin D level was reduced, and her urine phosphoethanolamine (PEA) level was mildly elevated. ALPL gene analysis revealed she was a heterozygous carrier of hypophosphatasia (c.1559delT). Serum intact PTH and urine PEA evaluations were helpful for diagnosing vitamin D deficiency and hypophosphatasia carrier status, respectively. Therefore, the possibility of vitamin D deficiency without elevation of serum ALP should be considered.

Adult hypophosphatasia with painful periarticular calcification treated with surgical resection

Hypophosphatasia is a rare inherited disorder characterized by a low serum alkaline phosphatase (ALP) activity and defective bone mineralization. Adult hypophosphatasia typically manifests in middle-age as a result of osteomalacia with recurrent stress fractures of the lower limb. However, considerable variation occurs in the clinical expression of hypophosphatasia, and no curative treatment has yet been established. We herein report a case of adult hypophosphatasia with painful calcific periarthritis, which showed improvement after surgical resection. A 32-year-old male was referred to our clinic complaining of pain in his elbows and knees. A painful subcutaneous mass was palpable on his right lateral epicondyle, where periarticular calcification was detected by plain radiography. The laboratory data showed a slight decrease in serum ALP activity and bone mineral density, and an elevation in the urinary phosphoethanolamine. Genomic DNA sequencing revealed an F310L mutation and a Y246H polymorphism in the tissue-nonspecific alkaline phosphatase gene, confirming the diagnosis of hypophosphatasia. The pain in the patient's right elbow was not responsive to nonsteroidal anti-inflammatory drugs, and triamcinolone diacetate was locally injected for treatment. His symptoms were ameliorated after the injection; however, they recurred in 3months, and he became refractory to additional steroid injection. Surgical debridement of the calcified lesion was performed, and his symptoms were successfully ameliorated after the surgery.

A case report of a rare type of skeletal dysplasia diagnosed by a common blood test

We report a rare case of enzyme defect affecting the skeleton. Antenatal scans gave suspicion of skeletal dysplasia (micromelia affecting all four limbs with bone echogenicity). This baby girl was...

Prevalence of c.1559delT in ALPL, a common mutation resulting in the perinatal (lethal) form of hypophosphatasia in Japanese and effects of the mutation on heterozygous carriers

Hypophosphatasia (HPP) is an inherited disorder caused by mutations in ALPL that encodes an isozyme of alkaline phosphatase (ALP), TNSALP. One of the most frequent ALPL mutations is c.1559delT, which causes the most severe HPP, the perinatal (lethal) form (pl-HPP). c.1559delT has been found only in Japanese and its prevalence is suspected to be high; however, the allele frequency of c.1559delT in Japanese remains unknown. We designed a screening system for the mutation based on high-resolution melting curve analysis, and examined the frequency of c.1559delT. We found that the c.1559delT carrier frequency is 1/480 (95% confidence interval, 1/1562-1/284). This indicates that ∼1 in 900 000 individuals to have pl-HPP caused by a homozygous c.1559delT mutation. In our analysis, the majority of c.1559delT carriers had normal values of HPP biochemical markers, such as serum ALP and urine phosphoethanolamine. Our results indicate that the only way to reliably detect whether individuals are pl-HPP carriers is to perform the ALPL mutation analysis.

Lack of Sustained Response to Teriparatide in a Patient with Adult Hypophosphatasia

Hypophosphatasia (HPP) is a rare genetic disorder characterized by low serum alkaline phosphatase (ALP) and defective bone mineralization predisposing to poorly healing pseudofractures and fractures. Experience with teriparatide in HPP is limited. A 53-yr-old woman was diagnosed with HPP on the basis of repeatedly low serum ALP (6-8 IU/liter; normal, 30-120 IU/liter), high urine phosphoethanolamine (PEA) and serum pyridoxal 5'-phosphate (PLP) concentrations, and pseudofractures on the lateral aspect of both proximal femurs. Teriparatide (20 microg/d sc) was initiated 4 months after surgery for a painful nonhealing left femoral fracture sustained after minimal trauma. The patient carried two missense mutations at exons 6 and 11 (Ala176Thr and Val423Ala) and one polymorphism at exon 12 (Val522Ala) of the tissue nonspecific ALP gene (TNSALP). Pain resolved and mobility improved with teriparatide treatment. Serum ALP doubled, and both urine PEA and serum PLP decreased. Markers of bone remodeling increased markedly. Comparison of bone biopsy before and 5 months after teriparatide revealed increased amounts of osteoid and osteoblast numbers. After 8 months, there was complete healing of the pseudofracture of the right femur, and bony callus was apparent on the left. Despite good compliance, serum ALP and PLP and urine PEA returned to baseline with between 8 and 13 months of treatment. This is the first bone biopsy report of teriparatide response in adult HPP. In contrast to the two previously reported cases, biochemical response to teriparatide was unsustained, suggesting that response may be variable depending on the TNSALP gene mutation.

Hypophosphatasia

Hypophosphatasia is a rare inherited disorder characterized by defective bone and teeth mineralization, and deficiency of serum and bone alkaline phosphatase activity. The prevalence of severe forms of the disease has been estimated at 1/100 000.The symptoms are highly variable in their clinical expression, which ranges from stillbirth without mineralized bone to early loss of teeth without bone symptoms. Depending on the age at diagnosis, six clinical forms are currently recognized: perinatal (lethal), perinatal benign, infantile, childhood, adult and odontohypophosphatasia. In the lethal perinatal form, the patients show markedly impaired mineralization in utero. In the prenatal benign form these symptoms are spontaneously improved. Clinical symptoms of the infantile form are respiratory complications, premature craniosynostosis, widespread demineralization and rachitic changes in the metaphyses. The childhood form is characterized by skeletal deformities, short stature, and waddling gait, and the adult form by stress fractures, thigh pain, chondrocalcinosis and marked osteoarthropathy. Odontohypophosphatasia is characterized by premature exfoliation of fully rooted primary teeth and/or severe dental caries, often not associated with abnormalities of the skeletal system.The disease is due to mutations in the liver/bone/kidney alkaline phosphatase gene (ALPL; OMIM# 171760) encoding the tissue-nonspecific alkaline phosphatase (TNAP). The diagnosis is based on laboratory assays and DNA sequencing of the ALPL gene. Serum alkaline phosphatase (AP) activity is markedly reduced in hypophosphatasia, while urinary phosphoethanolamine (PEA) is increased. By using sequencing, approximately 95% of mutations are detected in severe (perinatal and infantile) hypophosphatasia.Genetic counseling of the disease is complicated by the variable inheritance pattern (autosomal dominant or autosomal recessive), the existence of the uncommon prenatal benign form, and by incomplete penetrance of the trait. Prenatal assessment of severe hypophosphatasia by mutation analysis of chorionic villus DNA is possible. There is no curative treatment for hypophosphatasia, but symptomatic treatments such as non-steroidal anti-inflammatory drugs or teriparatide have been shown to be of benefit. Enzyme replacement therapy will be certainly the most promising challenge of the next few years.

Pyridoxine-responsive seizures as the first symptom of infantile hypophosphatasia caused by two novel missense mutations (c.677T > C, p.M226T; c.1112C > T, p.T371I) of the tissue-nonspecific alkaline phosphatase gene

Pyridoxine-responsive seizures (PRS) and the role of pyridoxine (PN, vitamin B 6) in hypophosphatasia (HPP) are incompletely understood. Typically, PRS and HPP are rare, independent, metabolic disorders. In PRS, seizures resist standard anticonvulsants apart from PN, yet have a good prognosis. In HPP, inactivation of the tissue nonspecific isoenzyme of alkaline phosphatase (TNSALP) impairs skeletal mineralization and causes rickets in infants that can be fatal. Here, we report a 7-month-old girl, newly diagnosed with infantile HPP, who presented as a neonate with PRS but without bony abnormalities. Analysis of biogenic amines in cerebrospinal fluid (CSF) suggested brain pyridoxal 5′-phosphate (PLP) deficiency, although PLP in CSF was not decreased. She had normal cognitive milestones but failure to thrive and rickets. Nearly undetectable serum ALP activity, elevated plasma PLP and urinary phosphoethanolamine (PEA) and inorganic pyrophosphate (PPi) levels, hypercalcemia, hypercalciuria and nephrocalcinosis were consistent with infantile HPP. Only prednisolone reduced serum calcium levels. Despite improved growth and weight gain, she developed rib fractures and died from respiratory failure at age 9 months. Sequence analysis of the TNSALP gene revealed novel missense mutations in exon 7 (c.677T > C, p.M226T) and exon 10 (c.1112C > T, p.T371I). Our patient demonstrated that PRS in neonates may not necessarily be “idiopathic”; instead, such seizures can be caused by severe HPP that becomes clinically apparent later in infancy. The pathophysiology of PRS in HPP differs from the three other genetic defects known to cause PRS, but all may lead to brain PLP deficiency reducing seizure thresholds. All reported HPP patients with neonatal seizures died within 18 months of birth, suggesting that PRS is an indicator of HPP severity and lethal prognosis. We recommend that assessment of any neonate with PRS should include measurement of serum ALP activity.

Neutrophil alkaline phosphatase (NAP) score in the diagnosis of hypophosphatasia

Hypophosphatasia is an inherited disease characterised by low tissue non-specific alkaline phosphatase (TNSALP) levels and skeletal defects. Diagnosis is usually made by measurement of serum total alkaline phosphatase (TALP, reference range 40–130 iu/l) and pyridoxal-5′-phosphate (PLP), and urine phosphoethanolamine (PEA). Neutrophil alkaline phosphatase (NAP) scores (reference range 20–150) have been reported to be low in isolated cases, but no comparison has been made of the diagnostic value of NAP, TALP, PEA and PLP in hypophosphatasia. We undertook such a comparison in six families with hypophosphatasia. In four families (Families 1, 2, 5, 6) with the adult type of hypophosphatasia, inherited as autosomal dominant, the NAP score and TALP (<40 iu/l), were low, <20 and <40 iu/l respectively, in all affected subjects, though the PEA and PLP were not consistently abnormal. In one of the two families (Family 3) with the autosomal recessive type of hypophosphatasia an affected subject had low NAP as well as low TALP, PLP and PEA. In another family (Family 4) one of the heterozygotes had a low NAP while the other had a normal NAP score (45). A child in this family had a normal TALP level. Her low NAP score (15) supported her to be a possible heterozygote. NAP score is readily available from most laboratories and may be diagnostically helpful in hypophosphatasia.

Characterization of a family with dominant hypophosphatasia.

A kindred with dominant hypophosphatasia resulting from an alanine to threonine substitution at position 99 of the alkaline phosphatase protein is described. The clinical findings of individual members of the kindred were assessed by oral and physical examinations, or from the descriptions of multiple family members. The proband displayed enamel hypoplasia and premature loss of fully rooted primary anterior teeth, which were shown by histological examination to lack cementum. Serum alkaline phosphatase (ALP) and a vitamin B6 panel, and urine phosphoethanolamine (PEA) were measured on 21 family members. Based upon the clinical and laboratory tests, affected and unaffected status was assigned. Parametric linkage analysis of the kindred using different dominant models and frequency distributions for the disease allele and the mutation gave lodscores > 4.2 and confirmed the strong linkage between the disease and the mutation. Assuming the defined mutation causes the disease, the reliability of clinical and laboratory tests is assessed.

Asp361Val Mutant of Alkaline Phosphatase Found in Patients with Dominantly Inherited Hypophosphatasia Inhibits the Activity of the Wild-Type Enzyme

Hypophosphatasia is characterized by the hypomineralization of bone associated with the mutation of the tissue-nonspecific alkaline phosphatase (TNSALP) gene. Although the disease is usually autosomal recessive, an autosomal dominant form is also recognized. Approximately 50 mutations have been found in the TNSALP gene in patients with hypophosphatasia. However, the mutations identified to date do not seem to account for the dominantly inherited form of the disease. We have examined a German family in which the father and all 4 children were affected with hypophosphatasia, whereas the mother was healthy. The affected members of this family showed premature loss of deciduous teeth at or shortly before 2 yr of age and low levels of serum ALP with elevated levels of urinary phosphoethanolamine. DNA analysis by direct sequencing revealed a heterozygous missense mutation that caused the conversion of amino acid Asp to Val at position 361 (D361V) in the patients. Another substitution was detected in exon 12 (Val to Ala conversion at codon 505: V505A) in 1 allele of the mother and 3 children, indicating no association of the substitution with the disease. Reconstruction experiments demonstrated that the D361V mutant protein lost its enzymatic activity and that it inhibited the function of wild-type enzyme when coexpressed in COS-7 cells. On the other hand, the V505A mutant exhibited enzymatic activities equal to those of the wild-type ALP. It is likely that the mutant D361V protein forms dimers with the wild-type protein, and the protein-protein interaction contributes to the dominant effect of the mutant D361V. The mutation that causes D361V is the first one proven to be associated with the dominant form of hypophosphatasia.

Hypophosphatasia: diagnostic application of linked DNA markers in the dominantly inherited adult form

Hypophosphatasia is a rare disease characterized by low serum levels of tissue non-specific alkaline phosphatase (TNSALP) and a spectrum of skeletal disease varying from the severest form with death in utero to mild with no clinical abnormality in adults. Currently, the diagnosis of hypophosphatasia is made on the basis of clinical findings, radiography, low serum alkaline phosphatase levels and raised abnormal phosphorylated metabolites; there are elevations in serum pyridoxal 5'-phosphate, urinary phosphoethanolamine and inorganic pyrophosphate. In borderline cases the biochemical diagnosis remains uncertain. Prenatally, diagnosis is made using radiography and ultrasonography together with chorionic villus tissue biopsy, in which TNSALP levels are measured using an antibody-based assay. Since hypophosphatasia results from mutations in the TNSALP gene we have, for the first time in two U.K. families, undertaken restriction fragment length polymorphism (RFLP) analysis using three intragenic RFLPs for BclI and MspI at the ALPL locus. One family was informative, and a mutant-allele-specific haplotype with respect to three RFLPs was defined. In the other family the disease was shown to segregate with one allele of the BclI RFLP, but the MspI RFLPs were not informative. The disease segregated in the two families with different alleles of the BclI RFLP, suggesting that the mutations are likely to be different. We confirm that DNA analysis is likely to be the way ahead for diagnosing hypophosphatasia, and that standardized screening methods need to be developed for detecting mutations in these and other families.

Retrospective study of children with hypophosphatasia with reference to dental changes

In the present retrospective study different dental and medical parameters have been analyzed in 17 Swedish children with established hypophosphatasia (HP). It was demonstrated that the basis for the establishment of the diagnosis varied among different dentists and physicians, and that the diagnostic parameters studied among the children varied. The most reliable parameters for HP included raised levels of phosphoethanolamine in urine, and clinical and radiologic findings associated with the legs. These findings were found among the children more often than lowered values of alkaline phosphatase in serum. Histologic analysis of an extracted tooth made a valuable diagnostic complement. It is concluded that a better diagnostic uniformity is recommended. In a well functioning collaboration with well defined tasks, both dentists and physicians can contribute to a reliable diagnosis.

Increased plasma pyridoxal‐5′‐phosphate levels before and after pyridoxine loading in carriers of perinatal/infantile hypophosphatasia

We measured plasma levels of pyridoxal-5'-phosphate (PLP), a cofactor form of vitamin B6 and apparent natural substrate for alkaline phosphatase (ALP), in carriers and in non-carriers of the severe perinatal and infantile forms of hypophosphatasia, both before and after an oral load of pyridoxine (i.e. 1/3 mg/kg body weight). The assignment of carrier status was determined by serum ALP activity, level of serum inorganic phosphate, and if necessary urinary phosphoethanolamine excretion. Plasma PLP levels were significantly increased in the carriers both before and especially after B6 loading.