Two children with hypophosphatasia with a heterozygous c.1559delT variant in the ALPL gene, the most common variant in Japanese populations
Hiroshi Kitoh,
Masako Izawa,
Hiroshi Kaneko,
Akiko Kitamura,
Saori Matsuyama,
Kohji Kato,
Tomoo Ogi
Affiliations
Hiroshi Kitoh
Department of Orthopaedic Surgery, Aichi Children's Health and Medical Center, 7-426 Morioka-cho, Obu, Aichi 474-8710, Japan; Department of Comprehensive Pediatric Medicine, Nagoya University Graduate School of Medicine, 65 Tsurumai-cho, Showa-ku, Nagoya, Aichi 466-8550, Japan; Corresponding author at: Department of Orthopaedic Surgery, Aichi Children's Health and Medical Center, 7-426 Morioka-cho, Obu, Aichi 474-8710, Japan.
Masako Izawa
Department of Endocrinology and Metabolism, Aichi Children's Health and Medical Center, 7-426 Morioka-cho, Obu, Aichi 474-8710, Japan
Hiroshi Kaneko
Department of Orthopaedic Surgery, Aichi Children's Health and Medical Center, 7-426 Morioka-cho, Obu, Aichi 474-8710, Japan
Akiko Kitamura
Department of Orthopaedic Surgery, Aichi Children's Health and Medical Center, 7-426 Morioka-cho, Obu, Aichi 474-8710, Japan
Saori Matsuyama
Department of Orthopaedic Surgery, Aichi Children's Health and Medical Center, 7-426 Morioka-cho, Obu, Aichi 474-8710, Japan
Kohji Kato
Department of Genetics, Research Institute of Environmental Medicine (RIeM), Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8601, Japan
Tomoo Ogi
Department of Genetics, Research Institute of Environmental Medicine (RIeM), Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8601, Japan
Hypophosphatasia (HPP), a genetic disorder characterized by decreased tissue-nonspecific alkaline phosphatase (TNSALP) activity, is caused by loss-of-function mutations in the ALPL gene, which encodes TNSALP. The most frequent pathogenic variant in Japanese patients with HPP is a frameshift mutation in the ALPL gene, c.1559delT, and its carrier frequency is reported to be one in 480 in the Japanese population. We report the cases of two Japanese children with HPP who had a heterozygous c.1559delT variant in the ALPL gene. One case (involving a neonate) exhibited respiratory insufficiency associated with vitamin B6 dependent convulsions, significant defective mineralization similar to the severe form of HPP, and extremely low ALP activity. Enzyme replacement therapy (ERT) using asfotase alfa promptly improved her respiratory insufficiency, bone mineralization, and maintained her motor development during infancy. The second case involved a 10-year-old boy who demonstrated diffuse musculoskeletal pain and weakness that progressively disturbed mobility. Although he showed no bony lesions, the clinical symptoms and biochemical abnormalities were compatible with childhood HPP. ERT successfully relieved the severe generalized pain and significantly improved motor function.
