Severe hypophosphatasia: characterization of fifteen novel mutations in the ALPL gene.

Hypophosphatasia is an inherited disorder characterized by defective bone mineralization and deficiency of serum and tissue liver/bone/kidney alkaline phosphatase (L/B/K ALP) activity. We report the characterization of ALPL gene mutations in a series of 11 families from various origins affected by perinatal and infantile hypophosphatasia. Sixteen distinct mutations were found, fifteen of them not previously reported: M45V, G46R, 388-391delGTAA, 389delT, T131I, G145S, D172E, 662delG, G203A, R255L, 876-881delAGGGGA, 962delG, E294K, E435K, and A451T. This confirms that severe hypophosphatasia is due to a large spectrum of mutations in Caucasian populations.

Stabilization of a terminal inversion duplication of 8p by telomere capture from 18q.

Terminal inversion duplications of the short arm of chromosome 8 are one of the more common chromosome rearrangements in humans. We report an infant with multiple congenital anomalies, in whom karyotype analysis showed a terminal inversion duplication of 8p including additional material at the distal end of the derivative chromosome, shown to be of chromosome 18q origin. Terminal inversion duplications of 8p are the result of meiotic recombination between inverted olfactory gene receptor repeats in 8p. This recombination generates a dicentric intermediate that breaks during anaphase, and the broken chromosome end is stabilized by telomere healing or telomere capture. The origin of the telomeric region in the majority of constitutional chromosome deletions studied to date was shown to be from telomere healing; the de novo addition of telomeric repeats. In the proband a cytogenetically detectable piece of chromosome 18q was present on the distal end of the derivative 8, suggesting that this chromosome was stabilized by telomere capture of 18q. FISH analyses of additional cases may yield information as to whether telomere capture or telomere-healing events are the predominant mechanism of chromosome stabilization in terminal inversion duplications of 8p.

A case of chondrodysplasia punctata with features of osteogenesis imperfecta type II.

The osteogenesis imperfecta syndromes constitute a group of heterogeneous, heritable skeletal dysplasias. Of the 4 types, type II is the most severe, with an incidence of 1 per 55,000. It is characterized by malformed bones secondary to abnormal collagen type I synthesis. Affected fetuses are divided into 3 groups: A, B, and C. All groups have long bones described as "wrinkled" or "crumpled" secondary to repeated fractures. Many bones also show evidence of demineralization, which is especially evident in the bones of the face and calvaria. In groups A and C, the chest is generally small, with thickened and shortened ribs, and each rib has characteristic "beading" patterns secondary to repeated fracturing. Sonography has traditionally been successful in the diagnosis of osteogenesis imperfecta at an early gestational age. Chondrodysplasia punctata describes a heterogeneous group of skeletal disorders characterized by abnormal mineralization of bones during gestation. There are many different causes of it, but some of the specific subtypes include rhizomelic, X-linked dominant (also known as Conradi-Hünermann syndrome), X-linked recessive, and tibia-metacarpal. We report a case of severe X-linked dominant chondrodysplasia punctata, which sonographically had common features with osteogenesis imperfecta type II.

Hyperammonemia in urea cycle disorders: role of the nephrologist.

Hyperammonemia associated with inherited disorders of amino acid and organic acid metabolism is usually manifested by irritability, somnolence, vomiting, seizures, and coma. Although the majority of these patients present in the newborn period, they may also present in childhood, adolescence, and adulthood with failure to thrive, persistent vomiting, developmental delay, or behavioral changes. Persistent hyperammonemia, if not treated rapidly, may cause irreversible neuronal damage. After the diagnosis of hyperammonemia is established in an acutely ill patient, certain diagnostic tests should be performed to differentiate between urea cycle defects and other causes of hyperammonemic encephalopathy. In a patient with a presumed inherited metabolic disorder, the aim of therapy should be to normalize blood ammonia levels. Recent experience has provided treatment guidelines that include minimizing endogenous ammonia production and protein catabolism, restricting nitrogen intake, administering substrates of the urea cycle, administering compounds that facilitate the removal of ammonia through alternative pathways, and, in severe cases, dialysis therapy. Initiation of dialysis in the encephalopathic patient with hyperammonemia is indicated if the ammonia blood level is greater than three to four times the upper limit of normal. Hemodialysis is the most effective treatment for rapidly reducing blood ammonia levels. Continuous hemofiltration and peritoneal dialysis are also effective modalities for reducing blood ammonia levels. An improved understanding of the metabolism of ammonia and neurological consequences of hyperammonemia will assist the nephrologist in providing optimal care for this high-risk patient population.

Male infertility: analysis of the markers and genes on the human Y chromosome.

The long arm of the human Y chromosome is required for male fertility. Deletions in three different regions can cause severe spermatogenic defects ranging from non-obstructive azoospermia to oligozoospermia. Use of intracytoplasmic sperm injection (ICSI) may allow Y chromosome defects to be passed from father to son. Thus, numerous reports have stressed the need to offer genetic testing to infertile men who select ICSI and a number of reproductive clinics have begun to do so. The primary objectives of this review were: firstly, to discuss the characteristics of the published set of polymerase chain reaction markers and how these characteristics affect interpretation of Y chromosome deletion analysis and secondly, to summarize the recent literature pertaining to the genes on the Y chromosome.